English Glossary

Since 02.06.2017

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Weibull scale parameter


adiabatic compressed air energy storage


Amorphous silicon, a thin film PV module semi-conductor material


The part of the solar thermal collector which absorbs solar radiation

absorption air vent

A device which releases air, but not fluid, out of a system by absorption

abstraction licence

A licence granted by the local environmental authority which permits a certain amount of water to be taken from a stream


alternating current


Africa Climate Change Fund


An apparatus by means of which energy can be stored, such as a rechargeable battery.


(bio.) The third step of anaerobic digestion. Products from fermentation (organic acids, alcohols) are converted into hydrogen (H2), carbon dioxide (CO2) and acetic acid (CH3COOH).


air changes per hour


Traditionally considered any chemical compound that, when dissolved in water, gives a solution with a pH less than 7.0.


(bio.) During acidogenesis the hydrolysis products which are relatively small, soluble compounds are diffused inside the bacterial cells through the cell membrane and then are either fermented or anaerobically oxidized. These processes occur by a complex consortium of hydrolytic and non-hydrolytic microorganisms which are the source of energy for the acidifying population.

active power

The power (in watts) used by a device to produce useful work. Term used when necessary to distinguish between apparent power, complex power and its components, and active and reactive power. Also called input power.


anaerobic digestion


Asian Development Bank

additional insured

Any entity, other than the insurance policy holder, that receives certain contractual benefits of an ԩnsuredԠunder the policy. To benefit from such status, the entity has to be named in the insurance policy.


A process in which there is no energy added or subtracted from a system by heating or cooling.

adiabatic compressed air energy storage

Compressed air energy storage is a method of storing energy generated at one time for use at another time, using compressed air. Adiabatic compressed air storage continues to keep the heat produced by compression and returns it to the air when the air is expanded to generate power.


Adaptation Fund


French Development Agency/ Agence Française du Développement


African Development Bank


Agriculture, Forest and Other Land Uses


automatic generation control

aggregated modeling

Modeling a generator as an equivalent generator having the size of the total installed capacity of several individual generators.

air changes per hour

The number of times that the inside air of a building is replaced in one hour.

air density

The mass per unit volume of air.

air mass

Air mass defines how many times a ray of sunlight passes the perpendicular thickness of the atmosphere. When the sun is located at a height of 90º, i.e. at noon of the spring or autumn equinox, the AM is equal to 1. Otherwise, the AM increases with the decreasing of the sun’s height.

air separator

A device which releases air, but not fluid, out of a system


The diffuse reflectivity or reflecting power of a surface. It is defined as the ratio of reflected radiation from the surface to incident radiation upon it.


A soluble salt obtained from the ashes of plants and consisting largely of potassium, sodium carbonate, calcium or ammonia.

alternating current

An electric current that reverses direction periodically.


An electromechanical device that converts mechanical energy to electrical energy in the form of alternating current.


air mass


An ammeter is a measuring instrument used to measure the electric current in a circuit.


A gaseous compound of hydrogen and nitrogen, NH3, with a pungent smell and taste.


Ion NH4+ derived from ammonia by combination with a hydrogen ion and known in compounds (as salts) that resemble in properties the compounds of the alkali metals.


Reduction of capital or up–front expenses (capitalized) over time, often with an equal amount per annum.

anaerobic bacteria

Micro-organisms that live and reproduce in an environment containing no 'free' or dissolved oxygen. Used for anaerobic digestion.

anaerobic digestion

Microbiological process of decomposition of organic matter, in the complete absence of oxygen, carried out by the concerted action of a wide range of micro-organisms. AD is common to many natural environments and is applied to produce biogas in airproof reactor tanks, commonly named digesters. (Syn. digestion, fermentation)

ancillary services

Services of generators to stabilize grid operation and to control voltage and frequency, e.g. reactive power.


Equipment fixed on a mast to measure wind speeds over a particular site. Anemometry masts are usually slender structures fixed to the ground with guy wires.


Anergy is the fraction of energy which cannot be transformed into work. It thus corresponds to the waste of heat.


available net generation capacity

angular frequency

ω = 2*π*f.


artificial neural network

annual debt service coverage ratio

The ratio between operating cash flow and debt service during any one-year period, used to determine a project’s debt capacity.

annual energy output

Total energy produced over the course of a year, for example by a wind turbine or a PV system.


annual debt service coverage ratio


An anode is an electrode through which conventional current flows into a polarized electrical device. ‘Conventional current’ describes the direction in which positive electronic charges move. Electrons have a negative charge, so the movement of electrons is opposite to the conventional current flow. Electrons flow out the anode to the outside circuit. The polarity of voltage on an anode with respect to an associated cathode varies depending on the device type and on its operating mode. This definition is sometimes remembered using the mnemonic ACID for 'anode current into device'.

Anti-reflex coating

A coating of a surface to reduce reflexion

antifreeze fluid

A fluid with a freezing point lower than water to prevent frozen working fluid.

aperture area

The area of a solar thermal collector through which solar radiation falls

apparent power

The product of the applied voltage and current in an AC circuit. Apparent power, or volt-amps, is not the true power of the circuit because the power factor is not considered in the calculation. Expressed in volt-amps [VA].


A PV 'array' is a collection of electrically connected photovoltaic (PV) modules.

artificial neural network

"An artificial neural network Is a family of statistical learning models inspired by biological neural networks (the central nervous systems of animals, in particular the brain) and is used to estimate or approximate functions that can depend on a large number of inputs that are generally unknown.


The physical project and its associated contracts, rights, and interests of every kind, in the present or future, which can be valued or used to repay debt


Zone of Earth’s mantle lying beneath the lithosphere and believed to be much hotter and more fluid than the lithosphere. The asthenosphere extends from about 100 km to about 700 km below Earth’s surface.


other cost that occur at a specific year t


Renewable energy auctions are procurement systems in which various bidders compete to be (partially) compensated for producing a given volume of electricity

automatic air vent

A device which releases air out of a system automatically but not fluid

auxiliary system

An additional heating device which will provide heat when the solar thermal system cannot (same as back-up system)

availability factor

The availability factor of a power plant is the amount of time that a power plant is able to produce electricity over a certain period, divided by the amount of the time in the period. Occasions where only partial capacity is available may or may not be deducted.

available cash flow

Total cash sources less total cash expenses before payment of debt service.

average debt service coverage ratio

The ratio between operating cash flow and debt service during any one-year period, used to determine a project’s debt capacity.

average energy demand

Average requirement for energy as an input to provide products and/or services.

average loan life

The average maturity for all repayments weighted by the principal outstanding.


average debt service coverage ratio


The entirety of all birds observable in a region.


Of or relating to birds of a particular region or period.

avoided costs

Estimated cost that electric utilities would have to pay either to generate power themselves, or to procure from another generator in the market. Commonly used as a benchmark in the industry to indicate the approximate value of new generation to utilities.

azimuth angle

The angle between true south and the point on the horizon directly below the sun.


back-up system

An additional heating device which will provide heat when the solar thermal system cannot (same as auxiliary system)

background noise level

Noise level already present in an environment, e.g. prior to the installation of a wind turbine.

Balance of System

All components of a PV system, excluding the PV modules. BoS includes components such as mounting structures, tracking systems, inverters and other electronics, transformers, cabling, connectors, switches, fuses, lightning and surge protection, and storage technologies in the case of off-grid systems. Sometimes even labor costs and land are considered to be a part of the BoS costs of a system.

balance sheet

The accounts which show assets, liabilities, net worth/shareholders’ equity.

balancing valve

A valve that controls fluid flow in a system (e.g. in parallel branches of a piping system)


The state or condition of being 'bankable'. A project is 'bankable' if it is considered capable of being financed (economically viable).


A project is 'bankable' if it is capable of being financed.


builders' all risk

barrel of oil equivalent

(BOE) the amount of energy contained in a barrel of crude oil, i.e. approx. 6.1 GJ, equivalent to 1,700 kWh.


Traditionally considered any chemical compound that, when dissolved in water, gives a solution with a pH greater than 7.0.

base case

A cash flow projection with variables measured at their expected values.

basis point

1/100 of 1%, one-hundredth of one percent, 0.0001.

basis risk

Type of risk in which the exposure and the hedging instrument are not perfectly matched or correlated.

batch feed

A process by which the digester / reactor is filled with feedstock in discrete amounts, rather than continuously.


An electric battery is a device consisting of two or more electrochemical cells that convert stored chemical energy into electrical energy.


Business as usual

Best Available Techniques Reference

Also "Best Available Techniques Reference Document“ or "BAT Reference“ or "BAT Reference Document". These documents are provided by the European Union and contain (among others) information on a specific industrial/agricultural sector, on the techniques and processes used in this sector, current emission and consumption levels, techniques to consider in the determination of the best available techniques and emerging techniques.

biochemical conversion

The use of biochemical processes to produce fuels and chemicals from organic sources.


Renewable energy generated from materials derived from biological sources, e.g. wood, organic waste, energy crops, agricultural residues. (Syn. biomass energy)


Biofuels are fuels which are derived from plants/biomass. The term covers liquid fuels and upgraded biogas for transportation purposes. Public and scientific interest in biofuels focusses on bioethanol and biodiesel.


Biogas is a gas produced in a decomposition process of suitable biomass utilizing micro-organisms. It is a flammable gas, as its energy carrier is methane, which is also a component of natural gas.

biological oxygen demand

The amount of dissolved oxygen needed by aerobic biological organisms in a body of water to break down organic material present in a given water sample at certain temperature over a specific time period. The term also refers to a chemical procedure for determining this amount.


Organic material from living organisms such as wood, organic waste, and agricultural residuals. Biomass can be converted into other usable forms of energy such as methane or liquid fuels (bioethanol, biodiesel).

biomass feedstock

Organic matter available on a renewable basis. Biomass includes forest and mill residues, agricultural crops and wastes, wood and wood wastes, animal wastes, livestock operation residues, aquatic plants, fast-growing trees and plants, and municipal and industrial wastes.

biomass to liquid

A process where biomass is being converted into liquid biofuel by using gasification and synthesis technologies.


Device for optimizing the anaerobic digestion of biomass and/or animal manure, and possibly to recover biogas for energy production. (Syn. digester)

black start

The procedure to recover from a total or partial shutdown of the transmission system. This entails isolated power stations being started individually and gradually being reconnected to each other.

black start capability

Ability of a power plant to help restart the grid after complete breakdown. These power plants receive their electrical supply from an auxiliary generating plant.

blade angle

See pitch angle definition




Federal Ministry for the Environment, Nature Conservation, Building and Nuclear Safety of Germany


biological oxygen demand


barrel of oil equivalent




Balance of System




basis point

Brayton cycle

The thermodynamic cycle that describes the operation of a constant pressure heat engine such as a gas turbine.

break-even point

The moment (calculated in time units or in monetary units) at which the revenue generated by a project compensates the initial investment and ongoing costs.


Best Available Techniques Reference



buffer store/tank

A tank filled with service water which is not consumed (also known as buffer storage)

builders' all risk

The standard insurance package used during construction.

building envelope

A building envelope is the physical separator between the conditioned and unconditioned environment of a building including the resistance to air, water, heat, light, and noise transfer. It consists of all of the elements of the outer shell that maintain a dry, heated, or cooled indoor environment and facilitate its 'internal climate' control.


Process whereby a private owner builds an infrastructure facility, leases it out, and then transfers it to another entity after a specified period.


Process whereby a private owner builds, owns, and operates an infrastructure facility and then transfers it to another entity after a specified period.


Process whereby a private owner builds, owns, and then transfers an infrastructure facility to another party, often at no cost, after a specified period.


Process whereby a private owner builds an infrastructure facility, transfers it to another entity, and then operates it on a contractual basis for a specified period.


A metallic strip or bar (typically copper, brass or aluminium) that conducts electricity within a switchboard, distribution board, substation, battery bank, or other electrical apparatus. Its main purpose is to conduct high currents. Also called bus bar or busbar.

bus bar

A metallic strip or bar (typically copper, brass or aluminium) that conducts electricity within a switchboard, distribution board, substation, battery bank, or other electrical apparatus. Its main purpose is to conduct high currents. Also called bus or busbar.


A secondary product that origins from the production of something else.

bypass diode

A diode connected in parallel with a a solar cells to provide an alternate current path in case of module shading or failure.



May refer to:

1) capacitance

2) concentration ratio of solar concentrators


crystalline silicon


centralised anaerobic digestion

cadmium telluride

A type of thin-film PV module


cash available for debt service


compressed air energy storage


Capacitance is the ability of a body to store an electrical charge. Any object that can be electrically charged exhibits capacitance.The SI unit of capacitance is the farad (F).


A capacitor is a passive two-terminal electrical component used to store energy electrostatically in an electric field.

capacity credit

The contribution of a power plant to the firm capacity of a system. Typically only used for VRE (variable renewable energy).

capacity factor

The ratio of the actual energy produced in a given period, to the hypothetical maximum possible amount of energy during that period, i.e. running full time at rated power. It is dimensionless.


capital expenditures

capital expenditures

Long-term expenditures for property, plant, and equipment, also called 'investment budget'.

capital markets

Capital markets are markets for buying and selling equity and debt instruments. Capital markets channel savings and investment between suppliers of capital such as retail investors and institutional investors, and users of capital like businesses, government and individuals.

capital structure

Capital structure refers to the way assets or investments are financed through some combination of equity, debt, or hybrid securities.


A carbohydrate is an organic compound carbon, hydrogen and oxygen. General formula is Cm(H2O)n.

Carbon finance

Finance generated through the sale of certified emission reduction credits

cash available for debt service

The amount of cash available to service debt after all essential operating expenses have been met.

cash flow

Flow of cash generated by a project.

cash flow cascade

The order of priorities under the financing documentation for the application of the project’s cash flow. (Syn. Cash waterfall)

cash waterfall

The order of priority for project cash flows as established under the loan and financing documents.(Syn. Cash flow cascade)

cash-flow analysis

An accounting methodology that analyses all incoming and outgoing cash-flows to understand the cash flows per year (or month) and to make sure that a company is solvent at all times.


A substance that speeds up a chemical reaction, but is not consumed by the reaction; it can be recovered chemically unchanged at the end of the reaction.


A cathode is an electrode from which a conventional current leaves a polarized electrical device. ‘Conventional current’ describes the direction in which positive electronic charges move. Electrons have a negative charge, so the movement of electrons is opposite to the conventional current flow. Electrons flow towards the cathode from the outside circuit. The polarity of voltage on a cathode with respect to an associated anode varies depending on the device type and on its operating mode. This definition is sometimes remembered using the mnemonic CCD for 'cathode current departs'.


circuit breakers


combined cycle gas turbine


clean development mechanism


cadmium telluride


California Energy Commission


Cellulose is a complex carbohydrate, (C6H10O5)n, which is composed of glucose units, forms the main constituent of the cell wall in most plants, and is important in the manufacture of numerous products, such as paper, textiles, pharmaceuticals, and explosives.

central PV systems

Large-scale PV power plants installed in a specific location to feed a central electricity grid. Also known as solar farms , solar parks and utility-scale PV.

centralised anaerobic digestion

Supplying slurry from several animal farms to a centrally located biogas plant, to be co-digested with other suitable feedstock.


Certified Emission Reduction

Certified Emission Reduction

A CER credit represents a unit of carbon awarded by the Executive Board of the Clean Development Mechanism. CERs are produced through hypothetical emissions reductions in projects funded in developing countries by developed countries. CERs, each equivalent to one tonne of CO2, can be bought and sold at a price set by the market.



charge controller

An electronic device on an off-grid PV system which regulates the voltage applied to the battery system from the PV array, and controls the connection from the PV array to the loads. Essential for ensuring that batteries are not overdischarged, are not overcharged and longest life.

check valve/one-way valve

A valve that normally allows fluid (liquid or gas) to flow through it in only one direction.

chemical vapour deposition

A chemical process which produces a vapour of a material which is then deposited in a thin layer onto a surface


Woody material cut into short, thin wafers. Chips are used as a raw material for pulping and fibreboard or as biomass fuel.


Braking resistor in the DC link of converter systems.


combined heat and power generation


copper indium (gallium) diselenide


Climate Investment Fund

circuit breakers

This is an automatically operated electrical switch/disconnect designed to protect an electrical circuit from damage caused by overload or short circuit.


Used in reference to insurance, a claim may be a demand by an individual or corporation to recover, under a policy of insurance, for loss that may come within that policy.


A section of a policy contract, or of an endorsement attached to it, dealing with a particular subject in the contract, for example, the "insuring clause" or the "coinsurance clause."

clean development mechanism

One of the Flexible Mechanisms defined in the Kyoto Protocol (IPCC, 2007) that provides for emissions reduction projects which generate Certified Emission Reduction units which may be traded in emissions trading schemes

clearness index

The clearness index Kt is defined as the ratio of the horizontal global irradiance to the corresponding irradiance available out of the atmosphere (i.e. the extraterrestrial irradiance multiplied by the sinus of the sun height).


compact linear Fresnel reflector


Condition Monitoring System


Combustion of more than one substrate at the same time


See 'combined heat and power generation' (CHP).


carbon dioxide


A unit used to standardize measurements of radiative forcing. For example, ton for ton, the 'greenhouse effect' of methane is a greenhouse gas that is 21 times more powerful than carbon dioxide. Therefore 1 ton of methane represents 21 tons of CO2 equivalents.


Certificate of Compliance


commercial operation date

coefficient of performance

The coefficient of performance or COP (sometimes CP) of a heat pump is the ratio of heating or cooling provided by the heat pump to the electrical energy consumed by the heat pump. Higher COPs equate to lower operating costs. The term is also used in refrigeration and air-conditioning trechnology.


Assets pledged as security under a loan to assure repayment of debt obligations.


A solar collector is device that collects solar radiation and converts it to heat.

combined cycle gas turbine

A combined cycle gas turbine is a widely-used gas turbine (operating by the Brayton cycle, burning natural gas or gas synthesised from coal) whose hot exhaust is used to also power a steam power turbine.

combined heat and power generation

The production of electricity and useful thermal energy from a common fuel source. Surplus heat from an electric generating plant can be used for industrial processes, or space and water heating purposes (topping cycle). Conversly, waste heat from industrial processes can be used to power an electric generator (bottoming cycle). (Syn. co-generation)

combiner box

A PV combiner box is a junction box where the cables coming from multiple module strings are combined. May also contain fuses, switchgear and surge protection units. Also called a PV junction box.

commercial operation date

The date on which an independent technical advisor certifies that a facility has passed all required performance tests and/or is built to the specifications outlined in an engineering procurement and construction (EPC) contract.

commercial risks

Those risks that can affect project operations, such as changes in input and output prices, demand fluctuations in demand, or mechanical failures.

compact linear Fresnel reflector

A specific type of linear Fresnel reflector (LFR) technology


The date on which the project's cash flows become the primary method of repayment. It occurs after a completion test typically involving both financial and physical performance criteria. Prior to completion, the primary source of repayment is usually from the sponsors or from the contractor.

completion guarantee

A guarantee that ensures a project will achieve physical and/or financial completion. A turnkey contractor guarantees physical completion (achievement of certain operating performance). The guarantees are normally secured by performance bonds and/or penalties in the form of liquidated damages. Alternatively, project sponsors sometimes provide lenders with completion guarantees by agreeing to pay the scheduled debt service in the event the project company does not or cannot pay.

completion risks

Construction, development, or cost overrun risk.

completion test

Test of the project's ability to perform as planned and generate the expected cash flows. In a limited-recourse deal, the time when the project moves from a full recourse to a non-recourse financing.

compound parabolic concentrator

parabolic mirrors fitted behind evacuated tube collectors to concentrate solar radiation onto the collector

compressed air energy storage

Compressed air energy storage is a method of storing energy generated at one time for use at another time, using compressed air.

Concentrated Solar Power

Solar-thermal process using mirrors or lenses to concentrate a large area of sunlight onto a small area in order to convert solar energy into electricity. Electricity is generated when the concentrated light is converted to heat, which drives a heat engine (usually a steam turbine) connected to an electrical power generator.

concentrating PV

PV technology whereby solar irradiance is concentrated on very small solar cells using lenses.

Concessional loans

Loans issued with minimal or non-existent interest rates, or with extended repayment deadlines.

Condition Monitoring System

A data acquisition system which monitors the condition parameters of machinery (vibration, temperature, etc.), in order to identify changes which can be indicative of a developing fault. The use of condition monitoring allows maintenance to be scheduled, or other actions to be taken to prevent failure and avoid its consequences. Condition monitoring (CM) enables conditions that would shorten normal equipment lifespan can be addressed before they develop into a major failure. Normally used on rotating equipment and other machinery (wind turbines, pumps, electric motors, internal combustion engines, presses).


A mode of heat (or electricity) transfer through a solid

conduction heat transfer

Heat transfer via diffusion in solid materials.


A material with a low electrical resistance, which allows for the flow of electrical current through it. Opposite of an insulator.

confidence interval

In statistics, a confidence interval (CI) is a type of interval estimate of a population parameter. It is an observed interval (i.e., it is calculated from the observations), in principle different from sample to sample, that frequently includes the parameter of interest if the experiment is repeated. How frequently the observed interval contains the parameter is determined by the confidence level or confidence coefficient.

connate water

Water trapped in the pores of a rock during formation of the rock. Might also be described as fossil water. Connate water can be dense and saline compared with seawater. Formation water, or interstitial water, in contrast, is simply water found in the pore spaces of a rock, and might not have been present when the rock was formed.

connection conditions

Specification minimum technical requirements regarding connection to the electricity grid that system operators and users need to comply with.

Consumption profile

A gradient of consumption e.g. water, energy


Pre-agreed cost overrun funding in the investment cost budget of a project company (a "money reserve" for unexpected cash shortages during project implementation).


An additional amount or percentage to any cash flow item (such as capital expenditures) that is needed to provide a cushion.


A mode of heat transfer through a liquid or gas

Convection brake

A device that preventes convection

convection heat transfer

Heat transfer via molecule movements in a fluid

conventional generation

Electricity generation driven by either fossil fuels (coal, gas), nuclear or large hydro power plants (hydro renewable, but considered 'conventional' in this case).

conversion losses

Energy that is lost during the conversion of one form of energy to another.


In mathematics and, in particular, functional analysis, convolution is a mathematical operation on two functions: f and g, producing a third function that is typically viewed as a modified version of one of the original functions, giving the area overlap between the two functions as a function of the amount that one of the original functions is translated.

cooling load

The amount of heat that must be removed from a building to maintain a comfortable temperature for its occupants. The amount of heat generated within a building space from occupants, electrical equipment, artificial lighting, and solar radiation that a HVAC (heating, ventilating, and air conditioning) system must remove. Usually expressed in watts per square meter of building floor space.

Coordinated Universal Time

This is the primary time standard by which the world regulates clocks and time.


May refer to:

1) coefficient of performance

2) Conference of the Parties

copper indium (gallium) diselenide

A type of thin film PV module

corporate financing

Corporate financing usually refers to financing a project using funds available to the company / organisation as a whole, with no additional funds raised for the particular project. As opposed to ‘project financing’ where funds are raised explicitly for a particular project.


The function of the power factor (cosphi) of the active power (P); This is not the power factor itself. It is used as a characteristic of the power factor and the active power, to which generators have to comply: for a certain active power output (e.g. 80% of the rated power) a certain cosphi is required.

cosphi(P) characteristics

Power factor versus active power characteristics. Such a characteristic ensures operation at unity power factor (minimum losses) for low active power outputs.

cost of capital

Cost incurred by a company in order to obtain the debt capital (borrowed funds) and social capital (equity) needed to finance their activities.

Cost of equity

In financial theory, the return that stockholders require for a company. It is represented in %.

cost of risk

The cost associated with the risk of a particular event occuring.


power factor

country risk

Narrowly defined, it refers to cross-currency and foreign exchange availability risks. More broadly defined, it can also include the political risks of doing business in a given country.


An agreement by a borrower to undertake (a positive covenant) or not to undertake (a negative covenant) a specific action. Breaching a covenant is considered an event of default.


The amount above 1.0x of a debt service coverage ratio.


Process whereby different lenders agree to fund under the same documentation and security packages yet may have different interest rates, repayment profiles, and terms. The lenders typically hold different debt tranches


performance coefficient


compound parabolic concentrator



credible contingency

Failure of a component that can occur with sufficiently high probability so that consequences of this contingency must be identified as a considerable risk.


An entitiy is considered 'credit worthy' if the risk of default on a debt obligation by that entity is considered low.


Additional resistor in the rotor circuit of the doubly-fed induction generator.

crystalline silicon

Refers to PV cell made from a single crystal or polycrystalline silicon wafer.


Concentrated Solar Power


Clean Technology Fund




Rate at which electricity flows through a conductor; measured in amps [A].

cut-in speed

The wind speed at which a wind turbine starts to generate electricity.

cut-out speed

The wind speed at which the turbine automatically stops the blades from turning and rotates out of the wind to avoid damage to the turbine.


chemical vapour deposition

cycling capability

Capability of a power plant to ramp the output power up and down.

cycling costs

Costs related to ramping the output power of a power plant up and down.


D:E Ratio

debt to equity ratio


A barrier that impounds water or underground streams


Data Acquisition Module

dark calm period

Dark calm refers to periods with low PV production (dark) and low wind power production (calm).

Data Acquisition Module

The automatic collection of data from sensors, instruments and devices: in a factory, laboratory or in the field.

data logger

A device that collects and stores data

data registration code

List of all data to be submitted by the system operator to a user or by a user to the system operator.

day-ahead forecast

Forecast made for the next day.

day-ahead market

A day-ahead market is where power is traded for delivery during the next day (usually hourly electricity products).

daylight facor

The ratio between the light level at a particular point in a building and the level simultaneously available outside.




direct current


discounted cash flow

debt service

Repayments of principle plus interest payable,usually expressed as the annual amount due per calendar or financial year.

debt service coverage ratio

A quantitative measure used by lenders to determine whether a project’s prospective net cash flow from operations can support (make timely service payment on) a given amount of debt at the indicated potentially available terms. For any given debt service period, the debt service coverage ratio is defined as the cash available for debt service (CADS) divided by the total amount of debt service.

debt service reserve account

A reserve account set up to ensure the timely payment of principal and interest.

debt to equity ratio

A ratio of a company’s debt to its total capitalization. The higher the D:E Ratio the greater the financial leverage of the company.


dedicated energy crops


The decibel (dB) is a logarithmic unit used to express the ratio between two values of a physical quantity, often power or intensity. A decibel scaleis used to express sound power and pressure level. When measuring environmental noise, a weighting network is used which filters the frequency of sound, and is expressed as dB(A).

dedicated energy crops

Crops grown specifically for their fuel value. These include food crops such as corn and sugarcane, and non-food crops such as poplar trees and switchgrass. Can be distinguished into short-rotation woody crops harvested in 5 to 8 years, and herbaceous energy crops harvested annually.


"An amount the insurer will deduct from the loss before paying up to its policy limits. Most property insurance policies contain a per-occurrence deductible provision that stipulates that the deductible amount specified in the policy declarations will be subtracted from each covered loss in determining the amount of the insured's loss recovery. Usually, the amount of the deductible is not subtracted from policy limits.


When a covenant has been broken or an adverse event has occurred. A monetary default occurs when a repayment is not made on time. A technical default occurs when a project parameter is outside defined or agreed-upon limits, or a legal matter is not yet resolved.

delivered energy

Energy that is actually received and paid for by a customer. Or energy that is actually delivered to a load (appliance) as opposed to energy generated by a process or technology.

demand side energy efficiency

Energy efficiency measure that reduces the consumption of final energy by a more efficient use while the same level of useful energy is delivered.

demand side management

The practice of reducing electrical energy consumption and/or costs by changing usage patterns via incentives (e.g. time-of-day rates), negotiating more favorable energy supply agreements, etc. Also known as 'energy demand management'.


The percentage of ‘emptiness’ of a battery or bank of batteries. DoD is the opposite of state-of-charge (DoD = 1 – SoC).

dew point

The temperature at which water vapor condenses and becomes a liquid (dew). The exact temperature at which this occurs will depend on air pressure and air humidity.


Doubly-Fed Induction Generator


domestic hot water

differential temperature controller

A device that switches an output according to the temperature difference between two input temperatures

diffuse irradiation

Radiation received from the sun after reflection and scattering by the atmosphere and ground.


The treated/ digested effluent from the anaerobic digestion process. (Syn. Anaerobic digestion residues, digested biomass digested slurry)


Electronic component that allows current flow in one direction only. See 'blocking diode' and 'bypass diode'.

direct costs

"Costs that can be completely attributed to the production of specific goods or services. Direct costs refer to materials, labor and expenses related to the production of a product.

direct current

Electric current flowing in only one direction.

direct normal irradiation

Beam irradiation perpendicular to a surface. Measured in W/m2.

direct radiation

Solar radiation that radiates direly from the sun, casting shadows on a clear day. (Syn 'beam radiation'). Noted: b (subscript) Solar irradiation received from the sun without scattering by e.g. clouds.

discharge vessel

A container which collects the fluid that is released out of a system


distribution companies

discount rate

The annual percentage rate used to determine the present value of future cash flows. (syn: discount factor)

discounted cash flow

The future net cash flow brought to its present value using a discount rate. DCF analysis uses projections of future cash flows and discounts them (typically by using the weighted average cost of capital, or WACC) to arrive at a present value (PV) for the project.


The schedule of production for all the generating units on a power system, generally varying from moment to moment to match the production with power requirements. As a verb, to dispatch means to direct the plant to produce power.

dispatchable loads

Loads that can be controlled.

distributed PV systems or decentralized PV systems

Many small or medium-scale PV installations of various sizes and connected to an electrical grid in many different locations, usually to the low-voltage grid.

distribution grid

Low or medium-voltage grid, usually having radial or ring topology for the local distribution of electricity. Sometimes sub-transmission grids are considered to be part of a distribution grid.

district heating and cooling

A district heating and cooling system is a system for distributing thermal energy generated at a central location for residential and commercial heating and/or cooling requirements.


The amount paid out per share, usually once, twice, or four times a year, by a company from its profits as decided by the board of directors.


double-layer capacitor


direct normal irradiation


distribution network operator



domestic hot water

Water that is consumed in a household for washing, showering, laundry, etc.

double-layer capacitor

Refers to capacitors in which electrostatic storage of electrical energy is achieved by separation of charge in a Helmholtz double layer at the interface between the surface of a conductor electrode and an electrolytic solution electrolyte.

Doubly-Fed Induction Generator

Doubly-fed electric machines are electric motors or electric generators that have windings on both stationary and rotating parts, where both windings transfer significant active power between shaft and electrical system. Usually the stator winding is directly connected to the three-phase grid and the three-phase rotor winding is fed from the grid through a rotating or static frequency converter. In wind turbine technology it is often referred to as a IEC Type 3 machine.


In the lower part of a stream, closer to its estuary

drain & fill armature

A device to drain and/or fill a system

draught proof

To 'draft proof' means to block up unwanted gaps that let cold air in and warm air out. Draughts occur where there are unwanted gaps in the construction of a building, and where openings are left uncovered.


An actual takedown (borrowing) of money by a borrower under the terms of a loan facility.

dry fermentation

Biomass with a high dry matter content ()15%) becomes difficult to stir and be digested in normal digesters. Dry fermentation processes are applied in such cases. Commonly the substrate is stackable and is digested in "garage box digesters", where no stirring is needed.


debt service coverage ratio


demand side management


debt service reserve account


differential temperature controller

due diligence

Banks lending to a project will undertake a thorough assessment of the project, inclunding financial, legal, technical, and insurance aspects of the project to ensure that there are no undisclosed or potential problems. This is known as 'exercising 'due dilligence'.

dumpy level

An optical instrument used to establish points in the same horizontal plane. It is used along with a calibrated staff to measure height difference, i.e. head.

dynamic calculations

Dynamic calculations explicitly take the time value of money into account by discounting future cash-flows and thereby transferring the future cash-flows into their present value equivalent (the opposite static calculations).



energy to power ratio

earth berms

An earth house berm (also known as an earth house or an earth sheltered home) is an architectural style characterized by the use of natural terrain to help form the walls of a house. An earth house is usually set partially into the ground and covered with thin growth. Modern earth houses are built with concrete walls and insulation.


earnings before interest payments adjusted for taxes


European Bank for Reconstruction and Development


Export Credit Agencies


energy cost centre


equity cash flow


equivalent firm capacity


The ratio of output power (or energy) to input power (or energy). Expressed as a percentage.


The liquid or gas discharged from a process or chemical reactor / digester, usually containing digestate from that process.


enhanced geothermal system


extra high voltage


environmental impact assessment


European Investment Bank


environmental impact statement


equivalent load carrying capability

electric power

The rate at which electric energy is transferred. Electric power is measured by capacity and is commonly expressed in megawatts (MW).

electrical capacity

The maximum power that a machine or system can produce or transmit safely. The maximum instantaneous output of a resource under specific conditions. The capacity of generating equipment is generally described in kW or MW.


Electrolysis is a technique that uses a direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction; commercially important as a stage in the separation of elements from naturally occurring sources such as ores using an electrolytic cell. Electrolysis of water produces hydrogen and oxygen.


A process for depositing a layer of metal onto an electrode by electrolysis

elevation angle

The angle between the horizon and a line intersecting the sun. Also called the sun height or altitude angle. The elevation angle of the sun changes throughout the day, and is highest around midday. When the sun is directly overhead, the elevation angle is 90°.

embedded generation

Generation that is connected to distribution grids (sometimes, also generation connected to sub-transmission grids is considered to be embedded generation).

embodied energy

Usually defined as the energy that is used to extract, transport, manufacture, install and deconstruct/decompose a product or a building.


Fumes or gases that come out of smokestacks and tailpipes, seep from inside factories or enter the atmosphere directly from oil well flares, garbage dumps, rotting vegetation, etc. They include carbon dioxide, methane and nitrous oxide, which cause most of the global greenhouse effect.


energy management system


energy not delivered


An insurance policy form that either changes or adds to the provisions included in one or more other forms used to construct the policy, such as the declarations page or the coverage form. Insurance policy endorsements may serve any number of functions, including broadening the scope of coverage, limiting or restricting the scope of coverage, clarifying the application of coverage to some unique loss exposure, adding other parties as insureds, or adding locations to the policy. They often effect these changes by modifying the existing insuring agreement, policy definitions, exclusions, or conditions in the coverage form or adding additional information, such as insured locations, to the declarations page.


The ability of a system to do work. Measured in joules or kilowatt-hours (kWh).

energy balance

Refers to all energy which is produced, transformed and consumed in a certain period. It can also be an accounting system which keeps track of energy in, energy out, and non-useful energy versus work done.

energy crops

Plant that are grown specifically to be used as a source of energy or fuel.

energy efficiency

May refer to: 1. Energy conversion efficiency, the ratio between the output and input of an energy conversion machine. 2. Energy conservation, efforts made to reduce energy consumption.

energy management system

1. An automated, computer-based system used to monitor, control and optimise an energy system; 2. A management tool to monitor and improve energy consumption in an organisation

energy not delivered

The energy that cannot be supplied due to limitations of the transmission grid operator, e.g. the installed nominal power of a wind farm is higher than the allowed power injection to the grid or substation

energy not supplied

Energy demand that cannot be supplied by the available generation.

energy to power ratio

The ratio of energy capacity of a storage system to installed power. Storage systems with a large E2P can deliver power for a longer time than storage systems with a small E2P.

enhanced geothermal system

The EGS concept is to produce energy from geothermal resources that are otherwise not economical due to lack of water and/or permeability. It extracts heat by artificially creating a subsurface fracture system to which water can be added through injection wells. Injected water is heated by contact with the rock and returns to the surface through production wells.


energy not supplied


Sum of the internal energy and the product of the pressure and volume of a thermodynamic system. Enthalpy is an energy-like property or state function. In symbols, the enthalpy, H, equals the sum of the internal energy, E, and the product of the pressure, P, and volume, V, of the system: H = E + PV.


European Network of Transmission System Operators for Electricity

environmental impact assessment

EIA - Formal process used to assess the environmental consequences (positive or negative) of a plan, policy, program, or project prior to the decision to move forward with the proposed action.

environmental impact statement

A statement of results of environmental impact assessment. Can specify measures which should be taken to eliminate or mitigate negative impacts to an acceptable level.

environmental risk

Economic or administrative consequences of incremental or catastrophic environmental pollution.


A substance produced by a living organism which acts as a catalyst to bring about a specific biochemical reaction.


May refer to:

1) energy performance contracting

2) Engineering Procurement Construction


energy performance indicators


Ensemble Prediction System


Cash or assets contributed by investors. In accounting terminologoy it is the difference between total assets and total liabilities. [%]

equity cash flow

Cash flow available to equity holders. It is equal to net income plus depreciation less capital expenditures less increases in net working capital (NWC) less principal repayment plus new debt proceeds.

equivalent firm capacity

In the case of wind power, EFC is defined as how much 100% reliable generation (firm capacity) would be required to replace the installed wind generation while maintaining the same level of system security.

equivalent load carrying capability

Additional load that can be supplied at the required reliability level when adding VRE (variable renewable) energy to a system.


energy supply contracting


energy service company


Environmental and Social Safeguards


amount of electricity generated in year t



ethylene-vinyl acetate

EVA - An encapsulant used between the glass cover and the solar cells in PV modules. It is durable, transparent, resistant to corrosion, and flame retardant.


European Union Emission Trading System

European Network of Transmission System Operators for Electricity

European Network of Transmission System Operators for Electricity - Association of Europe's transmission system operators (TSOs) for electricity. Successor of ETSO, the association of European transmission system operators founded in 1999 in response to the emergence of the internal electricity market within the European Union.


ethylene-vinyl acetate

evacuated tube collector

A solar thermal collector made up of cylindrical glass tubes which are evacuated to prevent heat losses by conduction and convection


see: principal exlusions


Exergy is the fraction of energy which can be transformed into work, it thus corresponds to usable energy.

expansion loop

A loop in a piping system to compensate for the thermal expansion of the pipe

expansion vessel

An essential component of a pressurised system which takes up the expansion of the system fluid when it gets hot

expected value

Expected value' is a stochastical term which describes the expected average result of an experiment if it is repeated over and over again. In its most simple form it is calculated as the product of the value of the result and the probability of that result.

export meter

Meter which counts how much electricity is fed into the public grid by a renewable power plant.

extra high voltage

Extra high voltage ()=245kV).




fault ride through

The requirement or ability of a generating unit to remain connected during grid faults which can result in temporary under voltages (during a fault) or over voltages (after a fault is cleared) outside of the normal operating range of voltage. It is also called low voltage ride through (LVRT), high voltage ride through (HVRT) or fault ride through (FRT).


free cash flow

feasibility study

An analysis of the ability to complete a project successfully, taking into account legal, economic, technological, scheduling and other factors. Rather than just diving into a project and hoping for the best, a feasibility study allows project managers to investigate the possible negative and positive outcomes of a project before investing too much time and money.

feed-in meter

A meter in a grid-connected installation used to measure the amount of electricity fed onto the grid.

feed-in premium

Similar to a FiT, but based on offering a floating or variable premium on top of the prevailing electricity market price.

feed-in tariff

Renewable energy support mechanism that offers a fixed purchase price ($/kWh) to renewable energy producers for the electricity they produce, often in the form of a long-term contract. Purchase prices are often differentiated by technology, project size, application (e.g. rooftop vs. ground-mounted PV), and occasionally by resource quality (to avoid windfall profits at higher quality resource sites)


Input material for a process, also called substrate.


Fermentation is a metabolic process that converts sugar to acids, gases or alcohol. Decomposition of an organic substance.


A device that collects impurities out of a fluid

financial close

The date on which all project contracts and financing documentation are signed and conditions precedent to initial drawing of the debt have been satisfied or waived.

financial residual

(fin.) The assumed value of an asset at the end of a loan, lease, or pro forma cash flow.

financial structure

The specific mixture of long–term debt and equity that a company or project uses to finance its purpose. This financial structure is a mixture that directly affects the risk and value of the business.

financial viability

The ability of a project to provide acceptable returns to equity holders and to service its debt on time and in full.

financing agreements

The documents which provide the project financing and sponsor support for the project as defined by the project contracts.


feed-in premium

firm capacity

Theoretical term describing a capacity with an availability of 100%. Sometimes also used for the total capacity of a system that has an extremely high availability (e.g. 99%). Firm capacity is the amount of energy available for production or transmission which can be (and in many cases must be) guaranteed to be available at a given time.

first generation of biofuels

First generation biofuels' are made from sugar, starch, vegetable oil or animal fats using conventional technology. Vegetable oils are converted into biodiesel, starch is fermented into bioethanol.


feed-in tariff

fixed cost

Operating cost which does not vary per unit of output.


farm layout program

Flash test

A procedure used to evaluate the output characteristics of a PV cell or module under specific Standard Test Conditions (STC).

flat plate collector

A solar thermal collector made up of a flat absorber plate covered with a sheet of glass and insulated at the back and sides


Periodic and rapid variations of AC voltage frequency.

Flow (vs. Return)

A hot line of a system (from heat source to consumer)

flow duration curve

A graph that shows the percentage of time that flow in a stream is likely to equal or exceed some specified value of interest

flow gauge

A device for measuring the rate of fluid flow that gives a visual indication (Syn. flow meter).

flow meter

A device for the accurate measuring the rate of fluid flow (Syn. flow gauge).

flow rate

Mass flow rate is the mass of fluid which passes per unit time (SI unit: kg/s); volume flow rate is the volume of fluid which passes per unit time (SI unit: m3/s)

flow resistance

Resistance to be overcome to circulate a fluid in a pipe system

fly ash

Small ash particles carried in suspension in combustion products.


A flywheel is a rotating mechanical device (heavy disk or wheel) that is used to store rotational energy. Its momentum gives almost uniform rotational speed to the shaft and to all connected machinery.

force majeure

It is a common clause in contracts that essentially frees both parties from liability or obligation when an extraordinary event or circumstance beyond the control of the parties, such as a war, strike, riot, crime, or an event described by the legal term act of God (such as hurricane, flooding, earthquake, volcanic eruption, etc.), prevents one or both parties from fulfilling their obligations under the contract. Most force majeure clauses do not excuse a party's non-performance entirely, but only suspends it for the duration of the force majeure.

forced circulation system

A system in which the fluid is circulated using a pump

forebay tank

A tank between the power canal and the penstock which allows sediment in the water to settle out before the water enters the penstock

forecast horizons

Time between deriving a forecast and the time the forecast is valid for.

forecast provider

Company that calculates forecasts of power generation from RES.

fossil fuel

Solid, liquid or gaseous fuels formed after millions of years by chemical and physical changes in plant and animal residues under high temperature and pressure. Crude oil, natural gas and coal are fossil fuels.


fully rated converter

free cash flow

Cash available for capital providers. It is defined as earnings before interest payments adjusted for taxes (EBIAT); plus depreciation, amortization, and other non-cash charges; less capital expenditures; less increases in net working capital.


The number of repetitions per unit time of a complete waveform, expressed in Hertz (Hz).


fault ride through

fuel cell

A device that converts the energy of a fuel directly to electricity and heat, without combustion.

fuel parity

The point of time when it is less costly to use energy/electricity from a renewable source than from a fossil fuel.

full cover

Guarantees or insurance for both political and commercial risks provided to a lender by an export credit agency or international finance institution.

full load hours

"Full load hours are calculated by dividing the power plants annual energy production by its rated power. The dimension is hours/time. Usually the timeframe is year.

full recourse

No matter what risk event occurs, the borrower agrees to repay the debt. By definition, this is not a project financing unless the borrower's sole asset is the project.

fully rated converter

Converter system designed for the full rating of the connected generation unit. In wind turbine technology it is often referred to as a IEC Type 4 machine. FRC means fully rated converter.

funding risk

Risk of impact on project cash flow caused by higher financing costs or lack of availability of funds.


A type of low resistance resistor that acts as a sacrificial device to provide overcurrent and short-circuit protection in an electrical circuit.



solar irradiation

galvanic isolation

A galvanic isolation prevents current flows between functional sections of electrical systems.

garage box digester

Anaerobic digesters in the form of a garage in which drier organic material is digested. Commonly there are a minimum of 3 digesters next to each other to allow a semi-continuous batch process. One digester is loaded with fresh organic material, in the second digester organic material is already producing biogas for half of the retention time, while the third digester is almost ready to be unloaded as most of the biogas has been extracted already.

gas turbine

A type of internal combustion engine in which the combustion of a fuel (normally a fossil fuel) occurs with an oxidizer (usually air) in a combustion chamber.


The process in which a solid fuel is converted into a gas, also known as pyrolitic distillation or pyrolysis.




generator connection (or combiner) box


Green Climate Fund


Gross Domestic Product


The gearbox adjusts the rotor speed to the generator speed. Different stages are achieved by spur or planetary gears.


The level of debt used in a particular transaction expressed as a percentage of equity or as a ratio to equity (also referred to as 'leverage').


Global Environment Facility

generation adequacy

Power generation adequacy refers to the the ability of a system to meet the aggregate power and energy requirement of all consumers at virtually all times. Also called 'power generation adequacy'.


A generator is a device that converts mechanical energy to electrical energy

generator connection (or combiner) box

A generator connection box or combiner box is a housing for electrical connections. They are also called PV combiner boxes or PV array combiner boxes.


The geosphere is considered that portion of the Earth system that includes the Earth's interior, rocks and minerals, landforms and the processes that shape the Earth's surface.

geothermal play type

A play type in petroleum geology represents a particular stratigraphic or structural geological setting, defined by source rock, reservoir rock and trap. Translated to geothermal systems, a play type might be defined by the heat source and the geological controls on heat transport and thermal energy storage capacity.


ground fault detector interrupter


gross generation capacity


Greenhouse Gas


global horizontal irradiation


GW - a measure of electric capacity equal to 1 billion watts or 1 million kilowatts.


geographical information system


Part of a wall or window that consists of glass.

global horizontal irradiation

Global irradiation on a horizontal surface. Measured in W/m2.

global solar radiation

Sum of direct and diffuse radiation.

global warming

Changes in the surface-air temperature, referred to as the global temperature, brought about by the greenhouse effect which is induced by emission of greenhouse gases into the air.


An organic fluid used for freeze protection


A transfer of funds with no expectation of a return payment. Grants are used in conjunction with other finance modalities.

gravitational potential energy

The energy stored in an object as the result of its vertical position or height

Green Bond

A green bond is a debt security that is issued to raise capital specifically to support climate-related or environmental projects.

green certificates

A tradable certificate certifying that certain electricity has been generated using renewable energy sources. Typically one certificate represents generation of 1 Megawatt hour (MWh) of electricity. (Syn. Renewable energy certificates or RECs, Tradable Green Certificates TGC)

greenhouse effect

The effect of certain gases in the Earth's atmosphere in trapping heat from the sun.

greenhouse gas

GHG - a gas that causes global warming.


Term used to describe an electrical utility distribution network.

grid code

Document specifying the technical standards relating to operation of a power grid and to which all parties involved are required to comply with.

grid frequency

The frequency at which the electricity grid operates, usually 50 or 60 Hz.

grid parity

The point of time when the LCOE of an alternative energy source, e.g. solar PV or wind power, is less than or equal to the costs of retail electricity in a given country or region.

grid system

An arrangement of power lines connecting power plants and consumers over a large area

grid-connected PV system

A PV system which feeds energy onto a national electricity grid. Also called a grid-tied PV system or a utility-interactive PV system.

Gross area

Outside dimensions

gross calorific value

Energy content of a substance, higher than net calorific value. For most combustion processes, the net calorific value is the relevant parameter.

gross generation capacity

The total amount of electric energy produced by generating units and measured at the generating terminal in kilowatthours (kWh) or megawatthours (MWh).

ground fault detector interrupter

Electrical wiring device that disconnects a circuit whenever it detects that the electric current is not balanced between the energized (line) conductor(s) and the return (neutral) conductor. (Syn. Ground fault interrupter (GFI) or residual-current device or RCD)




gigawatt hour



on the horizontal


Voltage or current distortions that can be expressed by additional sinusoidals at frequencies that are integer multiples of the fundamental frequency.




Higher Calorific Value




high density polyethylene


Vertical change in elevation (SI unit: metres)

head-for-the-hills clause

Mandatory loan prepayment using insurance proceeds. Project credit agreements often provide that, if any of the major project facilities are destroyed or damaged and the project company subsequently receives a major insurnace recovery, then the borrower must use the insurance moneys to prepay the loan if the lenders so require.

heat exchanger

A device to transfer heat between two fluids without the fluids mixing or coming into contact with each other

heat meter

A device which measures thermal energy provided by a source or delivered, by measuring the flow rate of the heat transfer fluid and the change in its temperature (ΔT) between the outflow and return legs of the system.

heat pipe

A cylinder that transferes heat by convection of an inside gas or fluid

heat transfer efficiency

Useful heat output released/actual heat produced in the firebox.

heat transfer fluid

A fluid which can both transfer and store thermal energy (heat). Examples of heat transfer fluids are water, anti-freeze, thermal oil and molten salts.

heating demand

Energy needed annually (usually) for heating, measured in kWh/m²a or kWh/m3a.

heating load

The amount of heat that needed to be added to a building to maintain a comfortable temperature for its occupants.

heating value

The maximum amount of energy that is available from burning a substance.


A strategy that eliminates a risk through the spot sale of the risk or through a transaction in an instrument that represents an obligation to sell the risk in the future. The goal is to ensure that any profit or loss on the current sale or purchase will be offset by the loss or profit on the future purchase or sale.


The name for the high molecular weight polysaccharides which, together with cellulose and lignin, are contained in the cell walls of plants.


((Hz) - The measure of frequency of a periodic phenomenon (1 Hz= 1 s–1). In alternating current grids all the generators are connected in parallel and run synchronously at the same frequency. During normal operation, the grid frequency varies slightly depending on the load on the grid. Synchronous frequency of large interconnected grids is 50 Hz (e.g. Europe) or 60 Hz (e.g. North America).

high density polyethylene

Polyethylene thermoplastic made from petroleum. It is sometimes called "alkathene" or "polythene" when used for pipes.

high frequency components

Frequency components in the voltage spectrum that occur at frequencies )2kHz.

high voltage

High voltage is )35kV, « = 230kV.

High Voltage Ride Through

Capability of a power plant to remain connected during high voltage conditions, e.g. resulting from load rejection or after voltage recovery.

high-speed cut-out

Shutting down of wind turbines due to high wind speeds (for safety reasons).

high-voltage direct current

A HVDC electric power transmission system is a system that uses direct current for the bulk transmission of electrical power, in contrast with the more common alternating current (AC) systems. For long-distance transmission, HVDC systems may be less expensive and suffer lower electrical losses.

Higher Calorific Value

The calorific value of a fuel is the quantity of heat produced by its combustion - at constant pressure and under ‘normal’ (‘standard’) conditions (i.e. to 0°C and under a pressure of 1,013 mbar). Energy content of a fuel per unit of mass or volume. The Higher Calorific Value (or Gross Calorific Value - GCV, or Higher Heating Value - HHV) of a fuel is its calorific value when the water of combustion is entirely condensed and the heat contained in the water vapour is recovered. The Lower Calorific Value (or Net Calorific Value - NCV, or Lower Heating Value - LHV) of a fuel is its calorific value when the products of combustion contains the water vapour and that the heat in the water vapour is not recovered.

hot spot

Damage caused by heat build-up in a PV solar cell, normally caused by shading. If the heat increase is significant, the cell can be irreversibly damaged.

hot water cylinder

tank that contains hot water for consumption


heat transfer fluid

hub height

Height of wind turbine tower from the ground to the central axis (hub) of a wind turbine rotor.

hurdle rate

The minimum acceptable rate of return, often abbreviated MARR, or 'hurdle rate' is the minimum rate of return on a project a manager or company is willing to accept before starting a project, given its risk and the opportunity cost of forgoing other projects. Sometimes called 'minimum attractive rate of return'.


high voltage


High Voltage Alternating Current


high-voltage direct current


High Voltage Ride Through


Chemicals which contain only hydrogen (H), carbon (C), fluorine (F) and chlorine (Cl). HCFCs are used as refrigerants (in refrigerators, freezers and air-conditioning systems) and also in insulative foams. They have a very potent greenhouse effect (global warming potential) that is almost 2,000 times higher than that of carbon dioxide.


A graph showing the water flow rate measured at a certain point in a river against time


(bio.) The first step of anaerobic digestion in which insoluble complex molecules such as carbohydrates and fats are broken down to short sugars, fatty acids and amino acids. Describes the cleavage of a chemical compound through the reaction with water.


Power derived from the energy of falling water or running water.

hydropower plant / hydro plant

A power plant that generates electricity from the flow of water





May refer to:

1) current

2) discount rate


overcurrent with inverse tripping characteristic

I-V Curve

The plot of the current versus voltage characteristics of a photovoltaic cell, module, or array. Three important points on the I-V curve are the open-circuit voltage, short-circuit current, and maximum power point.


May refer to: 1) initial investment cost, 2) extra terrestial irradiations


International Bank for Reconstruction and Development


International Climate Fund


direct-axis current

IDB (also IADB)

Inter-American Development Bank


International Energy Agency

IEC Standards

IEC standards are standards issued by the International Electric Committee (IEC) covering a vast range of technologies from power generation, transmission and distribution to home appliances and office equipment, semiconductors, fibre optics, batteries, solar energy, nanotechnology and marine energy as well as many others.


induction generator


Insulated Gate Bipolar Transistor


International Climate Initiative

immersion heater

An electric heater that is immersed in water to heat it up


1) Electrical impedance is the measure of the opposition that a circuit presents to a current when a voltage is applied. 2) The combination of resistance and reactance affecting the flow of an alternating current, generally expressed in ohms.

impulse turbine

Also known as action turbine. This is a turbine that has the same pressure before and after the impeller. It operates in air at atmospheric pressure.

inception date

The initial starting date from which a contracted insurance policy provides risk coverage to the insured party.


Intended Nationally Determined Contribution


Compensation to a party for a loss or damage that has already occurred, or to guarantee through a contractual clause to repay another party for loss or damage that might occur in the future. The concept of indemnity is based on a contractual agreement made between two parties in which one party (the indemnitor, e.g. the insurer) agrees to pay for potential losses or damages caused by the other party (the indemnitee; e.g. the insured).

indemnity period

The maximum duration over which the insurers will be liable to indemnify the insured parties. Example: in the case of business interruption insurance, the indemnity period refers to the number of days over which the insurer has to pay loss of revenue compensation to the insured.

Independent Power Producer

A corporation, person, agency, authority, or other legal entity or instrumentality that owns or operates facilities for the generation of electricity for use primarily by the public, and that is not an electric utility.


Inductance is the property of an electrical conductor by which a change in current flowing through it induces an electromotive force in both the conductor itself and in any nearby conductors by mutual inductance.

induction generator

An induction generator or asynchronous generator is a type of alternating current (AC) generator that uses the principles of induction motors to produce power. Induction generators operate by mechanically turning their rotors faster than synchronous speed. Usually draws its excitation power from an electrical grid. In wind turbine technology it is often referred to as a IEC Type 1 or Type 2 machine.


Passive electrical circuit element which stores magnetic energy

inflation premium

The increased return on an investment which is required to compensate investors for expected inflation.

Infrared light

Electromagnetic radiation with longer wavelengths than those of visible light. IR wavelengths range from approximately 700 nm to 300,000 nm. Because of the longer wavelengths, IR light tends to pass through many materials, including may solar cells, and also carries less energy compared with visible light or ultraviolet light. IR light is also emitted by thermal radiation. IR light, in the language of solar cells, is commonly referred to as ‘red light’.


Another term for irradiation.

installed capacity

The total capacity of electrical generation devices in a power station or system.

installed PV capacity

Refers to the total installed nominal power of a PV module or array (Wp) , as listed on a module’s datasheet and determined by a flash test under Standard Test Conditions (STC).

Insulated Gate Bipolar Transistor

A three-terminal power semiconductor device primarily used as an electronic switch which, as it was developed, came to combine high efficiency and fast switching.


Material to reduce electrical/thermal losses


A material with a high electrical resistance. Opposite of a conductor.

insurance proceeds account

In international project finance transactions, banks often open ԩnsurance proceeds accountsԠin the name of the borrowers. Such accounts are pledged to the banks. Any funds transferred to these accounts by the insurers following insured claims can only be used with the banks' permissions.


One who transfers a risk to another party. Interchangeable with ‘Assured’.


The insurance company who has agreed to accept the risk and to pay monies by way of an indemnity to an insured in the event of loss. The amount paid can be an agreed amount or actual loss sustained.

Integrated Solar Combined Cycle Plants

Hybrid technology in which a steam-generating solar-thermal plant is integrated with a combined cycle plant. In ISCC plants, solar energy is used as an auxiliary heat supply, supporting the steam cycle, which results in increased generation capacity or a reduction of fossil fuel use.

interest during construction

An amount that is usually equal to capitalized interest, usually part of the CAPEX of a project.


Frequency components in the voltage spectrum that occur at non-integer multiples of the fundamental frequency.

internal rate of return

IRR -the discount rate that makes the net present value equal to zero. Gives the return on the invested capital if one assumes that the project breaks even. It excludes all external factors such as the debt interest rate.

intra-day market

Electricity market in which the time between trading and physical delivery ranges from between a few minutes and up to 36 hours.


In a PV system, an inverter converts DC power from the PV array/battery to AC power compatible with the utility and/or AC loads.


Independent Power Producer


quadrature-axis current

IR light

Infrared light


internal rate of return


Power of the radiated light [unit: W/m²]


short circuit current


Integrated Solar Combined Cycle Plants


Isobars are lines drawn on a map joining places of equal average atmospheric pressure. They are used to map atmospheric or air pressure. An isobaric process is a process in which energy is transferred at a constant pressure.

isolating valve

A valve to shut-off a pipe and stop circulation (same as shut-off valve)


Process in which energy is transferred at a constant temperature.

iterative method

Method by which a (mathematical) problem is solved by following a systematic trial-and-error process, i.e. in a step-by-step manner.


Fraunhofer-Institut für Windenergie und Energiesystemtechnik (Institute for Wind Energy and Energy system Technology)





Joint Implementation


Japan International Cooperation Agency


J - unit of energy equal to 1/3,600 kilowatt-hours.





Kreditanstalt für Wiederaufbau




kV - 1,000 volts. Usually used in connection with medium-voltage and high-voltage transmission lines.


kW - unit electrical power equal to 1,000 watts. 1 kW = 3,413 Btu/hr = 1,341 horsepower.

kilowatt peak

kWp - nominal power output of a PV array under standard test conditions.


kWh - 1,000 watt-hours. Power multiplied by time. The most commonly-used unit of electrical energy, consumed or produced. 1 kWh means 1 kW of electricity supplied/prodcued for 1 hour.

kinetic energy

The energy an object possesses due to its motion

Kreditanstalt für Wiederaufbau

German Cooperation Agency


clearness index








kilowatt hour per square metre per Annum


kilowatt hour (electric)


kilowatt peak




landfill gas

Methane-containing gas, produced on landfills.

layer of scum

During the anaerobic digestion of biomass, structural matter (e.g. straw) can float to the top of the substrate and form a so-called layer of scum that hinders the penetration of biogas. Special stirring devices are needed to break up this layer.


Low-Carbon Development Strategies

LCL filter

Hardware filter in electrical circuits consisting of inductances L and capacitance C to enhance the power quality


levelised cost of electricity


load duration curve


Low-Emission Development Strategies


Bacteria which flourish in warm water (around 35-55°C) and cause Legionnaires' disease


Someone making funds available with the expectation that the funds will be repaid, plus an interest and/or fees. A lender can be an individual, or a public or private group.

levelised cost of electricity

The net present value of the unit-cost of electricity over the lifetime of a generating asset. It is often taken as a proxy for the average price that the generating asset must receive in a market to break even over its lifetime. In American literature the term "Levelised Cost Of Energy" is often used as a synonym which is also abbreviated with LCOE.


The level of debt used in a particular transaction expressed as a percentage of equity or as a ratio to equity (also referred to as 'gearing').


linear Fresnel reflectors


London Interbank Ofered Rate

light energy

Electromagnetic radiation in the form of energy carrying photons, integrated over time. Although light energy often only refers to the visible spectrum, light energy can be absorbed by solar cells across the whole solar spectrum, from the invisible infrared light to visible light to ultraviolet light.

light soaking

‘Light soaking’ in the context of photovoltaics refers to exposing PV cells/modules to radiation with solar spectrum, under controlled conditions. Part of IEC 61646 test routines, test used to measure degradation of thin film modules.


(bio.) A complex of lignin, cellulose and hemicellulose present in the cell walls of woody plants. Lignin is the complex constituent of wood that cements the cellulose fibres together and it is very difficult to digest, hardly producing any biogas.

lime scale

Deposit of calcium carbonate

limited recourse

A 'limited recourse' debt is a debt in which the creditor has limited claims on the loan in the event of default. Often a limited recourse debt contract is structured so that the debt transitions to unsecured, or 'non-recourse', debt pending the completion of a specific event. That event may be the completion of a project or the establishment of a specific revenue stream for which the debt was issued. Under certain conditions legal, financial, or other), lenders have access to the sponsors' credit or other legal security to fulfill a project’s debt obligations. There is usually recourse in the event of fraud, misrepresentation, or nondisclosure. For this reason, and because lenders often have some kind of recourse prior to completion, nonrecourse is often described as 'limited-recourse' financing.

linear Fresnel collector

A CSP technology which is a lower cost version of the parabolic trough collector. It uses a series of long, flat mirror segments arranged to approximate a parabolic shape. Just like the parablic trough collector, these concentrate solar radiation onto a central receiver tube running along the focal line of the mirror segments to produce high temperatures.

linear Fresnel reflectors

Linear Fresnel reflectors use long, thin segments of mirrors to focus sunlight onto a fixed absorber located at a common focal point of the reflectors. These mirrors are capable of concentrating the sun’s energy to approximately 30 times its normal intensity.


The liquidity (of a firm or a project) is defined as the ability to meet all financial obligations on time.


The rocky outer part of the Earth, made up of the brittle crust and the top part of the upper mantle. The lithosphere is the coolest and most rigid part of the Earth.


loan life coverage ratio


May refer to:

1) an electrical device or appliance which consumes electrical energy.

2) the total impedance of all the items in the output circuit.

load current

The current required by the electrical device.

load curve

The relationship of power supplied to the time of occurrence. Graphical plot Illustrating the varying magnitude of the load during the period covered.

load duration curve

LDC - a load duration curve is used in electric power generation to illustrate the relationship between generating capacity requirements and capacity utilization.

load factor

In electrical engineering the load factor is defined as the average load divided by the peak load in a specified time period.

load shedding

The act or process of disconnecting electric loads from a power supply system when the demand exceeds the supply of power available.

loan life coverage ratio

A financial ratio to estimate the ability of the borrowing company to repay an outstanding loan. The Loan Life Coverage Ratio (LLCR) is calculated by dividing the net present value (NPV) of the money available for debt repayment by the amount of senior debt owed by the company.


loss of load expectation


loss of load probability

London Interbank Ofered Rate

The rate at which banks sell deposits in the market / lend and borrow money to each other.

loss of load expectation

LOLE - expectancy (typically in d/year or h/year) of annual load interruptions.

loss of load probability

LOLP - probability at which a given load level cannot be supplied by the available generation (typically expressed in %).

loss payee

A beneficiary listed in the insurance policy (e.g. a project financing bank) that has a priority right to receive payments from the insurer. Once listed as a loss payee, proceeds payable as a result of an insured loss will be made to such party first.

low pass filter

Hardware filter in electrical circuits blocking frequencies above a specific cut-off frequency.

low voltage

A low voltage in AC systems are voltages lower than 1kV («=1kV) (IEC definition).

low-voltage grid

Distribution grid operated at low voltage for the supply of end customers.

Lower Voltage Ride Through

Capability of electrical devices, especially wind generators, to be able to operate through periods of low grid voltage. Also called Fault Ride Through (FRT) but without the overvoltage requirements.


line side converter (equivalent to GSC = Grid Side Converter)


low voltage


Lower Voltage Ride Through





Monitoring and Evaluation


measurement and verification


square metre per annum generation of one megawatt hour


mean Absolute Error

magnetic flux

Physical quantity describing the impact of a magnetic field. The SI unit of magnetic flux is the weber (Wb).

mains cold water connection

The connection where the cold water from the supplyer comes in

maintenance reserve account

A dedicated account in which cash sufficient to cover a project’s maintenance expenses is regularly deposited.


The amount expressed as a percent per annum above the interest rate basis or cost of funds. For hedging and futures contracts, the cash collateral deposited with a trader or exchange as insurance against default.

Markov process

A random process that has no memory – its result does not depend on earlier steps in the process. This means the next value of the process depends on the current value. It is independent of the previous values of the process. In probability theory, this property is also called the Markoff property.

maximum power point

That point on an I-V curve that represents the largest area rectangle that can be drawn under the curve. Operating a PV array at that voltage will produce maximum power.

maximum power point tracking

MPPT - operating the array at the peak power point of the array's I-V curve where maximum power is obtained.


Multilateral Development Bank

mean time between failures

Mean time to failure describes the expected average time between failures occuring in a system during operation.

mean time to failure

Average time that an item will function before it fails.

mean time to recover

The average time that a device will take to recover from any failure.

mechanical power

Mechanical work per unit time.

medium voltage

In AC voltages clasification, medium voltage is )1kV and «=35kV.

megavolt ampere

Unit for apparent power


Middle East and North Africa


Minimum Energy Performance Standards

merit order

A way of ranking available sources of energy, especially electrical generation, based on ascending order of price together with amount of energy that will be generated. In a centralized management, the ranking is so that those with the lowest marginal costs are the first ones to be brought online to meet demand, and the plants with the highest marginal costs are the last to be brought on line.


Modern Era Retrospective-Analysis for Research and Applications


(bio.) Mesophilic digestion process takes place optimally around 37°-41°C or at ambient temperatures between 20°-45°C where mesophiles are the primary micro-organism present. Synonym: low-temperature composting.


CH4 - a flammable, explosive, colourless, odourless, tasteless gas that is slightly soluble in water and soluble in alcohol and ether; boils at – 161.6°C and freezes at –182.5°C. It is formed in marshes and swamps from decaying organic matter, and is a major explosion hazard underground. Methane is a major constituent (up to 97%) of natural gas, and is used as a source of petrochemicals and as a fuel.


(bio.) Is the fourth and final step of anaerobic digestion. Methanogens, which are strictly anaerobic, transform the acetic acid (acetate), carbon dioxide and hydrogen into a mixture of methane and carbon dioxide (biogas) Synonym: Biomethanation

mezzanine debt

Refers to a type of debt which is between senior debt and equity. The cost of mezzanine debt is greater than senior debt as there is more risk involved.


Small combustion turbine with an output of 25 to 500 kW. Micro-turbines are composed of a compressor, combustor, turbine, alternator, recuperator and generator. Relative to other technologies for small-scale power generation, micro-turbines offer a number of advantages, including: a small number of moving parts, compact size, light weight, greater efficiency, lower emissions, lower electricity costs, potential for low cost mass production, and opportunities to utilize waste fuels.


An integrated local generation, transmission and distribution system/grid serving numerous customers, usually not connected to the national electricity grid. Also called micro-grid.

Minimum Energy Performance Standards

This term is used around the globe to define minimum legal efficiency requirements of equipment used in various industries.

minute reserve

Reserve available after 15 minutes of imbalances of power frequency (Syn. tertiary reserve)

mismatch losses

Losses due badly matched components in a system. For example, losses due to to varying electrical output characteristics (current) of single PV modules in a PV module string.

mixing valve

The device that mixes fluids e.g. to achive a certain temperature




modular multilevel converter


maximum net demand

molten salt

A salt that is in the liquid phase that is normally a solid at standard temperature and pressure (STP).

Monte Carlo Simulation

Monte Carlo simulations rely on repeated random sampling to obtain numerical results. To solve a problem that might be deterministic in principle Monte Carlo simulations use the randomness to solve a problem. They produce hundreds or thousands of possible results which are analyzed to get probabilities of different solutions.


A debt instrument, secured by the collateral of specified real estate property, that the borrower is obliged to pay back with a predetermined set of payments. Mortgages are used by individuals and businesses to make large real estate purchases without paying the entire value of the purchase up front. Over a period of many years, the borrower repays the loan, plus interest, until he/she eventually owns the property free and clear.


model output statistic


maximum power point


maximum power point tracking


Measurement, Reporting and Verification


May refer to: 1) Machine side converter (equivalent to RSC = Rotor Side Converter), 2) Mechanical Switched Capacitor


municipal solid waste


mean time between failures


mean time to failure


mean time to recover


Material that is solidified at such rate that many small crystals (crystallites) form. The atoms within a single crystallite are symmetrically arranged, whereas crystallites are jumbled together. These numerous grain boundaries reduce the device efficiency. A material composed of variously oriented, small individual crystals. (Sometimes referred to as polycrystalline or semicrystalline).

municipal solid waste

MSW - all types of solid waste generated by a community (households and commercial establishments), usually collected by local government bodies.


medium voltage


megavolt ampere


megavolt ampere reactive


motion vector Field




megawatt hour



May refer to: 1) Speed, 2) Normal to a surface 3) lifetime of the project

N-1 security

Ability of a power system to continue its unrestricted operation in case of failure of any one component.


The nacelle of a wind turbine contains the gear box and the generator. It is mounted at the top of the tower.


Nationally Appropriate Mitigation Action


sodium nickel chloride


Sodium Sulphur


National Aeronautics and Space Administration

Natura 2000 Site

Designated European sites that constitute Natura 2000 network of protected sites for habitats and species across the EU. They are defined in combination of Special Areas of Conservation and Special Protection Areas.

natural monopoly

A natural monopoly is a monopoly in an industry in which it is most efficient (involving the lowest long-run average cost) for production to be permanently concentrated in a single firm rather than contested competitively. Examples are infrastructures, such as electric power grids or natural gas grids, which cannot be operated in economic competition. Investment in these infrastructure will not justify parallel setups.


National Designated Authority


Nationally Determined Contribution

negative load

Distributed generation is sometimes seen as negative load, as it reduces the load on a feeder.


A tort involving failure to use a degree of care considered reasonable under a given set of circumstances. Acts of either omission or commission, or both, may constitute negligence.


North American Electric Reliability Corporation

net calorific value

The amount of heat released by a unit weight or unit volume of a substance during complete combustion. Lower than gross calorific value. For most combustion processes, the net calorific value is the relevant parameter.

net cash

A company's total cash minus total liabilities when discussing financial statements. Net cash is commonly used in evaluating a company's cash flow. More generally, net cash can refer to the amount of cash remaining after a transaction has been completed and all charges and deductions related to the transaction have been subtracted. (Syn. net cash flow).

net metering

Net metering allows residential and commercial customers who generate their own electricity from renewable power to feed electricity they do not use back into the grid, and to obtain credits for it.

net operating income

The net operating income equals all annual costs minus the annual revenue. The initial investment costs are not included in the net operating income.

net present value

NPV - the net present value or net present worth (NPW) is defined as the sum of the present values (PVs) of incoming and outgoing cash flows over a period of time.

network topology

"The physical structure of an electrical grid.


Non Governmental Organisation


Nickel Cadmium


National Implementing Entity


National Meteorological Centre


norm cubic meter


Nominal Operating Cell Temperature

Nominal Operating Cell Temperature

Temperature at which a solar cell operates when producing electricity over time under nearly full sunshine conditions, specifically 800 [W/m2], 20 ⁰C ambient temperature, and 1 [m/s] of wind speed. More realistic conditions that STC. Figure is given by manufacturers. Typically 20 ⁰C + upwards of 27 ⁰C = 47 ⁰C for standard modules. Sometimes used in sizing.

nominal voltage

Value of the voltage by which the electrical installation or part of the electrical installation is designated and identified.


Non-recourse debt or a non-recourse loan is a secured loan (debt) that is secured by a pledge of collateral, typically real property, but for which the borrower is not personally liable. If the borrower defaults, the lender/issuer can seize the collateral, but otherwise the lender's recovery is limited to the collateral.


Norwegian Agency for Development Cooperation


Short-term forecasts, normally with a forecast horizon between 0 and 8 hours.


net present value


turn ratio


Annoyance or disturbance that occurs to third parties and that can cause legal liability of the insured.


numerical weather prediction


mathematical model to forecast the weather usually running on super computers at a weather service.



operation and maintenance

O&M agreement

operations and maintenance agreement


open cycle gas turbine


The Organisation for Economic Co-operation and Development

off-grid system

An off-grid renewable energy system is a renewable energry system not connected to the national grid, e.g. an off-grid PV system.


(Also called: offtake purchaser). The purchaser of a project’s output.

open circuit voltage

VOC - the maximum voltage produced by an illuminated photovoltaic cell, module, or array with no load connected.

operating cash flow

Project revenues less cash operating expenses.

operating code

Regulations relating to a system’s operation.

operating reserve

Generating capacity available to an electricity network operator which can be activated within a short interval of time in order to meet demand if a generator goes down or there is another disruption to the supply.

operating risk

Cost, technology, and management components which affect operating expenses, output, or throughput.

operational expenditure

Costs of running a project.

operations and maintenance agreement

A contract obligating a party (usually the manufacturer of the project's equipment) to operate and maintain the project.


operational expenditure

opportunity costs

In microeconomic theory, the opportunity cost of a choice is the value of the best alternative forgone, in a situation in which a choice needs to be made between several mutually exclusive alternatives given limited resources. Assuming the best choice is made, it is the 'cost' incurred by not enjoying the benefit that would be had by taking the second best choice available


operating reserve


Organic Rankine Cycle


Substances that contain carbon, originating from living matter.

Organic Rankine Cycle

The Organic Rankine cycle (ORC) is named for its use of an organic, high molecular mass fluid with a liquid-vapour phase change, or boiling point, occurring at a lower temperature than the water-steam phase change. The fluid allows Rankine cycle heat recovery from lower temperature sources such as biomass combustion, industrial waste heat, geothermal heat, solar ponds, etc. The low-temperature heat is converted into useful work, that can itself be converted into electricity.

orogenic belt

An orogeny is an event that leads to a large structural deformation of the Earth's lithosphere (crust and uppermost mantle) due to the interaction between tectonic plates. Orogens or orogenic belts develop when a continental plate is crumpled and is pushed upwards to form mountain ranges.

OTC Market

over–the–counter market


Current higher than the nominal current.

overcurrent with inverse tripping characteristic

Slowest acting tripping element.


Describes the state of a generating plant when the plant voltage is greater than the network voltage. In this state the plant current lags the network voltage and the plant exports reactive power to the network


Voltage higher than the nominal voltage.

over–the–counter market

A market created by dealer trading as opposed to the auction market prevailing on organized exchanges.



active power




per unit


A device that can be run into a wellbore with a smaller initial outside diameter that then expands externally to seal the wellbore.

parabolic trough collector

A CSP technology which uses a long, parabolic-shaped mirror to concentrate solar radiation onto a central receiver tube running along the focal line of the parabolic mirror to produce high temperatures.

pay-back method

A method used to calculate a pay-back period and indicate how long it will take to recover the initial investment cost.

pay-back period

Is defined as the time it takes until the cumulated outgoing cash-flows equal the cumulated incoming cash-flows, i.e. until the project breaks even.


point of common coupling


phase change material


plan-do-check-act approach

peak demand

The highest energy (or power) demand during a specific period (generally, one year).

peak load hours

Hours within a period of time during where the load is highest.

peak power

The amount of electrical power a photovoltaic module will produce at Standard Test Conditions (normally 1,000 W/m2 and 25 ⁰C cell temperature), expressed in units of watt-peak (Wp) or a related unit such as kilowatt-peak (kWp) or megawatt-peak (MWp).

peak sun hours

If a location receives an average 1,200 kWh/m2/year, it is said to receive an average 1,200 PSH per day. If a location receives an average 5 kWh/m2/day, it is said to receive an average 5 PSH per day. A peak sun hour is equivalent to 1000 watts of solar energy falling on an area of 1 square meter for 1 hour or for example as 500 watts of solar energy falling on an area of 1 square meter for 2 hours.


electric power

penstock pipe

A pipe for transporting water to the hydro turbine

performance coefficient

Cp - a non-dimensional value describes the ratio of power that is captured by the wind turbine and fed into the grid. It is used to measure the wind turbine efficiency.

performance ratio

PR -the ratio of actual electricity output from a PV system and possible electricity output under 'ideal' conditions (no losses etc.). Expressed as a factor or a percentage.

permanent magnet synchronous generator

Generator where the excitation field is provided by a permanent magnet instead of a coil.The term synchronous refers here to the fact that the rotor and magnetic field rotate with the same speed, because the magnetic field is generated through a shaft mounted permanent magnet mechanism and current is induced into the stationary armature.

permanent magnetized synchronous generator

PMSG - synchronous generator equipped with an excitation system consisting of permanent magnets.

phase change material

A substance with a high latent heat of fusion which is capable of storing and releasing large amounts of energy as it changes state between liquid and solid, and vice versa.

phase errors

Forecast and measurement have the same shape but one lags behind the other in a manner similar to phase shift between voltage and current in AC systems.

phase-to-earth voltage

Root-mean-square value of the voltage in electrical circuits between phase and earth potential.

phasor diagram

Diagram giving a stationary representation of time-varying electrical quantities (e.g. voltage and currents) in a stationary representation.


Process by which chlorophyll-containing cells in green plants convert incident light to chemical energy, capturing carbon dioxide in the form of carbohydrates.


A photovoltaic process is a photoelectric process that converts solar energy into electricity

photovoltaic system

An installation of PV modules and other components designed to produce electric power from sunlight.


Photovoltaics (PV) refers to technologies which converting solar energy into direct current electricity using semiconducting materials that exhibit the photovoltaic effect.

physical vapour deposition

a physical process which produces a vapour of a material which is then deposited in a thin layer onto a surface


potential induced degradation

pilot scale

A system sized somehwere between a small laboratory model size (bench scale) and a full-size system.


A part of an engine that moves up and down inside a cylinder and that causes the main shaft of the engine to move.

pitch angle

The blade angle of a wind turbine blade is the angle between the chord of the blade and the plane of rotation, usually measured in degrees. It is called blade angle too.

pitch control

Power limitation in a wind trubine via movement of the rotor blade along its horizontal axis. Pitch controlled rotors are generally variable speed wind generators.

planning code

Definition of information exchange between the system users and the system operator enabling an optimized planning of the system.


A facility containing prime movers, electric generators, and other equipment for producing electric energy.


project life cover ratio


Market simulation and generation expansion planning software developed and released by Energy Exemplar Pty Ltd.


phase-locked loop


long-term flicker severity

plug flow process

Dry biomass (total solid dry matter content )15%) can be digested employing a plug flow process. The biomass substrate enters at one end of the digester, where it is pressed continuously through the reactor, while emitting biogas, and leaves the reactor at the other end.


A pluton is a deep-seated intrusion of igneous rock, a body that made its way into pre-existing rocks in a melted form (magma) several kilometers underground in the Earth's crust and then solidified.


maximum active power


mechanical power


permanent magnet synchronous generator


minimum active power


permanent magnetized synchronous generator


point of connection


provider of finance

point of common coupling

The point of a power supply network, electrically nearest to a particular load, at which other loads are, or may be, connected.

point of connection

Point of coupling (POC) is the point where transmission or distribution assets meet generator assets.

pole pair number

Number of magnetic pole pairs in electrical machines.

policy renewal date

A prolongation date that extends a previously contracted insurance poliy for a new insurance period. Insurance contracts usually have tenors of 3-5 years and can automatically or manually be prolonged at each policy renewal date.


Another word for multicrystalline.


A compound consisting of chains of large molecules, or macromolecules, composed of many repeated subunits.

polypropylene gylcol

An organic compound (alcohol) used for freeze protection

potential induced degradation

"Potential induced degradation (PID) is an undesirable property of some solar modules. Potential induced degradation, as the designation implies, occurs when a module’s voltage potential and leakage current drive ion mobility within the module between the semiconductor material and other elements of the module (e.g. glass, mount and frame), thus causing the module’s power output capacity to degrade.


Power is the rate of doing work. It is equivalent to an amount of energy consumed per unit time. In the SI unit is the watt (W), or the joule per second (J/s).

power canal

An open channel the purpose of which is to transport water

power curve

Graph that depicts the power output of a wind turbine as a function of wind speed. The power curve is one of the most important criteria for selecting the optimum wind turbine for specific wind conditions at selected sides.

power factor

(also: cos(phi), cos phi, cos.phi) - The power factor which is defined as the ratio of active power and apparent power. At the same time it is the phase shift in AC power systems, the cosine of the angle phi which is the angle between current and voltage.

power gradients

Gradients in power output.

power limitation

Power limitation prevents wind turbine performing above design criteria.

power purchase agreement

Contract with a large customer to purchase electricity from a power plant. Usually the most important type of contract relating to the construction and operation of a power plant.

power quality

Quality of the voltage in a power system. Any deviation from a pure sinusoidal voltage shape with constant amplitude and frequency is considered to be negative with regard to the quality of the voltage.

Power System Simulator for Engineering (power system analysis software released by Siemens)

PSS\E is a solftware used in the power industry for electric transmission system analysis and planning.

power-to-heat ratio

The proportion of electrical power and thermal power (heat) produced by a CHP or cogeneration system. It is an important design parameter. For example, if a system produces 25% electricity and 75% heat, it has a power-to-heat ratio of 1:3.


power purchase agreement


parts per million


Public-Private Partnership


performance ratio


‘Preconditioning’ means to prepare something for a later specific use. ‘Preconditioning’ in the context of photovoltaics refers to exposing PV cells/modules to UV radiation before initial performance check, heat-damp and thermal cycling tests; part of IEC 61215/61646 test routines. ‘Preconditioning’ in the context of biogas means that the raw biogas is prepared/treated so that it can be used for use in, for example, a specific engine or process.


The total annual remuneration that an insured party needs to pay to the insurer to maintain a given insurance coverage.

present value equivalent

An accounting measure that projects the value of a cash flow that lies in the future into the present, normally by discounting.

pressure drop

A drop in pressure in a piping system caused by flow resistance due to friction and turbulence (same as pressure loss)

pressure gauge

A device that gives a visual indication of the pressure in a system

pressure loss

A drop in pressure in a piping system caused by flow resistance due to friction and turbulence (same as pressure drop)

pressure relief valve

A valve that limits system pressure by releasing fluid when a certain safe pressure limit has been reached (same as safety valve)

pressure swing adsorption

Technology used to separate some gas species from a mixture of gases under pressure according to the species' molecular characteristics and affinity for an adsorbent material.

pressured water gas scrubbing

Process in which absorbed gas components are physically bound to the scrubbing liquid, in this case water.

primary control

First control mechanism activated within some seconds. It aims to restore the balance between generated and consumed active power at a certain frequency level. It is also known as primary frequency control.

primary energy

Total energy contained in a source, such as coal, oil or natural gas, before any conversion losses.

primary energy factor

The term 'primary energy factor' expresses the ratio between primary energy and delivered energy. For example, in Ireland the primary energy factor for electricity is 2.7; this means that for every 1kW consumed 2.7kW needs to be generated. The factor takes into account the losses in the energy chain including processing, storage, generation, transmission, distribution and delivery. Calculation methods vary from country to country.

primary reserve

Reserve available within 15 seconds.

prime mover

A machine that transforms energy from/to thermal, electrical or pressure to/from mechanical form, typically an engine or turbine.


The nominal or face amount of a bond or loan on which the issuer or borrower pays interest, and which, most commonly, has to be repaid at the end of the term.

principal exclusions

A provision of an insurance policy or bond referring to hazards, perils, circumstances, or property not covered by the policy. Exclusions are usually contained in the coverage form or causes of loss form used to construct the insurance policy.

pro forma

A financial projection based on a set of assumptions.

probability density function

A diagram that helps identify the probability of events, empirical basis can be a histogram.

process heat

Heat used in an industrial process.


A project is profitable if it makes a profit, i.e. if revenue exceeds the cost.

progressive cavity pump

Type of positive displacement pump that transfers fluid by means of the progress, through the pump, of a sequence of small, fixed shape, discrete cavities, as its rotor is turned.

project financing

Project financing usually refers to financing a project using funds explicitly raised for that particular project. As opposed to ‘corporate financing’ in which the funds used are those available to the company / organization as a whole, and with no additional funds raised for the particular project.

project life cover ratio

The net present value of a project's cash available for debt service (CADS) over the project’s defined life divided by the amount of principal outstanding at the time of calculation. (Syn. Loan life coverage ratio or loan life cover ratio or LLCR)


Energy consumers who also produce their own power from on-site generators (e.g. diesel generators, combined heat-and-power systems, wind turbines, and solar photovoltaic (PV) systems).


pressure swing adsorption


Private Sector Facility


peak sun hours


Power System Simulator for Engineering (power system analysis software released by Siemens)


short-term flicker severity


flicker Strength

Public Utilities Regulatory Policies Act

A landmark U.S. law that reformed electricity rates, and opened the market to non-utility generators, or independent power producers (IPPs) by requiring traditional utilities to purchase power from them at their avoided costs of generation. Pre-cursor to modern FiTs.

pulse width modulation

(PWM) - a commonly used technique for controlling power to inertial electrical devices, made practical by modern electronic power switches.


A device that forces fluid circulation in a system

pump head

Pressure produced by a pump to force flow of fluid


Public Utilities Regulatory Policies Act




power-voltage curve


physical vapour deposition


equivalent firm capacity including wind


pulse width modulation


pressured water gas scrubbing



reactive power


Quantum Geographical Information System


maximum reactive power


minimum reactive power

Quantum Geographical Information System

A cross-platform free and open-source desktop geographic information system (GIS) application that provides data viewing, editing, and analysis capabilities.





mode of energy transfer (e.g. heat, light) from a source to an object which does not require contact between source and object (i.e. the energy can be transmitted through a vacuum)

radiation heat transfer

Heat transfer via electromagnetic radiation. The only mode of heat transfer that can pass through a vacuum.

radioactive decay

Radioactive decay (also known as nuclear decay or radioactivity) is the process by which an unstable atomic nucleus loses energy (in terms of mass in its rest frame) by emitting radiation.


Weather measurement device with a radio transmitter connected to a balloon.

Rankine cycle

Thermodynamic cycle of a heat engine that converts heat into mechanical work. Used to predict the performance of steam turbine systems, such as steam-operated heat engines commonly found in thermal power generation plants.

rapid voltage changes

Voltage steps or other voltage variations (single events) that are a result of grid disturbances or switching actions.

rated power

Power of wind turbine at a given rated wind speed.

rated wind speed

The wind speed at which the turbine is producing its nameplate-rated power production.


residual-current device


Renewable Energy


Re-scheduling of power plant on short notice to solve congestion in the grid.


"Physical quantity in electrical AC systems which lead to a phase shift between voltage and current .

reaction turbine

A turbine which has a different pressure before and after the impeller. It is fully submerged in water and operates under pressure.

reactive power

A component of apparent power (volt-amps) which does not produce any real power (watts). It is measured in VARs (volt-amps reactive).


Reducing Emission from All Land Uses


renewable energy certificate

receiver tube

In a CSP installation, the receiver tube comprises an absorber tube which is inside an evacuated glass tube. A heat transfer fluid is inside the absorber tube. Solar radiation is absorbed by the absorber tube and transferred to the heat transfer fluid. The outer evacuated glass tube acts to minimise heat losses.


Recourse debt, also known as a recourse loan is a debt that is backed by collateral from the borrower. This type of debt allows the lender to collect from the debtor and the debtor's assets in the case of default as opposed to foreclosing on a particular property or asset. In the event that a project cannot service the financing or achieve completion, the financiers have 'recourse' to either cash from the project sponsor or other non–project security.


Reducing Emissions from Deforestation and Forest Degradation


The repayment of a debt or a bond to a lender in pre-specified amounts before the debt's a bond's maturity date.

reference yield

Energy output according to average wind speed of 5.5 m/s at 30 meters height and Rayleigh distributed wind speeds with a shape factor k = 2 and roughness length Z0 = 0.1 m.

reflection coefficient

It is defined as the ratio of reflected radiation from the surface to incident radiation upon it.


A transaction in which one party, the "reinsurer," in consideration of a premium paid to it, agrees to indemnify another party, the "reinsured," for part or all of the liability assumed by the reinsured under a policy of insurance that it has issued. The reinsured may also be referred to as the "original" or "primary" insurer or the "ceding company."


An electrical device by means of which a circuit is automatically controlled by a change in the same or another circuit.


Reliability of a power system refers to the probability of its satisfactory operation over the long run.

remote terminal unit

A microprocessor-controlled electronic device that interfaces objects in the physical world to a distributed control system or SCADA (supervisory control and data acquisition) system by transmitting telemetry data to a master system, and by using messages from the master supervisory system to control connected objects. In large PV systems it can be used for remote communication between the PV system and the electric grid; can transmit status information such as actual power production and receive control commands for inverters to reduce power output or activate reactive power.


Renewables Academy AG

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Renewables Academy Online

renewable generation

Electricity generation driven by renewable energy (sun, wind, hydro, biogas).

renewable resources

Naturally replenishable, but flow-limited energy resources. They are virtually inexhaustible in duration, but limited in the amount of energy that is available per unit of time. Renewable energy resources include: biomass, hydro, geothermal, solar and wind. In the future they could also include the use of ocean thermal, wave, and tidal action technologies. Utility renewable resource applications include bulk electricity generation, on-site electricity generation, distributed electricity generation, non-grid-connected generation, and demand-reduction (energy efficiency) technologies.


renewable energy sources


Renewable Energy Source - Electricity

reserve account

A separate cash account used to meet future payment obligations such as debt service, maintenance, or capital expenditure.

reserve margin

Excess of generation capacity needed for supplying the system load with sufficient reliability.


A body of water formed by damming a river or stream

residual asset value

The value of an asset at the conclusion of a lease term.

residual load

Remaining load that has to be provided by fossil fuel power plants once renewable energy generation has been substracted from total load. Load minus generation from VRE (variable renewable energy).

residual-current device

Electrical wiring device that disconnects a circuit whenever it detects that the electric current is not balanced between the energized (line) conductor(s) and the return (neutral) conductor. (Syn. Ground fault circuit interrupter or GFCI; or ground fault interrupter or GFI)


Restistance is the term used to describe the opposition to the passage of an electric current through a conductor. The SI unit of electrical resistance is the ohm (Ω).


An amount held back from construction contract payments to ensure the contractor completes the construction before the retention (typically 5-15% of the contract price) is returned to the contractor.

Return (vs. Flow)

cold line of a system (from consumer to heat source)

return on equity

Similar to IRR, the ROE represents the profitability of a given investment over a given time period. It refers to the return on investment that an equity investor (as opposed to a debt investor, such as a bank) expects to make from investing in a particular project.


The total amount of payments a firm receives during a specific period of time, also called 'gross income'.

reverse return

A special loop in pipe installation to guarantee good distribution of the flow in parrallel branches (also known as 'Tichelmann')


Event(s) which can possibly reduce the expected cash flow forecast for project financing.

risk-adjusted pricing

A pricing method for the determination of the interest rate of a loan or other funding which considers the risk involved. Low risk borrowers or projects will receive a lower interest rate than someone with higher risk.

risk-free interest rate

Risk-free interest rate is the theoretical rate of return of an investment with no risk of financial loss. One interpretation is that the risk-free rate represents the interest that an investor would expect from an absolutely risk-free investment over a given period of time


reserve margin


root mean square


root mean square error


return on equity

rotary lobe pumps

Rotary lobe pumps are used in a variety of industries including pulp and paper, chemical, food, beverage, pharmaceutical, and biotechnology. They offer good sanitary qualities, high efficiency, reliability, corrosion resistance and good clean-in-place and steam-in-place (CIP/SIP) characteristics.


Rotating component of an electrical machine.

rotor diameter

The rotor diameter describes the diameter of the circle that is swept by the blades of a wind turbine. As a rule of thumb, doubled rotor diameter quadruples the wind turbines rated power output.

roughness length

A parameter of some vertical wind profile equations that model the horizontal mean wind speed near the ground; in the log wind profile, it is equivalent to the height at which the wind speed theoretically becomes zero.


ratio between standard deviation and correlation


remote terminal unit


Refers to a type of small hydropower plant which has little or no water storage



apparent power


Special Area of Conservation

sacrificial anode

An easily corroded metal rod (usually magnesium) installed in a water tank to protect the less-easily corroded tank material from corroding

safety valve

A valve that limits system pressure by releasing fluid when a certain safe pressure limit has been reached (same as pressure relief valve)


System Average Interruption Duration Index

salvage value

The estimated selling price of an asset once it has been fully depreciated.


supervision control and data acquisition


squirrel cage induction generator


Process of identifying the significant issues that should be addressed by an environmental impact assessment.


German regulation speficying connection conditions for onshore wind generation. Part of German renewable energy legislation.

second generation biofuels

Second generation biofuels' are based on a broader spectrum of feedstock including cellulosic biomass. The aim is to increase efficiency and to reduce competition to food production. The potential feedstocks include waste biomass, the stalks of wheat and corn, wood, and special energy crops (e.g. miscanthus). Main technologies for second generation of biofuels are biomass to liquid (BtL) and cellulosic bioethanol production processes.

secondary control

Second grid control mechanism which is able to increase active power output within 15 seconds and is able to maintain the response for a further 30 minutes. It aims at bringing system frequency back to the set-point value. Also known as secondary frequency control.

secondary energy

Energy that has been extracted/generated from another primary energy source; examples of secondary energy include electricity or biogas.

secondary reserve

Reserve available after 5 minutes


"The process through which an issuer creates a financial instrument by combining other financial assets and then marketing different tiers of the repackaged instruments to investors. The process can encompass any type of financial asset and promotes liquidity in the marketplace.


1.(supply) Security of a power system refers to the degree of risk associated with its ability to survive imminent disturbances (contingencies) without interruption of customer service

selective coating

A special coating applied to a surface to improve the radiation absorption, reflection and emission properties of the surface


A material that has a limited capacity for conducting electricity. The silicon used to make PV cells is a semiconductor.

senior debt

Borrowed money that a company must repay first if it goes out of business.

serial damage

Loss or damage due to faulty design, defective material or casting, bad workmanship other than faults in erection arising out of the same cause to machines or equipment of the same type or design.

sewage sludge

Semisolid product of water purification in a sewage plant.


synchronous generator

shadow flicker

Term used to describe the short-lived effect of shadows cast by rotating blades of wind turbines when the sun passes behind them, and which occurs under certain combinations of geographical positions and time of day.


Mechanical connection between turbine and generator.

shape parameter (k)

k is the form parameter of the Weibull distribution. It specifies the shape of a Weibull distribution and takes on a value of between 1 and 3. A small value for k signifies very variable winds, while constand winds are characterized by a larger k.

shareholders agreement

The generic term for any contract between two or more shareholders governing their conduct in relation to the corporation, or partnership, in which they own shares.

short circuit current

The current produced by an illuminated PV cell, module, or array when its output terminals are shorted.


A device which allows electric current to pass around another point in the circuit. The term is also widely used in photovoltaics to describe an unwanted short circuit between the front and back surface contacts of a solar cell, usually caused by wafer damage.

shut-off valve

A valve to shut-off a pipe and stop circulation (same as isolating valve)


A compound having a molecular structure based on a chain of alternate silicon and oxygen atoms, especially (as in silicone) with organic groups attached to the silicon atoms.

slack node

The node in a load flow problem at which active and reactive power flows are balanced.


Slip is defined as the difference between synchronous speed and operating speed in induction or asynchronous motor or generator.

slip ring

A slip ring is an electromechanical device that allows the transmission of power and electrical signals from a stationary to a rotating structure. A slip ring is used in electromechanical systems that require unrestrained, intermittent or continuous rotation while transmitting power. It is mounted on a rotating part of a machine to provide a continuous electrical connection through brushes on stationary contacts.


Biosolids separated from liquids during processing. Sludge may contain up to 97 % water by volume.


synchronous machine

smart grid

An electricity network based on digital technology that is used to supply electricity to consumers via two-way digital communication. Includes a variety of operational and energy measures such as smart meters, smart appliances, renewable energy resources, and energy efficiency resources.


small and medium-sized enterprises




Solar Radiation Data

solar fraction

The proportion of the energy demand which is met by the solar thermal system (typically given as a %)

solar gain

The increase in temperature in a space, object or structure that results from solar radiation.

solar irradiance

Solar power incident on a surface at any one time. The solar power incident on a surface. Solar irradiance is literally the power (watts) of the sun incident to a surface. The international unit of scientific measurement of irradiance is W/m2.

solar irradiation

The total solar energy over a set period of time reaching a unit of surface area. Usually expressed in kilowatt-hours per square meter (kWh/m2). Also called insolation.

solar radiation

Energy from the sun is emitted as electromagnetic radiation, which includes visible light.

solar station

A compact and well-insulated unit that contains the main components and armatures of a solar thermal system

solar thermal

System that produces thermal energy (heat) from sun light

solar tower

A CSP technology which uses a ground-based field of mirrors to focus and concentrate direct solar irradiation onto a receiver mounted high on a central tower to produce high temperatures.

solid biomass

A material of recent biological origin, e.g. wood or plant matter. The most common form of solid biomass is wood fuel (energy content approx. 10-20 MJ/kg), used e.g. for heat and power generation.

sound power level

Describes the ability of a source to produce noise (strength of source). IEC 61400-11 is a standard for turbine noise measurement. Sound is measured using units of decibels (dB).

sound pressure level

Measure of the noise level at a receptor (neighbor of wind farms, microphone). Sound is measured using units of decibels (dB) and (dB(A)).


special protection area

space heating

The heating of rooms and buildings in cold climates

spatial resolution

Geographical resolution.

spatio-temporal grid

Spatial and time resolution of a numerical weather prediction model.


special purpose entity

Special Area of Conservation

SAC - protected area under EU Habitats Directive (92/43/EEC), designated for rare, vulnerable and endangered habitats and species (e.g. plants, mammals and fish), listed in Annexes I and II Habitats Directive.

special protection area

SPA - protected area under EU Birds Directive (79/409/EEC), designated for bird species listed in Annex I of the Directive, in particular internationally important concentrations of migratory and wetland birds. Designation is focused on habitats of these species.

special purpose entity

An entity established for a particular purpose, such as obtaining off-balance sheet financing, gaining tax advantages, or isolating the sponsors’ other assets from the project’s creditors. Also known as special purpose vehicle (SPV).

special purpose vehicle

SPV is interchangeable with the term "special purpose entity - SPE"

specific heat capacity

The heat required to raise the unit mass of a substance by unit temperature (SI unit: J/kgK)

specific power of wind turbines

Rated power of generator (W) / rotor swept area (m2).

spinning reserve

The difference between the total available capacity of all fossil fuelled power generators already coupled to the power system and their actual loading.


A party wishing to develop and finance (with equity) a project. Shareholders of project companies are known as sponsors.

spot market

The market for buying and selling a specific commodity, foreign currency, or asset at the prevailing price for immediate delivery.

spot price

The current market price of the actual physical commodity. Also called the cash price.


Small Power Producer

spread-skill relationship

For ensemble prediction the spread between the ensemble members gives a hint to the skill (accuracy) of the prediction. At higher spreads a larger forecast error is more likely.


special purpose vehicle

squirrel cage induction generator

SCIG - induction generator in which the rotor shape is a cylinder mounted on a shaft. Internally it contains longitudinal conductive bars (usually made of aluminum or copper) set into grooves and connected at both ends by shorting rings forming a cage-like shape. In wind turbine technology it is often referred to as a IEC Type 1 machine.


spinning reserve


Shuttle Radar Topography Mission


Stability of a power system refers to the abilitiy to continue intact operation following a disturbance.


An equilibrium state reached in a solar thermal collector (energy captured equals energy lost) during periods of continuous high solar irradiation without consumption

stagnation temperature

The solar thermal collector temperature at which stagnation occurs


Description of the aerodynamical effect that the air stream around an airfoil (e.g. rotor blade) breaks away and which results in a reduction of the lift coefficient

stall control

Power limitation method in a wind turbine. Stalling works by increasing the angle at which the relative wind strikes the blades (angle of attack), and it reduces the induced drag (drag associated with lift). Stall controlled rotors are generally operated at two speeds.

stand-alone PV System

A photovoltaic system that operates independent of the utility grid, an off-grid PV system.

stand-alone system

A power source/generator that operates independently of or is not connected to an electric transmission and distribution network; used to meet a load(s) physically close to the generator. (Syn. Off-grid system)

standard deviation

SD - a measure that is used to quantify the amount of variation or dispersion of a set of data values from the average value.

standard test conditions

STC - accepted standard for controlled laboratory testing and certification of PV cells and module output. Standard Test Conditions are defined as 1,000 W/m2 of light intensity with a replicated solar spectrum of AM 1.5 and 25°C cell (or module) temperature.


static synchronous compensator


The amount of energy remaining in a battery, as a percentage of its maximum capacity. SoC is the opposite of depth-of-discharge. (SoC = 1 – DoD) For example, a state of charge = 60% means that 40% of the battery has been discharged (they are 40% empty, or the depth-of-discharge = 40%).

static calculations

Static calculations neglect the time value of money. Future cash-flows are not discounted (opposite to dynamic calculations).

static height

The height of a vertical column of water at rest that produces a given pressure (e.g. 10 m vertical column of water cause a pressure of 1 bar)

static pressure

The pressure at a point caused by the weight of a vertical column of water at rest acting on that point

static synchronous compensator

(STATCOM) - a regulating device used on alternating current electricity transmission networks. It is based on a power electronics voltage-source converter and can act as either a source or sink of reactive AC power to an electricity network. If connected to a source of power it can also provide active AC power. It is a member of the FACTS (flexible alternating current transmission system) family of devices.

static VAR compensator

SVC - a device that supplies or consumes reactive power.


Stationary part of an electrical machine.


standard test conditions


(bio.) A device that is used to mix biomass substrates within a digester or digestate storage tank in order to facilitate the digestion process by increasing the contact zones of methanogenic bacteria with fresh biomass substrate, also called an agitator.

stochastic tree

A decision tree with branches that represent the probability of occurrence.


A formation of layers, e.g. of different temperature layers in a hot water tank



string of modules or solar cells

When PV modules or solar cells are connected in series, they are called a string of PV modules or solar cells.


Germany’s first Renewable Energy Feed-in Law, adopted in 1990, which required utilities to purchase power from renewable electricity producers at rates based on a percentage of retail prices (65-90%).


(fin.) The act of developing and setting up a ) financial structure.


Speed range lower than the synchronous speed.

sub-transmission grid

Electricity grid operated at HV or MV for regional power transfers (sometimes part of transmission, sometimes part of distribution grid).


A limitation in an insurance policy on the amount of coverage available to cover a specific type of loss. A sublimit is part of, rather than in addition to, the limit that would otherwise apply to the loss. In other words, it places a maximum on the amount available to pay that type of loss, rather than providing additional coverage for that type of loss.


The assignment to an insurer by terms of the policy or by law, after payment of a loss, of the rights of the insured to recover the amount of the loss from one legally liable for it.


Input material for a process, also called feedstock.


Speed range higher than the synchronous speed.

supervision control and data acquisition

Supervisory control and data acquisition (SCADA has the tasks control plants and to monitor, collect, store and analyse operating data.

supply side energy efficiency

Energy efficiency measures by utilities that reduce the losses in power generation and transmission processes. This leads to an increase of the supply of final energy (e.g. electric power at the consumer’s place), at a constant level of primary energy supply.


An ecosystem condition in which biodiversity, renewability and resource productivity are maintained over time.


static VAR compensator


An arrangement in which two entities lend to each other on different terms, for example, in different currencies or at different interest rates, fixed or floating.

swept rotor area

Area swept by the rotating blades of a wind turbine.

Sydney tube

A double walled evacuated glass tube

synchronous generator

Electrical machine which generates electrical power and carries a DC current for the magnetisation in the rotor. Thus the speed of the generator is synchronously to the grid frequency.

synchronous machine

An alternating current machine in which the frequency of the generated voltages and the speed of the machine are in a constant ratio.

System Average Interruption Duration Index

An indicator commonly used as a reliability indicator by electric power utilities. SAIDI is the average outage duration for each customer served. It is the sum of all customer interruption durations divided by the total number of customers served. Measured in units of time, hours per year or minutes per year.

systematic bias

A systematic deviation that has a non-zero average. Can be caused, for example, by errors in measurement devices. (syn. systematic error )

systematic error

A systematic deviation that has a non-zero average. Can be caused, for example, by errors in measurement devices. (syn. systematic bias )



on a tilted surface

tamper proof valve

A valve which is lockable or requires a special key to open to prevent operation by mistake


Generally a duty or tax on imports (charged/ levied based on a percentage of cost or specific amount per unit), but can also mean charge/payment for a service as in 'feed-in-tariff'.

tariff degression

Automatic (annual or monthly) reduction of feed-in tariff payment levels in order to anticipate technology improvements.


transmission Code 2007


total cost of ownership


transparent conductive oxide

temperature gauge

A device that gives a visual indication of the temperature in a system

temperature sensor

A device that senses the temperature in a system

temperature sensor pocket

A pocket or sleeve installed in the fluid flow of a system into which the temperature sensor is inserted


In loan finance, the number of years a loan is outstanding (i.e., the final maturity or term).

term sheet

A non-binding agreement setting forth the basic terms and conditions under which an investment will be made. A term sheet serves as a template to develop more detailed legal documents. Once the parties involved reach an agreement on the details, a binding agreement or contract is drawn up.

terminal voltage

Voltage level at the connection terminal of a certain electrical unit to the power system

tertiary control

Third grid control mechanism that has to be available within 15 minutes. It involves a manual or automatic change in the dispatching of power, e.g. changing power output of certain generators participating in secondary control. It is also known as tertiary frequency control, tertiary reserve is also known as minute reserve.

tertiary reserve

Reserve available after 15 min. (Syn. minute reserve)

thermal bridges

Area of an object (frequently a building) which has a significantly higher heat transfer than the surrounding materials, resulting in an overall reduction in the thermal insulation of the object or building.

thermal insulation

Material or construction that reduces the transfer of heat from one objects to another or to the outside environment.

thermal oil

Thermal oil is the most commonly used heat transfer fluid in parabolic trough CSP arrays. Its composition is 26.5% biphenyl, 73.5% diphenyl oxide. It operates in the temperature range 12-392C. It is non-corrosive but it is toxic.


(bio.) Thermophilic digestion process is an anaerobic digestion which takes place optimally around 50°C-52°C but also at elevated temperatures of up to 70°C, where thermophiles are the primary micro-organisms (bacteria) present.

thermosiphon system

A heating system in which the fluid circulates by natural convection due to the different densities of the fluid at different temperatures

thermostatic mixing valve

A valve that blends hot water with cold water to ensure constant, safe shower and bath outlet temperatures, preventing scalding.

thin film PV module

A PV module constructed with sequential layers of thin film semiconductor materials.

third–party liability insurance

Insurance against damage or injury caused to the project by third parties. Insurance policy purchased for protection against the actions of another (a third) party. It is purchased by the insured (the first party) from an insurance company (the second party) for protection against damage from the actions of another party (a third party).


Three-phase refers to a circuit consisting of three conductors where the current and voltage in each conductor (phase) is 120° out of phase with each other phase.


Switching element in power electronics based on semiconducting material. A solid-state semiconductor device with four layers of alternating N and P-type material. They act as bistable switches, conducting when their gate receives a current pulse, and continue to conduct while they are forward biased (that is, while the voltage across the device is not reversed).


A special loop in pipe installations to guarantee balanced flow in parallel branches (also known as 'reverse return')

tie lines

Tie line is the connection point between two or more power plants.

tilt angle

The angle of inclination of a solar collector measured from the horizontal.

tip speed ratio

The tip-speed ratio, λ, or TSR for wind turbines is the ratio between the tangential speed of the tip of a blade and the actual velocity of the wind, v. The tip-speed ratio is related to efficiency, with the optimum varying with blade design.


thermostatic mixing valve


tons of oil equivalent

tons of oil equivalent

toe - A unit of energy, the amount of energy released by burning one ton of crude oil, approx. 42 GJ.

topography data

Earth surface shape data


terms of reference


It is the tendency of a force to rotate an object about an axis. Mathematically, torque is defined as the cross product of the lever-arm distance vector and the force vector, which tends to produce rotation.

total cost of ownership

A financial estimate intended to help buyers and owners determine the direct and indirect costs of a product or system.

total solids

The residue remaining when water is evaporated away from the residue and dried under heat. (Syn. dry solid)


Transformers typically connect circuits of different voltage. The device transfers electrical energy from one circuit to another through inductively coupled conductors. Transformers induce either a voltage or current in a secondary circuit, which is proportional to the voltage or current in the primary circuit.

transmission Code 2007

German grid code for connection to HV and EHV grids.

transmission grid

Meshed grid operated at HV or EHV for long, inter-regional power transfers. Part of a national electricity grid operated at HV or EHV for long, inter-regional power transfers.

transmission system

Normally, the highest voltage network of an electric utility system. It carries high power over the longest distances. Typically operating at voltages in excess of 100 kV, and most usually at 200 kV and above.

transmission system operator

An entity entrusted with transporting energy in the form of natural gas and/or electrical power on a national or regional level, using fixed infrastructure.

transparent conductive oxide

Doped metal oxides used in optoelectronic devices such as flat panel displays (screens) and photovoltaics.


thyristor-switched capacitor


transmission system operator


time to failure


time to recover


A machine for converting the heat energy in steam or high temperature gas into mechanical energy. In a turbine, a high velocity flow of steam or gas passes through successive rows of radial blades fastened to a central shaft.

turnkey contract

A construction contract that provides for the complete engineering, procurement, construction, and start-up of a facility by a certain date, at a fixed price and at guaranteed performance levels.


Tera Watt hours



The overall heat transfer coefficient that describes how well a building element conducts heat or the rate of transfer of heat (in watts) through one square metre of a structure divided by the difference in temperature across the structure.


upflow anaerobic sludge blanket


Electromagnetic radiation with shorter wavelengths than visible light. Wavelengths of UV light range from approximately 10 nm to 400 nm. Because of the short wavelengths, UV light carries higher levels of energy per photon than infrared light or visible light. When speaking about solar cells, UV light is commonly referred to as ‘blue light’.


Ultra Mega Power Project


United Nations


Describes the state of a generating plant when the plant voltage is less than the network voltage at the POC. In this state the plant current leads the network voltage and the plant absorbs reactive power from the network.


United Nations Development Programme


United Nations Environment Programme


United Nations Framework Convention on Climate Change

unidirectional power flow

Power flow in only one direction.


internal voltage (synchronous generator)

upflow anaerobic sludge blanket

A form of anaerobic digester that is used for wastewater treatment and uses an anaerobic process whilst forming a blanket of granular sludge which suspends in the tank. Wastewater (liquids with relaitvely low organic loads) flows upwards through the blanket and is processed (degraded) by the anaerobic microorganisms.


In the higher part of a stream, closer to its source


US Agency for International Development

useful energy

Energy that can be used to perform a certain task, as opposed to total energy generated (some of which may not be capable of being used, such as waste heat).


Everybody that makes use of a power system, such as generators, consumers, network operators


terminal voltage


Coordinated Universal Time

UV light




May refer to:

1) volt

2) voltage



value–added tax

A form of consumption or sales tax. From the perspective of the buyer, it is a tax on the purchase price. From that of the seller, it is a tax only on the value added to a product, material, or service, from an accounting point of view, by this stage of its manufacture or distribution. The manufacturer remits to the government the difference between these two amounts, and retains the rest for themselves to offset the taxes they had previously paid on the inputs. Also know as a general Sales tax (GST).

variable renewable generation

The generation of electricity from a variable renewable resource such as wind power and solar power. Because of their fluctuating nature, the production of electricity from these resources also flucuates and is thus 'variable'.


value–added tax


virtual classroom


Voluntary Emission Reductions


volatile fatty acids


A viable project is a project that has the potential to be profitable.


(bio.) The ratio of the tangential frictional force per unit area to the velocity gradient perpendicular to the direction of flow of a fluid.

visible light

Electromagnetic radiation, which is visible to the human eye. The wavelengths of visible light range between 380 nm and 750 nm. Within that range, the different wavelengths are visible as colours, from longer to shorter: red, orange, yellow, green, blue, indigo and violet.


open circuit voltage

volatile fatty acids

VFA - these are acids that are produced by microbes in the silage from sugars and other carbohydrate sources. By definition they are volatile, which means that they will volatilize in air, depending on temperature. These are the first degradation product of anaerobic digestion prior to methane creation.

volatile solids

VS - those solids in water or other liquids that are lost on ignition of the dry solids at 550°C.


Unit of electromotive force or electric pressure analogous to water pressure. One volt is defined as the difference in electric potential between two points of a conducting wire when an electric current of one ampere dissipates one watt of power between those points


VA - apparent power is expressed in volt-amps. Apparent power product of the applied voltage and current in an AC circuit (VxI). It is not the true power of the circuit because the power factor is not considered in the calculation.


Measure of the electric potential difference between two points, usually measured in volts (V).

voltage source converter

VSC - converter technology consisting of two back-to-back connected converters linked together via a DC circuit consisting of DC link capacitor for storing the electrical energy

Voluntary Emission Reductions

Also known as "Verified Emission Reductions". VERs are commonly understood as tradable emission reductions that have been generated according to defined standards and requirements other than the Kyoto Protocol.


Variable Renewable Energy


volatile solids


voltage source converter


Very Small Power Producer





watt per square metre


weighted average cost of capital

wafer-based PV module

A PV module constructed with silicon wafers. A wafer is a rectangularly-shaped (rarely round) and very thin silicon disc.

waiver of subrogation

An agreement between two parties in which one party agrees to waive subrogation rights against another in the event of a loss. The intent of the waiver is to prevent one party's insurer from pursuing subrogation against the other party. Generally, insurance policies do not bar coverage if an insured waives subrogation against a third party before a loss. However, coverage is excluded from many policies if subrogation is waived after a loss because to do so would violate the principle of indemnity.

wake effect

A wind turbine located downstream of the air flow of another wind turbine 'sees' less wind speed than the first one and consequently produces less power. This is called the 'wake effect'.

wake losses

Reduced power ouput occurring in a wind turbine due to decreased wind speed caused by another wind turbine in front to it.


Wien Automatic System Planning Package

waste heat recovery

Process in which waste heat from an industrial process is used for another purpose or process. The aim is to reduce energy consumption.

watt peak

Amount of electrical power a photovoltaic module will produce at Standard Test Conditions (AM 1.5, 1,000 W/m2 and 25°C cell temperature).


World Business Council for Sustainable Development

weather service

Public or private company creating weather forecasts.

Weibull distribution

The Weibull wind speed distribution is a mathematical idealization of the distribution of wind speed over time.

Weibull scale parameter

The scale parameter (A) in the Weibull distribution is a measure for the characteristic wind speed distribution. A is proportional to the mean wind speed. Unit: m/s

weighted average cost of capital

WACC [%] - Formula used to calculate the actual cost of capital used to finance a project. Typically refers to the weighted cost of both debt (e.g. from a bank) and equity (from private investors). For instance, if a project uses 80% debt at a rate of 5% and 20% equity at a rate of 10%, the WACC will be 6%. This represents the cost of capital used to finance that project.


Wholesale Electricity Spot Market


waste heat recovery

Wien Automatic System Planning Package

An IAEA computer software for power generating system expansion planning.

wind power class

A scale from 1 (low) to 7 (high) based on average wind speed (m/s or mph) and power density (W/m2) which rates the quality of the wind resource in an area.

wind ramps

Steep increase or decrease of wind speed.

wind shear

Variation of wind speed with height above ground level.

wind turbine generator

WTG - device for the conversion of wind energy into electrical energy, including the nacelle, rotor, hub, blades, generator, tower and foundation.


Material (as wire) wound or coiled about an object (as an armature); also: a single turn of the wound material.

wound rotor induction generator

Induction generator with a wound rotor


watt peak


wind power management system


World Resources Institute


wound rotor induction generator


wind turbine


wind turbine generator





reactance to resistance ratio


synchronous reactance


sub-transient reactance


transient reactance

xd’’, xd’ and xd

(formula) Subtransient/transient and synchronous reactance.


yaw control

Yaw is the angle of rotation of the nacelle around its vertical axis. Yaw control ensures that a wind turbine always faces directly into the wind.


"(power plant ) Energy output of a renewable heat or power generating plant over a specified period of time.




zenith angle

Angle measured from directly overhead to the geometric centre of the sun's disc, as described using a horizontal coordinate system. The solar elevation angle is the altitude of the sun, the angle between the horizon and the centre of the sun's disc. If θs is the solar zenith angle, then the solar elevation angle αs = 90° – θs.

zero loss efficiency

Efficiency of a collector when there are no thermal losses

zone of theoretical visibility

ZTV - Maps produced are theoretical because they estimate exposure of proposed development based upon landform data only, and take no account of intermittent screening by vegetation or structures. ZTV maps estimate visibility of the proposed development in the surrounding landscape and not its 'visual influence'.

zone of visual influence

ZVI - Provides a visual representation, usually presented as a map with markings or colourings, of the area over which a site and/or a proposed development may be visible.


zone of theoretical visibility


zone of visual influence



temperature coefficient of PV cells



May refer to:

1) blade angle

2) pitch angle



load angle



efficiency of PV modules at maximum power point



rotor angle



tip speed ratio



air density



standard deviation



angular frequency

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