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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.
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.
Bypass Diode — A diode
connected across one or more solar cells in a photovoltaic module such that the
diode will conduct if the cell(s) become reverse biased. It protects these solar
cells from thermal destruction in case of total or partial shading of individual
solar cells while other cells are exposed to full light.
Crystalline Silicon — A
type of photovoltaic cell made from a slice of single-crystal silicon or
polycrystalline silicon.
Current at Maximum Power
(Imp) — The current at which maximum power is available from a module.
Days of Storage — The
number of consecutive days the stand-alone system will meet a defined load
without solar energy input. This term is related to system availability.
Disconnect — Switch gear
used to connect or disconnect components in a photovoltaic system.
Full Sun — The amount of
power density in sunlight received at the earth's surface at noon on a clear day
(about 1,000 Watts/square meter).
I-V Curve -is a
graphical presentation of the current versus the voltage from a photovoltaic
device as the load is increased from the short circuit (no load) condition to
the open circuit (maximum voltage) condition. The shape of the curve
characterizes cell performance. ..Of course at short circuit both voltage and
amperage are zero.
Maximum Power Point (MPP) —
The point on the current-voltage (I-V) curve of a module under illumination,
where the product of current and voltage is maximum. For a typical silicon cell,
this is at about 0.45 volts.
Maximum Power Point Tracker
(MPPT) — A power conditioning unit that automatically operates the
photovoltaic generator at its maximum power point under all conditions.
Module Derate Factor — A
factor that lowers the photovoltaic module current to account for field
operating conditions such as dirt accumulation on the module.
Monocrystalline -
A semiconductor (photovoltaic) material composed of a single crystalline
formation.
Multicrystalline — A
semiconductor (photovoltaic) material composed of variously oriented, small,
individual crystals. Sometimes referred to as polycrystalline or semicrystalline.
Multi-Stage Controller —
A charging controller unit that allows different charging currents as the
battery nears full state-of-charge.
Nominal Voltage — A
reference voltage used to describe batteries, modules, or systems (i.e., a
12-volt or 24-volt battery, module, or system).
Normal Operating Cell
Temperature (NOCT) — The estimated temperature of a photovoltaic module when
operating under 800 w/m2 irradiance, 20�C ambient temperature and wind speed of
1 meter per second. NOCT is used to estimate the nominal operating temperature
of a module in its working environment.
Open-Circuit Voltage
(Voc) — The maximum possible voltage across a photovoltaic cell; the voltage
across the cell in sunlight when no current is flowing.
Operating Point — The
current and voltage that a photovoltaic module or array produces when connected
to a load. The operating point is dependent on the load or the batteries
connected to the output terminals of the array.
Panel — See photovoltaic
(PV) panel.
Parallel Connection — A way of joining solar cells or photovoltaic
modules by connecting positive leads together and negative leads together; such
a configuration increases the current, but not the voltage.
Peak Power Current —
Amperes produced by a photovoltaic module or array operating at the voltage of
the I-V curve that will produce maximum power from the module.
Peak Power Point —
Operating point of the I-V (current-voltage) curve for a solar cell or
photovoltaic module where the product of the current value times the voltage
value is a maximum.
Peak Watt — A unit used
to rate the performance of solar cells, modules, or arrays; the maximum nominal
output of a photovoltaic device, in watts (Wp) under standardized test
conditions, usually 1,000 watts per square meter of sunlight with other
conditions, such as temperature specified.
Photovoltaic(s) (PV) —
Pertaining to the direct conversion of light into electricity.
Photon — A particle of
light that acts as an individual unit of energy.
Photovoltaic(s) (PV) — Pertaining to the direct conversion of light into
electricity.
Photovoltaic (PV) Array — An interconnected system of PV modules
that function as a single electricity-producing unit. The modules are assembled
as a discrete structure, with common support or mounting. In smaller systems, an
array can consist of a single module.
Photovoltaic (PV) Cell — The smallest semiconductor element within
a PV module to perform the immediate conversion of light into electrical energy
(direct current voltage and current). Also called a solar cell.
Photovoltaic (PV) Conversion Efficiency — The ratio of the
electric power produced by a photovoltaic device to the power of the sunlight
incident on the device.
Photovoltaic (PV) Device — A solid-state electrical device that
converts light directly into direct current electricity of voltage-current
characteristics that are a function of the characteristics of the light source
and the materials in and design of the device. Solar photovoltaic devices are
made of various semiconductor materials including silicon, cadmium sulfide,
cadmium telluride, and gallium arsenide, and in single crystalline,
multicrystalline, or amorphous forms.
Photovoltaic (PV) Effect — The phenomenon that occurs when
photons, the "particles" in a beam of light, knock electrons loose from the
atoms they strike. When this property of light is combined with the properties
of semiconductors, electrons flow in one direction across a junction, setting up
a voltage. With the addition of circuitry, current will flow and electric power
will be available.
Photovoltaic (PV) Generator — The total of all PV strings of a PV
power supply system, which are electrically interconnected.
Photovoltaic (PV) Module — The smallest environmentally protected,
essentially planar assembly of solar cells and ancillary parts, such as
interconnections, terminals, [and protective devices such as diodes] intended to
generate direct current power under unconcentrated sunlight. The structural
(load carrying) member of a module can either be the top layer (superstrate) or
the back layer (substrate).
Photovoltaic (PV) Panel — often used interchangeably with PV
module (especially in one-module systems), but more accurately used to refer to
a physically connected collection of modules (i.e., a laminate string of modules
used to achieve a required voltage and current).
Photovoltaic (PV) System — A complete set of components for
converting sunlight into electricity by the photovoltaic process, including the
array and balance of system components.
Polycrystalline Silicon —
A material used to make photovoltaic cells, which consist of many crystals
unlike single-crystal silicon.
Silicon (Si) — A
semi-metallic chemical element that makes an excellent semiconductor material
for photovoltaic devices. It crystallizes in face-centered cubic lattice like a
diamond. It's commonly found in sand and quartz (as the oxide).
Single-Crystal Silicon —
Material with a single crystalline formation. Many photovoltaic cells are made
from single-crystal silicon.
Silicon (Si) — A
semi-metallic chemical element that makes an excellent semiconductor material
for photovoltaic devices. It crystallizes in face-centered cubic lattice like a
diamond. It's commonly found in sand and quartz (as the oxide).
Solar Cell — see
photovoltaic (PV) cell.
Solar Constant — The average amount of solar radiation that reaches the
earth's upper atmosphere on a surface perpendicular to the sun's rays; equal to
1353 Watts per square meter or 492 Btu per square foot.
Solar-Grade Silicon —
Intermediate-grade silicon used in the manufacture of solar cells. Less
expensive than electronic-grade silicon.
Sputtering — A process
used to apply photovoltaic semiconductor material to a substrate by a physical
vapor deposition process where high-energy ions are used to bombard elemental
sources of semiconductor material, which eject vapors of atoms that are then
deposited in thin layers on a substrate.
String — A number of
photovoltaic modules or panels interconnected electrically in series to produce
the operating voltage required by the load.
Substrate — The physical material upon which a photovoltaic cell is
applied.
Superstrate — The
covering on the sunny side of a photovoltaic (PV) module, providing protection
for the PV materials from impact and environmental degradation while allowing
maximum transmission of the appropriate wavelengths of the solar spectrum.
System Availability —
The percentage of time (usually expressed in hours per year) when a photovoltaic
system will be able to fully meet the load demand.
System Operating Voltage — The photovoltaic array output voltage under
load. The system operating voltage is dependent on the load or batteries
connected to the output terminals.
Temperature Factors — It
is common for three elements in photovoltaic system sizing to have distinct
temperature corrections: a factor used to decrease battery capacity at cold
temperatures; a factor used to decrease PV module voltage at high temperatures;
and a factor used to decrease the current carrying capability of wire at high
temperatures.
Thick-Crystalline Materials
— Semiconductor material, typically measuring from 200-400 microns thick,
that is cut from ingots or ribbons.
Thin Film — A layer of semiconductor material, such as copper indium
diselenide or gallium arsenide, a few microns or less in thickness, used to make
photovoltaic cells.
Thin Film Photovoltaic Module — A photovoltaic module constructed with
sequential layers of thin film semiconductor materials. See amorphous silicon.
Tilt Angle — The angle at which a photovoltaic array is set to face the
sun relative to a horizontal position. The tilt angle can be set or adjusted to
maximize seasonal or annual energy collection.
Tracking Array — A
photovoltaic (PV) array that follows the path of the sun to maximize the solar
radiation incident on the PV surface. The two most common orientations are (1)
one axis where the array tracks the sun east to west and (2) two-axis tracking
where the array points directly at the sun at all times. Tracking arrays use
both the direct and diffuse sunlight. Two-axis tracking arrays capture the
maximum possible daily energy.
Two-Axis Tracking — A
photovoltaic array tracking system capable of rotating independently about two
axes (e.g., vertical and horizontal).
Voltage at Maximum Power
(Vmp) — The voltage at which maximum power is available from a
photovoltaic module.
Voltage Protection —
Many inverters have sensing circuits that will disconnect the unit from the
battery if input voltage limits are exceeded.
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