A
AC (Alternating Current): Electric current that reverses direction many times per second.
AC power (Alternating Current): An electrical current whose magnitude and direction varies continuously and sinusoidally.
Acceptor: A dopant material, such as boron, which has fewer outer shell electrons than required in an otherwise balanced crystal structure, providing a hole, which can accept a free electron. ”
Activation Voltage(s): The voltage(s) at which a charge controller will take action to protect the batteries.
Air mass ( or air mass ratio): Equal to the cosine of the zenith angle-that angle from directly overhead to a line intersecting the sun. The air mass is an indication of the length of the path solar radiation travels through the atmosphere. An air mass of 1.0 indicates the sun is directly overhead and the radiation travels through one atmosphere.
Alkali: A chemical “base” (or the opposite of an acid). Certain types of alkalis (especially potassium hydroxide) have been used as fuel cell electrolytes
Alternating Current (AC): A type of electrical current, the direction of which is reversed at regular intervals or cycles. (see AC)
Ambient Temperature: The temperature of the surrounding area.
Amorphous Semiconductor: A non-crystalline semiconductor material that has no long-range order.
Amorphous Silicon: A thin-film, silicon photovoltaic cell having no crystalline structure. Manufactured by depositing layers of doped silicon on a substrate. (see single-crystal silicon and polycrystalline silicon)
Amperage Interrupt Capability (AIC): A direct current fuses should be rated with a sufficient AIC to interrupt the highest possible current.
Ampere (amp): A unit of electrical current or rate of flow of electrons. One volt across one ohm of resistance causes a current flow of one ampere, expressed as E/R=I.
Ampere Hour Meter: An instrument that monitors current over time. The indication is the product of current (in amperes or I) and time (in hours or H).
Ampere-Hour (Ah/AH): A measurement of the flow of current (in amperes or I) over one hour of time; often used to measure battery capacity.
Angle of Incidence: The angle that a ray of sun makes with a line perpendicular to the surface. 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 while shining directly above), the angle of incidence is 90 degrees.
Anion: A negative ion. Alkali, molten carbonate and solid oxide fuel cells are “anion-mobile” cells – anions migrate through the electrolyte toward the anode.
Anode: One of two electrodes typically used in a battery or a fuel cell. In a fuel cell it is where the fuel reacts or “oxidizes”, and releases electrons. It is also refers to the positive terminal of a diode, vacuum tube or other electronic device.
Antireflection Coating: A thin surface coating of a material applied to a solar cell, which reduces the light reflection while it increases light transmission.
Array: see photovoltaic (PV) array.
Array Current: The electrical current produced by a photovoltaic array when exposed to sunlight.
Array Operating Voltage: The voltage produced by a photovoltaic array when exposed to sunlight and connected to a load.
Availability: A photovoltaic system being available to provide power to a load, measured in hours per year.
Azimuth Angle: The angle between true south and the point on the horizon directly below the sun.
B
BIPV (Building-Integrated Photovoltaics): A term for the design and integration of photovoltaic (PV) technology into the building envelope, typically replacing conventional building materials. Often designed into semitransparent skylights, roofing systems or other building envelope systems.
Balance of System: Comprised of components and costs other than the photovoltaic modules and array. It generally includes design costs, land and site preparation, installation, support structures, power conditioning, operation and maintenance costs, indirect storage, and related costs.
Band Gap: In a semiconductor, the energy difference between the highest valence band and the lowest conduction band.
Band Gap Energy (Eg): The amount of energy (in electron volts) required to free an outer shell electron from its orbit about the nucleus to a free state, and thus promote it from the valence to the conduction level.
Barrier Energy: The energy given up by an electron in penetrating 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 given timeframe.
Battery: One or more electrochemical cells enclosed in a container and electrically connected in an appropriate series or parallel arrangement to provide the designated voltage and current requirements. An electrochemical storage system.
Battery Available Capacity: The total maximum charge, expressed in ampere-hours, that can be withdrawn from a cell or battery under a specific set of operating conditions, including initial state of charge, discharge rate, age, cut-off voltage and temperature.
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 or enclosure for the various elements.
Battery Cycle Life: The number of cycles, to a specific depth of discharge, that a cell or battery can undergo before failing to meet its rated capacity.
Battery Energy Storage: Energy storage using electrochemical batteries. Typical examples include the spinning reserve at generating stations, load leveling at substations, and peak shaving at the point of use.
Battery Life: The point where a battery is capable of operating above a specific capacity or performance level.
Blocking Diode: A semiconductor connected in series with one or more solar cells and a storage battery to keep the battery from discharging through the cell when there is either low output or no output from the solar cell. It operates as a one-way electrical valve that allows electrons to flow in only one direction.
Boiling Point: The temperature at which a substance, such as water, changes from a liquid to a gas (steam) under normal atmospheric pressure. Water transitions to steam (boils) at 212°F. Boron (B): The chemical element often used as a dopant in a photovoltaic cell material.
Boule: A hotdog-shaped, synthetic single-crystal mass grown in a specially designed furnace. It is pulled and turned as 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, also equal to 252 calories.
Bypass Diode: A diode connected across one or more solar cells in a photovoltaic module, designed to conduct if the cells become reverse biased. It ultimately protects these PV cells from thermal destruction in cases of partial or complete shading of individual solar cells while other cells are not shaded.
C
Cadmium (Cd): A chemical element used in making various 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 specific time period.
Captive Electrolyte Battery: A battery having an immobilized electrolyte (gelled or absorbed in a material), also known as a sealed cell.
Carbon Dioxide (CO2): A gas often produced by the combustion of fossil fuels and other substances. CO2 also occurs naturally in large amounts in molten magma, which is involved in the explosive eruption of volcanoes, and is a byproduct of the air we breathe.
Carnot Limit: A theoretical limit on the efficiency of an engine based on the flow of heat between two reservoirs. Named for its discoverer Sadi Carnot (1796-1832) of France, this limit stems from basic physical laws and applies to all steam engines. Fossil fuel and nuclear power plants are bound by this limit, although most fuel cells are not.
Catalyst: A substance that causes or speeds a chemical reaction without itself being affected.
Cathode: One of two electrodes in a fuel cell or battery. In a fuel cell, it is where oxygen (usually taken from the air) “reduction” occurs. The negative pole or electrode of an electrolytic cell, vacuum tube, etc., where electrons enter (current leaves) the system. Also known as the opposite of an anode.
Cathodic Protection: A method used to preventing oxidation of exposed metal in structures by imparting a small electrical voltage between the structure and the ground.
Cation: A positive ion. Phosphoric acid and PEM fuel cells are “cation-mobile” cells. The cation moves through the electrolyte in the direction of the cathode.
Cavitation and Suction Head: Noise or vibration causing damage to the turbine blades as a results of bubbles that form in the water as it goes through the turbine which causes a loss in capacity, head loss, efficiency loss, and the cavity or bubble collapses when they pass into higher regions of pressure. The suction head Hs is the distance from the install level of the center line of turbine runner to the minimum tailrace level.
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. Consisting of one or more cells electrically connected together to produce higher voltages. The terms cell and battery are often used interchangeably.
Cell Barrier: A narrow region of static electric charge along the junction of the positive and negative layers in a photovoltaic cell. Has the effect of limiting the movement of electrons from one layer to another. This has the effect of forcing high energy electrons from one side of the junction to transfer preferentially through it in one direction.
Cell Junction: The positive and negative area of direct contact between two layers of a photovoltaic cell.
Charge: The process of adding electrical energy to a battery or capacitor.
Charge Carrier: A free conduction electron or hole in semiconductor material.
Charge Controller: A device in a photovoltaic system that controls the flow of current to and from the battery. Designed to protect it from over-charge or over-discharge. Often the charge controller provides operational status of the PV system.
Charge Factor: The time in hours, relative to the charge rate during, which a battery can be charged at a constant current without damage to the battery. The Charge Factor is usually expressed relative to total battery capacity, i.e., C/4 indicates a charge factor of 4 hours..
Charge Rate: The current applied to a battery or cell to restore its available capacity.
Chemical Energy: The energy inherent in chemical bonds, which hold molecules together. Coal and oil are some examples, which have energy potential that is released through combustion.
Chemical Vapor Deposition (CVD): A method used to deposit thin semiconductor films in the production of some types of photovoltaic devices. With CVD, a substrate is exposed to one or more vaporized compounds, which contain desirable elements. A chemical reaction near the substrate surface is used to produce the desired material, which condenses at the substrate material.
Cleavage of Lateral Epitaxial Films for Transfer (CLEFT): A process for making inexpensive photovoltaic cells of Gallium Arsenide (GaAs) whereby a thin film of GaAs is grown in a thick, single-crystal GaAs substrate and then cleaved from the substrate into a cell.
Cloud Enhancement: An increase in solar intensity caused by reflected irradiance from clouds.
Cogeneration: The use of waste heat from industrial processing, steam turbines, or fuel cells to generate electricity. Has the effect of processing otherwise wasted heat and boosts the efficiency of power-generating systems.
Combined Collector: A photovoltaic device or module that provides both useful heat energy and electricity.
Combustion: The burning of gas, liquid, or solid, in which the fuel is oxidized, producing heat and often light.
Concentrator: Optical components such as lenses (Fresnel lens) to direct or concentrate sunlight onto a solar cell of smaller area. Concentrator arrays must continuously track the sun, and can increase the power output sunlight many hundreds of times.
Condense: The conversion from a gas to drops of liquid. In a geothermal power plant, cooling towers are used to cool the used steam and condense it back to water for injection back to the reservoir. In binary power plants, an organic liquid is first vaporized (with heat from geothermal water) to drive a turbine, then cooled and condensed back to a liquid and recycled again and again in a closed loop.
Conduction: The transfer of heat as a result of the direct contact of rapidly moving molecules through a medium or from one medium to another, without movement of the media.
Conduction Band: 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 line. ”
Convection Currents: The currents caused by hot air or fluid rising and falling. Hot air or fluid expands and is therefore less dense than its cooler surroundings, thus it rises; as it cools it contracts, becomes more dense and sinks down creating something of a rolling motion.
Copper Indium Diselenide: (CuInSe2, or CIS): A polycrystalline thin-film photovoltaic material (sometimes incorporating gallium (CIGS) and/or sulfur).
Core (outer and inner): The extremely hot center of the Earth. The outer core is believed to be molten rock and is located about 3,200 miles below the earth’s surface. The inner core is believed to be solid iron and is found at the center of the Earth- or about 4,000 miles beneath the surface.
Crust: The solid outermost layer of the Earth, mostly consisting of rock, and ranging from 3 – 35 miles thick, comprises the topmost portion of the lithosphere.
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 level at which the charge controller disconnects the photovoltaic array from the battery.
Cycle: The charge/discharge of a battery.
Czochralski Process: A method used to growing large, high quality semiconductor crystal by slowly lifting a seed crystal from a molten bath of the material under careful cooling conditions.
D
DC: See direct current.
DC-to-DC Converter: Electronic circuit used to convert direct current voltages of one level to voltages of another level. Often used in Maximum Power Point trackers.
Days of Storage: The number of consecutive days the stand-alone system will meet a defined load without solar energy input, and is proportionate to the system availability.
Deep Discharge: A battery which is discharged to 20% or less of its rated 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 silicon material.
Density: The amount of mass in a given volume of something. Objects of the same size can have different densities due to more mass “packed” into the same space. Heat causes objects to expand and cold causes object to contract due to molecular movement.
Depletion Zone: A microscopically thin region that is depleted of charge carriers (free electrons and holes).
Depth of Discharge (DOD): A percentage of rated ampere-hours removed from a fully charged cell or battery.
Diffuse Insolation: Sunlight received indirectly as a result of scattering due to clouds, fog, haze, dust, or other elements in the atmosphere.
Diffuse Radiation: Radiation received from the sun after reflection and scattering by the atmosphere and ground.
Diffusion Furnace: A furnace used to make junctions in Photovoltaic cells by diffusing dopant atoms into the surface of the material.
Diode: An electronic device that allows current to flow in one direction only. Common examples are blocking diodes, bypass diodes and zener diodes.
Direct Beam Radiation: Solar Radiation received in a direct line from the sun. Direct beam radiation is measured with a Pyrheliometer.
Direct Current (DC): A type of electricity transmission and distribution by which electricity flows in only one direction through a conductor. Often DC is relatively low voltage and high current.
Direct Fuel Cell: A type of fuel cell in which a hydrocarbon fuel is fed directly to the fuel cell stack, without requiring an external “reformer” to generate hydrogen.
Direct Insolation: Sunlight falling directly upon a collector. The opposite of diffuse insolation.
Discharge: The consumption of electrical energy from a battery or storage device.
Discharge Factor: The time during which a battery or storage device is discharged at constant current, expressed as a percentage of the total (battery) capacity. Related to discharge rate.
Discharge Rate: The time at which electrical current is consumed from the battery or storage device.
Disconnect: Switchgear used to connect or disconnect components in an electrical system.
Distributed Energy Resources (DER): 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.
Distributed Generation: Localized or on-site power generation. As opposed to point to multi-point distribution.
Distributed Power: A power supply located near the point where the power is used.
District Heating System: A heating system that provides heat to a large number of buildings from a central facility. In geothermal district heating systems, one or more wells may serve entire districts.
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. The electron is easily exited into the conduction band where it increases the electrical conductivity over that of an undoped semiconductor.
Dopant: An impure chemical element added in small amounts to an otherwise pure semiconductor material, used 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, expressed as a percentage or hours per year.
Draft Tube: A water conduit, which can be straight or curved depending upon the turbine installation, that maintains a column of water from the turbine outlet and the downstream water level.
Dry Cell: A battery cell with a captive electrolyte. A primary battery that cannot be recharged.
Duty Cycle: The operating cycle of loads in a photovoltaic system, expressed as the ratio of active time to total time.
Duty Rating: The amount of time an inverter or other electrical device can produce at full rated power.
E
Edge-Defined Film-Fed Growth (EFG): A method for making sheets of polycrystalline silicon for photovoltaic devices using capillary action to draw molten silicon upward through a mold.
Efficiency η: A percentage obtained by dividing the actual power or energy by the theoretical power or energy. In hydropower, it represents how well the hydropower plant converts the energy of the water into electrical energy.
Electric Circuit: A path of electrons from a power source through a load and returning to the source.
Electric Current: The continuous flow of electrons; also referred to as electricity.
Electrical Grid: An integrated system of electricity distribution, usually covering large areas.
Electric Panel: An electrical distribution box or backer that houses electrical circuit breakers and connection points for distributed from the electric panel throughout a building.
Electricity: Energy resulting from the flow of electrons.
Electrochemical Cell: A battery device containing two conducting electrodes, one positive and one negative, made of dissimilar materials 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: An electrical terminal that conducts an electric current into or out of a fuel cell or battery. A conductor that is brought in conducting contact with a ground.
Electro deposition: 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: The smallest part of an atom (atoms are the tiny particles of which all substances are made). Electrons may be freed from atoms to produce an electric current. An elementary particle of an atom with a negative electrical charge and a mass of 1/1837th 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 ability to do work, such as making things move and heating them up. Energy can take many forms, including electrical, chemical, radiant, mechanical and heat.
Energy Audit: A survey that shows how much energy used in a home or business, which helps find ways to use less energy.
Energy Conversion: The changing of energy from one form to another. One of the many examples are heat energy being converted into mechanical energy, or mechanical energy into electrical energy, as is done in steam-driven electric power plants.
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 or fuel cells.
Energy Efficiency: The measure of the amount of energy which any technology can convert to useful work; technology with a higher energy efficiency will require less energy to do the same amount of work.
Energy Levels: The energy represented by an electron in the band model of a substance.
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 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.
F
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. Fill Factor is a key characteristic in evaluating PV cell performance.
Fixed Tilt Array: A photovoltaic array set in at a fixed angle with respect to horizontal.
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 Array (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 angle.
Float Charge: The voltage required to counteract the self-discharge of a battery at a particular temperature.
Float Life: The number of years 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; i.e., 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 losses, thus keeping the battery always up to full power.
Float-Zone Process: A method of growing a large-size high quality Photovoltaic Solar Cell. Coils heat a polycrystalline ingot placed atop a single-crystal seed. The coils are slowly raised and the molten interface beneath the coils becomes a single crystal.
Forbay, Trashrock, Penstock: Forbay is the upstream pool before the intake. Trashrock is the net screen to prevent large objects flowing into the turbine. Penstock is a steel closed conduit or pipe for conducting water to the powerhouse.
Flow Q: Volume of water, expressed as cubic meters per second, passing a point in a given amount of time. Rated flow is Qr in m3/s.
Fossil Fuel: Fuels that are derived from natural resources, usually in the form of coal, oil, or natural gas.
Frequency: The number of repetitions per unit time of a complete waveform, expressed in Hertz (Hz).
Frequency Regulation: The control of variability in the output frequency. Some loads will switch off or fail to 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 in space.
Fuel Cell: A device for generating electricity by the chemical combination of a fuel and oxygen.
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).
G
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 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: A lead-acid battery in which the electrolyte is composed of a silica gel or similar matrix.
Generator: A machine that converts mechanical power into electricity by spinning copper wires (conductors) within a magnetic field.
Generating Capacity: The maximum amount of electric power produced by a generator.
Geothermal (ground source) Heat Pump: A space heating/cooling system which moves heat from and to the earth, as opposed to making heat using a fuel source. Geothermal heat pumps take advantage of the almost constant temperature just a few feet underground — usually warmer than the air in winter and cooler than the air in summer.
Geothermal Power Plant: A facility which uses geothermal steam or heat to drive turbine-generators to produce electricity. Three different types make use of the various temperature ranges of geothermal resources: dry steam, flash and binary.
Geyser: A natural hot spring that sends up a fountain of water and steam into the air; some geysers “spout” at regular intervals and some are unpredictable.
Gigawatt (GW): A unit of power equal to 1 billion Watts.
Global Warming/Greenhouse Effect: The trapping of heat in the atmosphere. Incoming solar radiation goes through the atmosphere to the Earth’s surface, but outgoing radiation (heat) is absorbed by water vapor, carbon dioxide, ozone and other gasses in the atmosphere. At certain levels this is beneficial because it keeps the planet warm enough for life as we know it.
Graphite: A soft form of the element carbon. It is used for pencil leads, as a lubricant, as a moderator in nuclear reactors, and for other products. It does not burn easily or fuse at high temperatures, and is an important material in the construction of phosphoric acid fuel cells.
Greenhouse Gases: Gaseous components in the atmosphere that contribute to a gradual warming of the planet.
Grid: See electrical grid.
Grid Connected System: A solar electric or photovoltaic (PV) system in which the PV array acts like a central generating plant, connected in parallel with the electric utility 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-Interactive System: See grid-connected system.
Ground Mounted Systems: A structure that is built specifically to support the solar panels in a PV system that is not attached directly to a building. Often used with shaded buildings or buildings with insufficient roof area.
H
Harmonic Content: The number of frequencies in the output waveform in addition to the primary frequency. Energy in these harmonic frequencies is lost and may cause excessive heating of the load.
Head (H): Vertical change in elevation, expressed in meters, between the upstream water level and the tailrace water level. Rated head is Hr in meters.
Heat Exchanger: A device in which heat is transferred by conduction through a metal barrier from a hotter liquid or gas, to warm a cooler liquid or gas on the other side of the metal barrier. Typical heat exchangers include “shell and tube,” and “plate.”
Heat Transfer: The transmission of heat through conduction, convection, and radiation. Heterojunction: A region of electrical contact between two different materials.
High Voltage Disconnect Hysteresis: The difference in volts between the high voltage disconnect set point and the voltage where the PV array current will be reapplied.
Hole: As in semiconductor material, the vacancy where an electron would normally reside 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, hydro or diesel generators.
Hydrogen: A chemical element consisting of one proton and one electron. Two hydrogen atoms combine with one oxygen atom to form a molecule of water. Hydrogen serves as the fuel for most fuel cells.
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.
Hydrothermal: From the two terms hydro, which means water and thermal which means heat. Literally hydrothermal means hot water. Steam and hot water reservoirs are hydrothermal reservoirs.
I
Impermeable: Does not allow liquids to pass through easily.
Injection Well: A well through which geothermal water is returned to an underground reservoir after use. Geothermal production and injection wells are often constructed of pipes layered inside one another and cemented into the earth and to each other. This configuration protects any shallow drinking water aquifers from mixing with deeper geothermal water.
I-Type Semiconductor: A 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 representation 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.
Incident Light: Light that shines onto the face of a PV 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: Voltage that 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.
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 an enclosure, module or other means of connection that provides an electrical interconnection between devices or 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: See I-Type Semiconductor.
Inverter: A device used to convert direct current electricity produced by a PV cell, fuel cell or other power source to alternating current. A device that converts DC (direct current) electricity to alternating current for stand-alone systems or to supply power to an electricity grid.
Ion: An atom that carries a positive or negative charge due to the loss or gain of an electron. 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.
J
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) system junction box is an enclosure on the module where PV strings are electrically connected.
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.
K
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. The Watt is the standard unit used to measure power. A kilowatt is one thousand watts. The average home requires an energy system that produces between 3-5 kW.
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: a measurement of energy consumption. One kilowatt hour equals one “unit” of electricity. One kilowatt hour is defined as the amount of energy consumed by a 1000-Watt electrical device running continuously for 1 hour.
L
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-Cycle Cost: The estimated cost of owning and operating an energy 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, such that, if there is a failure in the power grid, the renewable energy system cannot feed power into the line.
Liquid Electrolyte Battery: A battery containing a liquid solution of sulfuric acid and distilled water. Also known as a flooded battery.
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 an electrical device.
Load Resistance: The resistance presented by the load to the circuit. 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.
M
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.
Matrix: A framework within a fuel cell or structure that supports an electrolyte.
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 at its maximum value. 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.
Mechanical Energy: The energy an object has because of its motion or position and the forces acting on it.
Megawatt (MW): A unit of power, equal to a thousand kilowatts (kW) or one million watts(W). The watt is a unit of power (energy/time), the rate energy is consumed or converted to electricity.
Megawatt-Hour: 1,000 kilowatt-hours or 1 million watt-hours.
Microgroove: A small groove scribed into the surface of a solar cell, which is filled with metal for making electrical 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.
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.
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.
Molecules: Extremely tiny particles of which all materials are made.
Monolithic: Fabricated as a single structure.
Movistor (MOV): 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. Also 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.
N
Nafion: Sulfuric acid in a solid polymer form. It is usually the electrolyte of PEM fuel cells.
Natural Gas: A fossil fuel gas mixture (mostly methane) trapped underground in many places near the surface of the Earth.
Net Metering: An agreement between a solar system owner and the local electric utility that allows the system owner to buy and sell energy in the form of electric credits. When the solar system produces excess energy, it is sold back to the electric utility at peak prices, literally causing the electric meter to spin backwards. When the system is not producing energy, the system owner can use the credits to buy back energy at off-peak prices.
Nitrogen Oxides (Nox): Gases formed in combustion; appear as yellowish-brown clouds; can irritate lungs, cause lung diseases, lead to formation of ozone (which is harmful in the lower atmosphere, but necessary as protection from UV rays in the upper atmosphere).
N-Type: Negative semiconductor material in which there are more electrons than holes; current is carried through it by the flow of electrons.
N-Type Semiconductor: A semiconductor produced by doping an intrinsic semiconductor with an electron-donor impurity (e.g., phosphorus in silicon).
N-Type Silicon: Silicon material that has been doped with a material that has more electrons in its atomic structure than does silicon.
National Electrical Code (NEC): Contains guidelines for all types of electrical installations. The 1984 and later editions of the NEC contain Article 690, “”Solar Photovoltaic Systems“” which should be followed when installing a PV system.
National Electrical Manufacturers Association (NEMA): This organization sets standards for some non-electronic products like junction boxes.
Nickel Cadmium Battery: A battery containing nickel and cadmium plates and an alkaline electrolyte.
Nominal Voltage: A reference voltage used to describe batteries, modules, or systems (i.e., a 12-volt or 24-volt battery, module, or system).
Nonrenewable Resource: Resources that are not replaced or regenerated naturally within a period of time that is useful; this includes fossil fuels, uranium and other minerals.
Normal Operating Cell Temperature (NOCT): The estimated temperature of a photovoltaic module when operating under 800 w/m2 irradiance, 20.
O
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.
One-Axis Tracking: A system capable of rotating about one axis.
Open-Circuit Voltage (Voc): The maximum voltage across a photovoltaic cell; the voltage across the cell in sunlight when no current is flowing.
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.
Orientation: Placement with respect to the cardinal directions, N, S, E, W; azimuth is the measure of orientation from north.
Overcharge: Forcing current into a fully charged battery. The battery will be damaged if overcharged for a long period.
Oxygen: A chemical element consisting of eight protons, eight neutrons and eight electrons. Two hydrogen atoms combine with one oxygen atom to form a molecule of water.
P
Permeable: Able to transmit water or other liquids; for example, rock with tiny passageways between holes, fractured rock, and gravel are permeable.
P-I-N: A semiconductor photovoltaic (PV) device structure that layers an intrinsic semiconductor between a p-type semiconductor and an n-type semiconductor; and 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.
PV: See photovoltaic(s).
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 electrical circuits, as in 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 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 at 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. As an example, 8 peak sun hours means that the energy received during total daylight hours equals the energy that would have been received had the irradiance for eight 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) at a specified temperature, under standardized test conditions, usually 1,000 watts per square meter of sunlight.
Phosphorous (P): A chemical element used as a dopant in making n-type semiconductor layers.
Phosphoric Acid: A solution of the elements phosphorus, hydrogen, and oxygen that serves as the electrolyte for one type of fuel cell. Chemically: 4H3PO4.
Photocurrent: An electric current induced by radiant energy.
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.
Photon: A particle of light that acts as an individual unit of energy.
Photovoltaic (PV) Array: An interconnected system of one or more PV modules that function as a single electricity-producing system. The modules may be discrete or combined structures, with common support or mounting.
Photovoltaic (PV) Cell: The smallest semiconductor element within a PV module to convert light into electrical energy (direct current voltage and current). Also called a solar cell. Elements of semiconducting material that capture sunlight and convert it into DC power.
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 (DC) electricity. PV devices are made of various semiconductor materials including gallium arsenide, silicon, cadmium sulfide and cadmium telluride.
Photovoltaic (PV) Effect: The phenomenon that occurs when photons in a beam of light, knock electrons loose from the atoms they strike. Combined with appropriate semiconductors, electrons flow in one direction across a junction, developing a voltage.
Photovoltaic (PV) Generator: The total of all PV strings of a PV power supply system, which are electrically interconnected.
Photovoltaic (PV) Module: The smallest assembly of solar cells and ancillary parts, intended to generate direct current power (DC) under unconcentrated sunlight.
Photovoltaic (PV) Panel: Used interchangeably with PV module to refer to a physically connected collection of modules.
Photovoltaic (PV) System: A component system for converting sunlight into electricity by the photovoltaic process, including the array and related system components.
Photovoltaic(s) (PV): The direct conversion of light into electricity.
Photovoltaic-Thermal (PV/T) System: A photovoltaic system that converts sunlight into electricity and collects residual heat energy, delivering both in usable form. Also referred to as a total energy system.
Physical Vapor Deposition: A method of depositing thin semiconductor photovoltaic films. Thermal evaporation or bombardments 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 a battery or fuel cell.
Pocket Plate: A battery plate in which active materials are held in a perforated metal pocket.
Point-Contact Cell: A high efficiency silicon PV concentrator cell that uses light trapping techniques and point-diffused contacts for current collection.
Polycrystalline: See Multicrystalline.
Polycrystalline Silicon: A material used to make some photovoltaic cells, which consist of many crystals of silicon.
Polymer: A natural or synthetic compound composed of repeated links of simple molecules.
Potassium Hydroxide: A solution of the elements potassium, hydrogen, and oxygen that serves as the electrolyte for one type of fuel cell. Chemically: KOH.
Power Conditioning: The process of modifying the characteristics of electrical power (e.g., inverting direct current to alternating current).
Power Conditioning Equipment: Electrical equipment, or power electronics, used to convert power from a generating source, i.e. a PV array, into a form suitable for subsequent use.
Power Conversion Efficiency: The ratio of output power to input power.
Power Density: The ratio of the power available from a battery to its mass (W/kg) or volume (W/l).
Power Factor (PF): The ratio of actual power being used in a circuit, expressed in watts or kilowatts, to the power that is apparently being drawn from a power source, expressed in volt-amperes or kilovolt-amperes.
Power Plant: A central station where electricity is produced.
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.
Proton Exchange Membrane (PEM): A polymer sheet that serves as the electrolyte in one type of fuel cell.
Pulse-Width-Modulated (PWM) Wave Inverter: A type of power inverter that produce a high quality (nearly sinusoidal) voltage.
Pyranometer: An instrument used for measuring global solar irradiance.
Pyrheliometer: An instrument used for measuring direct beam solar radiation.
Q
Quad: One quadrillion Btu (1,000,000,000,000,000 Btu).
R
Radiant Energy: Energy (heat) that is transferred by rays or waves, especially electromagnetic waves, through space or another medium. Radiation.
Rated Battery Capacity: The maximum amount of energy that can be withdrawn from a battery under specified discharge rate and temperature. See battery capacity.
Rated Module Current (A): The current output of a photovoltaic module measured at standard test conditions of 1,000 w/m2 and 25degrees C Cell temperature.
Rated Power: Rated power of a power device such as an inverter.
Reactive Power: The sine of the phase angle between the current and voltage waveforms in an alternating current system. See power factor.
Recombination: The action of a free electron falling back into a hole.
Rectifier: A device that converts alternating current to direct current. See inverter.
Regulator: A device that prevents overcharging of batteries by controlling the charge cycle.
Renewable Resource: A resource that can be used continuously without being used up (because it regenerates itself within a useful amount of time). Examples include hydro and wind power, solar energy, and geothermal energy.
Reformer: A device that extracts pure hydrogen from hydrocarbons.
Regenerative Fuel Cells: Several fuel cell types in which fuel and, in some types, the oxidant are regenerated from the oxidation product.
Reserve Capacity: The amount of generating capacity a power system must maintain to meet peak loads.
Resistance (R): The property of a conductor, which opposes the flow of an electric current, resulting in the generation of heat in the conducting material. The measure of the resistance of a given conductor is the electromotive force needed for a unit current flow. The unit of resistance is expressed as ohms.
Resistive Voltage Drop: The voltage developed across a device by the current flow through the device.
Reverse Current Protection: A method used to prevent reverse current flow from a battery to the photovoltaic array. Often active 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 silicon or similar elements to form a thin sheet of material.
Root Mean Square (RMS): The square root of the average square of the instantaneous values of an ac output. For a sine wave the RMS value is 0.707 times the peak value. The equivalent value of alternating current, I, that will produce the same heating in a conductor with resistance, R, as a dc current of value I.
Runner: The rotating part of the turbine that converts the energy of falling water into mechanical energy.
S
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.
Schottky Barrier: A cell barrier established as the interface between a silicon semiconductor and a sheet of metal.
Scribing: The process of cutting grooves in a semiconductor material to make interconnections.
Sealed Battery: A battery with a captive electrolyte and a resealing vent cap, also called a valve-regulated battery.
Seasonal Depth of Discharge: An adjustment factor used in some system sizing procedures whereby the battery is gradually discharged over a 30-90 day period of poor solar insolation. Secondary Battery: A rechargeable battery.
Self-Discharge: The rate at which a battery, without a load, will lose its charge.
Semiconductor: A material that has a limited capacity for conducting an electric current. Some examples include silicon, gallium arsenide, copper indium diselenide, and cadmium telluride.
Semicrystalline: See Multicrystalline.
Series Connection: A way of joining circuits by connecting positive leads to negative leads; such a configuration increases the voltage.
Series Controller: A charge control element is in series with the PV array and battery.
Shelf Life of Batteries: The length of time, under specified conditions, that a battery can be stored so that it keeps its guaranteed capacity.
Short-Circuit Current (Isc): The current flowing freely through an external circuit that has no load or resistance, passing the maximum current possible.
Shunt Controller: A charge controller that redirects or shunts the charging current away from the battery, which requires a large heat sink to dissipate the current from the short-circuit.
Shunt Regulator: Type of a battery charge regulator used to prevent overcharging of the battery. The charging current is controlled by a switch connected in parallel with the photovoltaic (PV) array.
Siemens Process: A commercial method of making purified silicon.
Silicon (Si): A semi-metallic chemical element used as an excellent semiconductor material for electronic devices. It crystallizes in face-centered cubic lattice like a diamond. It’s commonly found in sand and quartz.
Sine Wave: A waveform corresponding to a single-frequency oscillation that can be mathematically represented as a function of amplitude versus angle in which the value of the curve at any point is equal to the sine of that angle.
Sine Wave Inverter: An inverter that produces utility-quality, sine wave power.
Single-Crystal Material: A material that is composed of a single crystal.
Single-Crystal Silicon: Material with a single crystalline formation. Often used in photovoltaic cells.
Single-Stage Controller: A charge controller that redirects all charging current as the battery approaches a full state-of-charge.
Solar Array: A group of solar panels comprises a solar array. A solar array is the entire system of solar panels that capture sunlight to produce DC power.
Solar Cell: see photovoltaic (PV) cell.
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 square foot.
Solar Cooling: The use of solar thermal energy or solar electricity to power a cooling appartus. They can be comprised of photovoltaic systems to power evaporative coolers (swamp coolers), heat-pumps or air conditioners.
Solar Energy: Electromagnetic energy transmitted from the sun (solar radiation). The amount that reaches the earth is equal to one billionth of total solar energy generated, or the equivalent of about 420 trillion kilowatt-hours.
Solar Insolation: See insolation.
Solar Irradiance: See irradiance.
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 Panel: See photovoltaic (PV) panel.
Solar Resource: The amount of solar insolation a site receives, 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. Their wavelength range describes the different regions of the solar spectrum. The visible region extends from approximately 390 to 780 nanometers. The combined radiation in the wavelength region from 280 nm to 4,000 nm is called the broadband, or total, solar radiation.
Solar Thermal Electric Systems: Solar energy conversion technologies that convert solar energy to electricity, by heating a fluid to power a turbine that drives a generator. Some examples include parabolic dish and solar trough.
Solar-Grade Silicon: A less expensive intermediate-grade silicon used in the manufacture of solar cells.
Solid Oxide: A solid combination of oxygen and another element (often zirconium) that serves as the electrolyte for one type of fuel cell.
Space Charge: See cell barrier.
Specific Gravity: The ratio of the weight of the solution to the weight of an equal volume of water at a specified temperature. Used as an indicator of battery state-of-charge.
Spinning Reserve: Electric power plant or utility capacity on-line and running at low power in excess of actual load.
Spiral case: A spiral-shaped steel intake guiding the flow into the wicket gates located just prior to the turbine in a hydropower system.
Split-Spectrum Cell: An efficient photovoltaic device in which sunlight is optically divided into spectral regions. The regions are directed to PV cells optimized for converting that portion of the spectrum into electricity. See mulitjunction device.
Sputtering: A process used to apply photovoltaic semiconductor material to a substrate by a physical vapor deposition process. Vapors of atoms are deposited in thin layers on a substrate.
Square Wave: A waveform that has only two states, (i.e., positive or negative). A square wave contains a large number of harmonics.
Square Wave Inverter: A type of inverter that produces square wave output. It consists of a direct current source, four switches, and the load. The switches are power semiconductors that can carry a large current and withstand a high voltage rating. The switches are turned on and off at a correct sequence, at a particular frequency.
Stack: Individual fuel cells connected in series within a generating assembly.
Staebler-Wronski Effect: The tendency of the conversion efficiency of amorphous silicon photovoltaic devices to degrade (drop) upon initial exposure to light.
Stand-Alone System: An autonomous or hybrid photovoltaic system not connected to a grid. Stand-Off Mounting: A technique for mounting a photovoltaic array on a sloped roof, whereby the modules are mounted slightly above the pitched roof so they can be tilted to the desired angle.
Standard Test Conditions (STC): Conditions under which a PV module is normally tested in a laboratory.
Standby Current: The amount of current used by an inverter without an active load (lost power). Inverter efficiency is lowest when the load demand is low.
Starved Electrolyte Cell: A battery containing little or no free fluid electrolyte.
State-of-Charge (SOC): The percentage of available capacity remaining in a battery.
Steam: The vapor form of water that develops when water boils. Steam is made of very tiny heated water particles (molecules) that are bouncing around and bumping into each other at very high speeds. This force (the “power” of steam) can be put to work turning a turbine connected to an electricity generator.
Storage Battery: A device capable of transforming energy from electric to chemical form and vice versa. The reactions are almost completely reversible. During discharge, chemical energy is converted to electric energy and is consumed in an external circuit or apparatus.
Stratification: A condition that occurs when the acid concentration varies from top to bottom in the battery electrolyte. Periodic, controlled charging at voltages that produce gassing will mix the electrolyte. See equalization.
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.
Sulfation: A condition where large crystals of lead sulfate grow on the plate, instead of normal tiny crystals, making the battery extremely difficult to recharge. More common in unused and discharged batteries
Sulfur Oxides (Sox): Pungent, colorless gases (including sulfur dioxide (SO2); formed primarily by the combustion of fossil fuels.
Superconducting Magnetic Energy Storage (SMES): SMES technology uses low-temperature superconducting materials to produce intense magnetic fields to store energy and to smooth out fluctuations in power generation.
Superconductivity: The abrupt and large increase in electrical conductivity exhibited by some metals as the temperature approaches absolute zero.
Superstrate: The covering on the sunny side of a photovoltaic (PV) module, providing protection for the PV materials from impact and environmental degradation while allowing maximum transmission of the appropriate wavelengths of the solar spectrum.
Surge Capacity: The maximum power that can be provided over a short time.
Sustainable: material or energy sources which, if managed carefully, will provide the needs of a community or society indefinitely, without depriving future generations of their needs.
System Availability: The percentage of time when a photovoltaic system will be able to fully meet the load demand. (expressed in hours per year)
System Operating Voltage: The PV array output voltage while under load. Dependent on the load or batteries connected to the output terminals.
System Storage: See battery capacity.
T
Tailrace: The channel that carries water away from the powerhouse.
Tailwater: The downstream water of the powerhouse.
Tare Loss: Loss caused by a charge controller. The controller efficiency percentage is equal to one minus tare loss.
Temperature Compensation: A circuit that adjusts the charge controller activation points depending on battery temperature.
Temperature Factors: It is common for three elements in Photovoltaic systems correct for three common temperature corrections which affect system sizing: a cold battery capacity factor; a high temp PV module voltage factor; and a wire current derating factor for wire at high temperatures.
Thermophotovoltaic Cell (TPV): A device where sunlight concentrated onto a absorber heats to a high temperature, causing thermal radiation to be emitted by the absorber which becomes the energy source for a photovoltaic cell. This designed maximizes the conversion efficiency at the thermal radiation wavelength.
Thick-Crystalline Materials: Semiconductor material, that is cut from ingots or ribbons, and is typically 200-400 microns thick.
Thin Film: A thin layer (a few microns) of semiconductor material, such as copper indium diselenide or gallium arsenide, used in some PV cells.
Thin Film Photovoltaic Module: An amorphous photovoltaic module constructed with 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.
Tin Oxide: A wide band-gap semiconductor used in heterojunction solar cells or to make a transparent conductive film, called NESA glass when deposited on glass.
Total AC Load Demand: The sum of alternating current loads.
Total Harmonic Distortion: The measure of closeness in shape between a waveform and it’s fundamental component.
Tracking Array (Tracker): A photovoltaic (PV) array that follows the path of the sun to maximize the solar radiation incident on the PV surface. Tracking arrays use both the direct and diffuse sunlight.
Transmission Lines: Wires that transport electricity over long distances.
Transformer: An electromagnetic device that changes the voltage of alternating current electricity.
Tray Cable (TC): Cable used for interconnecting balance-of-systems.
Trickle Charge: A charge at a low rate, balancing through self-discharge losses, to maintain a cell or battery in a fully charged condition.
Tunneling: Quantum mechanical concept whereby an electron is found on the opposite side of an insulating barrier without having passed through or around the barrier.
Turbine: A machine with blades that are rotated by the forceful movement of liquid or gas, such as air, steam or water or a combination.
Two-Axis Tracking: A photovoltaic array tracking system capable of rotating independently about two axes (e.g., vertical and horizontal).
U
Ultraviolet: Electromagnetic radiation in the wavelength range of 4 to 400 nanometers.
Underground Service Entrance (USE): Sometimes used within battery enclosures and for interconnecting balance-of-systems.
Uninterruptible Power Supply (UPS): The designation of a power supply providing continuous uninterruptible service.
Urgeinuity© 2011 From the root; Urge, which means a strong desire, and Ingenuity, meaning clever and creative. Modern definition: The intense drive to move in a deliberate and creative way. : To push beyond the apparent limits of a confined space through creative manipulation of time and space, while remaining within said space. : use: The Non-Profit job demanded a candidate with urgeinuity, integrity and compassion.
Geography; Lexington Michigan
Utility Grid: The Utility company infrastructure that delivers electric power to homes and businesses.
Utility-Interactive Inverter: An inverter that only functions when connected to the utility grid, and uses the utility line-voltage and frequency on the utility line as a control parameter to ensure that the photovoltaic system’s output is synchronized with the utility power.
Utility Meter: A device that measures the flow of electricity between the electric utility and a utility customer.
V
Vacuum Evaporation: The deposition of thin films of semiconductor material by the evaporation of elemental sources in a vacuum.
Vacuum Zero: The energy of an electron at rest in empty space; used as a reference level in energy band diagrams.
Valence Band: The highest energy band in a semiconductor that can be filled with electrons.
Vaporize: The change into gas form anything which is normally a liquid or a solid; the term is most commonly is used in reference to water (which vaporizes to steam).
Varistor: A voltage-dependent variable resistor used to protect equipment from power spikes or lightning strikes by shunting the energy to ground.
Vented Cell: A battery designed with a vent mechanism to expel gases generated during charging.
Vertical Multijunction (VMJ) Cell: A compound cell made of different semiconductor materials in layers, one above the other. Sunlight entering the top passes through successive cell barriers, each of which converts a separate portion of the spectrum into electricity, thus achieving greater total conversion efficiency of the incident light. Also called a multiple junction cell. See multijunction device and split-spectrum cell.
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 measure of the amount of force that “pushes” an electric current..
Voltage Regulation: The control of variability in the output voltage. Some loads will not tolerate voltage variations greater than a few percent.
Voltage at Maximum Power (Vmp): The voltage at which maximum power is available from a photovoltaic module.
W
Wafer: A thin sheet of semiconductor material made by cutting it from a single crystal or ingot.
Watt (W): The measure of the amount of current flowing through a wire at a given time. The rate of energy transfer equivalent to one ampere under an electrical pressure of one volt. One watt equals 1/746 horsepower, or one joule per second. It is the product of voltage and current (amperage).
Waveform: The shape of the phase power at a certain frequency and amplitude.
Wet Shelf Life: The period of time that a charged battery, when filled with electrolyte, can remain unused before dropping below a specified level of performance.
Wicket Gates: Adjustable elements that control the flow of water to the turbine passage.
Window: The top layer wide band gap material chosen for its transparency to light in a PV device, allowing most of the light to reach the semiconductor layers below.
X
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Y
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Z
Zenith Angle: The angle between the direction of interest (of the sun, for example) and the zenith (directly overhead).
Definitions were complied from a variety of sources and our own archives at USREA. We will continue to add and modify as more submissions are cataloged.