Balance of System — Represents all components and costs other than the photovoltaic modules/array. It includes design costs, land, site preparation, system installation,

Cadmium (Cd) — A chemical element used in making certain types of solar cells and batteries.

Dangling Bonds — A chemical bond associated with an atom on the surface layer of a crystal. The bond does not join with another atom of the crystal, but extends in the direction of exterior of the surface.

Edge-Defined Film-Fed Growth (EFG) — A method for making sheets of polycrystalline silicon for photovoltaic devices in which molten silicon is drawn upward by capillary action through a mold.

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.

Gallium (Ga) — A chemical element, metallic in nature, used in making certain kinds of solar cells and semiconductor devices.

Harmonic Content — The number of frequencies in the output waveform in addition to the primary frequency (50 or 60 Hz.).

Incident Light — Light that shines onto the face of a solar cell or module.

Joule — A metric unit of energy or work; 1 joule per second equals 1 watt or 0.737 foot-pounds; 1 Btu equals 1,055 joules.

Kilowatt (kW) — A standard unit of electrical power equal to 1000 watts, or to the energy consumption at a rate of 1000 joules per second.

Kilowatt-Hour (kWh) — 1,000 thousand watts acting over a period of 1 hour. The kWh is a unit of energy. 1 kWh=3600 kJ.

Langley (L) — Unit of solar irradiance. One gram calorie per square centimeter. 1 L = 85.93 kwh/m2.

Maintenance-Free Battery — A sealed battery to which water cannot be added to maintain electrolyte level.

National Electrical Code (NEC) — Contains guidelines for all types of electrical installations.

Ohm — A measure of the electrical resistance of a material equal to the resistance of a circuit in which the potential difference of 1 volt produces a current of 1 ampere.

Packing Factor — The ratio of array area to actual land area or building envelope area for a system; or, the ratio of total solar cell area to the total module area, for a module.

Quad — One quadrillion Btu (1,000,000,000,000,000 Btu).

Qualification Test — A procedure applied to a selected set of photovoltaic modules involving the application of defined electrical, mechanical, or thermal stress in a prescribed manner and amount. Test results are subject to a list of defined requirements.

Rated Battery Capacity — The term used by battery manufacturers to indicate the maximum amount of energy that can be withdrawn from a battery under specified discharge rate and temperature. See battery capacity.

Sacrificial Anode — A piece of metal buried near a structure that is to be protected from corrosion. The metal of the sacrificial anode is intended to corrode and reduce the corrosion of the protected structure.

Tare Loss — Loss caused by a charge controller. One minus tare loss, expressed as a percentage, is equal to the controller efficiency.

Ultraviolet — Electromagnetic radiation in the wavelength range of 4 to 400 nanometers.

Vacuum Evaporation - The deposition of thin films of semiconductor material by the evaporation of elemental sources in a vacuum.

Wafer — A thin sheet of semiconductor (photovoltaic material) made by cutting it from a single crystal or ingot.

Zenith Angle — the angle between the direction of interest (of the sun, for example) and the zenith (directly overhead).