Glossary of Terms

AC Power (Alternating current)
This type of electric current is typically found in your home or business. It is an electrical current whose magnitude and direction varies continuously at a rate of 60 times a second in the US.

Amorphous semiconductor
Amorphous is a type semiconductor that is not made out of crystalline silicon. Although it's easier to make than crystalline semiconductors and typically found in some thin film solar panels, it's also less efficient.

Ampere (Amp)
A unit of measure that indicates how much electrical current is flowing through a wire. Current flow through a wire is similar, conceptually, to water flow through a hose.

Array
A set of photovoltaic panels. A home solar electric system might include several arrays on different parts of the roof.

Azimuth
An important measurement (usually in degrees) used to optimize the placement of photovoltaic panels. The azimuth angle is the compass direction from which the sunlight is coming, and therefore where solar panels should optimally face for the most solar power production. A positive azimuth angle generally indicates the sun is east of south, and a negative azimuth angle generally indicates the sun is west of south.

Balance of System (BOS)
All the parts of a solar electric system excluding the solar panels and the inverter. Balance of system usually includes items like racking, wires, conduit, and safety shut-offs. The balance of system might account for 15% of the total cost of a solar electric system.

Base load
The amount of electric power a utility must supply constantly to meet the demand for energy.

Battery
A battery back-up for a solar electric system stores the extra power the solar system makes. A home can use that power when the solar system isn't producing enough energy, at night, or in a power outage.

Cell
The smallest part of a solar panel that converts light into solar electricity.

DC Power (Direct Current)
Typically found in car and toy batteries, DC is an electrical current whose magnitude and direction stay constant. The photovoltaic cells on solar panels capture energy from sunlight converting it to DC power. DC electricity produced by solar cells must then be converted into AC by an inverter before it's usable in a house.

Electrical Current
The flow of charged electrons through a circuit. Depending upon its behavior, an electrical current can be alternating or direct (AC or DC).

Electrical Panel
An electrical distribution box that houses electrical circuit breakers. It is the main point at which power from the grid enters the building and where electricity is distributed throughout the building. It is otherwise known as a breaker box.

Fossil Fuel
Fuels that are derived from natural resources, usually in the form of coal, oil, or natural gas. There is a limited supply of these resources, and they are only located in certain parts of the world, making them subject to political and international maneuvering, and causing energy prices to be unstable.

Greenhouse Gases
Gaseous components in the atmosphere that contribute to a gradual warming of the planet. The most prevalent of these gases is carbon dioxide, which is released in large quantities when fossil fuels are burned. Nothing is burned to convert sunlight into power. Since solar energy does not have any gaseous by-products, it is considered "clean".

Gigawatt
One billion watts.

Grid
A system of high tension cables in a region that distributes electricity to homes, businesses, and other buildings.

Grid tied/Grid connected
A solar system that is connected in parallel with the electric utility power grid and uses the grid as a backup source of power.

Ground Mounted Systems
A solar electrical system that is mounted on the ground instead of on a roof. Ground mounts are ideal for sites with limited roof space and a lot of open land.

Interconnection
The process of hooking up a solar electrical system to the power grid that enables power to move seamlessly in either direction.

Inverter
A electronic device that converts DC power captured by the photovoltaic cells on solar panels into AC power that can be used to power your home or business. This device is an integral part of a solar system. Solar power systems may have one or many inverters depending on the size and design of the system.

Kilowatt (kW)
A measurement of power. A kilowatt is one thousand watts. The size of a solar system is often measured in kW. A typical size solar system for a home is 5 kW; for a medium sized business is 100 kW.

Kilowatt Hour (kWh)
A measurement of energy consumption. One kilowatt hour is defined as the amount of energy consumed by a 1000-Watt appliance running continuously for 1 hour. This is the measurement your utility company uses to calculate your electric bill.

Megawatt
One million watts.

Module
A solar panel, or a group of solar cells.

Monocrystalline panel
A solar panel made from a large, single silicon crystal and has a patchwork pattern. Monocrystalline panels are more expensive and more efficient than multi- or poly- crystalline panels.

Multicrystalline panel (also polycrystalline)
A solar panel made from small silicon crystals oriented in lots of different directions. Multicrystalline panels are less expensive and less efficient than monocrystalline panels.

Net Metering
An agreement between a solar system owner and the local electric utility that allows the system owner to buy and sell energy in the form of electric credits. When the solar system produces excess energy, it is sold back to the electric utility, in some areas at peak prices, literally causing the electric meter to spin backwards. When the system is not producing energy, the system owner can use the credits to buy back energy, in some areas, at off-peak prices.

On/Off Grid System
A solar energy system that is interconnected with the utility grid is said to be an on-grid or grid-tied system, while a system with battery storage is not interconnected and is described as an off-grid system. On-grid systems use the grid functionally as a battery.

Panel or Solar Panel
A group of solar cells forming a module or panel.

Photon
A "packet" of light energy.

Photovoltaic (PV)
The process of converting light into electricity.

Additional Solar Learning Resources