AC — see alternating current.

Activated Shelf Life — The period of time, at a specified temperature, that a charged battery can be stored before
its capacity falls to an unusable level.

Activation Voltage(s) — The voltage(s) at which a charge controller will take action to protect the batteries.

Adjustable Set Point — A feature allowing the user to adjust the voltage levels at which a charge controller will
become active.

Alternating Current (AC) — A type of electrical current, the direction of which is reversed at regular intervals or
cycles. In the United States, the standard is 120 reversals or 60 cycles per second. Electricity transmission
networks use AC because voltage can be controlled with relative ease.

Acceptor — A dopant material, such as boron, which has fewer outer shell electrons than required in an otherwise
balanced crystal structure, providing a hole, which can accept a free electron.

AIC — See amperage interrupt capability.

Air mass (sometimes called air mass ratio) — Equal to the cosine of the zenith angle-that angle from directly
overhead to a line intersecting the sun. The air mass is an indication of the length of the path solar radiation travels
through the atmosphere. An air mass of 1.0 means the sun is directly overhead and the radiation travels through
one atmosphere (thickness).

Ambient Temperature — The temperature of the surrounding area.

Amorphous Semiconductor — A non-crystalline semiconductor material that has no long-range order.

Amorphous Silicon — A thin-film, silicon photovoltaic cell having no crystalline structure. Manufactured by
depositing layers of doped silicon on a substrate. See also single-crystal silicon an polycrystalline silicon.

Amperage Interrupt Capability (AIC) — direct current fuses should be rated with a sufficient AIC to interrupt the
highest possible current.

Ampere (amp) — A unit of electrical current or rate of flow of electrons. One volt across one ohm of resistance
causes a current flow of one ampere.

Ampere-Hour (Ah/AH) — A measure of the flow of current (in amperes) over one hour; used to measure battery
capacity.

Ampere Hour Meter — An instrument that monitors current with time. The indication is the product of current (in
amperes) and time (in hours).

Angle of Incidence — The angle that a ray of sun makes with a line perpendicular to the surface. For example, a
surface that directly faces the sun has a solar angle of incidence of zero, but if the surface is parallel to the sun (for
example, sunrise striking a horizontal rooftop), the angle of incidence is 90°.

Annual Solar Savings — The annual solar savings of a solar building is the energy savings attributable to a solar
feature relative to the energy requirements of a non-solar building.

Anode — The positive electrode in an electrochemical cell (battery). Also, the earth or ground in a cathodic
protection system. Also, the positive terminal of a diode.

Antireflection Coating — A thin coating of a material applied to a solar cell surface that reduces the light reflection
and increases light transmission.

Array — see photovoltaic (PV) array.

Array Current — The electrical current produced by a photovoltaic array when it is exposed to sunlight.

Array Operating Voltage — The voltage produced by a photovoltaic array when exposed to sunlight and connected
to a load.

Autonomous System — See stand-alone system.

Availability — The quality or condition of a photovoltaic system being available to provide power to a load. Usually
measured in hours per year. One minus availability equals downtime.

Azimuth Angle — The angle between true south and the point on the horizon directly below the sun.
GLOSSARY OF TERMS
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