A to F
AGM (Absorbed Glass Mat)
battery that is maintenance free and holds acid in a fiberglass mat to
prevent it from spilling even if the outer battery case is broken. Typically
much more expensive and less cycle life than flooded acid batteries. Mats
can be assembled in flat layers or in a spiral design (Optima brand).
Absorption Charge: Second
stage of three stage battery charging in which voltage is held for a set
time period at the bulk voltage setting, while amperage is gradually reduced
as the batteries come up to charge. (See Bulk Charge, Float Charge)
AC: (See Alternating
AIC: Amps Interrupt Capacity:
DC fuses should be rated with a sufficient AIC to interrupt the highest
current possible in the circuit. See Arc
for what happens when the breaker or fuse isn't rated high enough.
Air Mass: 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). High Altitude
locations have less Air Mass and so higher irradiation levels.
Alternating Current (AC):
An electric current that alternates periodically. Household electricity
is of this type.
Ambient Temperature: The temperature
of the surrounding area.
Silicon: Thin film PV silicon
having no crystalline structure. Manufactured by depositing layers of
doped silicon on a substrate. Has inferior performance to, and shorter
life span than, Multi- and Mono-crystalline silicon.
Amorphous Panel: PV module
made with amorphous silicon cells.
Amperage (I): The measure
of electrical flow. The amount of "current" (the number of amps)
drawn by an electrical device. Rate that electrons pass a point in the
circuit per second
Ampere (Amp, A):
Unit of electrical current.
Amp-Hour (Ah): A measure
of electrical energy equal to one amp of current for one hour. Used to
measure the energy stored in a battery.
Angle of Incidence:
The angle that sunlight striking a solar module makes with a line perpendicular
to its surface.
Anode: The earth ground
in a cathodic protection system.
Array: (See PV Array)
Array Current: The electrical
current produced by a PV array when it is exposed to sunlight.
Array Operating Voltage:
The voltage produced by a PV array when exposed to sunlight and connected
to a load.
through the air itself. Used in welding metals, but also caused by loose
connections or conductors too close to each other and/ or other materials.
12 volt DC can arc a 1/4", while 100,000 volts (Lightning) can arc
thousands of feet. Within the arc, air turns into a plasma that has much
lower resistance than normal.
Drawing an Arc, starts by making full contact between electrical connectors,
and while current is flowing slowly pull the connectors apart. The arc
can burn these contact points badly if sustained for more than a split
AWG: (American Wire Gauge), standard for wire sizing
in the United States. Formerly known as Brown & Sharp. Wires are sized
from #40 (smallest) to #0000 (4/0) largest. See
wire & connectors guide for comparison table.
angle measured clockwise from true north; 180º is true south.
Balance of System (BOS):
the additional components besides the batteries, and Solar modules, that
are necessary to safely complete a Power system. (I.e. fuses, disconnects,
meters, junction boxes, charge controllers, etc.)
Base Load: The average
amount of electric power that a utility must supply to the grid at any
Battery: A device that
stores electrical energy. Usually, through a electrochemical reaction,
it produces electricity. A rechargeable battery can reverse the chemical
reaction to store electrical energy as chemical energy.
Battery Bank: A group
of batteries wired together in series and/or parallel to form a unified
electrical energy storage unit.
Battery Capacity: The
total number of ampere-hours that can be withdrawn from a fully charged
battery. (See Amp-Hour & Rated Battery Capacity)
Battery Cell: The smallest
unit or section of a battery that can store electrical energy and is capable
of furnishing a current to an external load. For lead-acid batteries the
voltage of a cell (fully charged) is about 2.2 volts dc. ( for example,
a 12 volt battery is actually made of 6 separate cells) NiCad and NiMh
cells are about 1.2 volts per cell.
Battery Cycle Life:
The number of times a battery can be discharged and recharged before failing.
Battery manufacturers specify Cycle Life as a function of discharge rate
Loss of energy by a battery that is not under load.
Battery State of Charge (SOC):
The percentage of total battery capacity available at that moment, or
100 percent minus the depth of discharge. (See Depth of Discharge)
BTS: Battery Temperature
Blocking Diode: A diode
used to prevent undesired current flow. In a PV array the diode is used
to prevent current flow towards a failed module or from the battery to
the PV array during periods of darkness or low current production.
British Thermal Unit (Btu): The quantity
of heat required to raise the temperature of one pound of water one degree
Bulk Charge: The first
stage of three stage charging in which full available current is sent
to the batteries. In this stage, voltage gradually rises to the bulk voltage
setting, when Absorption charging begins. (See Absorption Charge, Float
Bypass Diode: A diode
connected in parallel with a PV module to provide an alternate current
path in case of module shading or failure.
Capacitance (C): The storage
of energy in an electrostatic field, which creates an opposition to a
change in voltage. A capacitor has two metal plates, separated by an air
space or other insulating material, across which an electrical charge
can build up but not flow. Capacitance in a circuit creates a phase difference
between the voltage and the current in that circuit, in which the voltage
lags or peaks after the amperage. The unit of capacitance is the farad
Capacity: The total
number of ampere-hours that can be withdrawn from a fully charged battery
at a specified discharge rate and temperature. (See Battery Capacity)
Cathode: The negative
electrode in an electrochemical cell. Also, the negative terminal of a
CEC: California Energy
Commission, in charge of California's Grid tie Incentive programs that
rebate up to $5 per installed watt of PV power.
Cell: each separate
part of a larger whole. Batteries are made of separatebattery
cells. Each cell has its own independent chemical action. Solar
Modules are made of numerous separatePV cells.
Charge: The process
of adding electrical energy to a battery.
Charge Controller: A
device that controls the charging rate from a solar array or other charging
source, and prevents the batteries from being over charged. It also prevents
current from back flowing back into the panels at night.
Charge Rate (C): The
rate at which a battery is recharged. Normally expressed as a ratio of
battery capacity to charging current. For instance, C/10 indicates the
current that would recharge a battery in 10 hours (not factoring in loss
for efficiency) and would indicate a 1 amp charge for a 10 Ah battery,
a 10 amp charge for a 100Ah battery and a 22 amp charge for a 220Ah battery.
Cloud Enhancement: (See
Edge of Cloud Effect)
Compact Fluorescent (CF):
Fluorescent light bulb that can replace a regular light bulb in most fixtures
or lamps. Typically uses one quarter the energy that a standard incandescent
bulb uses for the same amount of light.
Concentrator: a PV module
that uses a lens or mirrors to magnify the amount of sunlight striking
a PV cell. Requires direct radiation--diffuse radiation is unusable by
concentrators. (See Diffuse Radiation; Direct Radiation)
Conductor: A material
through which electricity can flow, usually made of metal, and usually
a wire. Some types of metal conduct electricity better than others. Aluminum
is a better conductor than steel, copper is better than aluminum, and
silver is better than copper.
The ratio of the electrical energy produced by a PV cell to the total
solar energy striking the cell. Usually around 10%, but as high as 18%.
Converter: A device
that converts DC electricity from one voltage to another (up or down).
In battery charging, the ratio between amount of charge (Ah) output to
amount of charge (Ah) input. Efficiency drops at high charge rates, as
with generator charging. 85-90% is typical when charging from PV. This
is factored in during the design process at Solarray.com.
Current ( I ): The flow
of electricity in a conductor, measured in Amperes (Amps).
DC: (See Direct Current)
Daisy Chaining: Directly
interconnecting PV modules in parallel to boost current without separate
fusing. While permissible to some degree, this method of wiring solar
modules can exceed the module terminals' current rating and lead to meltdown
of the terminals especially in the last module that carries the most current.
Declination: The angle
in degrees difference between magnetic north, as read on a compass, and
true north. Declination is different on different parts of the globe.
The declination for one's locale can be determined in many ways. Contact
the nearest office of the Forest Service or BLM. Many compasses come with
Deep Cycle: Type of
battery that can be discharged close to its full capacity many times without
damaging the battery.
Depth of Discharge (DOD):
The percent of the rated battery capacity that has been withdrawn. (See
Battery State of Discharge)
Diffuse (Indirect) Radiation:
Light received from the sun after reflection and scattering by the atmosphere
(clouds) and ground. (See Concentrator; Direct Radiation)
Diode: Electronic component
that allows current flow in one direction only; like a check valve for
electricity. (See Blocking Diode; Bypass Diode)
Direct Current (DC):
Electric current flowing in only one direction.
Direct Radiation: Light
received by direct solar rays, unobstructed by clouds, haze, etc. (See
Discharge Rate: How
fast current is withdrawn from a battery. It is usually expressed in hours
. For instance, a C/5 discharge rate is a current that would discharge
the battery in 5 hours. Batteries have less capacity at higher discharge
rates, so their storage capacity is rated at 5 hr., 20 hr, and 100 hr
discharge rates. (See Puekert's Number)
A system of powering an electric grid, not from a few large central power
plants, but from many smaller power systems distributed over a wide area.
Dual Axis Tracking:
Tracking Array that follows the sun by both adjusting both up and down
tilt and side to side motion. The second adjustment may actually pivot
to track azimuth, or simply tilt the modules in both axis.
EMF: 1) Electromagnetic
flux/Electromagnetic field: the magnetic "force field" generated
around a conductor through which a varying current flows (as is the case
with a wire in an AC circuit). Other conductors in close proximity and
parallel to the first conductor will have an electric charge induced in
them. This is the principle (inductance) behind the transformer, in which
two coils of wire are placed next to each other, the EMF of one coil inducing
a voltage in the second coil. (See Inductance; Transformer)
2) Electromotive force: voltage.
Edge of Cloud Effect:
The increase in solar intensity caused by reflected irradiance from nearby
Efficiency: The ratio
of input power (or energy) to output power (or energy) expressed as a
Electricity: The flow
of electrons in a circuit. A circuit must be a circle (a loop) of a conductor
for electrons to flow. These electrons are part of the conductor material,
they don't leave the circuit, and they aren't used up. They flow in one
direction in a DC circuit, and they flow back and forth in an AC circuit.
Electrolyte: The medium
that provides the ion transport mechanism between the positive and negative
electrodes of a battery.
Electrical Grid: The
electrical utility distribution network that connects "on grid"
homes to power plants.
Energy: The capacity
or potential for doing work (e.g. electricity stored in batteries). (See
Energy Density: The
ratio of the energy available from a battery to its volume (Wh/m³)
or weight (Wh/kg).
Equalization (EQ): The
process of mixing the electrolyte in batteries (accomplished by the bubbling
of the electrolyte) by periodically overcharging the batteries for a short
Equinox: Time of year
when day and night are equal, and the sun is directly over the equator.
Occurs twice a year at the Spring equinox (beginning of spring, around
March 21) and the Fall equinox (beginning of autumn, around Sept. 21).
These are the ideal times of year when the angle of an adjustable array
should be changed from Winter tilt to Summer or back.
Tilt Array: A PV array set in at a fixed angle with respect to
Flat-Plate Array: A
PV array that consists of non-concentrating PV modules.
Float Charge: A charge
current to a battery that is equal to or slightly greater than the battery's
self discharge rate. The final stage of a three stage charger in which
voltage is held at the float voltage setting. (See Bulk Charge, Absorption
Flooded Acid Battery:
Most common lead acid battery, uses liquid electrolyte in each cell. Usually
open celled with removable caps to add water periodically. Some sealed
maintenance free versions of flooded acid batteries are used in cars,
but are not suitable for solar power.
Frequency: The number
of repetitions per unit time of a complete waveform, expressed in Hertz
(Hz) (cycles per second). AC electricity in America oscillates 60 times
a second, a frequency of 60 Hz.