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9.0 System Glossary
Ampere A unit of electrical current. Designates the number of electrons flowing per
second through a conductive material.
Ampere-Hour (Ahr or amp hour): A unit of energy, typically referring to battery
capacity. One ampere of current flowing for one hour.
Azimuth of the Sun: The angular measure between due south and the point on the
horizon directly below the sun.
Array: A number of photovoltaic modules electrically connected to produce a single
electrical output.
Angle of Incidence: The angle between a ray of sunlight striking a surface and a line
perpendicular to that surface. Rays perpendicular to a surface have a zero angle of
incidence.
Battery: Two or more electrochemical cells connected to provide energy storage.
May be used to designate one cell. PV system batteries may be “sealed” or “flooded”.
Blocking Diode: A diode application that prevents a battery from discharging through
the array at night or if the array becomes shaded. Most charge controllers are equipped
with a blocking diode.
Charge Controller (regulator): The PV system component that controls the battery’s
state of charge. It may also provide other system control functions. Also known as a
regulator.
Charge Rate: The current applied to a battery to restore its energy capacity. The
battery manufacturer will usually have a recommended charge rate for their product.
The rate is typically 10 –20 percent of the amp hour capacity at the 20-hour rate.
Current: DC or Direct Current is the type of electron flow provided by a battery or
solar cell, which flows in one direction. The unit for current is ampere or amp for short
and designated by the letter A.
Cycle: One battery cycle equals one discharge and one charge.
Deep Cycle Battery: Batteries that are designed to discharge as much as 80% of
their capacity as opposed to engine-starting or shallow cycle batteries which are designed
for heavy cranking but will not stand up to repeated deep discharges.
Depth of Discharge: A measure of how much energy has been withdrawn from a
battery, expressed as a percentage of full capacity. A 100 Ahr battery from which 30
Ahr has been withdrawn has undergone a 30% depth of discharge (DOD). This term is
the inverse of state of charge (SOC); the example battery would be at 70% SOC.
Diode: A semi-conductor device that allows current to flow in one direction only.
“Blocking diodes” and “isolation diodes” are standard diodes that have specific
applications.
Electrolyte: Battery acid.
Equalization: The process that equalizes the specific gravity of all the cells in a
battery by means of a controlled overcharge that breaks down sulfation on the battery
plates. Most inverter/chargers and some charge controllers are equipped with this
feature. Usually performed only on flooded batteries.
Flooded or Wet Cell Batteries: The most common type of PV battery. Battery caps
may be removed to expose the electrolyte inside the battery. Need proper ventilation
due to gassing and may need to be topped up with distilled water at regular intervals.
Grid-Connected: A power system interconnected with the grid (or mains) of the local
electric utility. Also referred to as utility-interactive or grid-tie.
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