Glossary of Terms used in the Solar Photovoltaic (PV) Industry

A · B · C · D · E · F · G · H · I · J · K · l · M · N · O · P · Q · R · S · T · U · V · W · X · Y · Z


Alternating Current (AC): A type of electrical current, the direction of which is reversed at regular intervals or cycles. In the United Kingdom, the standard is 100 reversals or 50 cycles per second, Hertz (50). Electricity transmission networks use AC because voltage can be controlled with relative ease.

Amorphous Silicon: A thin-film, silicon photovoltaic cell having no crystalline (regularly repeating) structure. Manufactured by deposition of layers of doped silicon on a substrate

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

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°. Generation from a cell is at its maximum when the angle of incidence is zero

Annual Solar Savings: The energy savings attributable to a building’s solar feature relative to the energy requirements of an equivalent non-solar building

Antireflection Coating: A thin coating applied to a solar cell surface that reduces the light reflection and increases light transmission

Return to top


BIPV (Building-Integrated Photovoltaics): A term for the design and integration of photovoltaic (PV) technology into the building shell, typically replacing conventional building materials. This can include the replacement of facades, glass, skylight systems or other increasingly innovative manners.

Return to top


Chemical Vapor Deposition (CVD): A method of depositing thin semiconductor films which is used to make certain types of photovoltaic cells. Inthis method, a substrate is exposed to vaporised compounds, which contain desirable constituents. A chemical reaction is initiated, at or near the substrate surface, to produce the desired material that then condenses on the substrate

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.

Return to top


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

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)

Return to top


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

Electrical grid: An integrated system of electricity distribution, usually covering a large area

Electricity: Energy resulting from the flow of charge particles, such as electrons or ions

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

Electron Volt (eV): The amount of kinetic energy gained by an electron when accelerated through an electric potential difference of 1 Volt; equivalent to 1.603 x 10^-19; a unit of energy or work

Energy: The capability of doing work; different forms of energy can be converted to other forms, but the total amount of energy remains the same

Energy Audit: A survey that shows how much energy used in a home, which helps find ways to use less energy

Return to top


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

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

Return to top


Gigawatt (GW): A unit of power equal to 1 billion Watts; 1 million kilowatts, or 1,000 megawatts

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

Return to top


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

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

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

Return to top


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

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

Return to top


Joule: A metric unit of energy or work; 1 joule per second equals 1 watt

Return to top


Kilowatt (kW): A standard unit of electrical power equal to 1000 watts, or to the energy consumption at a rate of 1000 joules per second

Kilowatt-Hour (kWh): 1,000 thousand watts acting over a period of 1 hour. The kWh is a unit of energy. 1 kWh=3600 kJ

Return to top


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

Life-Cycle Cost: The estimated cost of owning and operating a photovoltaic system for the period of its useful life

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

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

Load Current (A): The current required by the electrical device

Return to top


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

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

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

Return to top


Normal Operating Cell Temperature (NOCT): NOCT is used as an easy estimate of the nominal operating temperature of a module in its working environment. The estimated temperature of a photovoltaic module when operating under 800 w/m2 irradiance, 20C ambient temperature and wind speed of 1 meter per second.

N-Type: Negative semiconductor material in which there are more electrons than holes; current is carried through it by the flow of electrons. This is then combined with a P-Type system to create a diode

Return to top


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

Orientation: Placement of the solar cells with respect to the cardinal directions, N, S, E, W.

Return to top


Parallel Connection: The standard method of joining solar cells or photovoltaic modules in smaller systems formed by connecting positive leads together and negative leads together; such a configuration increases the current, but not the voltage. In larger commercial systems an array will consist of several parallel series each of which will go through a separate inverter

Peak Demand/Load: The maximum energy demand in a specified time period e.g. The annual peak load might be winter, whilst the daily peak load might be 18.00 – 21.00

Peak Power Point: Operating point of 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, 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

Phosphorous (P): A chemical element used as a dopant in making n-type semiconductor layers

Photon: the photon is the elementary particle responsible for ‘light energy’ or electromagnetic phenomena. It is the carrier of electromagnetic radiation of all wavelengths, including in decreasing order of energy, gamma rays, X-rays, ultraviolet light, visible light, infrared light, microwaves, and radio waves

Photovoltaic(s) (PV): The direct conversion of light into electricity

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. Not to be confused with a solar thermal 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 Different cells have different efficiencies, but come at different costs

Photovoltaic (PV) Device: A solid-state electrical device that converts light directly into direct current electricity 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 electrical 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 essentially planar assembly of solar cells and ancillary parts intended to generate direct current power under un-concentrated sunlight. The structural (load carrying) member of a module can either be the top layer (superstrate) or the back layer (substrate)

Photovoltaic (PV) Panel: Normally used interchangeably with PV module 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

P/N: A semiconductor photovoltaic device structure in which the junction is formed between a p-type layer and an n-type layer

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)

Return to top


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

Return to top


Rated Power: Rated power of the inverter, however, some units cannot produce rated power continuously. See duty rating

Resistance (R): The property of a conductor, which opposes the flow of an electric current resulting in the generation of heat in the conducting material. The measure of the resistance of a given conductor is the electromotive force needed for a unit current flow. The unit of resistance is ohms

Return to top


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

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). About 99 percent of solar radiation is contained in a wavelength region from 300 nm (ultraviolet) to 3,000 nm (near-infrared). The combined radiation in the wavelength region from 280 nm to 4,000 nm is called the broadband, or total, solar radiation

Solar Thermal Electric Systems: Solar energy conversion technologies that convert solar energy to electricity, by heating a working fluid to power a turbine that drives a generator. Examples of these systems include central receiver systems, parabolic dish, and solar trough. These are only used in large commercial systems

Return to top


Thin Film: A layer of semiconductor material, such as copper indium diselenide or gallium arsenide, a few microns or less in thickness, used to make photovoltaic cells.

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. Usually a domestic system will have an angle fixed

Total Harmonic Distortion: The measure of closeness in shape between a waveform and its fundamental component The level of closeness is handled automatically by the inverter and usually around 99% efficiency

Two-Axis Tracking: A photovoltaic array tracking system capable of rotating independently about two axes (e.g., vertical and horizontal) These are primarily used by solar power stations

Return to top


Ultraviolet: Electromagnetic radiation in the wavelength range of 4 to 400 nanometers

Return to top


Volt (V): A unit of electrical force equal to that amount of electromotive force that will cause a steady current of one ampere to flow through a resistance of one ohm

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

Voltage at Maximum Power (Vmp): The voltage at which maximum power is available from a photovoltaic module

Return to top


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 one joule per second. It is the product of voltage and current (amperage)

Waveform: The shape of the phase power at a certain frequency and amplitude. This normally takes the shape of a sinewave

Return to top


Zenith Angle: the angle between the zenith (the outward normal of the earth; directly up) and the object being observed (in this case the Sun)