The part of a solar thermal collector that receives the sun's radiant energy and transforms it into heat energy.

Alternating current (AC) is the cyclical flow of electrical current, reversing direction as it flows. It is the type of electrical current provided by utility companies.

An electrical box which is the central point of electrical distribution throughout a building.

A system that traps the sun's energy with solar collectors and uses an electromechanical subsystem to move that energy to its point of intended use for water heating, space heating, pool heating, industrial process heat, electrical generation, and space cooling.

A sun-dried earthen, un-compressed brick used for wall construction. Traditional adobe blocks are a standard 10"x14"x4" size.

An amp-hour (Ah) is one amp of current flowing for one hour. An amp-hour is the unit of measurement for capacity of a battery.

A material or structural element that inhibits air flow into and out of a building's envelope or shell. Often it allows water to diffuse through it. See also Vapor Barrier.

A device used to eliminate air in SWH system piping. It can have automatic or manual operation.

The cyclical flow of electrical current, reversing direction as it flows. It is the type of electrical current provided by utility companies.

A device that measures altitude (based on air pressure), and can be used to measure head on a hydro site. Readings are relative to background air pressure that may be changing. Altimeters can have varying levels of accuracy. It is advisable to use more than one technique to measure head.

Measure of the angle formed between the sun and the horizon.

A standardized nomenclature used to designate the cross-sectional diameter of electrically conducting wire; the cross-sectional area associated with a particular gauge is an important factor for determining its current-carrying capacity (or ampacity).

One amp of current flowing for one hour. An amp-hour is the unit of measurement for capacity of a battery.

The rate of the flow of electrons through a conductor, denoted by the electrical symbol A.

The AEO of a turbine depends on the average windspeed of the site. Expressed in kilowatt-hour units of electrical energy per year, this is the most important indicator of the value of a turbine to its owner, but it's difficult to determine the average windspeed of a site until a tower has been there long enough to measure it.

The American National Standards Institute (ANSI) oversees the making, broadcasting, and use of thousands of guidelines and standards that impact businesses in the United States.

A safety valve that limits hot water output by mixing cold water at a set maximum temperature.

A dangerous rapid release of energy from an electrical fault that overcomes the resistance of air, at temperatures high enough to vaporize conductors and create an arc blast of molten metal and expanding plasma.

A solar array's inclination as measured in degrees from horizontal. Modules collect the most solar radiation when they are angled perpendicular to the sun.

An asynchronous motor will back-feed the grid if driven faster than its motoring speed. Coils in the motor's body produce a magnetic field that rotates with the frequency of the grid.

An electronic control circuit used on stand-alone synchronous generators powered by hydro turbines. The AVR adjusts the current in the field coils to regulate the output voltage under changing load conditions.

The average amount of energy used in a day; this value is critical for off-grid system sizing.

American wire gauge (AWG) is a standardized nomenclature used to designate the cross-sectional diameter of electrically conducting wire; the cross-sectional area associated with a particular gauge is an important factor for determining its current-carrying capacity (or ampacity).