Solar Glossary



AC — see alternating current.

Alternating Current (AC) — 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 with relative ease.

Amorphous Silicon — A thin-film, silicon photovoltaic cell having no crystalline structure. Manufactured by depositing layers of doped silicon on a substrate. Efficiency of panels is generally 4-6% and performance does degrade rapidly - as much as 50% in the first year but will then slow. Advantages of Amorphous panels is the low cost and flexibility of application. See also single-crystal silicon and polycrystalline silicon.

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°.

Array — see photovoltaic (PV) array.

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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 Life — The period during which a cell or battery is capable of operating above a specified capacity or efficiency performance level. Life may be measured in cycles and/or years, depending on the type of service for which the cell or battery is intended.

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.

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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.

Concentrator — A photovoltaic module, which includes optical components such as lenses 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.

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

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

Crystalline Silicon — A type of photovoltaic cell made from a slice of single-crystal silicon or polycrystalline silicon.

Current — See electric current.

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DC — See direct current.

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.

Discharge — The withdrawal of electrical energy from a battery.

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.

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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.

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.

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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 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).

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).

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

Grid — See electrical grid.

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

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

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

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

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

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

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Joule — A metric unit of energy or work; 1 joule per second equals 1 watt or 0.737 foot-pounds; 1 Btu equals 1,055 joules.

Junction 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.

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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.

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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.

LEDLight Emitting Diode; A low energy bulb commonly used with low voltage lighting and solar lights

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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.

Module — See photovoltaic (PV) module.


Monocrystalline Silicon — A material used to make photovoltaic cells. It consists of silicon in which the crystal lattice of the entire solid is continuous, unbroken (with no grain boundaries) to its edges. Effiency is generally between 14 and 16% and the life span of panel is often 30 years plus. Panels will degrade by approximatley 1/2 a percent per year which meeans after 30 years of use should stil perform to 85% of there original capacity i.e 100w panel should still produce 85watts after 30 years constant use.

Multicrystalline — A semiconductor (photovoltaic) material composed of variously oriented, small, individual crystals. Sometimes referred to as polycrystalline or semicrystalline.

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Nickel Cadmium Battery — A battery containing nickel and cadmium plates and an alkaline electrolyte.

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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.

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Panel — See photovoltaic (PV) panel.

Parallel Connection — A way of joining solar cells or photovoltaic modules by connecting positive leads together and negative leads together; such a configuration increases the current, but not the voltage.

Peak Demand/Load — The maximum energy demand or load in a specified time period.

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.

Photoelectric Cell — A device for measuring light intensity that works by converting light falling on, or reach it, to electricity, and then measuring the current; used in photometers.

Photovoltaic(s) (PV) — Pertaining to 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.

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) Module — The smallest environmentally protected, essentially planar assembly of solar cells and ancillary parts, such as interconnections, terminals, [and protective devices such as diodes] intended to generate direct current power under unconcentrated sunlight. The structural (load carrying) member of a module can either be the top layer (superstrate) or the back layer (substrate).

Photovoltaic (PV) Panel — often used interchangeably with PV module (especially in one-module systems), but more accurately used to refer to a physically connected collection of modules (i.e., a laminate string of modules used to achieve a required voltage and current).

Photovoltaic (PV) System — A complete set of components for converting sunlight into electricity by the photovoltaic process, including the array and balance of system components.

Polycrystalline — See Multicrystalline.

Polycrystalline Silicon — A material used to make photovoltaic cells, which consist of many crystals unlike single-crystal silicon. Effiency is generally between 12 and 14% and the life span of panel is often 30 years plus. Panels will degrade by approximatley 1/2 a percent per year which meeans after 30 years of use should stil perform to 85% of there original capacity i.e 100w panel should still produce 85watts after 30 years constant use.

PV — See photovoltaic(s).

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Regulator — Prevents overcharging of batteries by controlling charge cycle-usually adjustable to conform to specific battery needs.

Remote Systems — See stand-alone systems.

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.

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Semicrystalline — See Multicrystalline.

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

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).

Single crystalline — See Monocrystalline.

Solar Cell — see photovoltaic (PV) cell.

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

Solar Panel — See photovoltaic (PV) panel.

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.

Stand-Off Mounting — Technique for mounting a photovoltaic array on a sloped roof, which involves mounting the modules a short distance above the pitched roof and tilting them to the optimum angle.

Storage Battery — A device capable of transforming energy from electric to chemical form and vice versa. The reactions are almost completely reversible. During discharge, chemical energy is converted to electric energy and is consumed in an external circuit or apparatus.

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

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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.

Tracking Array — A photovoltaic (PV) array that follows the path of the sun to maximize the solar radiation incident on the PV surface. The two most common orientations are (1) one axis where the array tracks the sun east to west and (2) two-axis tracking where the array points directly at the sun at all times. Tracking arrays use both the direct and diffuse sunlight. Two-axis tracking arrays capture the maximum possible daily energy.

Transformer — An electromagnetic device that changes the voltage of alternating current electricity.

Trickle Charge — A charge at a low rate, balancing through self-discharge losses, to maintain a cell or battery in a fully charged condition.

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

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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.

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Watt — The rate of energy transfer equivalent to one ampere under an electrical pressure of one volt. One watt equals 1/746 horsepower, or one joule per second. It is the product of voltage and current (amperage).

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

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