Biodiesel. A vehicle fuel for diesel-powered cars, trucks, buses, and other vehicles. Biodiesel is produced from oilseed crops such as soy, rapeseed (canola), and mustard, or from other vegetable oil sources such as waste cooking oil.

Biogas digester. Converts animal and plant wastes into gas usable for lighting, cooking, heating, and electricity generation.

Biomass power and heat. Power and/or heat generation from solid biomass, which includes forest product wastes, agricultural residues and waste, energy crops, and the organic component of municipal solid waste and industrial waste. Also includes power and process heat from biogas.

Capital subsidies or consumer grants. One-time payments by the government or utility to cover a percentage of the capital cost of an investment, such as a solar hot water system or rooftop solar PV system.

Ethanol. A vehicle fuel made from biomass (typically corn, sugar cane, or wheat) that can replace ordinary gasoline in modest percentages (see “gasohol”) or be used in pure form in specially modified vehicles.

Feed-in tariff. A policy that sets a fixed price at which power producers can sell renewable power into the electric power network. Some policies provide a fixed tariff while others provide fixed premiums added to market- or costrelated tariffs. Some provide both.

Gasohol. A blend of gasoline and ethanol, typically 10–25 percent ethanol (called E10, E25, etc.).

Geothermal power and heat. Heat energy emitted from within the Earth, usually in the form of hot water or steam, which can be used to produce electricity or direct heat for buildings, industry, and agriculture.

Gigawatt (GW)/Gigawatt-hour (GWh)/Gigawatt-thermal (GWth). See megawatt, kilowatt-hour, megawatt-thermal.

Green power purchasing. Voluntary purchases of green power by residential, commercial, government, or industrial customers, from utility companies (see “utility green pricing”), from a third-party renewable energy generator (also called “green marketing”), or with “renewable energy certifi- cates.”With utility green pricing or competitive sales, a customer’s electricity demand is matched by an equivalent amount of renewable energy generation feeding into the power grid. Green certificates allow the renewable energy production to be located anywhere.

Investment tax credit. Allows investments in renewable energy to be fully or partially deducted from tax obligations or income.

Kilowatt-hour (kWh). A unit of produced or consumed electricity. Also the most common unit for the retail price of electricity, as in cents/kWh.

Large hydropower. Electricity from water flowing downhill, typically from behind a dam. No international consensus exists on the threshold that separates large from small hydro power, but the upper limit varies from 2.5–50 MW, with 10 MW becoming more standard.

Megawatt (MW). A unit of power-generating capacity. Represents an instantaneous power flow and should not be confused with units of produced energy (i.e.,MWh, or megawatt-hours).

Megawatt-thermal (MWth). A unit of heat-supply capacity used to measure the potential output from a heating plant, such as might supply a building or neighborhood.More recently used to measure the capacity of solar hot water/heating installations. Represents an instantaneous heat flow and should not be confused with units of produced heat (i.e.,MWh(th), or megawatt-hours-thermal).

Modern biomass. Biomass-utilization technologies other than those defined for traditional biomass, such as biomass co-generation for power and heat, biomass gasification, biogas anaerobic digesters, and production of liquid biofuels for use in vehicles.

Multilateral agency. Commonly refers to public agencies that work internationally to provide development, environmental, or financial assistance to developing countries, such as the World Bank, or to broker international agreements and treaties, such as the United Nations.

Net metering. Allows a two-way flow of electricity between the electricity distribution grid and customers with their own generation. When instantaneous consumption exceeds self-generation, the meter runs forward. When instantaneous self-generation exceeds consumption, the meter runs backward and power flows to the grid. The customer pays for the net electricity used in each billing period and may be allowed to carry over net generation from month to month.

Production tax credit. Provides the investor or owner of qualifying property with an annual tax credit based on the amount of electricity generated by that facility.

Renewable energy target. A commitment, plan, or goal by a country to achieve a certain level of renewable energy by a future date. Some targets are legislated while others are set by regulatory agencies or ministries. Can take many forms with varying degrees of enforcement leverage. Also called “planning targets,” “development plans,” and “obligations.”

Renewables portfolio standard (RPS). A standard requiring that a minimum percentage of generation sold or capacity installed be provided by renewable energy. Obligated utilities are required to ensure that the target is met, either through their generation, power purchase from other producers, or direct sales from third parties to the utility’s customers.

Small/mini/micro/pico hydropower. (See “large hydropower.”) Small hydropower is commonly defined as below 10 MW, mini below 1 MW, micro below 100 kW, and pico below 1 kW. Pico hydro will typically not involve a dam but just captures the power of flowing water.

Solar home system. A rooftop solar panel, battery, and charge controller that can provide modest amounts of power to rural homes not connected to the electric grid. Typically provides an evening’s lighting (using efficient lights) and TV viewing from one day’s battery charging.

Solar hot water/heating. Rooftop solar collectors that heat water and store it in a tank for use as domestic hot water or for space heating.

Solar photovoltaic (PV) panel/module/cell. Converts sunlight into electricity. Cells are the basic building block, which is then manufactured into modules and panels.

Tradable renewable energy certificates. Each certificate represents the certified generation of one unit of renewable energy (typically one MWh). These certificates allow trading of renewable energy obligations among consumers and/or producers, and in some markets like the United States allow anyone to purchase separately the green power “attributes” of renewable energy.

Traditional biomass. Unprocessed biomass, including agricultural waste, forest products waste, collected fuel wood, and animal dung, that is burned in stoves or furnaces to provide heat energy for cooking, heating, and agricultural and industrial processing, typically in rural areas.

Utility green pricing. A utility offers its customers a choice of power products, usually at differing prices, offering varying degrees of renewable energy content. The utility guarantees to generate or purchase enough renewable energy to meet the needs of all green power customers.