Glossary

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | R | S | T | V | W

A

Alternating current (AC) – Electric current in which the direction of flow is reversed at frequent intervals. The most common type of household electricity.
Ampere or amp (A) – The unit of measurement for the electric current. One amp is produced by an electric force of 1 volt acting across a resistance of 1 ohm.
Ampere-Hour (Ah/AH) – A measure of the flow of current (in amperes) over one hour; used to measure battery capacity.
Annual solar savings – The amount of energy saved by using a solar system as compared to a nonsolar system.
Array – see photovoltaic array.

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B

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.
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.
Building-integrated PV (BIPV) – Used to describe a structure where PV replaces conventional materials and is integrated into the building.
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.

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C

Cell – see photovoltaic cell
Cell efficiency – The percentage of electrical energy that a solar cell produces (under optimal conditions) as compared to the total amount of energy from the sun falling on the cell.
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.
Circuit – A system of conductors that convey electricity.
Circuit breaker – A safety device that shuts off power when it senses too much current.
Conductor – A material that is used to convey electricity, i.e. wires.
Conversion efficiency – The percentage of electricity that is created by a solar cell as compared to the amount of energy needed to generate that electricity.
Current – The flow of electricity between two points. Measured in amps.
Current at Maximum Power (Imp) – The current at which maximum power is available from a module.

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D

Direct current (DC) – Electrical current that flows only in one direction. The most common form of electricity used in boats and RVs.
Disconnect – Switch gear used to connect or disconnect components in a photovoltaic system.
Distributed systems – Installed 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 Sharp residential solar system is a distributed system.
Duty Cycle – The ratio of active time to total time. Used to describe the operating regime of appliances or loads in photovoltaic systems.

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E

Efficiency – The ratio of output energy to input energy.
Electric Current – The flow of electrical energy (electricity) in a conductor, measured in amperes.
Electric circuit – The path followed by electricity, beginning from the generating source, continuing through the devices that use the electricity, and then traveling back to the source.
Electric current – The flow of electrons measured in amps.
Electrical grid – A large distribution network that delivers electricity over a wide area.
Electricity – The controlled flow of electrons through a conductor.
Electrode – A conductor used to lead current into or out of a nonmetallic part of a circuit.
Energy – Usable power. Measured in kWh.
Energy audit – A process that determines how much energy you use in your house or apartment.

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F

Fossil fuels – Fuels that are formed underground from the remains of dead plants and animals. i.e. oil, natural gas, and coal are fossil fuels.

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G

Greenhouse effect – When heat from the sun becomes trapped in the Earth’s atmosphere due to certain gases.
Greenhouse gases – The gases responsible for trapping heat from the sun within the Earth’s atmosphere. i.e. water vapor, carbon dioxide, methane, ozone, chlorofluorocarbons, and nitrogen oxides.
Grid – A distribution network, including towers, poles, and wires that a utility uses to deliver electricity.
Grid-connected PV system – A solar system that is tied in to the utility’s network. When generating more power than necessary, the system supplies the surplus to the grid. At night, the system draws power from the grid.

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H

Hertz (HZ) – The frequency of electrical current described in cycles per second, i.e. Appliances in the United States use 60 HZ.
Heterojunction – A region of electrical contact between two different materials.
HIT (Heterojunction with Intrinsic Thin layer) – Solar cells are hybrids of single crystalline silicon surrounded by ultra-thin amorphous silicon layers.
Hybrid System – A solar electric or photovoltaic system that includes other sources of electricity generation, such as wind or diesel generators.

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I

Insolation – 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.
Inverter – An inverter converts the electricity generated from a solar system from direct current (DC) to alternating current (AC) for use in the home.
Irradiance – The amount of solar energy that strikes a surface during a specific time period. Measured in kilowatts.
I-V curve – A graph that plots the current versus the voltage from the solar cell as the electrical load (or resistance) is increased from short circuit (no load) to open circuit (maximum voltage). The shape of the curve characterizing cell performance. Three important points on the IV curve are the open-circuit voltage, short-circuit current, and peak or maximum power (operating) point.

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J

Junction box – The point on a solar module where it connects, or is strung, to other solar modules.

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K

Kilowatt (kW) – A unit of electrical power, one thousand watts.
Kilowatt-hour (kWh) – One thousand watts acting over a period of one hour. The kWh is a unit of energy.

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L

Life-cycle cost – The estimated cost of owning, operating, and disposing of a system over its useful life.
Load – Anything that is connected to an electrical circuit and draws power from that circuit. Usually expressed in terms of amperes or watts in reference to electricity.

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M

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.
Megawatt (MW)– One million watts; 1,000 kilowatts.
Module – see photovoltaic module.
Monocrystalline solar cell – A type of solar cell made from a thin slice of a single large crystal silicon.
Multicrystalline – Material composed of many small crystals (crystallites). Because of the numerous grain boundaries, devices that employ this design will operate with reduced efficiency.

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N

National Electrical Code (NEC) – The U.S. minimum inspection requirements for all types of electrical installations, including solar systems.
NREL – The National Renewable Energy Laboratory. A national lab that concentrates on studying and developing renewable energy sources.
Net metering – A practice used in conjunction with a solar electric system where your electric meter tracks your net power usage, spinning forward when you use electricity from the utility, and spinning backward when your system is generating more electricity than you need.

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O

Open-Circuit Voltage (Voc) – The maximum possible voltage across a photovoltaic cell; the voltage across the cell in sunlight when no current is flowing.
Orientation – A term used to describe the direction that a solar module faces. The two components of orientation are the tilt angle (the angle the panel makes from the horizontal) and the aspect angle (the angle the panel makes from North).

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P

Panel – A term used to describe a solar module.
Passive solar home – A house that utilizes part of the building as a solar collector, as opposed to active solar, such as PV.
Peak load – The largest amount of electricity being used at any one point during the day.
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 (PV) – The conversion of light into electricity. Photo means “light”, voltaic means “electric.”
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 array – An interconnected system of solar modules that function as a single electricity-producing unit.

Photovoltaic cell – Made from silicon, this is the basic unit of a solar module that collects the sun’s energy.

Photovoltaic module – The layers of glass, plastic, and silicon cells framed in metal, which collect the sun’s energy.
Photovoltaic system – A complete set of components that converts sunlight into usable electricity.
PV – Abbreviation for photovoltaic.

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R

Rated power – Nominal power output of an inverter; some units cannot produce rated power continuously.

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S

Semiconductor – A material that has an electrical conductivity in between that of a metal and an insulator. Typical semiconductors for PV cells include silicon, gallium arsenide, copper indium diselenide, and cadmium elluride.
Short-Circuit Current (Isc) – The current flowing freely through an external circuit that has no load or resistance; the maximum current possible.
Silicon (Si) – A chemical element that is the most common semiconductor material used in making PV cells.
Single-crystal silicon – Silicon material with a single crystal structure. A common material for the construction of solar PV cells.
Solar cell – see photovoltaic cell.
Solar energy – Energy from the sun.
Solar module – see photovoltaic module.
Solar power – Electricity generated from sunlight.
Stand alone– A solar system that operates without connection to a grid or another supply of electricity. A battery bank stores unused daylight production for nighttime power. Commonly used in remote regions such as mountains, ocean platforms or communication towers.

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T

Thin film – A solar PV module constructed with sequential layers of thin film semiconductor materials usually only micrometers thick. Currently, thin-film technologies account for around 12 percent of all solar modules sold worldwide. This share is expected to increase, since thin-film technologies represent a potential route to lower costs.
Tilt angle – The angle of inclination of a module measured from the horizontal.

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V

Volt (V) – The measurement of the force given the electrons in an electric circuit.

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W

Watt (W) – The unit of electric power done in a unit of time. One ampere of current flowing at a potential of one volt produces one watt of power.
Watt-hour (Wh) – A unit of energy equal to one watt of power being used for one hour.

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