Glossary of Terms


The ratio of the radiation absorbed by a surface and the total energy falling on that surface.

Alternating Current (AC)

Electrical current that reverses its direction at regular intervals.

Ambient Temperature

The temperature of the surrounding area.

Ampere (amp)

A measure of electrical current, the amount of electricity that flows in a line.

Amp Hours

A measure of the flow of current (in amperes) over one hour.

Angle of Incidence

The angle that the sun’s rays make with a line perpendicular to a surface. The angle of incidence determines the percentage of direct sunshine intercepted by a surface.

Annual Solar Savings

The annual solar savings of a solar building is the energy savings attributable to a solar feature relative to the energy requirements of a non-solar building.

Antireflection Coating

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


A group of solar electric modules connected together in a power system.

Array Current

The electrical current produced by a photovoltaic array when it is exposed to sunlight.


The quality or condition of a photovoltaic system being available to provide power to a load. Usually measured in hours per year


The angular distance between true south and the point on the horizon directly below the sun.

Balance of System

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.

Base Load

The average amount of electric power that a utility must supply in any period.

BIPV (Building-Integrated Photovoltaic’s)

A term for the design and integration of photovoltaic technology into the building, typically replacing conventional building materials.

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 or over-discharge. It may also indicate the system operational status


The path of an electric current


Solar concentrators are lenses, mirrors, or reflectors that concentrate the light onto a small area.


A unit that converts a direct current voltage to another DC voltage.

Crystalline Silicon

A type of photovoltaic cell made from a slice of single-crystal silicon or polycrystalline silicon.


The rate of flow of an electric charge. Current is measured in amps.

Diffuse Insolation

Sunlight received indirectly as a result of scattering due to clouds, fog, haze, dust or other obstructions in the atmosphere.


An electronic device that allows current to flow in one direction.

Direct Current (DC)

A type of electricity transmission and distribution by which electricity flows in one direction through the conductor, usually relatively low voltage and high current.

Direct Insolation

Sunlight falling directly upon a collector.

Distributed Generation

Localized or on-site power generation.

Distributed System

Systems that are installed at or near the location where the electricity is used, as opposed to central systems that supply electricity to the grid.


Time when the photovoltaic system cannot provide power for the load. Usually expressed in hours (or percentage) per year.

Electric Circuit

The path followed by electrons from a power source, through an electrical system and returning to the source.

Electrical grid

An integrated system of electricity distribution, usually covering a large area.


The flow of electrical energy through a circuit.


Any source of usable power, such as fossil fuel, electricity or solar radiation.

Fixed Tilt Array

A photovoltaic array set at a fixed angle with respect to horizontal.

Flat-Plate Photovoltaics

A PV array or module that consists of nonconcentrating elements. Flat-plate arrays and modules use direct and diffused sunlight, but if the array is fixed in position, some portion of the direct sunlight is lost because of oblique sun-angles in relation to the array.

Flat-Plate Tracker

A device mounted under a photovoltaic panel that moves the panel to follow the path of the sun.

Full Sun

The amount of power density in sunlight received at the earth’s surface at noon on a clear day.

Gigawatt (GW)

A unit of power equal to 1 billion watts; 2 million kilowatts, or 1,000 megawatts.

Global Warming

The gradual warming of the earth due to buildup of greenhouse gases in the earth’s atmosphere.

Grid-Connected System

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

Ground Mount

A piece of equipment upon which solar modules are mounted.

Hybrid System

A solar electric or PV system that includes other sources of electricity generation, such as wind.


A conductor within a module or other means of connection that provides an electrical interconnection between the solar cells.


A device used to convert direct current electricity into alternating current. Direct current is created by photovoltaic modules or batteries and is converted to AC through the use of an inverter.

Kilowatt (KW)

A standard unit of electrical power equal to 1,000 watts.

Kilowatt-Hour (kWh)

1,000 watts acting over a period of 1 hour. The kWh is a unit of energy.


The period during which a solar system is capable of operating above a specified performance level.


The demand on an energy producing system; the energy consumption or requirement of a piece or group of equipment.

Megawatt (MW)

1,000 kilowatts, or 1 million watts; standard measure of electric power plant generating capacity.


1,000 kilowatt hours or 1 million watt hours.


Modular solar electric charger; used interchangeably with solar electric panel.

Net Metering

Measures the difference between the electricity you buy from your utility and the electricity you produce with your solar energy system. Any excess electricity produced by your solar energy system spins your existing meter backwards, effectively storing the electricity until it is needed. Your meter then spins forward when your solar energy system is not […]

Open-Circuit Voltage

The maximum possible voltage across a photovoltaic cell; the voltage across the cell in sunlight when no current is flowing.


Placement of solar panels with respect to the cardinal directions, N, S, E, W; azimuth is the measure of orientation from north.

Peak Demand/Load

The maximum energy demand or load in a specified time period.

Photovoltaic (PV)

Converting light into electricity. Photo means “light” voltaic means “electric”. Often referred to as “PV. More commonly referred to as “solar electric”.

Photovoltaic Array

An interconnected system of PV modules that function as a single electricity-producing unit.

Photovoltaic Cell

The smallest semiconductor element with a PV module to perform the immediate conversion of light into electrical energy. Also called a solar cell.

Renewable Energy

Any naturally occurring, theoretically inexhaustible source of energy, such as biomass, solar, wind, tidal, wave and hydroelectric power, that is not derived from fossil or nuclear fuel.


Some models have a special circuitry that keeps the battery from overcharging. This means that no controller is needed when the self-regulating modules are properly matched to battery storage capacity.

Solar Collector

A device for capturing solar energy.

Series Connection

A way of joining photovoltaic cells by connecting positive leads to negative leads; such a configuration increases the voltage.

Single-Crystal Silicon

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

Solar Cell

The smallest basic solar electric device, which generates electricity when exposed to light.

Solar Electricity

Electricity produced using solar energy technologies.

Solar Energy

Electromagnetic energy transmitted from the sun.

Solar Noon

The time of the day, at a specific location, when the sun reaches its highest, apparent point in the sky.

Stand-Alone System

A photovoltaic installation not connected to a utility power line.

Thin-Film Photovoltaic Module

A photovoltaic module constructed with sequential layers of thin film semiconductor materials.

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 array that follows the path of the sun to maximize the solar radiation incident on the PV surface.


An electromagnetic device that changes the voltage of alternating current to electricity.


A unit of electrical force equal to that amount of electromotive force that will cause a steady current of one ampere to flow through a resistance of one ohm.


The amount of electromotive force, measured in volts, that exists between two points.


A measurement of total electrical power. The rate of energy transfer equivalent to one ampere under an electrical pressure of one volt.

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