Alternating Current (AC)
is an electrical current whose magnitude and direction vary cyclically, as opposed to direct current, whose direction remains constant. It is the most common type of household electricity.

Ampere or amp (A)
The unit of electric current. One amp is produced by an electric force of 1 volt acting across a resistance of 1 ohm.

Building-integrated PV (BIPV)
Used to describe a structure where PV replaces conventional materials and is integrated into the building. Typically, a photovoltaic array is incorporated into the roof or walls of a building. Roof tiles with integrated PV cells can now be purchased. Arrays can also be retrofitted into existing buildings; in this case they are usually fitted on top of the existing roof structure. Alternatively, an array can be located separately from the building but connected by cable to supply power for the building.

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. The "standard" solar radiation (known as the "air mass 1.5 spectrum") has a power density of 1000 watts per square meter. Thus, a 12% efficiency solar cell having 1 square meter of surface area in full sunlight will produce approximately 120 watts of peak power.

Circuit
A system of conductors that convey electricity.

Circuit breaker
A safety device that shuts off power when it senses too much current.

Combiner box
Where the electrical wiring from the PV modules is joined together in parallel to combine electrical currents.

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.

Direct current (DC)
Electrical current that flows only in one direction. The most common form of electricity used in boats and RVs.

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.

Efficiency
The ratio of output energy to input energy.

Electrical grid
A large distribution network that delivers electricity over a wide area.

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.

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.

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.

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
When the electricity grid is available but electricity from a clean source (solar) is desired, solar panels can be connected to the grid. Provided that sufficient panels are placed, the appliances in the house/building will then run on solar electricity. A grid-connected solar electricity system basically consists of one or more solar panels, an inverter, cables, the electric load and a support structure to mount the solar panels.

Inverter
Converts the DC output of the PV system into usable AC output that can be fed directly into the building load.

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

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.

Life-cycle cost
The estimated cost of owning, operating, and disposing of a system over its useful life.

Load
The amount of electrical demand used in the building at any given time.

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.

Mounting
technology/equipment Used to mount the PV modules in place. Depending on the application, the PV modules can be mounted on rooftops, in parking structures, covered reservoirs and in open fields.

Multicrystalline
Material composed of many small crystals (crystallites). Because of the numerous grain boundaries, devices that employ this design will operate with reduced efficiency.

National Electrical Code (NEC)
The U.S. minimum inspection requirements for all types of electrical installations, including solar systems.

National Electrical Manufacturers Association (NEMA)
The U.S. trade association that develops standards for the electrical manufacturing industry.

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.

NREL The National Renewable Energy Laboratory
A national lab that concentrates on studying and developing renewable energy sources.

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).

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.

Photovoltaic (PV)
the conversion of light into electricity. The term "photo" comes from the Greek "phos," meaning light. "Voltaic" is named for Alessandro Volta (1745-1827), a pioneer in the study of electricity for whom the term "volt" was named. Photovoltaics, then, means "light electricity."

Photovoltaic (PV) module
A number of photovoltaic cells electrically interconnected and mounted together, usually in a sealed unit of convenient size for shipping, handling and assembling into arrays. The term "module" is often used interchangeably with the term "panel.

Photovoltaic array
An interconnected system of solar modules that function as a single electricity-producing unit.

Photovoltaic cell
This is the basic unit of a solar module that collects the sun's energy.

Photovoltaic system
A complete set of components that converts sunlight into usable electricity.

PV
Abbreviation for photovoltaic.

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

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
Solar cells are converters. They take the energy from sunlight and convert that energy into another form of energy, electricity. Solar cells convert sunlight to electricity without any moving parts, noise, pollution, radiation, or maintenance. The conversion of sunlight into electricity is made possible with the special properties of semiconducting materials.

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. Semi-Conductors Most solar cells are made from silicon, the 14th element. Silicon is a "semi-conductor" or a "semi-metal," and has properties of both a metal and an insulator. Atoms in a metal have loosely bound electrons that easily flow when electrical pressure is applied, whereas atoms in an insulator have tightly bound electrons that cannot flow when electric voltage is applied. Atoms in a semi conducting material bind their electrons tighter than metals, but they may be manipulated to have conductive properties. 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 7 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.

Transformer
Used to step up or down the voltage emerging from the inverter to match the required voltage of the onsite load or the utility interconnection.

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.