| Fan Coil | A component of a heating, ventilation and air conditioning (HVAC) system containing a fan and heating or cooling coil, used to distribute heated or cooled air. |
| Farad | The farad is the SI unit of the capacitance of an electrical system, that is, its capacity to store electricity. It is a rather large unit as defined and is more often used as a microfarad. It is named after the English chemist and physicist Michael Faraday (1791-1867). |
| Fault | a crack or break in the Earth’s crust along which movement has occurred, often resulting in earthquakes. |
| Favonius | The Latin word for the West Wind in Roman mythology. |
| Feathering | In wind generators, this refers to an adjustment of the blades so that they catch less wind. This can prevent damage to the machine in high winds. |
| Federal Emergency Management Agency (Fema) | The federal agency in charge of disaster recovery in locations that have been declared disaster areas by a state’s Governor and the President of the United States. |
| Federal Energy Regulatory Commission (Ferc) | An independent regulatory commission within the U.S. Department of Energy that has jurisdiction over energy producers that sell or transport fuels for resale in interstate commerce; the authority to set oil and gas pipeline transportation rates and to set the value of oil and gas pipelines for ratemaking purposes; and regulates wholesale electric rates and hydroelectric plant licenses. |
| Fenestration | In simplest terms, windows or glass doors. Technically fenestration is described as any transparent or translucent material plus any sash, frame, mullion or divider. This includes windows, sliding glass doors, French doors, skylights, curtain walls and garden windows. |
| Fermi Level | Energy level at which the probability of finding an electron is one-half. In a metal, the Fermi level is very near the top of the filled levels in the partially filled valence band. In a semiconductor, the Fermi level is in the band gap. |
| Fill Factor | On an I-V (current-voltage) curve characterizing the output of a solar cell or module, the ratio of the maximum power to the product of the open-circuit voltage and the short-circuit current. The higher the fill factor (FF) the "squarer" the shape of the I-V curve. |
| Finish Charge | The final stage of battery charging, when the battery is charged at a slow rate over a long period of time. |
| Firm Energy | Power supplies that are guaranteed to be delivered under terms defined by contract. |
| Fission | A release of energy caused by the splitting of an atom’s nucleus. This is the energy process used in conventional nuclear power plants to make the heat needed to run steam electric turbines. |
| Fissionable Material | A substance whose atoms can be split by slow neutrons. Uranium-235, plutonium-239 and uranium-233 are fissionable materials. |
| Fixed Tilt Array | A photovoltaic array set in at a fixed angle with respect to horizontal. |
| Flagging | Noticeable deformation of trees from prevailing winds. Flagging is an indication of an effective wind site. Lack of flagging is not necessarily an indication of a poor wind site. |
| Flare Gas | Unwanted natural gas that is disposed of by burning as it is released from an oil field. |
| Flat Plate | A device used to collect solar energy. It is a piece of metal painted black on the side facing the sun, to absorb the sun’s heat. |
| Flat Plate Collector | A solar thermal collector that converts the sun’s radiation into heat on a flat surface. Does not use reflecting surfaces or lens arrangements to concentrate the sun’s energy. |
| Flat-Plate Array | A photovoltaic (PV) array that consists of non-concentrating PV modules. |
| Flat-Plate Module | An arrangement of photovoltaic cells or material mounted on a rigid flat surface with the cells exposed freely to incoming sunlight. |
| Flat-Plate Photovoltaics (Pv) | A PV array or module that consists of nonconcentrating elements. Flat-plate arrays and modules use direct and diffuse sunlight, but if the array is fixed in position, some portion of the direct sunlight is lost because of oblique sun-angles in relation to the array. |
| Flat-Plate PV | A solar PV array or module that does not contain concentrating devices and so responds to both direct and diffuse sunlight. |
| Flexible Fuel Vehicle (Ffv) | a vehicle that can operate on either alcohol fuels (methanol or ethanol) or regular unleaded gasoline or any combination of the two from the same tank. |
| Float Charge | A battery charge current that is equal to, or slightly greater than, the self-discharge rate. |
| Float Life | The number of years that a battery can keep its stated capacity when it is kept at float charge. |
| Float Service | A battery operation in which the battery is normally connected to an external current source; for instance, a battery charger that supplies the battery load under normal conditions, while also providing enough energy input to the battery to make up for its internal losses, thus keeping the battery always at full charge and ready for service. |
| Float-Zone Process | A method of growing a large-size, high-quality crystal whereby coils heat a polycrystalline ingot placed atop a single-crystal seed. As the coils are slowly raised the molten interface beneath the coils becomes single crystal. |
| Flooded Cell Battery | A form of rechargeable battery where the plates are completely immersed in a liquid electrolyte. Most cars use flooded-cell batteries. Flooded cell batteries are the most commonly used type for independent and remote area power supplies. |
| Flow | In hydro-electric terms, flow refers to the quantity of water supplied to a water source or exiting a nozzle per unit of time. Commonly measured in gallons per minute. |
| Flue Gas | Gas that is left over after fuel is burned and which is disposed of through a pipe or stack to the outer air. |
| Fluidized Bed Combustion | A process for burning powdered coal that is poured in a liquid-like stream with air or gases. The process reduces sulfur dioxide emissions from coal combustion. |
| Fluorescent Lamp | A tubular electric lamp that is coated on its inner surface with a phosphor and that contains mercury vapor whose bombardment by electrons from the cathode provides ultraviolet light which causes the phosphor to emit visible light either of a selected color or closely approximating daylight. |
| Fluorescent Light | A form of lighting that uses long thin tubes of glass which contain mercury vapor and various phosphor powders (chemicals based on phosphorus) to produce white light. Generally considered to be the most efficient form of home lighting. |
| Fluorescent Lights | Lights where the source of light is produced by gas that glows when connected to electricity. Fluorescent light bulbs have a very long life – between 8000 and 20,000 hours. They use up to 75 percent less power than regular light bulbs. |
| Fluorocarbon Gases | Propellants used in aerosol products and refrigerants that are believed to be causing depletion of the earth’s ozone shield. See CFCs. |
| Foehn | Any warm, dry wind that blows down the leeward side of a mountain range, particularly the hot, dry winds that move down from snow-clad mountains through Alpine valleys. |
| Footcandle | A unit of illuminance on a surface that is one foot from a uniform point source of light of one candle and is equal to one lumen per square foot. |
| Forced Air Unit (Fau) | A central furnace equipped with a fan or blower that provides the primary means for circulation of air. |
| Fossil Fuel | Oil, coal, natural gas or their by-products. Fuel that was formed in the earth in prehistoric times from remains of living-cell organisms. |
| Fossil Fuels | Fuels formed in the ground from the decayed remains of dead plants and animals. It takes millions of years to form fossil fuels. Oil, natural gas, and coal are fossil fuels. |
| Fracture | a crack in the Earth’s crust along which no movement has occurred. |
| Framing Effects | The effect of framing (wood or metal studs, joists, beams, etc.) on the overall U-value of a wall, roof, floor, window or other building surface. Framing generally increases the U-Value and decreases the R-Value of insulated surfaces. |
| Framing Percentage | The area of actual framing in an envelope assembly divided by the overall area of the envelope assembly. This percentage is used to calculate the overall U-value of an assembly. |
| Francis Turbine | A type of reaction hydro-turbine used in low to medium heads. It consists of fixed vanes on a shaft. Water flows down through the vanes and out sideways. |
| Freestanding Tower | A wind generator tower with no guy wires. This can be either a lattice tower or a monopole. Freestanding towers are the most expensive type of tower, requiring large excavations and large amounts of concrete. |
| Frequency | The number of cycles or repetitions per unit time of a complete waveform, in electrical applications usually expressed in cycles per second or Hertz (Hz). Electrical equipment in the United States requires 60 Hz, in Europe 50Hz. |
| Frequency Regulation | This indicates the variability in the output frequency. Some loads will switch off or not operate properly if frequency variations exceed 1%. |
| Fresnel Lens | An optical device that focuses light like a magnifying glass; concentric rings are faced at slightly different angles so that light falling on any ring is focused to the same point. |
| Friagem | Like a “norther,” a winter wind that sweeps across the southern United States and then out over the Gulf of Mexico, only a friagem blows northward from the South Pole into South America. |
| Friction Loss | Lost energy due to friction. 1 In hydro systems, pipe sized too small can lead to serious friction losses. 2 In any belt drive system, there will be some losses due to friction. |
| Fuel | Any material that can be consumed to make energy. |
| Fuel Cell | A device in which a fuel, such as hydrogen gas, is combined with oxygen to produce electricity, water, and heat. |
| Fuel Gas | Synthetic gas used for heating or cooling. It has less energy content than pipeline-quality gas. |
| Fuel Oil | Petroleum products that are burned to produce heat or power. |
| Fuel Reprocessing (Nuclear) | The means for obtaining usable, fissionable material from spent reactor fuel. |
| Fuel Rod (Nuclear) | A long slender tube that holds fissionable material (fuel) for nuclear reactor use. Fuel rods are assembled into bundles called fuel elements or assemblies, which are loaded individually into the reactor core. |
| Fuel Security | See Energy Security. |
| Full Sun | The amount of power density in sunlight received at the earth’s surface at noon on a clear day (about 1,000 Watts/square meter). |
| Fumarole | a small hole or vent in the Earth’s surface, found near volcanic areas, from which steam or gases shoot out. |
| Funnel Cloud | A rotating, cone-shaped column of air extending downward from the base of a thunderstorm, but not in contact with the ground. (When it reaches the ground, it is called a tornado.) |
| Furling | Reducing a wind generator’s swept area to protect it from high winds. Common furling methods are to tilt the rotor (blades) up or sideways out of the wind, or to feather (twist) the blades to degrade the airfoil. |
| Fuse | A safety device with a metal wire or strip that melts when the current gets too strong, cutting off the flow of the electrical current. |
| Fusion Energy | A power source, now under development, based on the release of energy that occurs when atoms are combined under the most extreme heat and pressure. It is the energy process of the sun and the stars. |
