Glossary of Terms - G

• Gallium Arsenide - A compound used to make certain types of solar photovoltaic cells.
• Gamma - The sensitivity of an option's delta to changes in the price of the underlying futures contract.
• Gas - A fuel burned under boilers and by internal combustion engines for electric generation. These include natural, manufactured, and waste gas.
• 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.
• Gas Turbine Plant - A plant in which the prime mover is a gas turbine. A gas turbine consists typically of an axial-flow air compressor, one or more combustion chambers, where liquid or gaseous fuel is burned and the hot gases are passed to the turbine and where the hot gases expand to drive the generator and are then used to run the compressor.
• 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.
• Gasoil - European designation for No. 2 heating oil and diesel fuel.
• Gasoline - A refined petroleum product suitable for use as a fuel in internal combustion engines.
• Gasoline, Straight-Run - Also known as raw gasoline. Gasoline which is obtained directly from crude oil by fractional distillation. Straight-run gasoline generally must be upgraded to meet current motor fuel specifications.
• Gassing Current - Portion of charge current that goes into electrolytical production of hydrogen and oxygen from the electrolytic liquid. This current increases with increasing voltage and temperature.
• Gauss - The unit of magnetic field intensity equal to 1 dyne per unit pole.
• Gel-Type Battery - Lead-acid battery in which the electrolyte is composed of a silica gel matrix.
• Generating Station (Generating Plant or Power Plan) - The location of prime movers, electric generators, and auxiliary equipment used for converting mechanical, chemical, and nuclear energy into electric energy.
• Generating Unit - Any combination of physically connected generator(s), reactor(s), boiler(s), combustion turbine(s), or other prime mover(s) operated together to produce electric power.
• Generation (Electricity) - The process of producing electric energy by transforming other forms of energy; also, the amount of electric energy produced, expressed in watt-hours (Wh).
• Generation Charges - Part of the basic service charges on every customer's bill for producing electricity. Generation service is competitively priced and is not regulated by Public Utility Commissions. This charge depends on the terms of service between the customer and the supplier.
• Generation Company (Genco) - A regulated or non-regulated entity (depending upon the industry structure) that operates and maintains existing generating plants. The Genco may own the generation plants or interact with the short term market on behalf of plant owners. In the context of restructuring the market for electricity, Genco is sometimes used to describe a specialized "marketer" for the generating plants formerly owned by a vertically-integrated utility.
• Generation Dispatch and Control - Aggregation and dispatching (sending off to some location) generation from various generating facilities, providing backup and reliability services.
• Generator - Machine used to convert mechanical energy into electrical energy.
• Generator Nameplate Capacity - The full-load continuous rating of a generator, prime mover, or other electric power production equipment under specific conditions as designated by the manufacturer. Installed generator nameplate rating is usually indicated on a nameplate physically attached to the generator.
• 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 - An electric generating station in which steam tapped from the earth drives a turbine-generator, generating electricity.
• 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 Plant - A plant in which the prime mover is a steam turbine. The turbine is driven either by steam produced 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 energy is extracted by drilling and/or pumping.
• Geothermal Power Station - An electricity generating facility that uses geothermal energy.
• Gigajoule (GJ) - One billion joules, approximately equal to 948,211 British thermal units. One million Btus equals 1.0546175 GJ.
• Gigawatt (GW) - This is a unit of electric power equal to one billion watts, or one thousand megawatts - enough power to supply the needs of a medium-sized city. A unit of power equal to 1 billion Watts; 1 million kilowatts, or 1,000 megawatts.
• Gigawatthour (GWh) - One billion watthours.
• 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.
• 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.
• 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.
• Good Delivery - Approved metals brands acceptable for delivery against the metals contracts.
• Good till Canceled - An order to be held by a broker until it can be filled or until canceled.
• Good Utility Practice - Any of the practices, methods, and acts engaged in or approved by a significant portion of the electric utility industry during the relevant time period, or any of the practices, methods, and acts which, in the exercise of reasonable judgment in light of the facts known at the time the decision was made, could have been expected to accomplish the desired result of the lowest reasonable cost consistent with good business practices, reliability, safety and expedition. Good Utility Practice is not intended to be limited to the optimum practice, method, or act to the exclusion of all others, but rather to be acceptable practices, methods, or acts generally accepted in the region and consistently adhered to by the Transmission Provider.
• 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 Power - A popular term for energy produced from renewable energy resources.
• Green Pricing and Marketing - To price and sell green power/electricity higher than that produced from fossil or nuclear power plants, supposedly because some buyers are willing to pay a premium for green power.
• Greenfield Plant - This refers to a new electric power generating facility built from the ground up.
• Greenhouse Effect - The increasing mean global surface temperature of the earth caused by gases in the atmosphere (including carbon dioxide, methane, nitrous oxide, ozone, and chlorofluorocarbon). The greenhouse effect allows solar radiation to penetrate but absorbs the infrared radiation returning to space. 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 - Gases that trap the heat of the sun in the Earth's atmosphere, producing the greenhouse effect; the two major greenhouse gases are water vapor and carbon dioxide; lesser greenhouse gases include methane, ozone, chlorofluorocarbons, and nitrogen oxides.
• Greenwood - Freshly cut, unseasoned, wood.
• 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 - See 'Electrical grid.'
• Grid-Connected (PV system) - A PV system in which the PV array acts like a central generating plant, supplying power to the grid.
• Grid-Interactive (PV system) - See 'Grid-connected (PV system).'
• 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 electric energy produced by the generating units at a generating station or stations, measured at the generator terminals.
• Ground - A device used to protect the user of any electrical system or appliance from shock.
• Ground - Source Heat Pump (see geothermal systems)
• Ground Reflection - Solar radiation reflected from the ground onto a solar collector.