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Glossary of Solar Terms

Alternating Current (AC): A type of electrical current, the direction of which is reversed at regular intervals or cycles. In the United States, the standard is 120 reversals of 60 cycles per second. Electricity transmission networks use AC because voltage can be controlled with relative ease.

Battery Energy Capacity: The total energy available, expressed in watt-hours (kilowatt hours), which can be withdrawn from a fully charged cell or battery. The energy capacity of a given cell varies with temperature, rate, age, and cutoff voltage. This term is more common to system designers than it is to the battery industry where capacity usually refers to ampere hours.

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.

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

Direct Current (DC): A type of electricity transmission and distribution by which electricity flows in one direction through the conductor, usually relatively high voltage and low current. To be used for typical 120 volt or 220 volt household appliances DC must be converted to alternating current.

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

Energy Audit: A survey that shows how much energy in a home and helps identify ways to use less energy.

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. Also referred to as Grid-Tied or Grid-Interactive.

Inverter: Inverters convert the DC (Direct Current) that the PV system generates to AC (Alternating Current) at either 120 volts or 240 volts. The inverter sends this usable electricity into the home’s circuit breaker panel, where it is distributed to the home or electricity grid through the net meter.

Kilowatt (kW): A standard unit of electrical power equal to 1,000 watts or to the energy consumption of 1,000 joules per second.

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

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.

Net Metering: The process of calculating the electricity used by a Customer-Generator versus the amount of electricity generated by a qualifying system owned/operated by the customer generator.

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. Typically from 9am to 2pm, with peak 11:30am to 2pm.

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.

Photovoltaic (PV) Cell: The smallest semiconductor element within a PV module to perform the immediate conversion of light into electrical energy. Also referred to as a solar cell.

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). Often used interchangeably with solar panel.

Production Meter: Records every kWh produced from the solar array. This is used in calculating the annual state incentive payment by the utility provider.

Solar Resource: The amount of solar insolation a site receives, usually measured in kWh/m2/day, which is equivalent to the number of peak sun hours.

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

Compiled from Energy.gov: The Office of Energy Efficiency and Renewable Energy.