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ABSORBER The absorber is that part of a solar thermal collector that receives the incident radiant energy and transforms it into heat energy.

ACTIVE SOLAR THERMAL SYSTEM 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.

ALTERNATING CURRENT (AC) An electrical current in which the direction of electron flow reverses periodically, usually many times per second. Most U.S. household electrical systems use AC current rated at 120 volts and 60 cycles per second.

ALTERNATOR An mechanical device that generates alternating current electricity.

ALTITUDE ANGLE The angle of the sun above the horizon, measured in degrees. In winter, the sun is at a low solar altitude, and in the summer, the sun is at a high solar altitude.

AMMETER A device used for measuring the current (amperage) at any point in an electrical circuit.

AMORPHOUS SILICON A thin-film PV silicon cell having no crystalline structure.

AMPACITY Refers to the highest safe amount of electrical current through conductors, over current devices, or other electrical equipment. Ampacity is determined by the cross-sectional area and the material of the conductor, or the manufacturer’s equipment rating.

AMPERE (AMP; A, I) The rate of flow of electrical charge. Unit of electrical current. One volt across one ohm of resistance causes a current of one ampere. One ampere is equal to 6.235 x 10^18 electrons (one coulomb) per second passing a given point in a circuit.

AMPERE-HOUR (AMP-HOUR; AH) A measure of electron flow over time, used to measure battery capacity and state of charge. For example, a current of 1 amp drawn from a battery for 10 hours would result in 10 amp-hours of charge cycling through the battery.

AMPERE-HOUR METER An instrument that monitors electron flow over time. Amp-hours are the product of electron flow (in amperes) and time (in hours).

AMPLITUDE Generally refers to the maximum and minimum voltage attained by an alternating or pulsed current in each complete cycle or pulse of that current.

ANGLE OF INCIDENCE The angle between the sun’s rays and a line perpendicular to the active surface of a solar module or collector, in degrees.

ANGLE OF INCLINATION The angle that a solar collector or PV module is positioned above horizontal.

ANODE ( Battery ) The electrode within a battery cell that undergoes the chemical process of oxidation. Electrically, the anode is the cell’s positive terminal. (Water heater) An aluminum or magnesium sacrificial rod installed within steel tanks that is used to help prevent corrosion of the tank itself.

ARRAY Any number of photovoltaic modules connected together electrically to provide a single electrical output.

AWG American Wire Gauge, a set of standards in the U.S. specifying the diameter of wire. A higher number indicates smaller wire.

AZIMUTH The angle between true south and a point on the horizon, measured in degrees east or west of true south.