Absorber: In a photovoltaic device, the material that readily absorbs photons to generatecharge carriers (free electrons or holes).
Archives: Glossary
Acceptor: A dopant material, such as boron, has fewer outer shell electrons thanrequired in an otherwise balanced crystal structure, providing a hole that can accept a freeelectron
Activation Voltage(s): The voltage(s) at which a charge controller will take action to protectthe batteries
Adjustable Set Point: A feature allowing a user to adjust the voltage levels at which a charge controller will become active.
AIC: See amperage interrupt capability
Air Mass (sometimes called air mass ratio): Equal to the cosine of the zenith angle or thatangle from directly overhead to a line intersecting the sun. The air mass is an indication ofthe length of the path solar radiation travels through the atmosphere. An air mass of 1.0means the sun is directly overhead and the radiation travels...
Alternating current (AC): A type of electrical current, the direction of which is reversed at regular intervals or cycles. In the United States, the standard is 120 reversals or 60 cycles per second. Electricity transmission networks use AC because voltage can be controlled with relative ease.
Ambient Temperature: The temperature of the surrounding area.
Amorphous Semiconductor: A non‐crystalline semiconductor material that has no long-rangeorder.
Amorphous Silicon: A thin‐film, silicon photovoltaic cell has no crystalline structure.Manufactured by depositing layers of doped silicon on a substrate. See also single‐crystalsilicon and polycrystalline silicon.
Amperage Interrupt Capability (AIC): Direct current fuses should be rated with asufficient AIC to interrupt the highest possible current.
Ampere (amp): A unit of electrical current or rate of flow of electrons. One volt across oneohm of resistance causes a current flow of one ampere.
Ampere Hour Meter: An instrument that monitors current over time. The indication is theproduct of current (in amperes) and time (in hours).
Ampere‐Hour (Ah/AH): A measure of the flow of current (in amperes) over one hour; usedto measure battery capacity.
Angle of Incidence: The angle that a ray of sun makes with a line perpendicular to the surface. For example, a surface that directly faces the sun has a solar angle of incidence of zero, but if the surface is parallel to the sun (for example, sunrise striking a horizontal rooftop), the angle...
Annual Solar Savings: The annual solar savings of a solar building is the energy savingsattributable to a solar feature relative to the energy requirements of a non‐solar building.
Anode: The positive electrode in an electrochemical cell (battery). Also, the earth or groundin a cathodic protection system. Also, the positive terminal of a diode.
Antireflection Coating: A thin coating of a material applied to a solar cell surface that reducesthe light reflection and increases light transmission.
Array: A solar array is a collection of solar panels wired together to create the desired energy output. The typical residential solar array consists of 20–25 solar panels to cover 100% of its energy consumption.
Array Current: The electrical current produced by a photovoltaic array when it is exposedto sunlight.
Array Operating Voltage: The voltage produced by a photovoltaic array when exposed tosunlight and connected to a load.
Autonomous System: See stand‐alone system.
Availability: The quality or condition of a photovoltaic system available to provide power toa load. Usually measured in hours per year. One minus availability equals downtime.
Azimuth: The direction that your roof faces (in the context of solar). The azimuth is measured in degrees, representing the angle between your roof and true north.
Azimuth Angle: The angle between true south and the point on the horizon directly belowthe sun.
Balance of System: Represents all components and costs other than the photovoltaicmodules/array. It includes design costs, land, site preparation, system installation, supportstructures, power conditioning, operation and maintenance costs, indirect storage, andrelated costs.
Band Gap: In a semiconductor, the energy difference between the highest valence band andthe lowest conduction band.
Band Gap Energy (Eg): The amount of energy (in electron volts) required to free an outershell electron from its orbit about the nucleus to a free state, and thus promote it from thevalence to the conduction level.
Barrier Energy: The energy is given up by an electron in penetrating the cell barrier; a measure of the electrostatic potential of the barrier.
Base Load: The average amount of electric power that a utility must supply in any period.
Battery: Two or more electrochemical cells are enclosed in a container and electricallyinterconnected in an appropriate series/parallel arrangement to provide the requiredoperating voltage and current levels. Under common usage, the term battery also applies toa single cell if it constitutes the entire electrochemical storage system.
Battery Available Capacity: The total maximum charge, expressed in ampere‐hours, thatcan be withdrawn from a cell or battery under a specific set of operating conditions includingdischarge rate, temperature, the initial state of charge, age, and cut‐off voltage.
Battery Capacity: The maximum total electrical charge, expressed in ampere‐hours, which a battery can deliver to a load under a specific set of conditions.
Battery Cell: The simplest operating unit in a storage battery. It consists of one or more positive electrodes or plates, an electrolyte that permits ionic conduction, one or more negative electrodes or plates, separators between plates of opposite polarity, and a container for all the above.
Battery Cycle Life: The number of cycles, to a specified depth of discharge, that a cell or battery can undergo before failing to meet its specified capacity or efficiency performance criteria
Battery Energy Capacity: The total energy available, expressed in watt‐hours (kilowatthours), which can be withdrawn from a fully charged cell or battery. The energy capacity of a given cell varies with temperature, rate, age, and cut‐off voltage. This term is more common to system designers than it is to the battery industry where...
Battery Energy Storage:: Energy storage using electrochemical batteries. The three main applications for battery energy storage systems include spinning reserve at generating stations, load leveling at substations, and peak shaving on the customer side of the meter
Battery Life: The period during which a cell or battery is capable of operating above a specified capacity or efficiency performance level. Life may be measured in cycles and/or years, depending on the type of service for which the cell or battery is intended.
BIPV (Building‐Integrated Photovoltaic):: A term for the design and integration of photovoltaic (PV) technology into the building envelope, typically replacing conventional building materials. This integration may be in vertical facades, replacing view glass, spandrel glass, or other facade material; into semitransparent skylight systems; into roofing systems, replacing traditional roofing materials; into shading "eyebrows"...
Blocking Diode: A semiconductor connected in series with a solar cell or cells and a storage battery to keep the battery from discharging through the cell when there is no output, or low output, from the solar cell. It can be thought of as a one‐way valve that allows electrons to flow...
Boron (B): The chemical element commonly used as the dopant in photovoltaic device or cell material.
Boule: A sausage‐shaped, synthetic single‐crystal mass grown in a special furnace, pulled and turned at a rate necessary to maintain the single‐crystal structure during growth.
Btu (British Thermal Unit): The amount of heat required to raise the temperature of one pound of water one degree Fahrenheit; equal to 252 calories.
Bypass diode: A diode connected across one or more solar cells in a photovoltaic module such that the diode will conduct if the cell(s) become reverse biased. It protects these solar cells from thermal destruction in case of total or partial shading of individual solar cells while other cells are exposed to full light.
Bypass Diode: A diode connected across one or more solar cells in a photovoltaic module such that the diode will conduct if the cell(s) become reverse biased. It protects these solar cells from thermal destruction in case of total or partial shading of individual solar cells while other cells are exposed to...
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).
Cathode: 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...
Cell Junction: The area of immediate contact between two layers (positive and negative) ofa photovoltaic cell. The junction lies at the center of the cell barrier or depletion zone.
Cells: The smallest semiconductor element within a PV module to perform the immediate conversion of light into electrical energy (direct current voltage and current). Also called a solar cell.
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 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...
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...
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.
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 photovoltaicmaterial (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.
Czochralski Process: A method of growing large size, high quality semiconductor crystals by slowly lifting a seed crystal from a molten bath of the material under careful cooling conditions.
Days of Storage: The number of consecutive days the stand‐alone system will meet a defined load without solar energy input. This term is related to system availability.
DC: See direct current
DC‐to‐DC Converter: Electronic circuit to convert direct current voltages (e.g., photovoltaic module voltage) into other levels (e.g., load voltage). Can be part of a maximum power point tracker.
Deep Discharge: Discharging a battery to 20% or less of its full charge capacity.
Deep‐Cycle Battery: A battery with large plates that can withstand many discharges to a low state‐of‐charge.
Dendrite: A slender threadlike spike of pure crystalline material, such as silicon.
Depletion Zone: Same as cell barrier. The term derives from the fact that this microscopically thin region is depleted of charge carriers (free electrons and hole).
Depth of Discharge (DOD): The ampere‐hours removed from a fully charged cell or battery, expressed as a percentage of rated capacity. For example, the removal of 25 ampere‐hours from a fully charged 100 ampere‐hours‐rated cell results in a 25% depth of discharge. Under certain conditions, such as discharge rates lower than that used to...
Design Month: The month having the combination of insolation and load that requires the maximum energy from the photovoltaic array.
Diffuse Insolation: Sunlight received indirectly as a result of scattering due to clouds, fog,haze, dust, or other obstructions in the atmosphere. Opposite of direct insolation.
Diffuse Radiation: Radiation received from the sun after reflection and scattering by the atmosphere and ground.
Diffusion Furnace: Furnace used to make junctions in semiconductors by diffusing dopant atoms into the surface of the material.
Diffusion Length: The mean distance a free electron or hole moves before recombining with another hole or electron.
Diode: An electronic device that allows current to flow in one direction only. See blocking diode and bypass diode.
Direct Beam Radiation: Radiation received by direct solar rays. Measured by a pyrheliometer with a solar aperture of 5.7° to transcribe the solar disc.
Direct Current (DC): A type of electricity transmission and distribution by which electricity flows in one direction through the conductor, usually relatively low voltage and high current. To be used for typical 120 volt or 220‐volt household appliances, DC must be converted to alternating current, its opposite.
Direct Insolation: Sunlight falling directly upon a collector. Opposite of diffuse insolation.
Discharge Factor: A number equivalent to the time in hours during which a battery is discharged at constant current, usually expressed as a percentage of the total battery capacity, i.e., C/5 indicates a discharge factor of 5 hours. Related to discharge rate.
Discharge Rate: The rate, usually expressed in amperes or time, at which electrical current is taken from the battery.
Disconnect: Switch gear used to connect or disconnect components in a photovoltaic system.
Distributed Energy Resources (DER): A variety of small, modular power‐generating technologies that can be combined with energy management and storage systems and used to improve the operation of the electricity delivery system, whether or not those technologies are connected to an electricity grid.
Distributed Generation: A popular term for localized or on‐site power generation.
Distributed Power: Generic term for any power supply located near the point where the power is used. Opposite of central power. See stand‐alone systems.
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 that 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 berecharged.
Duty Cycle: The ratio of active time to total time that is 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 back 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 charged 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 Audit: A survey that shows how much energy used in a home and helps identify 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 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 23rd (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 are 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 Photovoltaic (PV): A PV array or module that consists of non concentrating 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 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...
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.
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 one percent.
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 MWs.
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 voltage 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.
I‐Type Semiconductor: Semiconductor material that is left intrinsic, or undoped, so that the concentration of charge carriers is characteristic of the material itself rather than of added impurities.
I‐V Curve: A graphical presentation of the current versus the voltage from a photovoltaic device as the load is increased from the short circuit (no load) condition to the open circuit (maximum voltage) condition. The shape of the curve characterizes cell performance.
III-V cell: A high-efficiency solar cell made from materials including Group III and Group V elements from the periodic table.
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 footpounds; 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.
Low Voltage Warning: A warning buzzer or light that indicates the low battery voltage set point has been reached.
Maintenance‐Free Battery: A sealed battery to which water cannot be added to maintain electrolyte level.
Majority Carrier: Current carriers (either free electrons or holes) that are in excess in a specific layer of a semiconductor material (electrons in the n‐layer, holes in the p‐layer) of a cell.
Maximum Power Point (MPP): The point on the current‐voltage (I‐V) curve of a module under illumination, where the product of current and voltage is maximum. For a typical silicon cell, this is at about 0.45 volts.
Maximum Power Point Tracker (MPPT): Means of a power‐conditioning unit that automatically operates the photovoltaic generator at its maximum power point under all conditions.
Maximum Power Tracking: Operating a photovoltaic array at the peak power point of the array's I‐V curve where maximum power is obtained. Also called peak power tracking.
Microgroove: A small groove scribed into the surface of a solar cell, which is filled with metal for contacts.
Minority Carrier: A current carrier, either an electron or a hole, that is in the minority in a specific layer of a semiconductor material; the diffusion of minority carriers under the action of the cell junction voltage is the current in a photovoltaic device.
Minority Carrier Lifetime: The average time a minority carrier exists before recombination.
Modified Sine Wave: A waveform that has at least three states (i.e., positive, off, and negative). Has less harmonic content than a square wave.
Modularity: The use of multiple inverters connected in parallel to service different loads.
Module: See photovoltaic (PV) module
Module Derate Factor: A factor that lowers the photovoltaic module current to account for field operating conditions such as dirt accumulation on the module.
Monolithic: Fabricated as a single structure.
Movistor: Metal Oxide Varistor. Used to protect electronic circuits from surge currents such as those produced by lightning.
Multi‐Stage Controller: A charging controller unit that allows different charging currents as the battery nears full state‐of‐charge.
Multicrystalline: A semiconductor (photovoltaic) material composed of variously oriented, small, individual crystals. Sometimes referred to as polycrystalline or semicrystalline.
Multijunction Device: A high‐efficiency photovoltaic device containing two or more cell junctions, each of which is optimized for a particular part of the solar spectrum.
MW (MW): 1,000 kilowatts, or 1 million watts; standard measure of electric power plant generating capacity.
MW‐Hour: 1,000 kilowatt‐hours or 1 million watt‐hours.
Ohm: A measure of the electrical resistance of a material equal to the resistance of a circuitin which the potential difference of 1 volt produces a current of 1 ampere.
One‐Axis Tracking: A system capable of rotating about one axis.
Operating Point: The current and voltage that a photovoltaic module or array produces when connected to a load. The operating point is dependent on the load or the batteries connected to the output terminals of the array.
Outgas: See gassing.
P‐I‐N: A semiconductor photovoltaic (PV) device structure that layers an intrinsic semiconductor between a p‐type semiconductor and an n‐type semiconductor; this structure is most often used with amorphous silicon PV devices.
P‐Type Semiconductor: A semiconductor in which holes carry the current; produced by doping an intrinsic semiconductor with an electron acceptor impurity (e.g., boron in silicon).
P/N: A semiconductor photovoltaic device structure in which the junction is formed between a p‐type layer and an n‐type layer.
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.
Panel: See photovoltaic (PV) panel.
Parallel Connection: A way of joining solar cells or photovoltaic modules by connecting positive leads together and negative leads together; such a configuration increases the current, but not the voltage.
Passivation: A chemical reaction that eliminates the detrimental effect of electrically reactive atoms on a solar cell's surface.
Peak Demand/Load: The maximum energy demand or load in a specified time period
Peak Power Current: Amperes produced by a photovoltaic module or array operating at the voltage of the I‐V curve that will produce maximum power from the module.
Peak Power Point: Operating point of the I‐V (current‐voltage) curve for a solar cell or photovoltaic module where the product of the current value times the voltage value is a maximum.
Peak Power Tracking: See maximum power tracking.
Peak Sun Hours: The equivalent number of hours per day when solar irradiance averages 1,000 w/m2. For example, six peak sun hours means that the energy received during total daylight hours equals the energy that would have been received had the irradiance for six hours been 1,000 w/m2.
Peak Watt: A unit used to rate the performance of solar cells, modules, or arrays; the maximum nominal output of a photovoltaic device, in watts (Wp) under standardized test conditions, usually 1,000 watts per square meter of sunlight with other conditions, such as temperature specified.
Peak Watt: A unit used to rate the performance of solar cells, modules, or arrays; the maximum nominal output of a photovoltaic device, in watts (Wp) under standardized test conditions, usually 1,000 watts per square meter of sunlight with other conditions, such as temperature specified.
Phosphorous (P): A chemical element used as a dopant in making n‐type semiconductor layers.
Photocurrent: An electric current induced by radiant energy.
Photoelectric Cell: A device for measuring light intensity; used in photometers.
Photoelectrochemical Cell: A type of photovoltaic device in which the electricity induced in the cell is used immediately within the cell to produce a chemical, such as hydrogen, which can then be withdrawn for use
Photon: A particle of light that acts as an individual unit of energy.
Photovoltaic (PV) Array: An interconnected system of PV modules that function as a single electricity‐producing unit. The modules are assembled as a discrete structure, with common support or mounting. In smaller systems, an array can consist of a single module.
Photovoltaic (PV) Cell: The smallest semiconductor element within a PV module to perform the immediate conversion of light into electrical energy (direct current voltage and current). Also called a solar cell.
Photovoltaic (PV) Conversion Efficiency: The ratio of the electric power produced by a photovoltaic device to the power of the sunlight incident on the device.
Photovoltaic (PV) Device: A solid‐state electrical device that converts light directly into direct current electricity of voltage‐current characteristics that are a function of the characteristics of the light source and the materials in and design of the device. Solar photovoltaic devices are made of various semiconductor materials including silicon,cadmium sulfide, cadmium telluride, and...
Photovoltaic (PV) Effect: The phenomenon that occurs when photons, the "particles" in a beam of light, knock electrons loose from the atoms they strike. When this property of light is combined with the properties of semiconductors, electrons flow in one direction across a junction, setting up a voltage. With the addition of circuitry,...
Photovoltaic (PV) Generator: The total of all PV strings of a PV power supply system, which are electrically interconnected.
Photovoltaic (PV) Module: The smallest environmentally protected, essentially planar, assembly of solar cells and ancillary parts, such as interconnections, terminals, (and protective devices such as diodes) intended to generate direct current power under unconcentrated sunlight. The structural (load carrying) member of a module can either bethe top layer (superstrate) or the back layer...
Photovoltaic (PV) Panel: Often used interchangeably with PV module (especially in onemodule systems), but more accurately used to refer to a physically connected collection of modules (i.e., a laminate string of modules used to achieve a required voltage and current).
Photovoltaic (PV) System: A complete set of components for converting sunlight into electricity by the photovoltaic process, including the array and balance of system components.
Photovoltaic‐Thermal (PV/T) System: A photovoltaic system that, in addition to converting sunlight into electricity, collects the residual heat energy and delivers both heat and electricity in usable form. Also called a total energy system.
Photovoltaic(s) (PV): Pertaining to the direct conversion of light into electricity.
Physical Vapor Deposition: A method of depositing thin semiconductor photovoltaic films. With this method, physical processes, such as thermal evaporation or bombardment of ions, are used to deposit elemental semiconductor material on a substrate.
Plates: A metal plate, usually lead or lead compound, immersed in the electrolyte in abattery.
Pocket Plate: A plate for a battery in which active materials are held in a perforated metal pocket.
Point‐Contact Cell: A high efficiency silicon photovoltaic concentrator cell that employs light trapping techniques and point‐diffused contacts on the rear surface for current collection.
Polycrystalline: See Multicrystalline
Polycrystalline Silicon: A material used to make photovoltaic cells, which consist of many crystals, unlike single‐crystal silicon.
Power Conditioning: The process of modifying the characteristics of electrical power (e.g., for inverting direct current to alternating current).
Power Conditioning Equipment: Electrical equipment, or power electronics, used to convert power from a photovoltaic array into a form suitable for subsequent use. A collective term for inverter, converter, battery charge regulator, and blocking diode.
Primary Battery: A battery whose initial capacity cannot be restored by charging.
Projected Area: The net south‐facing glazing area projected on a vertical plane.
Pulse‐Width‐Modulated (PWM) Wave Inverter: A type of power inverter that produces a high quality (nearly sinusoidal) voltage, at minimum current harmonics.
PV: See photovoltaic(s).
Pyranometer: An instrument used for measuring global solar irradiance.
Pyrheliometer: An instrument used for measuring direct beam solar irradiance. Uses an aperture of 5.7° to transcribe the solar disc
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
Reactive Power: The sine of the phase angle between the current and voltage waveforms in an alternating current system. See power factor.
Reverse Current Protection: Any method of preventing unwanted current flow from the battery to the photovoltaic array (usually at night). See blocking diode.
Ribbon (Photovoltaic) Cells: A type of photovoltaic device made in a continuous process of pulling material from a molten bath of photovoltaic material, such as silicon, to form a thin sheet of material.
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.
Satellite Power System (SPS): Concept for providing large amounts of electricity for use on the Earth from one or more satellites in geosynchronous Earth orbit. A very large array of solar cells on each satellite would provide electricity, which would be converted to microwave energy and beamed to a receiving antenna on the ground....
Schottky Barrier: A cell barrier established as the interface between a semiconductor, such as silicon, and a sheet of metal.
Scribing: The cutting of a grid pattern of grooves in a semiconductor material, generally for the purpose of making interconnections.
Sealed Battery: A battery with a captive electrolyte and a resealing vent cap, also called a valve‐regulated battery. Electrolyte cannot be added.
Semicrystalline: See Multicrystalline.
Series Connection: A way of joining photovoltaic cells by connecting positive leads to negative leads; such a configuration increases the voltage.
Series Controller: A charge controller that interrupts the charging current by open‐circuiting the photovoltaic (PV) array. The control element is in series with the PV array and battery.
Series Regulator: Type of battery charge regulator where the charging current is controlled by a switch connected in series with the photovoltaic module or array
Series Resistance: Parasitic resistance to current flow in a cell due to mechanisms such as resistance from the bulk of the semiconductor material, metallic contacts, and interconnections
solar constant: The average amount of solar radiation that reaches the earth's upper atmosphere on a surface perpendicular to the sun's rays; equal to 1353 watts per square meter or 492 Btu per
Solar Cooling: The use of solar thermal energy or solar electricity to power a cooling appliance. Photovoltaic systems can power evaporative coolers (swamp coolers), heat pumps, and air conditioners.
Solar Noon: The time of the day, at a specific location, when the sun reaches its highest, apparent point in the sky; equal to true or due geographic south.
Solar Resource: The amount of solar insolation a site receives, usually measured in kWh/m2/day, which is equivalent to the number of peak sun hours.
Solar Spectrum: The total distribution of electromagnetic radiation emanating from the sun. The different regions of the solar spectrum are described by their wavelength range. The visible region extends from about 390 to 780 nanometers (a nanometer is one billionth of one meter).
Solar Thermal Electric Systems: Solar energy conversion technologies that convert solar energy to electricity, by heating a working fluid to power a turbine that drives a generator. Examples of these systems include central receiver systems, parabolic dish, and solar trough.
Solar‐Grade Silicon: Intermediate‐grade silicon used in the manufacture of solar cells. Less expensive than electronic‐grade silicon.
Split‐Spectrum Cell: A compound photovoltaic device in which sunlight is first divided into spectral regions by optical means. Each region is then directed to a different photovoltaic cell optimized for converting that portion of the spectrum into electricity. Such a device achieves significantly greater overall conversion of incident sunlight into electricity. See...
Sputtering: A process used to apply photovoltaic semiconductor material to a substrate by a physical vapor deposition process where high‐energy ions are used to bombard elemental sources of semiconductor material, which eject vapors of atoms that are then deposited in thin layers on a substrate.
Stand‐Alone System: An autonomous or hybrid photovoltaic system not connected to a grid. May or may not have storage, but most stand‐alone systems require batteries or some other form of storage.
String: A number of photovoltaic modules or panels interconnected electrically in series to produce the operating voltage required by the load
Substrate: The physical material upon which a photovoltaic cell is applied.
Subsystem: Any one of several components in a photovoltaic system (i.e., array, controller, batteries, inverter, load).
Temperature Factors: It is common for three elements in photovoltaic system sizing to have distinct temperature corrections: a factor used to decrease battery capacity at cold temperatures; a factor used to decrease PV module voltage at high temperatures; and a factor used to decrease the current carrying capability of wire at high...
Thermophotovoltaic Cell (TPV): A device where sunlight concentrated onto a absorber heats it to a high temperature, and the thermal radiation emitted by the absorber is used as the energy source for a photovoltaic cell that is designed to maximize conversion efficiency at the wavelength of the thermal radiation.
Thick‐Crystalline Materials: Semiconductor material, typically measuring from 200‐400 microns thick, that is cut from ingots or ribbons.
Thin‐Film Photovoltaic Module: A photovoltaic module constructed with sequential layers of thin‐film semiconductor materials. See amorphous silicon.
Tilt Angle: The angle at which a photovoltaic array is set to face the sun relative to a horizontal position. The tilt angle can be set or adjusted to maximize seasonal or annual energy collection.
Tin Oxide: A wide band‐gap semiconductor similar to indium oxide; used in heterojunction solar cells or to make a transparent conductive film, called NESA glass when deposited on glass.
Tracking Array: A photovoltaic (PV) array that follows the path of the sun to maximize the solar radiation incident on the PV surface. The two most common orientations are: (1) one axis where the array tracks the sun east to west; and (2) two‐axis tracking where the array points directly at the...
Two‐Axis Tracking: A photovoltaic array tracking system capable of rotating independently about two axes (e.g., vertical and horizontal).
Ultraviolet: Electromagnetic radiation in the wavelength range of 4 to 400 nanometers.
Underground Feeder (UF): May be used for photovoltaic array wiring if sunlight‐resistant coating is specified; can be used for interconnecting balance‐of‐system components but not recommended for use within battery enclosures
Vacuum Zero: The energy of an electron at rest in empty space; used as a reference level in energy band diagrams.
Volt (V): A unit of electrical force equal to that amount of electromotive force that will cause a steady current of one ampere to flow through a resistance of one ohm.
Voltage: The amount of electromotive force, measured in volts, that exists between two points.
Wafer: A thin sheet of semiconductor (photovoltaic material) made by cutting from a single crystal or ingot.
Window: A wide band gap material chosen for its transparency to light. Generally used as the top layer of a photovoltaic device, the window allows almost all of the light to reach the semiconductor layers beneath.
Zenith Angle: The angle between the direction of interest (the sun, for example) and the zenith (directly overhead).