English Glossary

Since 02.06.2017

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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 )

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