Solar Glossary

Click the term to see the definition!


Air Mass (sometimes called air mass ratio)

Equal to the cosine of the zenith angle or 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).


The quality or condition of a photovoltaic system available to provide power to a load. Usually measured in hours per year. One minus availability equals downtime.


In a photovoltaic device, the material that readily absorbs photons to generate charge carriers (free electrons or holes).

AC (Alternating Current)

 A type of electrical current, the direction of which is reversed at regular intervals or cycles. In the United States, the standard is 120 reversals or 60 cycles per second. Electricity transmission networks use AC because voltage can be controlled with relative ease.


 A dopant material, such as boron, which has fewer outer shell electrons than required in an otherwise balanced crystal structure, providing a hole that 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 a user to adjust the voltage levels at which a charge controller will become active.

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 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 (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.

Ampere Hour Meter

An instrument that monitors current over time. The indication is the product of current (in amperes) and time (in hours).

Ampere‐Hour (Ah/AH)

A measure of the flow of current (in amperes) over one hour; used to measure battery capacity.

Angle of Incidence

 The angle that a ray of sun makes with a line perpendicular to the surface. For example, a surface that directly faces the sun has a solar angle of incidence of zero, but if the surface is parallel to the sun (for example, sunrise striking a horizontal rooftop), the angle 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. In other words, a comparison of what you save with solar vs. not having solar.


 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 Coating

A thin coating of material applied to a solar cell surface that reduces the light reflection and increases light transmission.


 solar 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.

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.

Azimuth Angle

The angle between true south and the point on the horizon directly below the sun. This term is used to describe the direction of your solar panels.


Balance of System

 Represents all components and costs other than the photovoltaic modules/array. It includes design costs, land, site preparation, system installation, support structures, power conditioning, operation and maintenance costs, indirect storage, and related costs.

Ballast Mount

 ballast mount solar for flat roof The majority of solar mounts are attached directly to a home's rafters, while a ballasted mount is used to install solar panels on flat roofs using weights to keep the array in place. No penetration of the roof is required.

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 the cell barrier; a measure of the electrostatic potential of the barrier.

Base Load

The average amount of electric power that a utility must supply in any period.

Batteries/Energy Storage

 A device to enable the storage of energy, in a chemical form, which can later be drawn on to supply power. While batteries are not a requirement to go solar, it can be a great option for anyone concerned about power outrages or backup power. Batteries CAN be integrated at a later time, even if your solar panels have already been installed.


 Two or more electrochemical cells enclosed in a container and electrically interconnected in an appropriate series/parallel arrangement to provide the required operating voltage and current levels. Under common usage, the term battery also applies to a single cell if it constitutes the entire electrochemical storage system.

Battery Available Capacity

The total maximum charge, expressed in watt hours (Wh) or 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 Capacity

The total energy available, expressed in watt‐hours (kilowatthours), which can be withdrawn from a fully charged cell or battery. The energy capacity of a given cell varies with temperature, rate, age, and cut‐off voltage. This term is more common to system designers than it is to the battery industry where capacity usually refers to ampere hours.

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 Chemistry

The chemistry of the rechargeable battery, such as nickel cadmium, nickel metal hydride, lithium ion, lithium polymer, rechargeable alkaline, or lead acid.

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 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 number of charging and discharging cycles a battery is expected to have.

BIPV (Building‐Integrated Photovoltaic)

 A term for the design and integration of photovoltaic (PV) technology into the building envelope, typically replacing conventional building materials. This integration may be in vertical facades, replacing view glass, spandrel glass, or other facade material; into semitransparent skylight systems; into roofing systems, replacing traditional roofing materials; into shading "eyebrows" over windows; or other building envelope systems.

Blocking Diode

 A semiconductor connected in series with a solar cell or cells and a storage battery to keep the battery from discharging through the cell when there is no output, or low output, from the solar cell. It can be thought of as a one‐way valve that allows electrons to flow forwards, but not backwards.

Boron (B)

The chemical element commonly used as the dopant in photovoltaic device or cell material.


 A sausage‐shaped, synthetic single‐crystal mass grown in a special furnace, pulled and turned at a rate necessary to maintain the single‐crystal structure during growth.

Btu (British Thermal Unit)

The amount of heat required to raise the temperature of one pound of water one degree Fahrenheit; equal to 252 calories.

Bypass Diode

A diode connected across one or more solar cells in a photovoltaic module such that the diode will conduct if the cell(s) become reverse biased. It protects these solar cells from thermal destruction in case of total or partial shading of individual solar cells while other cells are exposed to full light.


Cadmium (Cd)

A chemical element used in making certain types of solar cells and batteries.

Cadmium Telluride (CdTe)

A polycrystalline thin‐film photovoltaic material. 


The amount of energy a battery can store measured in kilowatt-hours.

Capacity Factor

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

Captive Electrolyte Battery

A battery having an immobilized electrolyte (gelled or absorbed in a material).


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

Cathodic Protection

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

Cell (battery)

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

Cell Barrier

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

Cell Junction

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


The process of adding electrical energy to a battery.

Charge Carrier

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

Charge Controller

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

Charge Rate

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

Chemical Vapor Deposition (CVD)

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

Cleavage of Lateral Epitaxial Films for Transfer (CLEFT)

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

Cloud Enhancement

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

Combined Collector

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


 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.


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

Contact Resistance

The resistance between metallic contacts and the semiconductor.

Conversion Efficiency

The ratio of the electric power produced by a photovoltaic device to the power of the sunlight incident on the device.


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

Copper Indium Diselenide (CuInSe2, or CIS)

A polycrystalline thin‐film photovoltaic material (sometimes incorporating gallium (CIGS) and/or sulfur).

Crystalline Silicon

A type of photovoltaic cell made from a slice of single‐crystal silicon or polycrystalline silicon.


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

Current at Maximum Power (Imp)

The current at which maximum power is available from a module.

Cutoff Voltage

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


The discharge and subsequent charge of a battery.

Czochralski Process

 A method of growing large size, high quality semiconductor crystals by slowly lifting a seed crystal from a molten bath of the material under careful cooling conditions.


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 the exterior of the surface.

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‐to‐DC Converter

 Electronic circuit to convert direct current voltages (e.g.,photovoltaic module voltage) into other levels (e.g., load voltage). Can be part of a maximum power point tracker.

Deep Discharge

Discharging a battery to 20% or less of its full charge capacity.

Deep‐Cycle Battery

A battery with large plates that can withstand many discharges to a low state‐of‐charge.


 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 (DOD)

 The ampere‐hours removed from a fully charged cell or battery, expressed as a percentage of rated capacity. For example, the removal of 25 ampere‐hours from a fully charged 100 ampere‐hours‐rated cell results in a 25% depth of discharge. Under certain conditions, such as discharge rates lower than that used to rate the cell, depth of discharge can exceed 100%.

Depth Of Discharge (DoD)

 solar storage The DoD refers to the amount of battery capacity that has been used. Most batteries for solar have a guaranteed depth of discharge they will allow within the warrantied output. For example, Sonnen batteries allow for 100% DoD, allowing to use the entire capacity before needing to be recharged.

Design Month

The month having the combination of insolation and load that requires the maximum energy from the photovoltaic array.

Diffuse Insolation

 Sunlight received indirectly as a result of scattering due to clouds, fog, haze, dust, or other obstructions in the atmosphere. Opposite of direct insolation.

Diffuse Radiation

Radiation received from the sun after reflection and scattering by the atmosphere and ground.

Diffusion Furnace

Furnace used to make junctions in semiconductors by diffusing dopant atoms into the surface of the material.

Diffusion Length

The mean distance a free electron or hole moves before recombining with another hole or electron.


An electronic device that allows current to flow in one direction only. See blocking diode and bypass diode.

Direct Beam Radiation

Radiation received by direct solar rays. Measured by a pyrheliometer with a solar aperture of 5.7° to transcribe the solar disc.

Direct Current (DC)

 A type of electricity transmission and distribution by which electricity flows in one direction through the conductor, usually relatively low voltage and high current. To be used for typical 120 volt or 220‐volt household appliances, DC must be converted to alternating current, its opposite.

Direct Insolation

Sunlight falling directly upon a collector. Opposite of diffuse insolation.

Discharge Factor

 A number equivalent to the time in hours during which a battery is discharged at constant current, usually expressed as a percentage of the total battery capacity, i.e., C/5 indicates a discharge factor of 5 hours. Related to discharge rate.

Discharge Rate

 The rate, usually expressed in amperes or time, at which electrical current is taken from the battery.


Switch gear used to connect or disconnect components in a photovoltaic system.

Distributed Energy Resources (DER)

 A variety of small, modular power‐generating technologies that can be combined with energy management and storage systems and used to improve the operation of the electricity delivery system, whether or not those technologies are connected to an electricity grid.

Distributed Generation

A popular term for localized or on‐site power generation.

Distributed Power

Generic term for any power supply located near the point where the power is used. Opposite of central power. See stand‐alone systems.

Distributed Systems

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


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

Donor Level

The level that donates conduction electrons to the system.


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).


The addition of dopants to a semiconductor.


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

Dry Cell

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

Duty Cycle

The ratio of active time to total time that is used to describe the operating regime of appliances or loads in photovoltaic systems.

Duty Rating

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


Edge‐Defined Film‐Fed Growth (EFG)

A method for making sheets of polycrystalline silicon for photovoltaic devices in which molten silicon is drawn upward by capillary action through a mold.


 solar panel efficiency The portion of energy in the form of sunlight that can be converted from a solar panel into electricity. The higher the efficiency, the more usable power you can get from your solar panel. Make sure your solar installer is using high efficiency solar panels for your home.

Electric Circuit

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

Electric Current

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

Electrical Grid

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


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

Electrochemical Cell

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


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


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


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.


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

Electron Volt (eV)

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


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

Energy Audit

A survey that shows how much energy used in a home and helps identify ways to use less energy.

Energy Contribution Potential

Recombination occurring in the emitter region of a photovoltaic cell.

Energy Density

 The ratio of available energy per pound, usually used to compare storage batteries.

Energy Levels

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

Epitaxial Growth

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


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

Equalization Charge

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

Equalizing Charge

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


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

Extrinsic Semiconductor

The product of doping a pure semiconductor.


Fermi Level

Energy level at which the probability of finding an electron is one‐half. In a metal, the Fermi level is very near the top of the filled levels in the partially filled valence band. In a semiconductor, the Fermi level is in the band gap.

Fill Factor

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

Fixed Tilt

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

Fixed Tilt Array

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

Flat‐Plate Array

A photovoltaic (PV) array that consists of non‐concentrating PV modules.

Flat‐Plate Module

An arrangement of photovoltaic cells or material mounted on a rigid flat surface with the cells exposed freely to incoming sunlight.

Flat‐Plate Photovoltaic (PV)

A PV array or module that consists of nonconcentrating elements. Flat‐plate arrays and modules use direct and diffuse sunlight, but if the array is fixed in position, some portion of the direct sunlight is lost because of oblique sun‐angles in relation to the array.

Float Charge

The voltage required to counteract the self‐discharge of the battery at a certain temperature.

Float Life

The number of years that a battery can keep its stated capacity when it is kept at float charge.

Float Service

A battery operation in which the battery is normally connected to an external current source; for instance, a battery charger which supplies the battery load under normal conditions, while also providing enough energy input to the battery to make up for its internal quiescent losses, thus keeping the battery always up to full power and ready for service.

Float‐Zone Process

In reference to solar photovoltaic cell manufacture, a method of growing a large‐size, high‐quality crystal whereby coils heat a polycrystalline ingot placed atop a single‐crystal seed. As the coils are slowly raised the molten interface beneath the coils becomes a single crystal.


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

Frequency Regulation

This indicates the variability in the output frequency. Some loads will switch off or not operate properly if frequency variations exceed one percent.

Fresnel Lens

An optical device that focuses light like a magnifying glass; concentric rings are faced at slightly different angles so that light falling on any ring is focused to the same point.

Full Sun

The amount of power density in sunlight received at the earth's surface at noon on a clear day (about 1,000 Watts/square meter).


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.


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

Gassing Current

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

Gel‐Type Battery

Lead‐acid battery in which the electrolyte is composed of a silica gel matrix.

Gigawatt (GW)

A unit of power equal to 1 billion Watts; 1 million kilowatts, or 1,000 MWs.

Grid Lines

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

Grid-Connected System (Grid Tied)

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

Grid‐Interactive System

Same as grid‐connected system.


Harmonic Content

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


A region of electrical contact between two different materials.

High Voltage Disconnect

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

High Voltage Disconnect Hysteresis

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


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


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

Hybrid System

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

Hydrogenated Amorphous Silicon

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


Incident Light

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

Indium Oxide

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

Infrared Radiation

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

Input Voltage

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


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.


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


The linkage of transmission lines between two utilities, or between a utility and an end-user, enabling power to be moved in either direction. This is required to have your solar system connected to the local utility grid. Positive Energy solar takes care of all the interconnection paperwork for you!

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.


Inverters are equipment that converts the type of electricity generated by the solar panels--direct current (DC)-- into electricity that can be used in your home--alternating current-- (AC). Many modern inverters also prevent electricity from flowing back to the electrical grid should the local grid go down. This rapid shutdown without exporting energy to the grid is known as anti-islanding. This is a required feature designed to protect workers repairing the power grid.


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.


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

ISPRA Guidelines

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

I‐Type Semiconductor

Semiconductor material that is left intrinsic, or undoped, so that the concentration of charge carriers is characteristic of the material itself rather than of added impurities.

I‐V Curve

A graphical presentation of the current versus the voltage from a photovoltaic device as the load is increased from the short circuit (no load) condition to the open circuit (maximum voltage) condition. The shape of the curve characterizes cell performance.



 A metric unit of energy or work; 1 joule per second equals 1 watt or 0.737 footpounds; 1 Btu equals 1,055 joules.


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

Junction Box

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

Junction Diode

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


Kilowatt (kW)

 A standard unit of electrical power equal to 1000 watts, or to the energy consumption at a rate of 1000 joules per second.

Kilowatt-Hour (KWh)

 A measure of electrical energy equivalent to power consumption of 1,000 watts for one hour.


Langley (L)

Unit of solar irradiance. One gram calorie per square centimeter. 1 L = 85.93 kwh/m2.


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.


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

Life‐Cycle Cost

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

Light Trapping

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

Light‐Induced Defects

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

Line‐Commutated Inverter

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

Liquid Electrolyte Battery

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

Lithium Ion/ Lithium Iron Phosphate (LiFePO 4)Battery

 A battery technology that uses one of a number of possible compositions of lithium ion or lithium iron chemical to store energy. Currently, this technology is the most popular for use in solar applications because lithium ion batteries are compact and offer the longest lifespan at a reasonable cost.


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

Load Circuit

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

Load Current (A)

The current required by the electrical device.

Load Resistance

The resistance presented by the load. See resistance.

Low Voltage Cutoff (LVC)

The voltage level at which a charge controller will disconnect the load from the battery.

Low Voltage Disconnect

The voltage at which a charge controller will disconnect the load from the batteries to prevent over‐discharging.

Low Voltage Disconnect Hysteresis

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

Low Voltage Warning

A warning buzzer or light that indicates the low battery voltage set point has been reached.


Maintenance‐Free Battery

A sealed battery to which water cannot be added to maintain electrolyte level.

Majority Carrier

 Current carriers (either free electrons or holes) that are in excess in a specific layer of a semiconductor material (electrons in the n‐layer, holes in the p‐layer) of a cell.

Maximum Power Point (MPP)

 The point on the current‐voltage (I‐V) curve of a module under illumination, where the product of current and voltage is maximum. For a typical silicon cell, this is at about 0.45 volts.

Maximum Power Point Tracker (MPPT)

Means of a power‐conditioning unit that automatically operates the photovoltaic generator at its maximum power point under all conditions.

Maximum Power Tracking

Operating a photovoltaic array at the peak power point of the array's I‐V curve where maximum power is obtained. Also called peak power tracking.


 A small groove scribed into the surface of a solar cell, which is filled with metal for contacts.


 A micro-inverter system has multiple inverters (one for each solar panel). Think of solar panels like bulbs in a string of holiday lights. In conventional inverter systems, when one panel fails, the whole system goes out. Or when one panel’s output drops -- thanks to fallen leaves, a passing cloud, or some other unavoidable factor -- the system’s overall performance drops to match that lowest-performing panel. With microinverters, each panel operates independently!

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.


The use of multiple inverters connected in parallel to service different loads.

Module Derate Factor

A factor that lowers the photovoltaic module current to account for field operating conditions such as dirt accumulation on the module.

Monitoring Systems

 solar monitoring system Devices or applications provide details about a solar power system and energy storage system. Data may include energy usage, a display of the amount of stored energy remaining stored, as well as details on the cost for electricity supply at different times of the day.


Fabricated as a single structure.


Metal Oxide Varistor. Used to protect electronic circuits from surge currents such as those produced by lightning.


 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.


 1,000 kilowatts, or 1 million watts; standard measure of electric power plant generating capacity.


 1,000 kilowatt‐hours or 1 million watt‐hours.


NABCEP® (North American Board of Certified Energy Practitioners)

 The North American Board of Certified Energy Practitioners® (NABCEP®) is the most respected, well-established and widely recognized national certification organization for professionals in the field of renewable energy. It is a voluntary certification that a solar installer or solar sales representative may receive after extensive testing. This is the gold standard for hiring a solar energy company.

Net Metering

 solar net metering Net metering is a solar program in New Mexico that provides credits to you for supplying excess electricity from your solar power system into the grid. Depending on your utility company, the terms of Net Metering may vary. Typically, you receive a credit for any excess solar energy that can be used at a later time -- think "rollover minutes" but with solar power!



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

The open circuit voltage is the maximum voltage that the solar panel can produce with no load on it 

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.



A semiconductor photovoltaic device structure in which the junction is formed between a p‐type layer and an n‐type layer.

Packing Factor

 The ratio of array area to actual land area or building envelope area for a system; or, the ratio of total solar cell area to the total module area, for a module.

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.


A chemical reaction that eliminates the detrimental effect of electrically reactive atoms on a solar cell's surface.

Peak Demand/Load

The maximum energy demand or load in a specified time period.

Peak Power Current

Amperes produced by a photovoltaic module or array operating at the voltage of the I‐V curve that will produce maximum power from the module.

Peak Power Point

Operating point of the I‐V (current‐voltage) curve for a solar cell or photovoltaic module where the product of the current value times the voltage value is a maximum.

Peak Sun Hours

 The equivalent number of hours per day when solar irradiance averages 1,000 w/m2. New Mexico receives an average of 6.77 peak sun hours a day on a fixed solar panels.

Peak Watt

 A unit used to rate the performance of solar cells, modules, or arrays; the maximum nominal output of a photovoltaic device, in watts (Wp) under standardized test conditions, usually 1,000 watts per square meter of sunlight with other conditions, such as temperature specified.

Phosphorous (P)

A chemical element used as a dopant in making n‐type semiconductor layers.


An electric current induced by radiant energy.

Photoelectric Cell

A device for measuring light intensity; used in photometers.

Photoelectrochemical Cell

 A type of photovoltaic device in which the electricity induced in the cell is used immediately within the cell to produce a chemical, such as hydrogen, which can then be withdrawn for use.


A particle of light that acts as an individual unit of energy.

Photovoltaic (PV) Array

 An interconnected system of PV modules that function as a single electricity‐producing unit. The modules are assembled as a discrete structure, with common support or mounting. In smaller systems, an array can consist of a single module.

Photovoltaic (PV) Cell

The smallest semiconductor element within a PV module to perform the immediate conversion of light into electrical energy (direct current voltage and current). Also called a solar cell.

Photovoltaic (PV) Conversion Efficiency

The ratio of the electric power produced by a photovoltaic device to the power of the sunlight incident on the device.

Photovoltaic (PV) Device

 A solid‐state electrical device that converts light directly into direct current electricity of voltage‐current characteristics that are a function of the characteristics of the light source and the materials in and design of the device. Solar photovoltaic devices are made of various semiconductor materials including silicon, cadmium sulfide, cadmium telluride, and 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 onemodule systems), but more accurately used to refer to a physically connected collection of modules (i.e., a laminate string of modules used to achieve a required voltage and current).

Photovoltaic (PV) System

 A complete set of components for converting sunlight into electricity by the photovoltaic process, including the array and balance of system components.

Photovoltaic(s) (PV)

Pertaining to the direct conversion of light into electricity.

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.

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.


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.


 A metal plate, usually lead or lead compound, immersed in the electrolyte in a battery.

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.

Portable Power Station

 Portable power stations are mainly comprised of a large battery, with multiple output options – like AC or wall outlets, USB plugins, and 12V ports. They store energy safely and deliver power efficiently. When attached to solar panels, stores solar energy in a battery, and converts it to usable AC power. But unlike solar-only power systems, a dual-source portable power station can also plug directly into an electrical outlet or other power sources – so you can pre-charge it “on the grid” before you need it and then keep it charged “off the grid” using portable solar panels.

Power Conditioning

 The process of modifying the characteristics of electrical power (e.g., for inverting direct current to alternating current).

Power Conditioning Equipment

 Electrical equipment, or power electronics, used to convert power from a photovoltaic array into a form suitable for subsequent use. A collective term for inverter, converter, battery charge regulator, and blocking diode.

Power Conversion Efficiency

The ratio of output power to input power of the inverter.

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).

Pulse‐Width‐Modulated (PWM) Wave Inverter

 A type of power inverter that produces a high quality (nearly sinusoidal) voltage, at minimum current harmonics.


An instrument used for measuring global solar irradiance.


An instrument used for measuring direct beam solar irradiance. Uses an aperture of 5.7° to transcribe the solar disc.


Qualification Test

 A procedure applied to a selected set of photovoltaic modules involving the application of defined electrical, mechanical, or thermal stress in a prescribed manner and amount. Test results are subject to a list of defined requirements.


Rated Battery Capacity

The term used by battery manufacturers to indicate the maximum amount of energy that can be withdrawn from a battery under specified discharge rate and temperature. See battery capacity.

Rated Power

Solar panels are rated in Watts of output. This wattage rating is derived by multiplying a panel's peak power voltage by its peak power amperage

Reactive Power

The sine of the phase angle between the current and voltage waveforms in an alternating current system. See power factor.

Renewable Energy Certificates

Also known as RECs, Renewable Energy Credits, Green Tags, green energy certificates or tradable renewable certificates are tradable commodities that prove one megawatt-hour of electricity was generated from a renewable energy source. One megawatt-hour equals 1,000 kilowatt-hours, and the average residential customer consumes about 800 kilowatt-hours a month. Most utility companies in New Mexico are not currently buying REC's (or are buying them at a price so low it doesn't cover the application cost).

Reverse Current Protection

Any method of preventing unwanted current flow from the battery to the photovoltaic array (usually at night). See blocking diode.

Ribbon (Photovoltaic) Cells

 A type of photovoltaic device made in a continuous process of pulling material from a molten bath of photovoltaic material, such as silicon, to form a thin sheet of material.


Sacrificial Anode

A piece of metal buried near a structure that is to be protected from corrosion. The metal of the sacrificial anode is intended to corrode and reduce the corrosion of the protected structure.

Satellite Power System (SPS)

 Concept for providing large amounts of electricity for use on the Earth from one or more satellites in geosynchronous Earth orbit. A very large array of solar cells on each satellite would provide electricity, which would be converted to microwave energy and beamed to a receiving antenna on the ground. There, it would be reconverted into electricity and distributed the same as any other centrally generated power, through a grid.

Schottky Barrier

 A cell barrier established as the interface between a semiconductor, such as silicon, and a sheet of metal.


 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.

Series Connection

A way of joining photovoltaic cells by connecting positive leads to negative leads; such a configuration increases the voltage.

Series Controller

A charge controller that interrupts the charging current by open‐circuiting the photovoltaic (PV) array. The control element is in series with the PV array and battery.

Series Regulator

Type of battery charge regulator where the charging current is controlled by a switch connected in series with the photovoltaic module or array.

Series Resistance

 Parasitic resistance to current flow in a cell due to mechanisms such as resistance from the bulk of the semiconductor material, metallic contacts, and interconnections.

Shallow‐Cycle Battery

A battery with small plates that cannot withstand many discharges to a low state‐of‐charge.

Short Circuit Current

Silicon (Si)

A semi‐metallic chemical element that makes an excellent semiconductor material for photovoltaic devices. It crystallizes in face‐centered cubic lattice like a diamond. It's commonly found in sand and quartz (as the oxide).

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‐quality, sine wave power forms.

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 appliance. Photovoltaic systems can power evaporative coolers (swamp coolers), heat pumps, and 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 Generator Kit

 A solar generator is a device that uses solar panels to convert sunlight into electricity, which is then stored in a battery. The battery can then be used to power a variety of electrical devices, such as lights, appliances, and even power tools. Solar generators are often used as a source of backup power in case of a power outage, or as a portable power source for camping or other outdoor activities. Some solar generators are small and portable, while others are larger and more powerful, with the ability to power a whole house.Solar generator kits combine the components you need to capture, store and use solar power for portable, off-grid and emergency use – all in one fully integrated package. The major components of a solar generator kit are the portable solar generator(s) and portable solar panel(s) – along with the compatible cables, adapters and accessories

Solar ITC / Inflation Reduction Act

 solar tax credits As a homeowner, you can apply for a credit when filing your income taxes under the Solar Investment Tax Credit. This Federal tax credit is used when a solar system is purchased outright (or with financing) and installed in your home. You may want to consult your tax advisor for more details on how it may apply to you. Thanks to the recently passed Inflation Reduction Act, the ITC is 30% of your solar costs. For example, if a solar energy system costs $20,000 you may be eligible to claim $6,000 as a tax credit. Some states also provide additional incentives. In New Mexico, there is an additional 10% tax credit for solar, meaning your potential tax credit savings could be 40%!

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 Power/Performance Warranty

 The amount of electricity a solar panel produces declines a very small % every year, known as degradation. That’s true of all solar panels, but to varying degrees. A power/performance warranty is the manufacturers guarantee that the panels will not lose more than the designated % of power output capacity over time. To ensure the best return on investment and long-term value, look for solar panels with the higher output warranties (lower degradation rates).

Solar Panel Product/Equipment Warranty

 solar warranty A solar panel’s product warranty covers the integrity of the panel itself, and protects you against problems such as manufacturing defects, environmental issues, premature wear and tear etc. As with most warranties, a longer period is generally more advantageous to you. The terms and conditions of the solar product warranty can very dramatically. For example, The solar panels Positive Energy installs have a 25-year warranty covers shipping and labor to replace any panels, while other manufactures may require the homeowner to pay these fees. On top of that, an additional limited warranty (extended warranty) may be available. Positive Energy systems include a 30-year limited warranty through SolarInsure creating the most robust warranty and peace of mind in the industry.

Solar Panels

 Also known as Photovoltaic (PV) panels, solar panels take sunlight (photons) and, through the use of specially designed material (commonly, silicon), create electricity (voltage) that can be used or stored.

Solar Resource

 The amount of solar insolation a site receives, usually measured in kWh/m2/day, which is equivalent to the number of peak sun hours.

Solar Spectrum

The total distribution of electromagnetic radiation emanating from the sun. The different regions of the solar spectrum are described by their wavelength range. The visible region extends from about 390 to 780 nanometers (a nanometer is one billionth of one meter).

Solar Thermal Electric Systems

 Solar energy conversion technologies that convert solar energy to electricity, by heating a working fluid to power a turbine that drives a generator. Examples of these systems include central receiver systems, parabolic dish, and solar trough.

Solar‐Grade Silicon

Intermediate‐grade silicon used in the manufacture of solar cells. Less expensive than electronic‐grade silicon.

Split‐Spectrum Cell

A compound photovoltaic device in which sunlight is first divided into spectral regions by optical means. Each region is then directed to a different photovoltaic cell optimized for converting that portion of the spectrum into electricity. Such a device achieves significantly greater overall conversion of incident sunlight into electricity. See mulitjunction device.


 A process used to apply photovoltaic semiconductor material to a substrate by a physical vapor deposition process where high‐energy ions are used to bombard elemental sources of semiconductor material, which eject vapors of atoms that are then deposited in thin layers on a substrate.

Stand‐Alone System

 An autonomous or hybrid photovoltaic system not connected to a grid. May or may not have storage, but most stand‐alone systems require batteries or some other form of storage.


A number of photovoltaic modules or panels interconnected electrically in series to produce the operating voltage required by the load.


The physical material upon which a photovoltaic cell is applied.


 Any one of several components in a photovoltaic system (i.e., array, controller, batteries, inverter, load).


Temperature Factors

It is common for three elements in photovoltaic system sizing to have distinct temperature corrections

The Electricity Grid

 The electricity grid is the system which delivers electricity from power generators to power users. For the owner of a solar power system, the grid can, in effect, be an energy storage device, since you are sending excess power into it when your solar power system is producing electricity, and you can draw electricity from the grid when your solar power system is not producing.

Thermophotovoltaic Cell (TPV)

 A device where sunlight concentrated onto a absorber heats it to a high temperature, and the thermal radiation emitted by the absorber is used as the energy source for a photovoltaic cell that is designed to maximize conversion efficiency at the wavelength of the thermal radiation.

Thick‐Crystalline Materials

 Semiconductor material, typically measuring from 200‐400 microns thick, that is cut from ingots or ribbons.

Thin‐Film Photovoltaic Module

A photovoltaic module constructed with sequential layers of thin‐film semiconductor materials. See amorphous silicon.

Tilt Angle

The angle at which a photovoltaic array is set to face the sun relative to a horizontal position. The tilt angle can be set or adjusted to maximize seasonal or annual energy collection.

Tin Oxide

 A wide band‐gap semiconductor similar to indium oxide; used in heterojunction solar cells or to make a transparent conductive film, called NESA glass when deposited on glass.

Tracking Array

A photovoltaic (PV) array that follows the path of the sun to maximize the solar radiation incident on the PV surface. The two most common orientations are

Two‐Axis Tracking

 A photovoltaic array tracking system capable of rotating independently about two axes (e.g., vertical and horizontal).



Electromagnetic radiation in the wavelength range of 4 to 400 nanometers.

Underground Feeder (UF)

May be used for photovoltaic array wiring if sunlight‐resistant coating is specified; can be used for interconnecting balance‐of‐system components but not recommended for use within battery enclosures.


Vacuum Zero

The energy of an electron at rest in empty space; used as a reference level in energy band diagrams.

Volt (V)

A unit of electrical force equal to that amount of electromotive force that will cause a steady current of one ampere to flow through a resistance of one ohm.


 The amount of electromotive force, measured in volts, that exists between two points.



A thin sheet of semiconductor (photovoltaic material) made by cutting from a single crystal or ingot.

Watt And Kilowatt (KW)

A watt is a unit of power (Amps X Volts=Watts). A kilowatt is 1000 watts.


 A wide band gap material chosen for its transparency to light. Generally used as the top layer of a photovoltaic device, the window allows almost all of the light to reach the semiconductor layers beneath.


Zenith Angle

 The angle between the direction of interest (the sun, for example) and the zenith (directly overhead).