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

Cadmium Telluride (CdTe) - A polycrystalline thin-film photovoltaic material.

Capacity (C) - See battery capacity.

Capacity Factor - The ratio of the average load on (or power output of) an electricity generating unit or system to the capacity rating of the unit or system over a specified period of time.

Captive Electrolyte Battery - A battery having an immobilized electrolyte (gelled or absorbed in a material).

B - The negative pole or electrode of an electrolytic cell, vacuum tube, etc., where electrons enter (current leaves) the system; the opposite of an anode.

Cathodic Protection - A method of preventing oxidation of the exposed metal in structures by imposing a small electrical voltage between the structure and the ground.

Cd - see cadmium.

CdTe - see cadmium telluride.

Cell (battery) - A single unit of an electrochemical device capable of producing direct voltage by converting chemical energy into electrical energy. A battery usually consists of several cells electrically connected together to produce higher voltages. (Sometimes the terms cell and battery are used interchangeably). Also see photovoltaic (PV) cell.

Cell Barrier - A very thin region of static electric charge along the interface of the positive and negative layers in a photovoltaic cell. The barrier inhibits the movement of electrons from one layer to the other, so that higher-energy electrons from one side diffuse preferentially through it in one direction, creating a current and thus a voltage across the cell. Also called depletion zone or space charge.

Cell Junction - The area of immediate contact between two layers (positive and negative) of a photovoltaic cell. The junction lies at the center of the cell barrier or depletion zone.

Charge - The process of adding electrical energy to a battery.

Charge Carrier - A free and mobile conduction electron or hole in a semiconductor.

Charge Controller - A component of a photovoltaic system that controls the flow of current to and from the battery to protect it from over-charge and over-discharge. The charge controller may also indicate the system operational status.

Charge Factor - A number representing the time in hours during which a battery can be charged at a constant current without damage to the battery. Usually expressed in relation to the total battery capacity, i.e., C/5 indicates a charge factor of 5 hours. Related to charge rate.

Charge Rate - The current applied to a cell or battery to restore its available capacity. This rate is commonly normalized by a charge control device with respect to the rated capacity of the cell or battery.

Chemical Vapor Deposition (CVD) - A method of depositing thin semiconductor films used to make certain types of photovoltaic devices. With this method, a substrate is exposed to one or more vaporized compounds, one or more of which contain desirable constituents. A chemical reaction is initiated, at or near the substrate surface, to produce the desired material that will condense on the substrate.

Cleavage of Lateral Epitaxial Films for Transfer (CLEFT) - A process for making inexpensive Gallium Arsenide (GaAs) photovoltaic cells in which a thin film of GaAs is grown atop a thick, single-crystal GaAs (or other suitable material) substrate and then is cleaved from the substrate and incorporated into a cell, allowing the substrate to be reused to grow more thin-film GaAs.

Cloud Enhancement - The increase in solar intensity caused by reflected irradiance from nearby clouds.

Combined Collector - A photovoltaic device or module that provides useful heat energy in addition to electricity.

Concentrator - A photovoltaic module, which includes optical components such as lenses (Fresnel lens) to direct and concentrate sunlight onto a solar cell of smaller area. Most concentrator arrays must directly face or track the sun. They can increase the power flux of sunlight hundreds of times.

Conduction Band (or conduction level) - An energy band in a semiconductor in which electrons can move freely in a solid, producing a net transport of charge.

Conductor - The material through which electricity is transmitted, such as an electrical wire, or transmission or distribution line.

Contact Resistance - The resistance between metallic contacts and the semiconductor.

Conversion Efficiency - See photovoltaic (conversion) efficiency.

Converter - A unit that converts a direct current (dc) voltage to another dc voltage.

Copper Indium Diselenide (CuInSe2, or CIS) - A polycrystalline thin-film photovoltaic material (sometimes incorporating gallium (CIGS) and/or sulfur).

Crystalline Silicon - A type of photovoltaic cell made from a slice of single-crystal silicon or polycrystalline silicon.

Current - See electric current.

Current at Maximum Power (Imp) - The current at which maximum power is available from a module.

Cutoff Voltage - The voltage levels (activation) at which the charge controller disconnects the photovoltaic array from the battery or the load from the battery.

Cycle - The discharge and subsequent charge of a battery.