Alternating current (AC): Flow of electricity that constantly changes direction between positive and negative sides.

Alternator: A device that produces alternating current (AC) electricity from the rotation of a shaft. Used in wind and water turbines to generate electricity.

Amps: The volume of electricity flowing through a conductor.

Availability factor: A percentage representing the number of hours a generating unit is available to produce power (regardless of the amount of power) in a given period, compared to the number of hours in the period.

Base load: The minimum load experienced by an electric utility system over a given period of time.

Baseload capacity – Generating equipment operated to serve loads 24-hours per day (eg. nuclear power plants).

Biodiesel: A liquid fuel made from vegetable oils, made by combining alcohol (usually methanol) with vegetable oil, animal fat, or recycled cooking grease. It can be used as an additive (typically 20%) to reduce vehicle emissions or in its pure form as a renewable alternative fuel for diesel engines.

Bioenergy: Useful, renewable energy produced from organic matter, which may either be used directly as a fuel or processed into liquids and gases.

Biofuels: Unlike other renewable energy sources, biomass can be converted directly into liquid fuels, called ‘biofuels,’ to help meet transportation fuel needs. The two most common types of biofuels are ethanol and biodiesel. Also refers to Biomass converted directly to energy or converted to liquid or gaseous fuels, such as ethanol methane, and hydrogen.

Biomass: Organic nonfossil material of biological origin constituting a renewable energy source. Renewable fuels derived from purpose grown energy crops and the biodegradable proportion of industrial, municipal, agricultural and forestry residues.

Biomass gas (Biogas): A medium Btu gas containing methane and carbon dioxide, resulting from the action of microorganisms on organic materials such as a landfill.

Biopower: Is the use of biomass to generate electricity. Biopower system technologies include ‘direct-firing,’ ‘cofiring,’ ‘gasification,’ ‘pyrolysis,’ and ‘anaerobic digestion.’ Most biopower plants use direct-fired systems. Paper mills, the largest current producers of biomass power, generate electricity or process heat as part of the process for recovering pulping chemicals. Also referred to as ‘biomass power.’

Blade: The part of a wind generator rotor that catches the wind.

CBM: Coal bed methane; gas actively extracted from coal seams.

Capacity: The maximum load a generating unit, generating station, or other electrical apparatus is rated to carry.

Capacity factor: The ratio of the electrical energy produced by a generating unit relative to the electrical energy that could have been produced at continuous full power operation during the same period of time.

CCGT: Combined cycle gas turbine; modern gas powered electricity generating technology.

CMG: Compressed methane gas.

CNG: Compressed natural gas.

Co-firing: The burning of mixed fuels (typically refers to biomass with fossil fuel in a coal-fired power station).

Coefficient of performance: The measure of how many units of heat are generated per unit of electricity used.

Combined cycle: An electric generating technology in which electricity is produced from otherwise lost waste heat exiting from one or more gas (combustion) turbines. The exiting heat is routed to a conventional boiler or to a heat

Combined heat and power (CHP) plant: A plant designed to produce both heat and electricity from a single heat source.

Commissioned: In relation to generating station, the completion of such procedures and tests in relation to that station as constitute, at the time they are undertaken, the usual industry standards and practices for commissioning that type of generating station in order to demonstrate that that generating station is capable of commercial operation.

Concentrator: A reflective or refractive device that focuses incident solar energy onto an area smaller than the reflective or refractive surface, resulting in increased solar energy at the point of focus.

Conservation: A foregoing or reduction of electric usage for the purpose of saving natural energy resources and limiting peak demand in order to ultimately reduce the capacity requirements for plant and equipment.

Cut-in: The rotational speed at which an alternator or generator starts pushing electricity hard enough (ie has a sufficiently high voltage) to make electricity flow in a circuit. Current (electric): Flow of electrons in an electric conductor.

Digester gas: Biogass that is produced using a digester which is an airtight vessel or enclosure in which bacteria decomposes biomass in water to produce biogas.

Diode: A solid-state device that allows electricity to flow in only one direction.

Direct current (DC): An electric current that flows in a constant direction. The magnitude of the current does not vary, or has only a slight variation.

Direct radiation: Sunlight received directly, which has travelled in a straight path from the sun. Also referred to as beam radiation.

Distributed generation (embedded generation): A distributed generation system involves small amounts of generation located on a utility’s distribution system for the purpose of meeting local (substation level) peak loads and/or displacing the need to build additional (or upgrade) local distribution lines.

Distribution: The system of wires, switches, and transformers which serve neighbourhoods and businesses; A distribution system reduces the voltage from high-voltage transmission lines (275,000 volts or 400,000 volts) to a level that can be distributed to homes or businesses; 132,000V, 33,000V, 11,000V, 3,300V, 440V.

Distribution system: That part of the electric system that delivers electrical energy to consumers.

Diversion load: Water and wind turbines require diversion loads to use the excess power they generate after the battery bank is fully charged. Ventilation fans and heating elements are popular choices.

Energy: This is broadly defined as the capability of doing work. In the electricity industry, energy is more narrowly defined as electricity supplied over time, normally expressed in kilowatt-hours

Energy consumption: The amount of energy consumed in the form in which it is acquired by the user. The term excludes electrical generation and distribution losses.

Energy crops: Crops grown specifically for their fuel value. These include food crops such as corn and sugarcane

Energy efficiency: Programmes that reduce energy consumption whilst maintaining a given level of output.

Energy equipment payback time: The time required for generating the energy spent in manufacturing the energy systems. A modern photovoltaic module’s energy payback time is typically from one to four years, depending on the module type and location. A typical module lifetime is 20 to 30 years. This means that modern solar systems are net energy producers, i.e. they generate significantly more energy over their lifetime than the energy used in producing them. Also referred to as ‘energy payback time.’

Energy mix: the distribution or proportion of different energy sources within the total energy supply.

Energy resources: Everything which could be used by society as a source of energy.

Energy security: The extent to which a nation’s or region’s energy supplies are robust against potential disruption, including factors such as depletion of natural resources, variability and the political stability of regions where the energy supplies are obtained or trans-shipped.

Energy use: Energy consumed during a specified time period for a specific purpose (usually expressed in kWh).

Fuel cells: One or more cells capable of generating an electrical current by converting the chemical energy of a fuel directly into electrical energy. Fuel cells differ from conventional electrical cells in that the active materials such as fuel and oxygen are not contained within the cell but are supplied from outside.

Gasification systems: Use high temperatures and an oxygen-starved environment to convert biomass into ‘synthesis gas,’ a mixture of hydrogen and carbon monoxide. The synthesis gas, or ‘syngas,’ can then be chemically converted into other fuels or products, burned in a conventional boiler, or used instead of natural gas in a gas turbine. Gas turbines are very much like jet engines, only they turn electric ‘generators’ instead of propelling a jet. See ‘Syngas’

Generation (Electricity): Process of producing electric energy by transforming other forms of energy.

Generator: Machine used to convert mechanical energy into electrical energy.

Geothermal energy: As used at electric power plants, hot water or steam extracted from geothermal reservoirs in the Earth’s crust that is supplied to steam turbines at electric power plants that drive generators to produce electricity.

Geothermal plant: A plant in which a turbine is driven either from hot water or by natural steam that derives its energy from heat found in rocks or fluids at various depths beneath the surface of the earth. The fluids are extracted by drilling and/or pumping.

Gigawatt (GW): The unit of electrical power equal to one thousand-million watts, or one thousand megawatts.

Global generation: Total solar radiant energy impinging on a surface, equal to the sum of direct and diffuse radiation.

Grid: Matrix of an electrical distribution system

Heat pump (Geothermal): A heat pump in which the refrigerant exchanges heat (in a heat exchanger) with a fluid circulating through an earth connection medium (ground or ground water). The fluid is contained in a variety of loop (pipe) configurations depending on the temperature of the ground and the ground area available. Loops may be installed horizontally or vertically in the ground or submersed in a body of water.

Hertz: The frequency with which an alternating current waveform rises and falls (as it changes polarity).

Intermittent resources: Resources whose output depends on some other factor that cannot be controlled by the utility e.g. wind or sun. Thus, the capacity varies by day and by hour

Inverter: Used to convert direct current (DC) electricity to alternating current (AC), so that it can power domestic appliances or be exported to the grid.

J: Joule. Defined as the amount of work done by a force of one newton moving an object through a distance of one metre. Also defined as the work required to move an electric charge of one coulomb through an electrical potential difference of one volt; or one coulomb volt (C·V). This relationship can be used to define the volt. Also defined as the work required to continuously produce one watt of power for one second; or one watt second (W·s). This relationship can be used to define the watt.

Kilowatt (kW): The electrical unit of power equal to 1,000 watts.

Kilowatt-hour (kWh): The basic unit of electric energy equal to one kilowatt of power supplied to or taken from an electric circuit for one hour.

kWh/year: Kilowatt hour per year. This can be used in terms of heat output, or the amount of energy needed to heat a house. For example, my solar thermal system is predicted to generate 2,517kWh of heat per year.

kWp: Kilowatt peak is the measure of how much power a photovoltaic system produces from the sun under test conditions. It measures the power produced under 1kW per m2 of light. The more efficient the system, the smaller the area of panels needed.

kTOE: Equivalent to 1000 tonnes of oil.

kVA: One thousand volt-amps; similar to one kW.

Landfill Gas: Gas that is generated by decomposition of organic material at landfill disposal sites. Landfill gas is approximately 50 percent methane.

Lead: The situation in an electrical circuit in which an electric current leads the voltage.

Load: The amount of electric power delivered or required at any specified point or points on a system. Load originates primarily at the power consuming equipment of the customer.

Load factor: The ratio of the average load supplied to the peak or maximum load during a designated period. Similar to capacity factor, but more often used when describing conventional plant.

Losses: The general term applied to energy (kWh) and capacity (kW) lost in the operation of an electric system. Losses occur principally as energy transformations from kWh to waste-heat in electrical conductors and apparatus.

Maximum power: Also referred to as peak power. The point on a device’s I-V curve where the product of I and V (Pmax, measured in watts) is maximized. The points on the I and V scales which describe this curve point are named Imp (current @ max power) and Vmp (voltage @ max power.).

Megawatt (MW): One million watts. A large coal-fired power station in the UK typically has an installed capacity of between 2,000 MW and 4,000 MW.

Megawatt-hour (MWh): One thousand kilowatt-hours or one million-watt hours.

Methane: A gas that is naturally produced when organic matter decomposes. The gas can be collected from sources such as landfills, water treatment plants, and livestock farms, and then used as an energy source. Methane gas collection is considered a green power source.

Microgeneration: The generation of heat or power by renewable or low carbon means, by individuals, businesses or communities for their own use.

MJ: Megajoule (one thousand kJ).

Module: A number of solar cells electrically connected, protected from environmental stresses, self-contained and not subdividable, providing a single electrical output.

Net Metering: Arrangement that permits a facility (using a meter that reads inflows and outflows of electricity) to sell any excess power it generates over its load requirement back to the electrical grid to offset consumption.

Ocean tidal / wave-action: Where water in motion caused by ocean tides and shoreline wave action is used to generate electricity.

Off-peak: Periods of relatively low system demands.

Open circuit voltage: The voltage that an alternator or generator produces when it is NOT connected to anything drawing electrical power.

Outage: Time during which service is unavailable from a generating unit, transmission line, or other facility.

Parabolic dish: A high-temperature (above 180 degrees Fahrenheit) solar thermal concentrator, generally bowl-shaped, with two-axis tracking.

Parabolic trough: A high-temperature (above 180 degrees Fahrenheit) solar thermal concentrator with the capacity for tracking the sun using one axis of rotation.

Passive solar: A system in which solar energy alone is used for the transfer of thermal energy. Pumps, blowers, or other heat transfer devices that use energy other than solar are not used.

Payback: The length of time it takes for the savings received to cover the cost of implementing the technology.

Peak: Periods of relatively high system demands.

Peak demand: Maximum power used in a given period of time.

Peak watt: A manufacturer’s unit indicating the amount of power a photovoltaic cell or module will produce at standard test conditions (normally 1,000 watts per square meter and 25 degrees Celsius).

Phase: One of the characteristics of the electric service supplied or the equipment used. Practically all residential customers have singlephase service at 240 volts. Large commercial and industrial customers typically have threephase service from 440 volts upwards.

Photovoltaic (PV) cell: An electronic device consisting of layers of semiconductor materials fabricated to form a junction (adjacent layers of materials with different electronic characteristics) and electrical contacts and being capable of converting incident light directly into electricity (direct current).

Photovoltaic (PV) module: An integrated assembly of interconnected photovoltaic cells designed to deliver a selected level of working voltage and current at its output terminals, packaged for protection against environment degradation, and suited for incorporation in photovoltaic power systems.

Power: The rate at which energy is transferred.

Power plant: A generating station where electricity is produced.

Pumped storage: A facility designed to generate electric power during peak load periods with a hydroelectric plant using water pumped into a storage reservoir during off-peak periods.

Pyrolysis: Using a similar process but different conditions (totally excluding rather than limiting oxygen, in a simplified sense) will ‘pyrolyze’ biomass to a liquid rather than gasify it. As with syngas, pyrolysis oil can be burned to generate electricity or used as a chemical source for making plastics, adhesives, or other bioproducts.

Rated capacity: The power rating of a generating station, (usually in kVA or MW) at which it would operate under the design operating conditions and input fuel (or resource – e.g. wind speed).

Reliability: Electric system reliability has two components – adequacy and security. Adequacy is the ability of the electric system to supply the aggregate electric demand and energy requirements of the customers at all times, taking into account scheduled and unscheduled outages of system facilities. Security is the ability of the electric system to withstand sudden disturbances such as electric short circuits or unanticipated loss of system facilities

Reserve capacity: Capacity in excess of that required to carry peak load.

Scheduled outage: An outage that results when a component is deliberately taken out of service at a selected time, usually for the purposes of construction, maintenance, or testing.

Sellback: When an alternative energy system is connected to the grid, and excess power is sold back to the local utility.

Solar thermal collector: A device designed to receive solar radiation and convert it into thermal energy. Normally, a solar thermal collector includes a frame, glazing, and an absorber, together with the appropriate insulation. The heat collected by the solar thermal collector may be used immediately or stored for later use.

Substation: A facility used for switching and/or changing or regulating the voltage of electricity. Service equipment, line transformer installations, or minor distribution or transmission equipment are not classified as substations.

Supplier: A person or corporation, generator, broker, marketer, aggregator or any other entity, that sells electricity to customers, using the transmission or distribution facilities of an electric distribution company.

Switchgear: The combination of electrical disconnect switches, fuses or circuit breakers used to control, protect and isolate electrical equipment. The switchgear may used to deenergise equipment to permit maintenance work or to clear faults.

Syngas: A syntheses gas produced through gasification of biomass. Syngas is similar to natural gas and can be cleaned and conditioned to form a feedstock for production of methanol. See ‘Gasification Systems’.

System (Electric): Physically connected generation, transmission, and distribution facilities operating as a single unit. Terawatt (TW): One thousand gigawatts. Three-phase power system: A power system with at least three conductors carrying alternating current voltages that are offset in time by one-third of the period.

System (Electric): Physically connected generation, transmission, and distribution facilities operating as a single unit.

Terawatt (TW): One thousand gigawatts.

Three-phase power system: A power system with at least three conductors carrying alternating current voltages that are offset in time by one-third of the period.

Transformer: A device for changing the voltage of alternating current.

Transmission: The act or process of transporting electric energy in bulk.

Transmission and distribution (T&D) losses: Losses that result from the heating effect of current as it flows through wires to travel from the generation facility to the customer. Because of losses, the electricity produced by the utility is greater than the electricity that shows up on the customer bills.

Transmission and distribution (T&D) system: An interconnected group of electric transmission lines and associated equipment for the movement or transfer of electrical energy in bulk between points of supply and points at which it is transformed for delivery to the ultimate customers.

Transmission lines: Heavy wires that carry large amounts of electricity over long distances from a generating station to places where electricity is needed. Transmission lines are held high above the ground on tall towers called transmission towers.

Utility: A regulated vertically-integrated electricity company. ‘Transmission utility’ refers to the regulated owner/operator of the transmission system only. ‘Distribution utility’ refers to the regulated owner/operator of the distribution system which serves retail customers.

Variability: The non-continuous nature of some forms of energy generation, e.g. wind power, solar, hydro, wave and tidal which can be made more predictable through accurate forecasting.

Volt: The unit of electrical potential. It is the electromotive force which, if steadily applied to a circuit having a resistance of one ohm, will produce a current of one ampere.

Volt-amperes: The volt-amperes of an electric circuit; the mathematical product of the volts and amperes. Equals the power in a direct current circuit.

Voltage: Measure of the force of moving electrical energy.

Watt: The electrical unit of power or rate of doing work. One horsepower is equivalent to approximately 746 watts.

Watt-hour: One watt of power expended for one hour.