English Glossary

Since 02.06.2017

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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.

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