glossary of terms, acronyms, and abbreviations

More detailed glossaries of solar and sustainable energy terms can be found at these sites:

U.S. Department of Energy, Energy Efficiency and Renewable Energy Program
California's Public Interest Energy Research Glossary
Institute for Sustainable Energy Glossary
National Renewable Energy Lab's Glossary List

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Active Solar System

A system that uses a mechanical device, such as pumps or fans run by electricity in addition to solar energy, to transport air or water between a solar collector and the interior of a building for heating or cooling.
See also: Passive Solar System

BIPV: Building-integrated Photovoltaics

A building integrated photovoltaics (BIPV) system consists of integrating photovoltaics modules into the building envelope, such as the roof or the façade. By simultaneously serving as building envelope material and power generator, BIPV systems can provide savings in materials and electricity costs, reduce use of fossil fuels and emission of ozone depleting gases, and add architectural interest to the building.
See examples of BIPV projects


Building Research Establishment Environmental Assessment Method
British standards for assessing energy responsiveness of buildings.
Building Research Establishment - U.K.


Device that converts DC power to another voltage.


Entities seeking to become carbon-neutral can:
-Limit energy usage and emissions from transportation, buildings, equipment and processes;
- Obtaining energy from renewable sources either directly by generating it or by selecting an approved green energy provider, and by using low-carbon alternative fuels such as biofuels; - Offsetting remaining emissions that can not currently be avoided or generated from renewables in a responsible carbon project, or by buying carbon credits.


The admission of natural light into a space through windows, to reduce or eliminate electric lighting. Learn more about daylighting


Ecotourism description and links

Full sun

The amount of power density in sunlight as received onto the earth's surface at noon on a clear day (about 1,000 Watts/square meter).

Gigawatt (GW)

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

Hybrid System

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


The direct, diffuse, and reflected solar radiation that strikes a surface. Usually expressed in kilowatts per square meter. Irradiance multiplied by time equals insolation.


A metric unit of work or energy; 1 joule per second equals 1 watt or 0.737 foot-pounds; 1 Btu equals 1,055 joules.

Kilowatt (kW)

A standard unit of electrical power equal to 1000 watts, or to the energy consumption at a rate of 1000 joules per second.

Kilowatt Hour(kWh)

1,000 thousand watts acting over a period of 1 hour. The kWh is a unit of energy. 1 kWh=3600 kJ.


Leadership in Energy and Environmental Design
managed by the U.S. Green Building Council, a green building rating system created to define green building by establishing common standards.


A small combustion turbine with an output between 25 and 500 kW. Components of a microturbine are: compressor, combustor, turbine, alternator, recuperator, and generator. Benefits include: a small number of moving parts, compact size, light weight, greater efficiency, lower emissions, lower electricity costs.

Net Metering

A policy that allows surplus solar-generated electricity to be stored in the utility grid by essentially spinning the meter backwards. Surplus power can then be drawn upon at night and during periods of cloudy weather. Although a home may also have a bank of batteries as a power source when the utility fails, a net metering relationship with a local utility company is considered a fundamental prerequisite to meeting the home's power needs with solar generation. Net metering provides 100% efficient electric "storage", eliminating the costs and losses of on-site storage. Both the homeowner and the utility benefit.


The direction that a solar energy collector faces. The two components of orientation are the tilt angle (the angle the collector makes from the horizontal) and the aspect angle (the angle the collector makes from North).

Passive Solar System

A system that distributes collected heat via direct transfer from a thermal mass rather than mechanical power. Passive systems rely on building design and materials to collect and store heat and to create natural ventilation for cooling.
See also: Active Solar System

Qualification Test

A procedure applied to a selected set of photovoltaic modules involving the application of defined electrical, mechanical, or thermal stress in a prescribed manner and amount. Test results are subject to a list of defined requirements.

Renewable energy

Energy produced from renewable sources, such as the rays of the sun, the wind, or ocean tides. Use of these energy sources preserves the earth's resources instead of depleting them. It does not pollute the environment - by avoiding dispersal of toxic gases such as those produced by burning fossil fuels, use of renewable energy sources does not contribute to the pollution that leads to detrimental climate change.

Steven Strong

Founder and CEO of Solar Design Associates; Solar designer and advocate; author of The Solar Electric House

Superinsulated building envelope

Three elements are present in a superinsulated house:
  • They are constructed to be air tight.
  • They have a higher level of insulation, compared to conventionally-constructed houses
  • They have a ventilation system to control air quality.

Thermal Envelope

Five components of a building that ensure maximum retention and minimal loss of heat, minimal chemical fumes and other factors that contribute to a safe, secure living environment.
  • Weather Barrier - a building's outer skin that keeps it dry
  • Air Barrier - limits air leakage or infiltration from outside
  • Thermal Barrier - prevents movement of heat in or out
  • Vapor Barrier - prevents movement of moisture in or out
  • Interior Finish - overall design, low- or no-VOC paints, UL ratings
The thermal envelope is becoming much more of a concern and certainly the first consideration for reaching our environmental and economical goals including more livable space and longer building life.


A PV system that interfaces with a utility grid.


Volatile Organic Compounds, chemical fumes given off by paints and other finishes.


The rate of energy transfer equivalent to one ampere under an electrical pressure of one volt. One watt equals 1/746 horsepower, or one joule per second. It is the product of voltage and current (amperage).

Zeo-energy building

A building that produces at least as much energy as it consumes.
Learn more about zero-energy technologies