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Solar Glossary

A list of terms and acronyms frequently used in relation to solar energy.



Alternating Current (AC)
The flow of electricity that constantly changes direction between positive and negative sides. Most power produced by electric utilities in the United States moves in current that shifts direction at a rate of 60 times per second.

Ampere (Amp)
The unit of electrical current. An ampere is a measure of the amount of electric charge passing a point per unit time.

Average Demand
The energy demand for a given location over a period of time.

Avoided Cost
The amount of money an electric utility would need to spend for the next increment of electric generation to produce or purchase.


Batteries are often sold with a photovoltaic system. The primary purpose is to store the electricity not immediately used, which could be used later.


Carbon Footprint
A carbon footprint is “the total set of GHG (greenhouse gas) emissions caused directly and indirectly by an individual, organization, event or product” (UK Carbon Trust 2008).

One or more conductors through which electricity flows.

An apparatus that changes the voltage of an electrical power source and is usually combined with other components to create a power supply.

Customer load
The amount of power a residential or commercial site uses. Load may be expressed in kilowatts (capacity) or kilowatt-hours (energy). A site's peak kilowatts generally refers to when electric demand requirements are highest.


The level at which electricity (or natural gas) is delivered to end-users at a given point in time. Electric demand is measured in kilowatts.

Direct Current (DC)
Electricity that flows continuously in one direction (produced by sources such as batteries or photovoltaic cells).


Expected Performance Based Buydown (EPBB)
Owners of solar systems less than 50 kilowatt (kW*) may apply for an up-front cash rebate known as the Expected Performance Based Buydown (EPBB)**. Program Administrators calculate a customer's rebate using the expected performance of the owner's system based on equipment ratings and installation factors such as geographic location, tilt, orientation and shading. Customers receive their incentive payment in a lump sum after their system in fully installed and interconnected.
Click here to go to the CSI EPBB/PBI Calculator


The number of cycles through which an alternating current moves in each second. Standard electric utility frequency in the United States is 60 cycles per second, or 60 hertz.


The electricity transmission and distribution system that links power plants to customers through high-power transmission line service.

Grid-connected systems operate in parallel with and are connected to the electric utility grid.

Ground Mount
A method for installing a solar system. Ground mounted systems are installed using a solar specific structure that supports the solar panels.


The unit of electromagnetic wave frequency equal to one cycle per second.


The linkage of transmission lines between two utilities, or between a utility and an end-user, enabling power to be moved in either direction.

Device used to change solar power to direct current electricity and to alternating current electricity.


Kilowatt (kW)
or 1000 watts. A unit of measure of the amount of electricity needed to operate given equipment. (Ex. one kW is enough power to illuminate 10 light bulbs at 100 watts each - volts x amps = watts.)

Kilowatt-hour (kWh)

The amount of kW produced over a period of time, or one kilowatt of electricity supplied for one hour. For example, a one kW system, if operating at full capacity for 5 hours will produce 5 kWh of electricity.


Leadership in Environmental and Energy Design (LEED)
Developed by the U.S. Green Building Council, the LEED Green Building Rating System provides standards for environmentally sustainable construction. It is the nationally accepted benchmark that provides building owners and operators with the tools they need to have an immediate and measurable impact on their building's green performance.


One thousand kilowatts or one million watts.

A device that measures levels and volumes of customers' electricity and gas use.

Mounting equipment
Equipment/apparatus used to fasten PV modules to the roof.


North American Board of Certified Energy Practioners (NABCEP)
A national program that awards professional certification to photovoltaic installers. NABCEP's high standards are designed to protect customers and enhance the profession.

Net Metering
Net Metering is a billing arrangement between your energy utility company, such as SDG&E, and customers who generate their own electricity with photovoltaic, by which the excess electricity produced using your own generating equipment, is fed back onto the utility grid and is deducted from your electric bill.


Performance Based Incentive (PBI)
Customers with solar systems between 50 kW* and 1 MW must* apply for the Performance Based Incentive (PBI) structure. PBI incentives are a five-year stream of fixed monthly payments determined by the actual output of the system, as metered and reported to the utility. After January 1, 2010, all systems greater than 30 kW must choose the Performance Based Incentive structure. The PBI incentive path is available at any time to ANY size system.

The table below shows the effect of prices as these step declines occur, with current prices in the three territories highlighted in yellow. Residential and commercial incentives are the same price in each step; however, local governments and other tax-exempt organizations receive a slightly higher incentive because cannot qualify for Federal Investment Tax Credits on their solar systems.

The table below shows the rebate levels available at various steps, and information on currently applicable step in your region is available at the California Solar Initiative Trigger Tracker.

Peak load
The highest electrical demand within a particular period of time.

Photovoltaic (PV) Cell
A device that produces electricity from light. Cells are the building block for modules.

Photovoltaic Module
A group of photovoltaic cells combined in series and/or parallel and encapsulated in an environmentally protective laminate. Modules are the building block of panels.

Photovoltaic Panel
A group of photovoltaic modules. Panels are the building blocks for arrays.

Photovoltaic Array
A group of photovoltaic panels.

Power Purchase Agreements (PPAs)
PPAs are long-term contracts between the customer and the developer where the developer retains ownership of the system and sells the kWhs to the customer at a specified rate for a specified amount of time. Essentially, the customer leases the solar system from the developer. PPAs have been standard throughout the power industry but are relatively new to the solar industry.


Roof Mount
The method by which the solar system is attached to the roof of your home or building.


Solar Energy
Heat and light radiated from the sun.

Solar Panel
A group of solar photovoltaic cells combined into a larger system to produce electrical power.

Solar Site Plan
An architectural drawing of a facility and its grounds with a possible solar solution drawn in place and to scale.

Storage refers to saving surplus electricity produced by a PV system. Generally batteries are used as storage devices.


Tracking equipment
Structure that houses PV modules and that can automatically follow the sun across the sky throughout the day to maximize output.


Utility grid
The interconnection of electricity generation plants through the transmission and distribution lines to customers. The grid also refers to the interconnection of utilities through the electric transmission and distribution systems.


The amount of force required to drive a steady current of one ampere through a resistance of one ohm. Electrical systems of most homes and offices use 120 volts. (Volts = watts/amps)


Watt (W)
Electric measurement of power at one point in time, as capacity or demand. For example, light bulbs are classified by wattage. (1000 watts = 1 kilowatt)


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