Gallium Arsenide — A compound used to make certain types of solar photovoltaic cells.
Gasification — 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.
Gasifier — A device for converting a solid fuel to a gaseous fuel.
Gasket/Seal — A seal used to prevent the leakage of fluids, and also maintain the pressure in an enclosure.
Gasohol — 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.
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.
Gauss — The unit of magnetic field intensity equal to 1 dyne per unit pole.
Generator — 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.
Glare — The discomfort or interference with visual perception when viewing a bright object against a dark background.
Glazing — 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.
Glazing — 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.
Governor — A device used to regulate motor speed, or, in a wind energy conversion system, to control the rotational speed of the rotor.
Grain Alcohol — Ethanol.
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.
Greenwood — 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.
Greywater — 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.
Grid — 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.
Ground — 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.
Harmonic(s) — A sinusoidal quantity having a frequency that is an integral multiple of the frequency of a periodic quantity to which it is related.
Head — A unit of pressure for a fluid, commonly used in water pumping and hydro power to express height a pump must lift water, or the distance water falls. Total head accounts for friction head losses, etc.
Heat — A form of thermal energy resulting from combustion, chemical reaction, friction, or movement of electricity. As a thermodynamic condition, heat, at a constant pressure, is equal to internal or intrinsic energy plus pressure times volume.
Heat Absorbing Window Glass — A type of window glass that contains special tints that cause the window to absorb as much as 45% of incoming solar energy, to reduce heat gain in an interior space. Part of the absorbed heat will continue to be passed through the window by conduction and reradiation.
Heat Balance — Energy output from a system that equals energy input.
Heat Content — The amount of heat in a quantity of matter at a specific temperature and pressure.
Heat Engine — A device that produces mechanical energy directly from two heat reservoirs of different temperatures. A machine that converts thermal energy to mechanical energy, such as a steam engine or turbine.
Heat Exchanger — A device used to transfer heat from a fluid (liquid or gas) to another fluid where the two fluids are physically separated.
Heat Gain — The amount of heat introduced to a space from all heat producing sources, such as building occupants, lights, appliances, and from the environment, mainly solar energy.
Heating Capacity (Also specific heat) — The quantity of heat necessary to raise the temperature of a specific mass of a substance by one degree.
Heating Degree Day(s) (HDD) — The number of degrees per day that the daily average temperature (the mean of the maximum and minimum recorded temperatures) is below a base temperature, usually 65 degrees Fahrenheit, unless otherwise specified; used to determine indoor space heating requirements and heating system sizing. Total HDD is the cumulative total for the year/heating season. The higher the HDD for a location, the colder the daily average temperature(s).
Heating Fuels — Any gaseous, liquid, or solid fuel used for indoor space heating.
Heating Fuel Units — Standardized weights or volumes for heating fuels.
Heating Load — The rate of heat flow required to maintain a specific indoor temperature; usually measured in Btu per hour.
Heating Season — The coldest months of the year; months where average daily temperatures fall below 65 degrees Fahrenheit creating demand for indoor space heating.
Heating Seasonal Performance Factor (HSPF) — The measure of seasonal or annual efficiency of a heat pump operating in the heating mode. It takes into account the variations in temperature that can occur within a season and is the average number of Btu of heat delivered for every watt-hour of electricity used by the heat pump over a heating season.
Heating Value — The amount of heat produced from the complete combustion of a unit of fuel. The higher (or gross) heating value is that when all products of combustion are cooled to the pre-combustion temperature, water vapor formed during combustion is condensed, and necessary corrections have been made. Lower (or net) heating value is obtained by subtracting from the gross heating value the latent heat of vaporization of the water vapor formed by the combustion of the hydrogen in the fuel.
Heating, Ventilation, and Air-Conditioning (HVAC) System — All the components of the appliance used to condition interior air of a building.
Heat Loss — The heat that flows from the building interior, through the building envelope to the outside environment.
Heat Pipe — A device that transfers heat by the continuous evaporation and condensation of an internal fluid.
Heat Pump — An electricity powered device that extracts available heat from one area (the heat source) and transfers it to another (the heat sink) to either heat or cool an interior space or to extract heat energy from a fluid.
Heat Pump Water Heaters — A water heater that uses electricity to move heat from one place to another instead of generating heat directly.
Heat Rate — The ratio of fuel energy input as heat per unit of net work output; a measure of a power plant thermal efficiency, generally expressed as Btu per net kilowatt-hour.
Heat Recovery Ventilator — A device that captures the heat from the exhaust air from a building and transfers it to the supply/fresh air entering the building to preheat the air and increase overall heating efficiency.
Heat Register — The grilled opening into a room by which the amount of warm air from a furnace can be directed or controlled; may include a damper.
Heat Sink — A structure or media that absorbs heat.
Heat Source — A structure or media from which heat can be absorbed or extracted.
Heat Storage — A device or media that absorbs heat for storage for later use.
Heat Storage Capacity — The amount of heat that a material can absorb and store.
Heat Transfer — The flow of heat from one area to another by conduction, convection, and/or radiation. Heat flows naturally from a warmer to a cooler material or space.
Heat Transfer Fluid — A gas or liquid used to move heat energy from one place to another; a refrigerant.
Heat Transmission Coefficient — Any coefficient used to calculate heat transmission by conduction, convection, or radiation through materials or structures.
Heliochemical Process — The utilization of solar energy through photosynthesis.
Heliodon — A device used to simulate the angle of the sun for assessing shading potentials of building structures or landscape features.
Heliostat — A device that tracks the movement of the sun; used to orient solar concentrating systems.
Heliothermal — Any process that uses solar radiation to produce useful heat.
Heliothermic — Site planning that accounts for natural solar heating and cooling processes and their relationship to building shape, orientation, and siting.
Heliothermometer — An instrument for measuring solar radiation.
Heliotropic — Any device (or plant) that follows the sun's apparent movement across the sky.
Hemispherical Bowl Technology — A solar energy concentrating technology that uses a linear receiver that tracks the focal area of a reflector or array of reflectors.
Hertz — A measure of the number of cycles or wavelengths of electrical energy per second; U.S. electricity supply has a standard frequency of 60 hertz.
Heterojunction — A region of electrical contact between two different materials.
Higher Heating Value (HHV)- The maximum heating value of a fuel sample, which includes the calorific value of the fuel (bone dry) and the latent heat of vaporization of the water in the fuel. (See moisture content and net (lower) heating value, below.)
High-Intensity Discharge Lamp — A lamp that consists of a sealed arc tube inside a glass envelope, or outer jacket. The inner arc tube is filled with elements that emit light when ionized by electric current. A ballast is required to provide the proper starting voltage and to regulate current during operation.
High-Pressure Sodium Lamp — A type of High-Intensity Discharge (HID) lamp that uses sodium under high pressure as the primary light-producing element. These high efficiency lights produce a golden white color and are used for interior industrial applications, such as in warehouses and manufacturing, and for security, street, and area lighting.
Hole — The vacancy where an electron would normally exist in a solid; behaves like a positively charged particle.
Home Energy Rating Systems (HERS) — A nationally recognized energy rating program that gives builders, mortgage lenders, secondary lending markets, homeowners, sellers, and buyers a precise evaluation of energy losing deficiencies in homes. Builders can use this system to gauge the energy quality in their home and also to have a star rating on their home to compare to other similarly built homes.
Homojunction — The region between an n-layer and a p-layer in a single material, photovoltaic cell.
Horizontal-Axis Wind Turbines — Turbines in which the axis of the rotor's rotation is parallel to the wind stream and the ground.
Horizontal Ground Loop — In this type of closed-loop geothermal heat pump installation, the fluid-filled plastic heat exchanger pipes are laid out in a plane parallel to the ground surface. The most common layouts either use two pipes, one buried at six feet, and the other at four feet, or two pipes placed side-by-side at five feet in the ground in a two-foot wide trench. The trenches must be at least four feet deep. Horizontal ground loops are generally most cost-effective for residential installations, particularly for new construction where sufficient land is available. Also see closed-loop geothermal heat pump systems.
Horsepower (hp) — A unit of rate of operation. Electrical hp: a measure of time rate of mechanical energy output; usually applied to electric motors as the maximum output; 1 electrical hp is equal to 0.746 kilowatts or 2,545 Btu per hour. Shaft hp: a measure of the actual mechanical energy per unit time delivered to a turning shaft; 1 shaft Hp is equal to 1 electrical Hp or 550 foot pounds per second. Boiler Hp: a measure to the maximum rate to heat output of a steam generator; 1 boiler Hp is equal to 33,480 Btu per hour steam output.
Horsepower Hour (hph) — One horsepower provided over one hour; equal to 0.745 kilowatt-hour or 2,545 Btu.
Hot Air Furnace — A heating unit where heat is distributed by means of convection or fans.
Hot Dry Rock — A geothermal energy resource that consists of high temperature rocks above 300 F (150 C) that may be fractured and have little or no water. To extract the heat, the rock must first be fractured, then water is injected into the rock and pumped out to extract the heat. In the western United States, as much as 95,000 square miles (246,050 square km) have hot dry rock potential.
Hot Water Heating Systems (see hydronic)
Hub Height — The height above the ground that a horizontal axis wind turbine's hub is located.
Humidifier — A device used to maintain a specified humidity in a conditioned space.
Humidity — A measure of the moisture content of air; may be expressed as absolute, mixing ratio, saturation deficit, relative, or specific.
Hybrid System — A renewable energy system that includes two different types of technologies that produce the same type of energy; for e.g., a wind turbine and a solar photovoltaic array combined to meet a power demand.
Hydroelectric Power Plant — A power plant that produces electricity by the force of water falling through a hydro turbine that spins a generator.
Hydrogen — A chemical element that can be used as a fuel since it has a very high energy content.
Hydrogenated Amorphous Silicon — Amorphous silicon with a small amount of incorporated hydrogen. The hydrogen neutralizes dangling bonds in the amorphous silicon, allowing charge carriers to flow more freely.
Hydronic Heating Systems — A type of heating system where water is heated in a boiler and either moves by natural convection or is pumped to heat exchangers or radiators in rooms; radiant floor systems have a grid of tubing laid out in the floor for distributing heat. The temperature in each room is controlled by regulating the flow of hot water through the radiators or tubing.
Hydrothermal fluids — These fluids can be either water or steam trapped in fractured or porous rocks; they are found from several hundred feet to several miles below the Earth's surface. The temperatures vary from about 90 F to 680 F (32 C to 360 C) but roughly 2/3 range in temperature from 150 F to 250 F (65.5 C to 121.1 C). The latter are the easiest to access and, therefore, the only forms being used commercially.
Air Conditioning Units
