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It is a material in a photovoltaic device which absorbs the photons to generate charge carriers


Alternating Current(AC)

It is a type of electrical current, the direction of which is reversed at regular intervals or cycles. Electricity transmission networks use AC because voltage can be controlled in a relatively easier manner.



it is a dopant material like boron, where the outer shell electrons are less than required in a balanced crystal structure, providing a hole that can accept a free electron.


Ambient Temperature

It is the temperature of the surrounding area around the cell.


Amorphous Semiconductor

it is a non-crystalline semiconductor material that has no long-range order.


Amorphous Silicon

it is a thin-film, silicon photovoltaic cell which does not have a defined crystalline structure. It is manufactured by depositing layers of doped silicon on a substrate.


Ampere (amp)

It is a unit of electrical current or rate of flow of electrons.



The positive electrode in an electrochemical cell (battery) is known as an anode. Also, the earth or ground in a cathodic protection system is also termed as an anode.


Antireflection Coating

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


Array Current

The electrical current produced by a photovoltaic array during its exposure to sunlight is known as array current.


Array Operating Voltage

it is The voltage produced by a photovoltaic array when exposed to sunlight and connected to a load.


Balance of System

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


Band Gap

In a semiconductor, the energy difference between the highest valence band and the lowest conduction band is known as band gap.


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 is known as band gap energy.



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 in known as a battery. The term battery is also used for a single cell if it constitutes the entire electrochemical storage system.


Battery Capacity

The maximum total electrical charge, expressed in ampere-hours, which a battery can deliver to a load under a specific set of conditions is known as battery capacity.


Battery Cycle Life

It is 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 in watt-hours which can be withdrawn from a fully charged cell or battery. Factors like temperature, rate, age, and cut-off voltage affect the capacity of a battery.


Battery Energy Storage

it is the 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. It is measured in cycles and/or years, depending on the type of service for which the cell or battery is used.


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 the output is very low from the solar cell. It can be thought of as a one-way valve that allows electrons to flow forwards, but not backward.


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 Telluride (CdTe)

A polycrystalline thin-film photovoltaic material.


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 and the depletion zone.


Charge Controller

A component of a photovoltaic system that controls the flow of current to and from the battery to protect it from overcharge and over-discharge. It may also indicate the system’s operational status.


Chemical Vapor Deposition (CVD)

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



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 where the electrons move freely for the 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.



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.


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.


Czochralski Process

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


DC-to-DC Converter

Electronic circuit to convert direct current voltages (e.g.,Photovoltaic module voltage) into other levels (e.g., load voltage).


Deep-Cycle Battery

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


Deep Discharge

a situation where the battery is discharged to 20% or less of its full charge capacity.


Depth of Discharge (DOD)

The ampere-hours removed from a fully charged cell or battery expressed as a percentage of rated capacity.


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).


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.


Diffuse Radiation

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


Diffusion Furnace

A furnace used to make junctions in 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 only in one direction.


Direct Beam Radiation

Radiation received directly by the solar rays.


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.


Direct Insolation

Sunlight falling directly upon a collector.


Discharge Rate

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



A chemical element (impurity) added in small amounts to an otherwise pure semiconductor material to modify the electrical properties of the material.


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 with the help of a mold.


Electric Circuit

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


Electric Current

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


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.


Fermi Level

The energy level at which the probability of finding an electron is one-half. In a metal, the Fermi level is very near to the top of the filled levels in the partially filled valence band.


Fill Factor

The ratio of a photovoltaic cell’s actual power to its power if both current and voltage are at their maxima.


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.



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


Fresnel Lens

An optical device that focuses light like a magnifying glass. Here, the 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 Arsenide (GaAs)

A crystalline, a high-efficiency compound used to make certain types of solar cells and a semiconductor material.


Gigawatt (GW)

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


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 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.


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.



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 the wind or diesel generators.


Hydrogenated Amorphous Silicon

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


Indium Oxide

A wide band gap semiconductor that can be heavily doped with tin to make a highly conductive, transparent thin film.


Infrared Radiation

Electromagnetic radiation whose wavelengths lie in the range from 0.75 micrometers to 1000 micrometers. It is an 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.



The solar power density incident on a surface of stated area and orientation which is expressed as Watts per square meter or Btu per square foot per hour.



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



The direct, diffuse and reflected solar radiation that strikes a surface. Usually expressed in kilowatts per square meter.


I-Type Semiconductor

The semiconductor material that is left intrinsic, or undoped, so that the concentration of charge carriers is similar to that of the material itself rather than that of any 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.



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)

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


Kilowatt-Hour (kWh)

1,000 watts acting over a period of 1 hour. The kWh is a unit of energy. 1 kWh=3600 kJ.



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.


Light-Induced Defects

Defects, such as dangling bonds, induced in an amorphous silicon semiconductor when it is initially exposed to light.


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.


Minority Carrier

A current carrier, either an electron or a hole, that is in the minority in a specific layer of a semiconductor material.


Modified Sine Wave

A waveform that has at least three states (i.e., positive, off, and negative).


Module Derate Factor

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



A semiconductor (photovoltaic) material composed of variously oriented, small, individual crystals.


Multi-Stage Controller

A charging controller unit that allows different charging currents as the battery nears full state-of-charge.



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.


Parallel Connection

A way of joining solar cells or photovoltaic modules by connecting positive leads together and negative leads together.



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


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 Watt

A unit used to rate the performance of solar cells, modules, or arrays; the maximum nominal output of a photovoltaic device.


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 the intensity of light.


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 a hydrogen, which can then be withdrawn for use.



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


Photovoltaic(s) (PV)

Pertaining to the direct conversion of light into electricity.


Photovoltaic (PV) Array

An interconnected system of PV modules that functions as a single electricity-producing unit. The modules are assembled as a discrete structure, with common support or mounting.


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.


Photovoltaic (PV) Effect

The phenomenon that occurs when photons, the “particles” in a beam of light, knock electrons loose from the atoms they strike.


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 intended to generate direct current power under unconcentrated sunlight.


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.


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.


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.


Polycrystalline Silicon

A material used to make photovoltaic cells, which consist of many crystals, unlike single-crystal silicon.


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.


Primary Battery

A battery whose initial capacity cannot be restored by charging.


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).



An instrument used for measuring global solar irradiance.



An instrument used for measuring direct beam solar irradiance.


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.


Reverse Current Protection

Any method of preventing unwanted current flow from the battery to the photovoltaic array.


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.


Sealed Battery

A battery with a captive electrolyte and a resealing vent cap also called a valve-regulated battery.


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.


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.


Silicon (Si)

A semi-metallic chemical element that makes an excellent semiconductor material for photovoltaic devices. It crystallizes in a face-centered cubic lattice like a diamond.


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.


Solar Energy

Electromagnetic energy transmitted from the sun (solar radiation).


Solar-Grade Silicon

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


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.


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.



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.



The physical material upon which a photovoltaic cell is applied.


Thin-Film Photovoltaic Module

A photovoltaic module constructed with sequential layers of thin-film semiconductor materials.


Tilt Angle

The angle at which a photovoltaic array is set to face the sun relative to a horizontal position.


Tin Oxide

A wide band-gap semiconductor similar to indium oxide which is used in hetero-junction solar cells.


Tracking Array

A photovoltaic (PV) array that follows the path of the sun to maximize the solar radiation incident on the PV surface.


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.


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. Why Solar EnergySolar Cell TypesHow does a Solar Cell workSolar Glossary