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.
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Renewable Energy Glossary
Geothermal 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.
GFPD
Ground fault protection device (GFPD) is a device that detects whether fault current is being carried by the equipment-grounding conductors and can disable the system.
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.
Glazing
The glass layer of windows and doors that transmits light.
Glycol
An antifreeze, heat transfer fluid that is circulated through closed loop solar hot water collectors.
Governing
Limiting the output and speed of a wind generator. In respect to small wind generators, governing typically is accomplished via furling, pitch control, or stall.
Gravity Head
The atmospheric resistance that a pump must overcome to raise a fluid above its level at rest.
Grid-Connected System
A PV system that is tied to the utility grid, including both grid-direct and grid-tied with battery back-up systems.
Grid-Direct System
A PV system that can sell electricity to the utility grid. These systems do not have energy storage and are required to shut down if the utility is not present, such as during a blackout.
Grid-Direct Systems
PV systems that can sell electricity to the utility grid. These systems do not have energy storage and are required to shut down if the utility is not present, such as during a blackout.
Grid-Tied with Battery Backup System
A PV system that is connected to the utility, and can sell excess energy back to the grid. Because these systems have batteries, some specified backed-up loads can be powered during a utility outage.
Ground
Ground means the earth.
Ground Fault
An unintentional, electrically conducting connection between a current-carrying conductor of an electrical circuit and the normally non-current-carrying conductors, metallic enclosures, metallic raceways, metallic equipment, or earth.
Ground Fault Protection Device
A device that detects whether fault current is being carried by the equipment-grounding conductors and can disable the system.
Ground Mounts
PV racking structures affixed to the ground via concrete piers, metal or wood piles, or other attachments or ballast that provide support and stability.
Grounded
To be intentionally connected to earth through a ground connection, at a reference point of zero volts or zero potential.
Grounded Conductor
A current-carrying conductor that is intentionally connected to earth ground at one point to create a zero-voltage reference.
Grounding Electrode
A conducting object, often a rod, ring, or plate, establishing a direct connection to earth.
Grounding Electrode Conductor
The conductor used to connect the grounding electrode or grounding electrode system to the system grounded conductor, to the equipment, or to both.
Guy Wires
Steel cables that support a tower. Tilt-up towers have four sets of guy wires, and therefore four guy anchors. Fixed-guyed towers have three sets of guy wires and three anchors.
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