Solar Energy Dictionary

Photovoltaic systems are solar energy systems that produce electricity directly from the sun. PV systems produce clean, reliable, and renewable energy without consuming fossil fuels.  They are used in a wide variety of applications. While research in PV began as early as 1873, the technology wasn’t developed to a usable extent until the 1950’s when Bell Laboratories was searching for a dependable source of power for remote communication systems. NASA was the next in line to further develop and improve the technology using it on the United States’ first satellite, Vanguard I. Today, over 1 million homes in the U.S. are powered by solar. PV technology is refined, efficient, and user-friendly. It is regarded as one of the most effective technologies available to reduce our consumption of non-renewable fuels.

Alternating Current (AC) 

Electrical current in which the direction of flow is reversed at frequent intervals. This is the type of current common in households and supplied by utilities

Ampere (Amp)

A unit of electrical current; the flow of electrons.


Quantity of electrical energy equal to the flow of one ampere of current for one hour.


Any number of photovoltaic modules connected together to provide a single electrical output.

Balance of System

All of the system components and costs other than the PV modules. It includes design costs, site preparation, power conditioning components, storage cells (batteries), etc.


Two or more “cells” electrically connected for storing electrical energy.

Battery capacity 

The total number of amp-hours that can be withdrawn from a fully charged battery.

Charge Controller 

A device that controls the charging rate and/or state of charge for the batteries connected to the PV array.

Cycle Life

The number of charge and discharge cycles a battery can tolerate. Number of cycles a battery can withstand depends on the depth of discharge of each cycle.

Days of Autonomy

The number of consecutive days a battery bank can withstand without solar charging input.

Direct Current (DC)

Electrical current in which electrons flow in one direction only. This is the type of current generated by solar cells and also stored in a battery bank.


The ability to do work. Stored energy becomes working energy when we use it. Measured in Watts (Amps X Volts = Watts)

Grid Interconnected Or Grid-tied

A PV system in which the PV array acts like a central generating plant, supplying power to the grid.


Device that converts DC electricity into AC electricity. Inverters are used in both stand alone systems (off-grid) and grid interconnected systems.

Kilowatt (KW)

1000 watts

Kilowatt-hour (KWh)

One thousand watt hours. A unit of energy.


Anything in an electrical circuit that, when the circuit is turned on, draws power from the circuit.

Net Metering

A grid interconnected system where the power produced by the solar array offsets the consumption of power.  A user’s electric meter either slows down or actually spins backward depending on the amount of power produced by the array vs. the amount of power being demanded by the user. Essentially power is sold back to the utility at the same rate that the user purchases power rather than a wholesale rate.


Not connected to a central utility. An independent power generation system. Sometimes referred to as “stand alone system”.


The direct conversion of photons from sunlight into electricity.


A unit of measure of the force, or “push”, given the electrons in an electrical circuit.


The unit of electrical power, or amount of work (energy). One amp flowing at a potential of one volt equals one watt. (Volts x Amps = Watts)

Watt-hour (Wh)

A quantity of electrical energy when one watt is used for one hour.