Solar Energy Glossary
You can call it a solar dictionary, a solar glossary, or list of solar terms. But here you can improve your solar vocabulary with this comprehensive list of solar industry terms and their definitions. I’ll keep this updated to include new developments in solar. Additionaly, I will get this into a more usable format, but this long list will have to suffice in the meantime.
absorbed glass mat ((AGM) – A fibrous silica glass mat used to suspend the electrolyte in batteries. it provides pockets that assist in the recombination gasses generated during charging back into water.
absorber – In a photovoltaic device, the material that readily absorbs photons to generate charge carriers (free electrons or holes).
AC – See alternating current.
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.
activated shelf life – The period of time, at a specified temperature, that a charged battery can be stored before its capacity falls to an unusable level.
activation voltage(s) – The voltage(s) at which a charge controller will take action to protect the batteries.
adjustable set point – A feature allowing the 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-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 means the sun is directly overhead and the radiation travels through one atmosphere (thickness).
Alternating Current (AC) – The flow of electricity that constantly changes direction between positive and negative sides. Almost all power produced by electric utilities in the United States moves in current that shifts direction at a rate of 60 times per second.
Alternator – A device that produces alternating current (AC) electricity, either through a motor or other sources, such as water and wind power.
altitude – The angle between the horizon and the sun position in the sky. Altitude is measured in degrees.
Ambient Temperature – The temperature of the surrounding area.
ambient temperature – The temperature of the surrounding area.
ammeter – A device that is used to measure current flow in an electrical circuit
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 also single-crystal silicon an polycrystalline silicon.
amperage interrupt capability (AIC) – direct current fuses should be rated with a sufficient AIC to interrupt the highest possible current.
ampere (A) or amp – The unit for the electric current – the flow of electrons. One amp is 1 coulomb passign for 1 second. The formula for measuring production of one amp is: One amp is produced by electric force of 1 Volt across a resistance of 1 Ohm. Sometimes this is abbreviated as I for “Intensity”.
ampere hour meter – An instrument that monitors current with time. The indication is the product of current (in amperes) and time (in hours).
ampere-hour (Ah) – Quantity of electric energy equal to the flow of one amp of current for one hour. Typically used to quantify battery bank capacity with solar systems that use batteries.
ancillary services – Services that assist the grid operator in maintaining system balance. These include regulation and the contingency reserves: spinning, non-spinning, and in some regions, supplemental operating reserve.
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 of incidence is 90°.
annual solar savings – The annual solar savings of a solar building is the energy savings attributable 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 ground in a cathodic protection system. Also, the positive terminal of a diode.
antireflection aoating – A thin coating of a material applied to a solar cell surface that reduces the light reflection and increases light transmission.
array – A group of solar panels wired together.
array current – The electrical current produced by a photovoltaic array when it is exposed to sunlight.
array operating voltage – The voltage produced by a photovoltaic array when exposed to sunlight and connected to a load.
autonomous system – A stand-alone PV system that has no back up generating source (no grid to compensate). may or may not include batteries.
availability – The quality or condition of a photovoltaic system being available to provide power to a load. Usually measured in hours per year. One minus availability equals downtime.
average demand – The energy demand for a given location over a period of time. For example, the number of kilowatt-hours used in a 24-hour period, divided by 24 hours, tells the average demand for that location in that time.
avoided cost – The minimum amount an electric utility is required to pay an independent power producer (YOU, if you have solar installation), under the PURPA regulations of 1978, equal to the costs the utility calculates it avoids in not having to produce that power. Usualy, this amount is substantially less than the retail price charged by that same utility for power it sells to its customers.
azimuth – Angle between “true south” and the point directly below the location of the sun. Measured in degrees east or west of true south in northern latitudes.
balance of system (BOS) – all the components and costs other than the solar panels. It includes design costs, site preparation, system installation, support structures, operation and maintenance costs, etc.
balancing area – A metered segment of the power system, maintained by a balancing area authority, that ensures the total of all electrical generation equals the total of all system loads.
band gap – In a semiconductor, the energy difference between the highest valence band and the lowest conduction band.
barrier energy – The energy given up by an electron in penetrating the cell barrier; a measure of the electrostatic potential of the cell barrier.
base load -The average amount of electric power that a utility must supply in any period.
base load generating plants – Typically coal or nuclear generating units that are committed and dispatched at constant or near-constant levels with minimum cycling. They are often the sources of lowest-cost of energy when run at very high capacity factors.
base power – Power generated by a utility unit that operates at a very high capacity factor.
baseline performance value – Intitial values of: Isc, Voc, Pmp, Imp – measured by an accredited laboratory and corrected to Standard Test Conditions, used to validate the manufacturer’s performance measurements provided with the qualification modules per IEEE 1262.
battery – a battery back-up for a solar electric system stores the extra power the solar system makes. A home can use that power when the solar system isn’t producing enough energy, at night, or in a power outage.
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 discharge rate, temperature, initial state of charge, age, and cut-off voltage.
battery bank - A group of batteries connected together to store energy for a solar electric (or pv) system. This provides a back-up source of power in case added power or back-up power is needed to supplement the pv system.
battery capacity – The total number of Ah (amp hours) that can be withdrawn from a cell or a battery that is fully charged.
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 (kilowatt-hours), 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 capacity usually refers to ampere-hours.
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. For example, with lead-acid batteries, end-of-life is generally taken as the point in time when a fully charged cell can deliver only 80% of its rated capacity. Beyond this state of aging, deterioration and loss of capacity begins to accelerate rapidly. Life may be measured in cycles and/or years, depending on the type of service for which the cell or battery is intended.
battery self-discharge – The rate at which a battery without a load will lose its charge.
bimodal PV system: A PV system that can operate in either utility-interactive or stand-alone mode and uses battery storage.
BIPV (Building-Integrated Photovoltaics) – 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” over windows; or other building envelope systems.
blocking diode – A semi-conductor device connected in series with a PV module and a storage baterry to prevent a reverse current discharge of the battery through the module when there is no output, or low output from the cells. When connected ins eries to PV strings it protects its modules from a reverse power flow preventing against the risk of thermal destruction of solar cells.
boron (B) – A chemical element with atomic number 5, semi-metallic in nature, used as a dopant to make p-semiconductor layers.
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.
breaker box -A breaker box holds all of your circuit breakers. Circuit breakers turn electricity on/off to areas of your house.
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.
building integrated photovoltaics – 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” over windows; or other building envelope systems.
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.
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 factor – The amount of energy that the system produces at a particular site as a percentage of the total amount that it would produce if it;s operated at a rated capacity during the entire year. For example, a capacity factor for a wind farm ramges from 20% to 35%.
captive electrolyte battery – A battery having an immobilized electrolyte (gelled or absorbed in a material).
carbon dioxide (CO2) – Carbon dioxide is an atmospheric gas that is present in the Earth’s atmosphere at a low concentration and acts as a greenhouse gas. The most common global warming theories attribute temperature increases to increases in the greenhouse effect caused primarily by human-generated carbon dioxide (CO2).
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 (rusting) of exposed emtal structures, such a bridges or pipelines, by imposing between the structure and the ground a small electrical voltage that opposes the flow of electrons and that is greater than the voltage present during oxidation.
cell – The basic unit of a photovoltaic module. This word is also used to describe the basic unit of batteries (for example a 6 Volt battery has 3 2 Volt cells).
cell barrier – A very thin region of static electric charge along the interface of the positive and negative layers in a photovoltaic cell. The barrier inhibits the movement of electrons from one layer to the other, so that higher-energy electrons from one side diffuse preferentially through it in one direction, creating a current and thus a voltage across the cell. Also called depletion zone or space charge.
cell efficiency - The amount of electrical energy a photovoltaic cell can produce as a percentage of the total energy of sunlight falling upon the cell.
cell junction – The area of immediate contact between two layers (positive and negative) of a photovoltaic cell. The junction lies at the center of the cell barrier or depletion zone.
central power – The generation of electricity in large power plants with distribution through a network of transmission lines (grid distribution) for sale to a number of users. Oposite of distributed power.
charge – The process of adding electrical energy to a battery.
charge carrier – A free and mobile conduction electron or hole in a semiconductor.
charge controller – A component of a photovoltaic system that controls the flow of current to and from the battery to protect it from over-charge and over-discharge. The charge controller may also indicate the system operational status.
charge factor – A number representing the time in hours during which a battery can be charged at a constant current without damage to the battery. Usually expressed in relation to the total battery capacity, i.e., C/5 indicates a charge factor of 5 hours. Related to charge rate.
charge rate – The current applied to a cell or battery to restore its available capacity.
chemical vapor deposition (CVD) – A method of depositing thin semiconductor films used to make certain types of photovoltaic devices. With this method, a substrate is exposed to one or more vaporized compounds, one or more of which contain desirable constituents. A chemical reaction is initiated, at or near the substrate surface, to produce the desired material that will condense on the substrate.
circuit – One or more conductors through which electricity flows.
circuit breaker – A device that shuts down power when sensing an overload of current.
cleavage of lateral epitaxial films for transfer (CLEFT) – A process for making inexpensive gallium arsenide (GaAs) photovoltaic cells in which a thin film of GaAs is grown atop a thick, single-crystal GaAs (or other suitable material) substrate and then is cleaved from the substrate and incorporated into a cell, allowing the substrate to be reused to grow more thin-film GaAs.
cloud enhancement – The increase in solar intensity caused by reflected irradiance from nearby clouds.
coal – A black, solid fossil fuel usually found underground. coal is often burned to make electricity in utility scale production.
combined collector – A photovoltaic device or module that provides useful heat energy in addition to electricity.
combined collector – A photovoltaic device or module that provides useful heat energy in addition to electricity.
combiner box – A box connecting multiple solar panels into a system.
compact fluorescent lights – Lights that use a lot less energy than regular light bulbs. Compact fluorescent lights are used for reading lights and ceiling lights.
concentrating photovoltaics (CPV) – A solar technology that uses lenses or mirrors to concentrate sunlight onto high-efficiency solar cells.
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.
conduit – A pipe or enclosure to protect electrical cables and wires
contact resistance – The resistance between metallic contacts and the semiconductor.
contingency reserves – Reserve services that are sufficient to cover the unplanned trip (disconnect) of a large generator or transmission line and maintain system balance. Contingency reserves are generally split between spinning and non-spinning reserves, and are often based on the largest single hazard (generator or transmission capacity).
controller – Also known as a Charge Controller. A device regulating the flow of current to and from a battery system as part of a battery-based solar electric (or pv) system.
conversion efficiency – The ratio of the electric energy produced by a photovoltaic device (under full sun conditions) to the energy from sunlight incident upon the cell.
converter – A unit that converts a direct current (dc) voltage to another dc voltage.
copper indium diselenide (CIS or CuInSe2) – A polycrystalline thin-film photovoltaic material, sometimes incorporating gallium (CIGS) and/or sulfur.
copper zinc tin sulfide/selenide (CZTS) – A polycrystalline thin-film photovoltaic material.
crystalline silicon – A type of PV cell made from a single crystal or polycrystalline slice of silicon.
current – The flow of electric charge in a conductor between 2 points having a difference in potential (voltage).
current at maximum power (Imp) – The current at which maximum power is available from a module (UL 1703).
customer load – The amount of power your site uses. Load may be expressed in kilowatts (capacity) or kilowatt-hours (energy). A site’s peak kilowatts generally refers to when electric demand requirements are highest.
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.
cycle life – Number id sischarge-charge cycles that a battery can tolerate under specified conditions before it faisl to meet specified criteria as to performance (e.g. capacity decreases to 80% of the nominal capacity).
Czochralski process – A method of growing large size, high quality semiconductor crystal by slowly lifting a seed crystal from a molten bath of the material under careful cooling conditions.
dangling bonds – A chemical bond associated with an atom on the surface layer of a crystal. The bond does not join with another atom of the crystal, but extends in the direction of exterior of the surface.
days of autonomy – The number of consecutive days a stand-alone system battery bank will meet a defined load without solar energy input.
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 Lighting – Lighting loads that are able to run on direct current (DC). Typically lights in a home or business are powered by alternating current (AC). Many off–grid homes use DC lighting to avoid losses in the inverter.
DC Power (Direct Current) – An electrical current whose magnitude and direction stay constant. The photovoltaic cells on solar panels capture energy from sunlight in the form of DC. In order to power your home or business, this current must be converted to AC by an inverter.
DC to DC converter – Electronic circuit to convert DC voltages (such as PV voltage for example) into other levels (e.g. load voltage). Can be a part of a maximum power point tracker (MPPT).
deep cycle battery – Type of battery that can be discharged to a large fraction of capacity many times without damaging the battery.
deep discharge – Discharging the most of the charge of a battery.
deep-cycle battery – A battery with large plates that can withstand many discharges to a low state-of-charge.
demand – The level at which electricity is delivered to end-users at a given point in time. Electric demand in measured in kilowatts.
demand response – The process of using voluntary load reductions during peak hours.
dendrite – A slender threadlike spike of pure crystalline material, such as silicon.
dendritic web technique – A method for making sheets of polycrystalline silicon in which silicon dendrites are slowly withdrawn from a melt of silicon whereupon a web of silicon forms between the dendrites and solidifies as it rises from the melt and cools.
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 – The amount of ampere-hours removed from a fully charged cell or a battery, expressed as a percentage of rated capacity.
design month – The month having the combination of insolation and load that requires the maximum energy from the 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 – Electronic component that allows current flow in one direction only.
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.
direct-coupled PV system: A type of stand-alone system where the output of a PV module or array is directly connected to a DC load.
discharge – The withdrawal of electrical energy from a battery.
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 (expressed in amperes over time) at which electrical current is taken from the battery.
disconnect – Switch gear used to connect or disconnect components of a PV system for safety or service.
dispatching (economic dispatch) – A method by which system operators decide how much output should be scheduled from plants.
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.
distributed systems – Systems that are installed at or near the location where the electricity is used, as opposed to central systems that supply electricity to grids. A residential photovoltaic system is a distributed system.
donor – In a photovoltaic device, an n-type dopant, such as phosphorus, that puts an additional electron into an energy level very near the conduction band; this electron is easily exited into the conduction band where it increases the electrical conductivity over than of an undoped semiconductor.
donor level – The level that donates conduction electrons to the system.
dopant -A chemical element (impurity) added in small amounts to an otherwise pure semiconductor material to modify the electrical properties of the material. An n-dopant introduces more electrons. A p-dopant creates electron vacancies (holes).
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 such as boron and phosphorous to a semiconductor.
downtime – Time when the photovoltaic system cannot provide power for the load. Usually expressed in hours per year or that percentage.
dry cell – A cell (battery) with a captive electrolyte. A primary battery that cannot be recharged.
dual metering: The arrangement that measures energy exported to and imported from the utility grid separately.
duty cycle – The ratio of active time to total time. Used to describe the operating regime of appliances or loads in photovoltaic systems.
duty rating – The amount of time an inverter (power conditioning unit) can produce at full rated power.
edge-defined film-fed growth (EFG) – A method for making sheets of polycrystalline silicon for photovoltaic devices in which molten silicon is drawn upward by capillary action through a mold.
edge-defined film-fed growth(FED) – A method for making sheets of plycrystalline silicon in which molten silicon is drawn upward by capillary action through a mold.
efficiency – The ratio of output power to input power. Expressed as a percent.
electric circuit – The path followed by electrons from a power source (generator or battery), through an electrical system, and returning to the source.
electric current – A flow of electrons, electricity.
electric current – The flow of electrical energy (electricity) in a conductor, measured in amperes.
electric panel – An electrical distribution board that houses electrical circuit breakers. It is the main point at which electricity is distributed throughout a building. It is otherwise known as a breaker box or electrical cabinet.
Electric Vehicle Supply Equipment (EVSE) - This is the industry name for an Electric Vehicle charging station. The terms “EVSE”, “EV Charging Station”, and “Charging Station” all mean the same thing and are interchangeable.
electrical current – The flow of charged electrons through a circuit. Depending upon its behavior, an electrical current can be alternating or direct (AC or DC).
electricity – Energy resulting from the flow of charge particles, such as electrons or ions.
electrochemical cell – A device containing two conducting electrodes, one positive and the other negative, made of dissimilar materials (usually metals) that are immersed in a chemical solution (electrolyte) that transmits positive ions from the negative to the positive electrode and thus forms an electrical charge. One or more cells constitute a battery.
electrode – A conductor that is brought in conducting contact with a ground.
electrodeposition – Electrolytic process in which a metal is deposited at the cathode from a solution of its ions.
electrolyte – A liquid conductor of electricity in which flow of current takes place by migration of ions. The electrolyte for a lead-acid storage cell is a watery (aquaeous) solution of sulfuric acid. .
electrolyzer - An electrochemical device that uses electricity to split water into hydrogen and oxygen.
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 hole pair – The result of light of sufficient energy dislodging an electron from its bond in a crystal, which creates a hole. The free electron (negative charge) and the hole (positive charge) are a pair. These pairs are the constituents of electricity.
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 the work. Stored energy becomes working energy when we use it.
energy audit – A survey that shows how much energy you use in yoru house, apartment or business. It can indicate your most intensive energy consuming appliances and even identify heating and cooling leaks that will help you find ways to use less energy.
energy contribution potential – Recombination occurring in the emitter region of a photovoltaic cell.
energy density – The ratio of energy available from a battery to its volume (Wh/1) or mass (Wh/kg).
energy density – The ratio of available energy per pound; usually used to compare storage batteries.
energy imbalance service – A market service that provides for the management of unscheduled deviations in individual generator output or load consumption.
energy levels – The energy represented by an electron in the band model of a substance.
energy pay back time – The time required for any energy producing system or device to produce as much energy as was required in its manufacture.
epitaxial growth – The growth of one crystal on the surface of another crystal. The growth of the deposited crystal is oriented by the lattice structure of the original crystal.
equalization – The process of restoring all cells in a battery to an equal state-of-charge. Some battery types may require a complete discharge as a part of the equalization process.
equalization charge – The process of mixing the electrolyte in batteries by periodically overcharging the batteries for a short time.
equinox – The two times of the year when the sun crosses the equator and night and day are of equal length; occurring around March 20 or 21 (spring equinox) and September 22 or 23 (fall equinox).
exciton – A quasi-particle created in a semiconductor that is composed of an electron hole pair in a bound state. An exciton can be generated by and converted back into a photon.
external quantum efficiency (external QE or EQE) – Quantum efficiency that includes the effect of optical losses, such as transmission through the cell and reflection of light away from the cell.
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 – A key factor in evaluation of solar cell performance. The ratio of solar cell’s actual power to that same solar cell’s power IF both its current AND voltage were at their maximum.
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 collector: A solar energy collector that absorbs solar energy on a flat surface without concentrating it, and can utilize solar radiation directly from the sun as well as radiation that is reflected or scattered by clouds and other surfaces.
flat-plate module – An arrangement of photovoltaic cells or material mounted on a rigid flat surface with the cells exposed freely to incoming sunlight.
flat-plate photovoltaics (PV) – A PV array or module that consists of nonconcentrating elements. Flat-plate arrays and modules use direct and diffuse sunlight, but if the array is fixed in position, some portion of the direct sunlight is lost because of oblique sun-angles in relation to the array.
float charge – The voltage required to counteract the self-discharge of the battery at a certain temperature.
float life – Number of years that a battery can keep its stated capacity when it is kept at a float charge, see float charge above.
float service – A battery operation in which the battery is normally connected to an external current source; for instance, a battery charger which supplies the battery load< under normal conditions, while also providing enough energy input to the battery to make up for its internal quiescent losses, thus keeping the battery always up to full power and ready for service.
float-zone process – In reference to solar photovoltaic cell manufacture, a method of growing a large-size, high-quality crystal whereby coils heat a polycrystalline ingot placed atop a single-crystal seed. As the coils are slowly raised the molten interface beneath the coils becomes single crystal.
fossil fuels – Fuels formed int he ground from the remains of dead plants and animals. It takes millions of years to form fossil fuels. Oil, natural gas and coal are fossil fuels.
frequency – Number of cycles per unit time within a complete waveform, usually measured in cycles per second or hertz (Hz). Electrical devices in the USA require 60 Hz.
frequency regulation – This indicates the variability in the output frequency. Some loads will switch off or not operate properly if frequency variations exceed 1%.
Fresnel lens – An optical device that focuses light like a magnifying glass; concentric rings are faced at slightly different angles so that light falling on any ring is focused to the same point.
fuel – Any material that can be burned to make energy.
fuel cell - An electrochemical device that uses hydrogen and oxygen to produce DC electricity, with water and heat as byproducts.
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).
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 – A portion of charge current that goes into electrolytical production of hydrogen and oxygen from the electrolytic liquid inside the battery. Gassing current increases when the voltage and temperature increases. .
gel-type battery – Lead-acid battery in which the electrolyte is composed of a silica gel matrix.
generator: A device that converts mechanical energy into electricity by means of electromagnetic induction.
gigawatt (GW) – A unit of power equal to 1 billion Watts; 1 million kilowatts, or 1,000 megawatts.
glazings – Clear materials (such as glass or plastic) that allwo sunlight to pass into solar collectors and solar buildings, trapping heat inside.
grain boundaries – The boundaries where crystallites in a multicrystalline material meet.
greenhouse gases – Gaseous components in the atmosphere that contribute to a gradual warming of the planet. The most prevalent of these gases is carbon dioxide, which is released in large quantities when fossil fuels are burned. Nothing is burned to convert sunlight into power. Since solar energy does not have any gaseous by-products, it is considered “clean.”
grid – a system of high tension cables in a region that distributes electricity to homes, businesses, and other buildings.
grid connected cystem – A solar system 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 tied/Grid connected – a solar system that is connected to the power grid and uses the grid as a backup source of power.
Grid: The utility’s network of conductors, substations, and equipment that distributes electricity from its central generation point to the consumer.
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.
grid-tied system – A “grid-connected” solar electric (or pv) system generates its own electricity and feeds its excess power into the utility grid.
ground mounted systems – A solar system that is not attached directly to a building, but is supported by a structure that is built low to the ground. Ground mounts are ideal for sites with limited roof space and a lot of open land.
grounding – The process of connecting equipment to a common ground or “earth”. This is done as a safety mechanism in order to avoid the unsafe energizing of equipment.
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.
hertz – The unit of electromagnetic frequency that is equal to one cycle per second.
heterojunction – A region of electrical contact between two different materials.
high voltage disconnect – The voltage at which a charge controller will disconnect the photovoltaic array from the batteries to prevent overcharging.
high voltage disconnect hysteresis – The voltage difference between the high voltag disconnect set point and the voltage at which the full photovoltaic array current will be reapplied.
hole – The vacancy where an electron would normally exist in a solid; behaves like a positively charged particle.
homojunction – The region between an n-layer and a p-layer in a single material, photovoltaic cell.
hybrid system – A solar electric or photovoltaic system that includes other sources of electricity generation, such as wind or diesel generators.
hydrogenated amorphous silicon – Amorphous silicon with a small amount of incorporated hydrogen. The hydrogen neutralizes dangling bonds in the amorphous silicon, allowing charge carriers to flow more freely.
incident light – Light that shines onto the surface of a solar cell or module.
independent system operator (ISO) – The entity responsible for maintaining system balance, reliability, and electricity market operation.
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 int he range from 0.75 micrometer to 1000 micrometer.
ingot – A casting of material, usually crystalline silicon, from which slices or wafers can be cut for use in a solar cell.
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 also diffuse insolation and direct insolation.
insulation – Materials that reduce the rate or slow down the movement of heat.
integrator: A business that designs, builds, and installs complete PV system for particular applications by matching components from various manufacturers.
interconnect – A conductor within a module or other means of connection which provides an electrical interconnection between the solar cells.
interconnection – The link between your utility company and your building that enables power to move seamlessly in either direction..
internal quantum efficiency (internal QE or IQE) – A type of quantum efficiency. Refers to the efficiency with which light not transmitted through or reflected away from the cell can generate charge carriers that can generate current.
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.
inverted metamorphic multijunction (IMM) cell – A photovoltaic cell that is a multijunction device whose layers of semiconductors are grown upside down. This special manufacturing process yields an ultra-light and flexible cell that also converts solar energy with high efficiency.
inverter – Devices that convert DC electricity into AC electricity either single or multiphase. could be used either for a stand-alone system (not connected to the grid) or for utility-interactive systems.
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.
Islanding: The undesirable condition where an interactive inverter continues to supply power to the utility grid during a utility outage.
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.
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.
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 – An electrical box designed to be a safe enclosure in which to make proper electrical connections. On PV modules this is 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.
kerf – The width of a cut used to create wafers from silicon ingots, often resulting in the loss of semiconductor material.
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.
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.
levelized cost of energy (LCOE) - The cost of energy of a solar system that is based on the system’s installed price, its total lifetime cost, and its lifetime electricity production.
life – The period during which a system is capable of operating above a specified performance level.
life cycle cost – An estimate of the cost of owning and operating a system for the period of its useful life, usually expressed in terms of the present value of all lifetime costs. .
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.
Lightning Arrestor – a type of fuse used to protect the solar power system in the event of a lightning strike.
line-commutated inverter – An inverter that is tied to a power grid or line. The commutation of power (conversion from DC to AC) is controlled by the power line so that if there is a failute in the power grid, the PV 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 – Anything in an electrical circuit that, when the circuit is turned on, draws power from that circuit.
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 forecast – Predictions of future demand. For normal operations, daily and weekly forecasts of the hour-by-hour demand are used to help develop generation schedules to ensure that sufficient quantities and types of generation are available when needed.
load resistance – The resistance presented by the load. See also resistance.
locational marginal price (LMP) - The price of a unit of energy at a particular electrical location at a given time. LMPs are influenced by the nearby generation, load level, and transmission constraints and losses.
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-coltage (I-C) 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.
measurement and characterization – A field of research that involves assessing the characteristics of photovoltaic materials and devices.
megawatt (MW) – 1,000 kilowatts, or 1 million watts; standard measure of electric power plant generating capacity.
megawatt-hour – 1,000 kilowatt-hours or 1 million watt-hours.
metrology - The science of measurement.
micro Inverter – this is a small inverter (see Inverter) that mounts to the back of each solar panel instead of having one large inverter. While it works better when partial shading is a concern, it also introduces multiple points of potential failure, which is a concern for roof mounted solar panels.
micro-grid - Small-scale, local power production within neighborhoods and communities.
microgroove – A small groove scribed into the surface of a solar cell, which is filled with metal for contacts.
micrometer (micron) – One millionth of a meter.
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 – a solar panel, or a group of solar cells.
module derate factor – A factor that lowers the photovoltaic module current to account for field operating conditions such as dirt accumulation on the module.
monocrystalline panel – a solar panel that’s made from a large, single silicon crystal and has a patchwork pattern. Monocrystalline panels are more expensive and more efficient than multi- or poly- crystalline panels.
monolithic – Fabricated as a single structure.
mounting equipment - Equipment/apparatus used to fasten solar (PV) modules to the roof. Peak Load – The highest electrical demand within a particular period of time.
movistor – Short for metal oxide varistor. Used to protect electronic circuits from surge currents such as those produced by lightning.
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.
multi-stage controller – A charging controller unit that allows different charging currents as the battery nears full state_of_charge.
nanometer - One billionth of a meter.
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.
NEC – An abbreviation for the National Electric Code® which contains safety guidelines and required practices for all types of electrical installations. article 690 of NEC® pertains to solar photovoltaic systems specifically.
NEMA – National Electrical Manufacturers Association.
net meter – an electricity meter that spins both forward and backwards. It can track how much electricity your solar system puts into the power grid and how much electricity your home pulls out of the grid. electric grid and ‘drawing’ from the electric grid when more power is needed.
Net metering – A practice used in conjunction with a solar electric system where your electric meter tracks your net power usage, spinning forward when you use electricity from the utility, and spinning backward when your system is generating more electricity than you need.
nickel cadmium battery – A battery containing nickel and cadmium plates and an alkaline electrolyte.
Nitrogen oxides (NOx) – Pollutant gases produced by burning fossil fuels.
nominal operating cell temperature (NOCT) – The reference cell (module) operating temperature presented in manufacturer’s literature. Generally the NOCT is referenced at 25 degrees Celsius, or 77 degrees Fahrenheit.
nominal voltage – A reference voltage used to describe batteries, modules or systems (e.g 12 volts, 24 volts, 48 volts… of battery, module or systems).
normal operating cell temperature (NOCT) – The estimated temperature of a photovoltaic module when operating under 800 w/m2 irradiance, 20°C ambient temperature and wind speed of 1 meter per second. NOCT is used to estimate the nominal operating temperature of a module in its working environment.
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, for example 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.
off-grid system – Also called an independent standalone system, when generated energy is stored in batteries and then subsequently used. These systems are not connected to the utility grid.
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.
on/off grid system – A solar energy system that is interconnected with the utility grid is said to be an on-grid or grid-tied system, while a system with battery storage is not interconnected and is described as an off-grid system.
one-axis tracking – A system capable of rotating about one axis, aslo reffered to as single axis system. These tracking systems usually folow the sun from east to west throughout the day. Same principle as sunflower.
open-circuit voltage (Voc) – The maximum possible 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.
outgas – See gassing.
overcharge – Forcing current into a fully charged battery. The battery will be damaged if overcharged for a long period.
p/n – A semiconductor 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 – 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.
parallel connection- A wiring configuration used to increase current (amperage). Parallel wiring is positive to positive (+ to +) and negative to negative (- to -). Opposite of a series connection.
parallel paring – A group of electrical devices, such as PV modules, wired together to increase ampacity, while voltage remains constant.
passivation – A chemical reaction that eliminates the detrimental effect of electrically reactive atoms on a solar cell’s surface.
passive solar building – A building the utilizes non-mechanical, non-electrical methods for heating, cooling or lighting.
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.
Performance Based Incentive (PBI). – This is a program where rebates are paid based on energy production, designed to benefit owners of larger solar power systems.
phosphorus (P) – A highly reactive, poisonous, nonmetallic element occurring naturally in phosphates, especially apatite, and existing in three allotropic forms, white (or sometimes yellow), red, and black. An essential constituent of protoplasm, it is used in safety matches, pyrotechnics, incendiary shells, and fertilizers and to protect metal surfaces from corrosion.
photocurrent – An electric current induced by radiant energy.
photoelectric cell – A device for measuring light intensity that works by converting light falling on, or reach it, to electricity, and then measuring the current; used in photometers.
photon – A particle of light that acts as an individual unit of energy.
Photovoltaic (PV) – the direct conversion of light into electricity. Photo means “light”, voltaic means “electric”.
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 gallium arsenide, and in single crystalline, multicrystalline, or amorphous forms.
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, current will flow and electric power will be available.
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 be the top layer (superstrate) or the back layer (substrate).
photovoltaic (PV) panel – often used interchangeably with PV module (especially in one-module 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 or solar thermal system.
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.
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.
plates – A metal plate, usually lead or lead compound, immersed in the electrolyte in a battery.
plug-and-play PV system – A commercial, off-the-shelf photovoltaic system that is fully inclusive with little need for individual customization. The system can be installed without special training and using few tools. The homeowner plugs the system into a PV-ready circuit and an automatic PV discovery process initiates communication between the system and the utility. The system and grid are automatically configured for optimal operation.
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 silicon – A material used to make photovoltaic cells, which consist of many crystals unlike single-crystal silicon.
polycrystalline thin film – A thin film made of multicrystalline material.
power – The amount of electrical energy available for doing work, measured in horsepower, Watts, or Btu per hour.
power conditioning – The process of modifying the characteristics of electrical power (for e.g., 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.
power conversion efficiency – The ratio of output power to input power of the inverter.
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.
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.
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-type silicon – Semi-conductor grade silicon doped with boron giving it a positive boas.
pulse-width-modulated (PWM) wave inverter – A type of power inverter that produce a high quality (nearly sinusoidal) voltage, at minimum current harmonics.
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.
quad – A measure of energy equal to one trillion BTUs; an energy equivalent to approximately 172 million barrels of oil.
quad – One quadrillion Btu (1,000,000,000,000,000 Btu).
qualification test – A procedure applied to a selected set of PV 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.
quantum efficiency (QE) – The ratio of the number of charge carriers collected by a photovoltaic cell to the number of photons of a given energy shining on the cell. Quantum efficiency relates to the response of a solar cell to the different wavelengths in the spectrum of light shining on the cell. QE is given as a function of either wavelength or energy. Optimally, a solar cell should generate considerable electrical current for wavelengths that are most abundant in sunlight.
ramp – A change in generation output.
ramp rate – The ability of a generating unit to change its output over some unit of time, often measured in MW/min.
Rankine cycle – A thermodynamic cycle used in steam turbines to convert heat energy into work. Concentrating solar power plants often rely on the Rankine cycle. In CSP systems, mirrors focus sunlight on a heat-transfer fluid. This is used to creates steam, which spins a turbine to generate electricity.
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 also battery capacity.
rated module current (A) – The current output of a photovoltaic module measured at standard test conditions of 1,000 w/m2 and 25°C cell temperature.
rated power – Rated power of the inverter. However, some units can not produce rated power continuously. See also duty rating.
reactive power – The sine of the phase angle between the current and voltage waveforms in an alternating current system. See also power factor.
recombination – The action of a free electron falling back into a hole. Recombination processes are either radiative, where the energy of recombination results in the emission of a photon, or nonradiative, where the energy of recombination is given to a second electron which then relaxes back to its original energy by emitting phonons. Recombination can take place in the bulk of the semiconductor, at the surfaces, in the junction region, at defects, or between interfaces.
rectifier – A device that converts alternating current to direct current. See also inverter.
regulator – Prevents overcharging of batteries by controlling charge cycle-usually adjustable to conform to specific battery needs.
remote site – Site which is not located nowhere near the utility grid, thus a site with no electricity poles nearby.
remote systems – Systems located away from the utility grid.
renewable energy – Flows of energy that are regenerative or virtually inexhaustible. Most commonly includes solar (electric and thermal), biomass, geothermal, wind, tidal, wave, and hydro power sources.
reserve capacity – The amount of generating capacity a central power system must maintain to meet peak loads.
resistance (R) – Material that resists the flow of electric current, measured in ohms.
resistive voltage drop – The voltage developed across a cell by the current flow through the resistance of the cell.
reverse current protection – Any method of preventing unwanted current flow from the battery to the photovoltaic array (usually at night). See also 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.
RMS – Amps, excluding the effects of all harmonic exponents; it could be called fundamental power factor.
Roof Mounted System – A solar system in which solar panels are mounted directly on the roof of a building or adjacent structure. The majority of solar systems are mounted on a roof.
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.
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. There, it would be reconverted into electricity and distributed the same as any other centrally generated power, through a grid.
scheduling – The general practice of ensuring that a generator is committed and available when needed. It also can refer to scheduling of imports or exports of energy into or out of a balancing area.
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.
seasonal depth of discharge – An adjustment factor used in some system sizing procedures which “allows” the battery to be gradually discharged over a 30-90 day period of poor solar insolation. This factor results in a slightly smaller photovoltaic array.
secondary battery – A battery that can be recharged.
self-discharge – The rate at which a battery, without a load, will lose its charge.
Self-regulating PV system: A type of stand-alone system that uses no active control systems to protect the battery, except through careful design and component sizing.
semiconductor – Any material that has a limited capacity for conducting an electric current. Certain semiconductors, including silicon, gallium arsenide, copper indium diselenide, and cadmium telluride, are uniquely suited to the photovoltaic conversion process.
series connection – A way of joining electrical equipment by connecting positive leads to negative leads and negative leads to positive leads. This configuration increases the voltage while current remains the same.
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 PV 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.
shallow-cycle battery – A battery with small plates that cannot withstand many discharges to a low state-of-charge.
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 from a photovoltaic cell through an external circuit that has no load or resistance; the maximum current possible.
shunt controller – A charge controller that redirects or shunts the charging current away from the battery. The controller requires a large heat sink to dissipate the current from the short-circuited photovoltaic array. Most shunt controllers are for smaller systems producing 30 amperes or less.
shunt regulator – Type of a battery charge regulator where the charging current is controlled by a switch connected in parallel with the PV generator. Overcharging of the battery is prevented by shorting the PV generator.
Siemens process – A commercial method of making purified silicon.
silicon (Si) – A chemical element, atomic number 14, semimetallic in nature, dark gray, an excellent semiconductor material. Commonly found in sand and quartz (as the oxide). Crystallizes like a diamond, in shape. The most common semiconductor material in making photovoltaic devices.
sine wave – A waveform corresponding to a single-frequency periodic 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-grade, quality, sine wave power forms.
single-crystal material – A material that is composed of a single crystal or a few large crystals.
single-stage controller – A charge controller that redirects all charging current as the battery nears full state-of-charge.
smart grid – An intelligent electric power system that regulates the two-way flow of electricity and information between power plants and consumers to control grid activity.
smart meter – An updated electric meter showing the varying price of electricity and usage, allowing consumers to become more informed and make wiser decisions.
soft costs – Non-hardware costs related to PV systems, such as financing, permitting, installation, interconnection, and inspection.
solar cell – Smallest basic solar electric device that generates electricity when exposed to sunlight
solar constant – The strength of sunlight; 1353 watts per square meter in space and about 1000 watts per square meter at a sea level at the equator at solar noon.
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 energy – Energy from the sun. For example, the heat that builds up in your car in the summer when the windows are closed is solar energy.
solar noon – The moment of the day that divides the daylight hours for that day exactly in half. To determine solar noon, calculate the length of the day from the time of sunset and sunrise and divide the two. The moment the sun is highest in the sky.
solar panel – See photovoltaic (PV) panel.
solar panel efficiency – the percent of electrical energy that a solar panel produces (under optimal conditions) as compared to the total amount of energy from the sun falling on the solar panel. Typical solar panel efficiency is currently between 12% and 18%, although this value is improving over time. See solar panel efficiency for an example and more details
solar power – power obtained by harnessing the energy of the sun’s rays.
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 shingles – Roof material that converts light into electricity without conventional solar panels.
solar spectrum – The total distribution of electromagnetic radiation emanating from the sun.
solar thermal - The process of concentrating sunlight to create high temperatures that are needed to heat fluids, like water (solar hot water) or to vaporize fluid to drive a turbine for electric power generation.
solar-grade silicon -Intermediate-grade silicon used int he manufacture of solar cells. Less expensive than electronic-grade silicon.
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.
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 also mulitjunction device.
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.
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 -The inverter consists of a DC source, four switches and the load. The switches are power semiconductors that can carry a large current and withstand a high voltage rating.
Staebler-Wronski effect – The tendency of amorphous silicon photovoltaic devices to lose efficiency upon initial exposure to light; named for Dr David Staebler and Dr Christopher Wronski; work performed at RCA Corp.
stand-alone – An autonomous or hybrid photovoltaic system not connected to a grid. Some stand-alone systems require batteries or some other form of storage. Also called “stand-alone PV system”.
standard reporting conditions (SRC) – A fixed set of conditions (including meteorological) to which the electrical performance data of a photovoltaic module is translated from the test of actual test conditions [ASTM E 1036]
standard test conditions (STC) – Conditions under which a module is typically tested in a laboratory: (1) Irradiance intensity of 1000 W/square meter (0.645 watts per square inch), AM1.5 solar reference spectrum and (3) a cell (module) temperature of 25 degrees C, plus or minus 2 C (or 77 F plus or minus 3.6 F).
standby current – This is the amount of current (power) used by the inverter when no load is active (lost power). The efficiency of the inverter is lowest when the load demand is low.
stand-off mounting – Technique for mounting a photovoltaic array on a sloped roof, which involves mounting the modules a short distance above the pitched roof and tilting them to the optimum angle.
starved electrolyte cell – A battery containing little or no free fluid electrolyte.
state of charge (SOC) – The available capacity remaining in a cell or battery, expressed as a percentage of the rated capacity. For example, if 25 amp-hours have been removed from a fully charged 100 amp-hour cell, the state of charge is then 75%. .
Storage – Storage refers to saving surplus electricity produced by a photovoltaic (PV) system. Generally, batteries are used as storage devices.
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 also equalization.
string – A number of photovoltaic modules or panels interconnected electrically in series to produce the operating voltage required by the load.
sub-hourly energy markets – Electricity markets that operate on time steps of 5 minutes. Approximately 60% of all electricity in the United States is currently traded in sub-hourly markets, running at 5-minute intervals so that maximum flexibility can be obtained from the generation fleet.
substrate – The physical material upon which a photovoltaic cell is made.
subsystem – Any one of several components in a photovoltaic system (i.e., array, controller, batteries, inverter, load).
sulfation – A condition that afflicts unused and discharged batteries; large crystals of lead sulfate grow on the plate, instead of the usual tiny crystals, making the battery extremely difficult to recharge.
Sulfur dioxide (SO2) – Pollutant, colorless gas with a choking odor produced by burning fossil fuels.
superconducting magnetic energy storage (SMES) – SMES technology uses the superconducting characteristics of low-temperature materials to produce intense magnetic fields to store energy. It has been proposed as a storage option to support large-scale use of photovoltaics as a means 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 sun side of a 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 – The momentary start-up condition of a motor requiring a large amount of electrical current.
surge capacity – Capability of an inverter or generator to deliver instantaneous high currents when starting devices such as motors.
surge capacity -The ability of an inverter or generator to deliver high currents momentarily required when starting a motor.
Swanson Effect – Named after Richard Swanson, the founder of SunPower, this law suggests that the cost of the photovoltaic cells needed to generate solar power falls by 20% with each doubling of global manufacturing capacity.
system availability – The percentage of time (usually expressed in hours per year) when a photovoltaic system will be able to fully meet the load demand.
system operating voltage – The photovoltaic array output voltage under load. The system operating voltage is dependent on the load or batteries connected to the output terminals.
tare loss – Loss caused by a charge controller. One minus tare loss, expressed as a percentage, is equal to the controller efficiency.
telemetry device – Devices used to transmit or receive data in a digital form.
temperature compensation – A circuit that adjusts the charge controller activation points depending on battery temperature. This feature is recommended if the battery temperature is expected to vary more than ±5°C from ambient temperature.
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 temperatures.
thermal electric -Electric energy derived from heat energy, usually by heating a working fluid, which drives a turbogenerator. See also “solar thermal electric”.
thermal mass – materials, typically masonry, that store heat in a passive solar home.
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 – A layer of semiconductor material, such as copper indium diselenide, cadmium telluride, gallium arsenide or amorphous silicon, a few microns or less in thickness, used to make photovoltaic cells.
tilt angle – Angle of inclination of collector as measured in degrees from the horizontal. For maximum performance solar collectors/modules should be set at a perpendicular to the sun.
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.
total AC load demand – The sum of the alternating current loads. This value is important when selecting an inverter.
total harmonic distortion – The measure of closeness in shape between a waveform and it’s fundamental component.
total internal reflection – The trapping of light by refraction and reflection at critical angles inside a semiconductor device so that it cannot escape the device and must be eventually absorbed by the semiconductor.
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 sun at all times. Tracking arrays use both the direct and diffuse sunlight. Two-axis tracking arrays capture the maximum possible daily energy.
tracking equipment – Structure that houses PV modules and that can automatically follow the sun across the sky throughout the day to maximize output.
tracking panels – solar panels that can change the direction they face to follow the sun’s movements.
transformer – An electromagnetic device used to convert AC electricity, either to increase or decrease the voltage.
transmission lines – Conductors used to transmit high-voltage electricity from the transformer to the electric distribution system.
transparent conducting oxide (TCO) – A doped metal oxide used to coat and improve the performance of optoelectronic devices such as photovoltaics and flat panel displays. Most TCO films are fabricated with polycrystalline or amorphous microstructures and are deposited on glass. The current industry-standard TCO is indium tin oxide. Indium is relatively rare and expensive, so research is ongoing to develop improved TCOs based on alternative materials.
tray cable (TC) – may be 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.
true or pure sine wave inverter – Inverter producing utility-quality sine wave power.
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.
two-axis tracking – A photovoltaic array tracking system capable of rotating independently about two axes (e.g., vertical and horizontal).
ultra violet (UV) – 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.
underground service entrance (USE) – May be used within battery enclosures and for interconnecting balance-of-systems.
uninterruptible power supply (UPS) – The designation of a power supply providing continuous uninterruptible service. The UPS will contain batteries.
utility grid – The infrastructure of power lines, transformers and substations that delivers electric power to homes and businesses. The utility grid is owned and managed by electric utility companies.
utility meter – A device that measures the flow of electricity between a site that uses electricity and the electric utility company. When your solar system produces excess power, your meter literally spins backward.
utility: A company that produces and/or distributes electricity to consumers in a certain region or state.
utility-interactive inverter – An inverter that can function only when tied to the utility grid, and uses the prevailing line-voltage frequency on the utility line as a control parameter to ensure that the PV system;s output is fully synchronized with the utility power.
utility-interactive PV system: A PV system that operates in parallel with and is connected to the electric utility grid.
Vac – Volts AC.
vacuum deposition – Method of depositing thin coatings of a substance by heating it in a vacuum system.
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.
valence level energy/valence state – Energy content of an electron in orbit about an atomic nucleus. Also called bound state.
varistor – A voltage-dependent variable resistor. Normally used to protect sensitive equipment from power spikes or lightning strikes by shunting the energy to ground.
Vdc – Volts DC
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 also multijunction device and split-spectrum cell.
Voc – Open-circuit voltage.
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 rate at which energy is drawn from a source that produces a flow of electricity.
voltage at maximum power (Vmp) – The voltage at which maximum power is available from a module.
voltage protection – Many inverters have sensing circuits that will disconnect the unit from the battery if input voltage limits are exceeded.
voltage regulation – This indicates the variability in the output voltage. Some loads will not tolerate voltage variations greater than a few percent.
wafer – A thin sheet of semiconductor (photovoltaic material) made by cutting it from a single crystal or ingot.
watt – 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).
watt – a unit of power equal to amps times volts.
watt-hour (Wh) – Unit of energy equal to one watt of power being used for one hour
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.
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.
wire types – See Article 300 of National Electric Code for more information.
work function – The energy difference between the Fermi level and vacuum zero. The minimum amount of energy it takes to remove an electron from a substance into the vacuum.
zenith angle – the angle between the direction of interest (of the sun, for example) and the zenith (directly overhead).