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

Array see photovoltaic (PV) array.

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.

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

Azimuth Angle
The angle between true south and the point on the horizon directly below the sun.

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.

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.

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.

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

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).

I-V Curve -is 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. ..Of course at short circuit both voltage and amperage are zero.

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) A power conditioning unit that automatically operates the photovoltaic generator at its maximum power point under all conditions.

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

Monocrystalline - A semiconductor (photovoltaic) material composed of a single crystalline formation.

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

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

Nominal Voltage A reference voltage used to describe batteries, modules, or systems (i.e., a 12-volt or 24-volt battery, module, or system).

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

Open-Circuit Voltage (Voc) The maximum possible voltage across a photovoltaic cell; the voltage across the cell in sunlight when no current is flowing.

Operating Point The current and voltage that a photovoltaic module or array produces when connected to a load. The operating point is dependent on the load or the batteries connected to the output terminals of the array.

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 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, in watts (Wp) under standardized test conditions, usually 1,000 watts per square meter of sunlight with other conditions, such as temperature specified.

Photovoltaic(s) (PV) Pertaining to the direct conversion of light into electricity.

Photon 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 function as a single electricity-producing unit. The modules are assembled as a discrete structure, with common support or mounting. In smaller systems, an array can consist of a single module.

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

Photovoltaic (PV) Conversion Efficiency The ratio of the electric power produced by a photovoltaic device to the power of the sunlight incident on the device.

Photovoltaic (PV) Device A solid-state electrical device that converts light directly into direct current electricity of voltage-current characteristics that are a function of the characteristics of the light source and the materials in and design of the device. Solar photovoltaic devices are made of various semiconductor materials including silicon, cadmium sulfide, cadmium telluride, and gallium arsenide, and in single crystalline, multicrystalline, or amorphous forms.

Photovoltaic (PV) Effect The phenomenon that occurs when photons, the "particles" in a beam of light, knock electrons loose from the atoms they strike. When this property of light is combined with the properties of semiconductors, electrons flow in one direction across a junction, setting up a voltage. With the addition of circuitry, current will flow and electric power will be available.

Photovoltaic (PV) Generator The total of all PV strings of a PV power supply system, which are electrically interconnected.

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

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

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

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

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-Crystal Silicon Material with a single crystalline formation. Many photovoltaic cells are made from single-crystal silicon.

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).

Solar Cell see photovoltaic (PV) cell.

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

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

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

Substrate The physical material upon which a photovoltaic cell is applied.

Superstrate The covering on the sunny side of a photovoltaic (PV) module, providing protection for the PV materials from impact and environmental degradation while allowing maximum transmission of the appropriate wavelengths of the solar spectrum.

System Availability The percentage of time (usually expressed in hours per year) when a photovoltaic system will be able to fully meet the load demand.

System Operating Voltage The photovoltaic array output voltage under load. The system operating voltage is dependent on the load or batteries connected to the output terminals.

Temperature Factors It is common for three elements in photovoltaic system sizing to have distinct temperature corrections: a factor used to decrease battery capacity at cold temperatures; a factor used to decrease PV module voltage at high temperatures; and a factor used to decrease the current carrying capability of wire at high temperatures.

Thick-Crystalline Materials Semiconductor material, typically measuring from 200-400 microns thick, that is cut from ingots or ribbons.

Thin Film A layer of semiconductor material, such as copper indium diselenide 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.

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

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

Voltage Protection Many inverters have sensing circuits that will disconnect the unit from the battery if input voltage limits are exceeded.

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