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US Department of Energy - Solar power glossary
Category: Sciences > Solar power
Date & country: 01/06/2011, US
Words: 396


Distributed Systems
Systems that are installed at or near the location where the electricity is used, as opposed to central systems that supply electricity to grids. A residential photovoltaic system is a distributed system.

Donor
In a photovoltaic device, an n-type dopant, such as phosphorus, that puts an additional electron into an energy level very near the conduction band; this electron is easily exited into the conduction band where it increases the electrical conductivity over than of an undoped semiconductor.

Donor Level
The level that donates conduction electrons to the system.

Dopant
A chemical element (impurity) added in small amounts to an otherwise pure semiconductor material to modify the electrical properties of the material. An n-dopant introduces more electrons. A p-dopant creates electron vacancies (holes).

Doping
The addition of dopants to a semiconductor.

Downtime
Time when the photovoltaic system cannot provide power for the load. Usually expressed in hours per year or that percentage.

Dry Cell
A cell (battery) with a captive electrolyte. A primary battery that cannot be recharged.

Duty Cycle
The ratio of active time to total time. Used to describe the operating regime of appliances or loads in photovoltaic systems.

Duty Rating
The amount of time an inverter (power conditioning unit) can produce at full rated power.

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.

Electric Circuit
The path followed by electrons from a power source (generator or battery), through an electrical system, and returning to the source.

Electric Current
The flow of electrical energy (electricity) in a conductor, measured in amperes.

Electrical grid
An integrated system of electricity distribution, usually covering a large area.

Electricity
Energy resulting from the flow of charge particles, such as electrons or ions.

Electrochemical Cell
A device containing two conducting electrodes, one positive and the other negative, made of dissimilar materials (usually metals) that are immersed in a chemical solution (electrolyte) that transmits positive ions from the negative to the positive electrode and thus forms an electrical charge. One or more cells constitute a battery.

Electrode
A conductor that is brought in conducting contact with a ground.

Electrodeposition
Electrolytic process in which a metal is deposited at the cathode from a solution of its ions.

Electrolyte
A nonmetallic (liquid or solid) conductor that carries current by the movement of ions (instead of electrons) with the liberation of matter at the electrodes of an electrochemical cell.

Electron
An elementary particle of an atom with a negative electrical charge and a mass of 1/1837 of a proton; electrons surround the positively charged nucleus of an atom and determine the chemical properties of an atom. The movement of electrons in an electrical conductor constitutes an electric current.

Electron Volt (eV)
The amount of kinetic energy gained by an electron when accelerated through an electric potential difference of 1 Volt; equivalent to 1.603 x 10^-19; a unit of energy or work.

Energy
The capability of doing work; different forms of energy can be converted to other forms, but the total amount of energy remains the same.

Energy Audit
A survey that shows how much energy used in a home, which helps find ways to use less energy.

Energy Contribution Potential
Recombination occurring in the emitter region of a photovoltaic cell.

Energy Density
The ratio of available energy per pound; usually used to compare storage batteries.

Energy Levels
The energy represented by an electron in the band model of a substance.

Epitaxial Growth
The growth of one crystal on the surface of another crystal. The growth of the deposited crystal is oriented by the lattice structure of the original crystal.

Equalization
The process of restoring all cells in a battery to an equal state-of-charge. Some battery types may require a complete discharge as a part of the equalization process.

Equalization Charge
The process of mixing the electrolyte in batteries by periodically overcharging the batteries for a short time.

Equalizing Charge
A continuation of normal battery charging, at a voltage level slightly higher than the normal end-of-charge voltage, in order to provide cell equalization within a battery.

Equinox
The two times of the year when the sun crosses the equator and night and day are of equal length; usually occurs on March 21st (spring equinox) and September 23 (fall equinox).

Extrinsic Semiconductor
The product of doping a pure semiconductor.

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
The ratio of a photovoltaic cell's actual power to its power if both current and voltage were at their maxima. A key characteristic in evaluating cell performance.

Fixed Tilt Array
A photovoltaic array set in at a fixed angle with respect to horizontal.

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.

Float Charge
The voltage required to counteract the self-discharge of the battery at a certain temperature.

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 which supplies the battery load< under normal conditions, while also providing enough energy input to the battery to make up for its internal quiescent losses, thus keeping the battery always up to full power and ready for service.

Float-Zone Process
In reference to solar photovoltaic cell manufacture, 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 a single crystal.

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.

Frequency
The number of repetitions per unit time of a complete waveform, expressed in Hertz (Hz).

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.

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).

Ga
See gallium.

GaAs
See gallium arsenide.

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

Gallium Arsenide (GaAs)
A crystalline, high-efficiency compound used to make certain types of solar cells and semiconductor material.

Gassing
The evolution of gas from one or more of the electrodes in the cells of a battery. Gassing commonly results from local action self-discharge or from the electrolysis of water in the electrolyte during charging.

Gassing Current
The portion of charge current that goes into electrolytical production of hydrogen and oxygen from the electrolytic liquid. This current increases with increasing voltage and temperature.

Gel-Type Battery
Lead-acid battery in which the electrolyte is composed of a silica gel matrix.

Gigawatt (GW)
A unit of power equal to 1 billion Watts; 1 million kilowatts, or 1,000 megawatts.

Grid
See electrical grid.

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

Grid-Connected System
A solar electric or photovoltaic (PV) system in which the PV array acts like a central generating plant, supplying power to the grid.

Grid-Interactive System
Same as grid-connected system.

Harmonic Content
The number of frequencies in the output waveform in addition to the primary frequency (50 or 60 Hz.). Energy in these harmonic frequencies is lost and may cause excessive heating of the load.

Heterojunction
A region of electrical contact between two different materials.

High Voltage Disconnect
The voltage at which a charge controller will disconnect the photovoltaic array from the batteries to prevent overcharging.

High Voltage Disconnect Hysteresis
The voltage difference between the high voltag disconnect set point and the voltage at which the full photovoltaic array current will be reapplied.

Hole
The vacancy where an electron would normally exist in a solid; behaves like a positively charged particle.

Homojunction
The region between an n-layer and a p-layer in a single material, photovoltaic cell.

Hybrid System
A solar electric or photovoltaic system that includes other sources of electricity generation, such as wind or diesel generators.

Hydrogenated Amorphous Silicon
Amorphous silicon with a small amount of incorporated hydrogen. The hydrogen neutralizes dangling bonds in the amorphous silicon, allowing charge carriers to flow more freely.

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

Indium Oxide
A wide band gap semiconductor that can be heavily doped with tin to make a highly conductive, transparent thin film. Often used as a front contact or one component of a heterojunction solar cell.

Infrared Radiation
Electromagnetic radiation whose wavelengths lie in the range from 0.75 micrometer to 1000 micrometers; invisible long wavelength radiation (heat) capable of producing a thermal or photovoltaic effect, though less effective than visible light.

Input Voltage
This is determined by the total power required by the alternating current loads and the voltage of any direct current loads. Generally, the larger the load, the higher the inverter input voltage. This keeps the current at levels where switches and other components are readily available.

Insolation
The solar power density incident on a surface of stated area and orientation, usually expressed as Watts per square meter or Btu per square foot per hour. See diffuse insolation and direct insolation.

Interconnect
A conductor within a module or other means of connection that provides an electrical interconnection between the solar cells.

Intrinsic Layer
A layer of semiconductor material, used in a photovoltaic device, whose properties are essentially those of the pure, undoped, material.

Intrinsic Semiconductor
An undoped semiconductor.

Inverter
A device that converts direct current electricity to alternating current either for stand-alone systems or to supply power to an electricity grid.

Ion
An electrically charged atom or group of atoms that has lost or gained electrons; a loss makes the resulting particle positively charged; a gain makes the particle negatively charged.

Irradiance
The direct, diffuse, and reflected solar radiation that strikes a surface. Usually expressed in kilowatts per square meter. Irradiance multiplied by time equals insolation.

ISPRA Guidelines
Guidelines for the assessment of photovoltaic power plants, published by the Joint Research Centre of the Commission of the European Communities, Ispra, Italy.

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.

Junction
A region of transition between semiconductor layers, such as a p/n junction, which goes from a region that has a high concentration of acceptors (p-type) to one that has a high concentration of donors (n-type).

Junction Box
A photovoltaic (PV) generator junction box is an enclosure on the module where PV strings are electrically connected and where protection devices can be located, if necessary.

Junction Diode
A semiconductor device with a junction and a built-in potential that passes current better in one direction than the other. All solar cells are junction diodes.

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.

Lattice
The regular periodic arrangement of atoms or molecules in a crystal of semiconductor material.

Lead-Acid Battery
A general category that includes batteries with plates made of pure lead, lead-antimony, or lead-calcium immersed in an acid electrolyte.

Life
The period during which a system is capable of operating above a specified performance level.

Life-Cycle Cost
The estimated cost of owning and operating a photovoltaic system for the period of its useful life.

Light Trapping
The trapping of light inside a semiconductor material by refracting and reflecting the light at critical angles; trapped light will travel further in the material, greatly increasing the probability of absorption and hence of producing charge carriers.

Light-Induced Defects
Defects, such as dangling bonds, induced in an amorphous silicon semiconductor upon initial exposure to light.

Line-Commutated Inverter
An inverter that is tied to a power grid or line. The commutation of power (conversion from direct current to alternating current) is controlled by the power line, so that, if there is a failure in the power grid, the photovoltaic system cannot feed power into the line.

Liquid Electrolyte Battery
A battery containing a liquid solution of acid and water. Distilled water may be added to these batteries to replenish the electrolyte as necessary. Also called a flooded battery because the plates are covered with the electrolyte.

Load
The demand on an energy producing system; the energy consumption or requirement of a piece or group of equipment. Usually expressed in terms of amperes or watts in reference to electricity.

Load Circuit
The wire, switches, fuses, etc. that connect the load to the power source.

Load Current (A)
The current required by the electrical device.

Load Resistance
The resistance presented by the load. See resistance.

Low Voltage Cutoff (LVC)
The voltage level at which a charge controller will disconnect the load from the battery.

Low Voltage Disconnect
The voltage at which a charge controller will disconnect the load from the batteries to prevent over-discharging.

Low Voltage Disconnect Hysteresis
The voltage difference between the low voltage disconnect set point and the voltage at which the load will be reconnected.