Gallium Arsenide
A compound used to make certain types of solar photovoltaic cells.


The process in which a solid fuel is converted into a gas; also known as pyrolitic distillation or pyrolysis. Production of a clean fuel gas makes a wide variety of power options available.


A device for converting a solid fuel to a gaseous fuel.


A seal used to prevent the leakage of fluids, and also maintain the pressure in an enclosure.


A registered trademark of an agency of the state of Nebraska, for an automotive fuel containing a blend of 10 percent ethanol and 90 percent gasoline.


A refined petroleum product suitable for use as a fuel in internal combustion engines.

Gas Turbine

A type of turbine in which combusted, pressurized gas is directed against a series of blades connected to a shaft, which forces the shaft to turn to produce mechanical energy.


The unit of magnetic field intensity equal to 1 dyne per unit pole.


A device for converting mechanical energy to electrical energy.

Geopressurized Brines

These brines are hot (300 F to 400 F) (149 C to 204 C) pressurized waters that contain dissolved methane and lie at depths of 10,000 ft (3048 m) to more than 20,000 ft (6096 m) below the earth’s surface. The best known geopressured reservoirs lie along the Texas and Louisiana Gulf Coast. At least three types of energy could be obtained: thermal energy from high-temperature fluids; hydraulic energy from the high pressure; and chemical energy from burning the dissolved methane gas.

Geothermal Energy

Energy produced by the internal heat of the earth; geothermal heat sources include: hydrothermal convective systems; pressurized water reservoirs; hot dry rocks; manual gradients; and magma. Geothermal energy can be used directly for heating or to produce electric power.

Geothermal Heat Pump

A type of heat pump that uses the ground, ground water, or ponds as a heat source and heat sink, rather than outside air. Ground or water temperatures are more constant and are warmer in winter and cooler in summer than air temperatures. Geothermal heat pumps operate more efficiently than “conventional” or “air source” heat pumps.

Geothermal Power Station

An electricity generating facility that uses geothermal energy.

Gigawatt (GW)

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

Gin Pole

A pole used to assist in raising a tower.


The discomfort or interference with visual perception when viewing a bright object against a dark background.


A term used for the transparent or translucent material in a window. This material (i.e. glass, plastic films, coated glass) is used for admitting solar energy and light through windows.

Glauber’s Salt

A salt, sodium sulfate decahydrate, that melts at 90 degrees Fahrenheit; a component of eutectic salts that can be used for storing heat.


Transparent or translucent material (glass or plastic) used to admit light and/or to reduce heat loss; used for building windows, skylights, or greenhouses, or for covering the aperture of a solar collector.

Global Insolation (or Solar Radiation)

The total diffuse and direct insolation on a horizontal surface, averaged over a specified period of time.

Global Warming

A popular term used to describe the increase in average global temperatures due to the greenhouse effect.


A device used to regulate motor speed, or, in a wind energy conversion system, to control the rotational speed of the rotor.

Grain Alcohol


Green Certificates

Green certificates represent the environmental attributes of power produced from renewable resources. By separating the environmental attributes from the power, clean power generators are able to sell the electricity they produce to power providers at a competitive market value. The additional revenue generated by the sale of the green certificates covers the above-market costs associated with producing power made from renewable energy sources. Also known as green tags, renewable energy certificates, or tradable renewable certificates.

Greenhouse Effect

A popular term used to describe the heating effect due to the trapping of long wave (length) radiation by greenhouse gases produced from natural and human sources.

Greenhouse Gases

Those gases, such as water vapor, carbon dioxide, tropospheric ozone, methane, and low level ozone that are transparent to solar radiation, but opaque to long wave radiation, and which contribute to the greenhouse effect.


Freshly cut, unseasoned, wood.

Green Power

A popular term for energy produced from clean, renewable energy resources.

Green Pricing

A practice engaged in by some regulated utilities (i.e. power providers) where electricity produced from clean, renewable resources is sold at a higher cost than that produced from fossil or nuclear power plants, supposedly because some buyers are willing to pay a premium for clean power.


Waste water from a household source other than a toilet. This water can be used for landscape irrigation depending upon the source of the greywater.


A common term referring to an electricity transmission and distribution system.

Grid-Connected System

Independent power systems that are connected to an electricity transmission and distribution system (referred to as the electricity grid) such that the systems can draw on the grid’s reserve capacity in times of need, and feed electricity back into the grid during times of excess production.

Gross Calorific Value

The heat produced by combusting a specific quantity and volume of fuel in an oxygen-bomb colorimeter under specific conditions.

Gross Generation

The total amount of electricity produced by a power plant.


A device used to protect the user of any electrical system or appliance from shock.

Ground Loop

In geothermal heat pump systems, a series of fluid-filled plastic pipes buried in the shallow ground, or placed in a body of water, near a building. The fluid within the pipes is used to transfer heat between the building and the shallow ground (or water) in order to heat and cool the building.

Ground Reflection

Solar radiation reflected from the ground onto a solar collector.

Ground-Source Heat Pump

(See Geothermal Systems)

Guy Wire

Cable use to secure a wind turbine tower to the ground in a safe, stable manner.