The complex process by which organic matter is decomposed by anaerobic bacteria. The decomposition process produces a gaseous byproduct often called "biogas" primarily composed of methane, carbon dioxide, and hydrogen sulfide.

In reference to solar energy systems, the angle that a solar collector is positioned above horizontal.

A unit of power equal to 1 billion Watts; 1 million kilowatts, or 1,000 Megawatts.

An enzyme complex, produced by fungi and bacteria, capable of decomposing cellulose into small fragments, primarily glucose.

A unit of heat containing 100,000 British thermal units (Btu).

A type of impulse hydropower turbine where water passes through nozzles and strikes cups arranged on the periphery of a runner, or wheel, which causes the runner to rotate, producing mechanical energy. The runner is fixed on a shaft, and the rotational mo ...

A type of heat pump that transfers heat from outdoor air to indoor air during the heating season, and works in reverse during the cooling season.

The mean wind speed over a specified period of time.

The transparent or opaque sphere in an electric light that the electric light transmits through.

A generic term for a glazed opening that allows daylight to enter into a building and can be opened for ventilation.

To disconnect a transmission and/or distribution line; a power line that is not carrying a current; to open a circuit.

The heating capacity of a steam boiler; expressed in Btu per hour (Btu/h), or horsepower, or pounds of steam per hour.

The potential energy available in a fuel as received, taking into account the energy loss in evaporating and superheating the water in the fuel. Equal to the higher heating value minus 1050W where W is the weight of the water formed from the hydrogen in t ...

A mound of dirt next to exterior walls to provide wind protection and insulation.

The pressure corresponding to the outlet velocity of a fan; the kinetic energy per unit volume of flowing air.

The transformation on a compound or material into one or more substances by heat alone (without oxidation). Often called destructive distillation. Pyrolysis of biomass is the thermal degradation of the material in the absence of reacting gases, and occus ...

A long, underground metal or plastic pipe through which air is drawn. As air travels through the pipe it gives up some of its heat to the soil, and enters the house as cooler air.

Energy terms

A total life cycle cost divided into equal amounts.

A type of combustion heating appliance in which the combustion gases are vented to the outside, either with a fan (forced) or by natural convection.