Renewable Energy Vocabulary: G-I

A-C • D-F • G-I • J-M • N-P • R-S • T-Z

GASSING
The production of hydrogen and oxygen gas from one or more of the electrodes in the cells of a battery. Gassing commonly results from the electrolysis of water in the electrolyte during charging.

GENERATOR
A device that converts mechanical energy into electrical energy.

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. Compare to HEAT PUMP.

GIN POLE
Either of two different types of devices used with wind generator towers. With a tilt-up tower, it describes the lever that helps tilt the tower up. With a fixed tower, it describes a temporary crane used to raise tower sections or the wind generator.

GLYCOL (Propylene Glycol)
An antifreeze, heat transfer fluid that is circulated through closed loop solar hot water collectors.

GOVERNOR
A device that limits the output of another device, such as a wind generator.

GOVERNING
Limiting the output of a device. In respect to small wind generators, governing normally happens through furling.

GRID
Transmission line network used to distribute electrical energy, generally by a commercial power utility.

GRID LINES
Metallic contacts fused to the surface of a solar cell to provide a low resistance path for electrons to flow out to the cell interconnect wires.

GRID-TIE SYSTEM
A renewable energy system that is connected to the utility grid, selling excess energy back to the utility. Also called a utility-interactive system.

GROUND
The connection of electrical components to the earth and/or each other for the purposes of dissipating static charge or protecting against a short circuit or lightning.

GROUND FAULT
Unwanted current path to ground.

GROUND MOUNT
A photovoltaic (PV) rack designed to be installed on the ground or other flat surface.

GROUND ROD (ELECTRODE)
A metal rod (typically 5/8 inch diameter) that is driven into the earth (typically 8 feet deep) and is electrically connected to the negative conductor and/or any metal parts, wiring enclosures, or conduit of an electrical circuit.

GUY WIRES
Steel cables that support a tower.

HEAD
The difference in elevation between two parts of a liquid-based system. In hydro power, the difference between a source of water and the location at which the water from that source may be used (synonym: vertical drop). With pumps, the vertical distance the pump must move the water.

HEADRACE
A flume or channel that feeds water into a hydro turbine.

HEAT EXCHANGER
A device that is used to transfer heat between fluids or gases through an intervening surface.

HEAT PUMP
A device typically used for heating and cooling of buildings by drawing  from or dissipating into the ambient temperature of air or water. When cooling, a heat pump works like a refrigerator. When heating, it also works like a fridge, except the heat produced is used to heat a space.

HEAT SINK
A medium or container to which heat flows. Thermal mass walls and floors in a passive solar home act as a heat sink during the day.

HEAT TRANSFER
Heat is transferred from one substance or location to another by three methods—radiation, convection and conduction. The sun’s rays are a good example of radiation; warm air rising is heat movement by convection; and touching a hot iron or frying pan with your hand is heat transfer by conduction.

HERTZ (Hz)
Cycles per second. Generally refers to the number of complete cycles of the AC sine wave per second, or the frequency at which a radio or computer processor works.

HYDRO-ELECTRICITY
Any electricity that is generated by the flow of water.

HYDROGEN FUEL CELL
A device that converts hydrogen to DC electricity.

HYDROMETER
A hydrometer is an instrument for measuring the density of liquids in relation to the density of water. The hydrometer is used to indicate the state of charge in lead-acid cells by measuring the specific gravity of the electrolyte.

HYDRONIC HEATING SYSTEM
A type of heating system where water is heated in a solar collector or boiler, and is pumped to heat exchangers or radiators in rooms. Radiant floor systems have a grid of tubing laid out in the floor for distributing the heat. Temperature of the space is controlled by regulating the flow and/or temperature of the circulating water.

HORSEPOWER
A measure of the capacity to generate energy or do work. 1 horsepower = 746 watts.

HYBRID SYSTEM
An energy system consisting of two or more generating subsystems, such as the combination of a wind turbine or diesel generator and a photovoltaic system.

INCANDESCENT LIGHT
An electric lamp that is evacuated or filled with an inert gas and contains a filament (commonly tungsten). The filament emits visible light when heated to extreme temperatures by electric current through it. Incandescent lightbulbs are one of the most inefficient ways to light a home. They produce a great deal of heat along with the light, and use three to four times as much energy for the same light output as compact fluorescent lightbulbs.

INDUCTION MOTOR (AC)
A type of electric motor that requires a high surge to start, and a stable voltage supply, making it a challenge to run using a solar-electric system.

INSOLATION
The amount of sunlight reaching an area. Usually expressed in watts per square meter.

INTAKE
In a hydro system, the structure that receives the water and feeds it into the penstock (pipeline). Usually incorporates screening or filtering to keep debris and aquatic life out of the system.

INVERTER
A device that converts DC electricity (anywhere from 12 to 600 VDC) to AC electricity (typically 120/240 VAC).

ION
An electrically charged particle or molecule.

ISC
See SHORT CIRCUIT CURRENT.

IV CURVE
The graphical representation of the current versus the voltage of a photovoltaic cell, module, or array as the load is increased from zero voltage to maximum voltage, under standard test conditions.