A B
C D E F
G H I J
K L M N
O P Q R
S T U V
W Z
Absorber : In a photovoltaic
device, the material that readily absorbs photons to generate
charge carriers (free electrons or
holes).
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.
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Balance of System
: Represents all components and costs other than the photovoltaic
modules/array. It includes
design costs, land, site preparation, system installation,
support structures, power conditioning, operation and maintenance
costs, indirect storage, and related costs.
Band Gap : In a semiconductor,
the energy difference between the highest valence
band and the lowest conduction
band.
Band Gap Energy (Eg) : The amount of energy (in electron
volts) required to free an outer shell electron
from its orbit about the nucleus to a free state, and thus
promote it from the valence to
the conduction level.
Barrier Energy : The energy given up by an electron
in penetrating the cell barrier;
a measure of the electrostatic potential of the barrier.
Base Load : The average amount of electric power that
a utility must supply in any period.
Battery : Two or more electrochemical
cells enclosed in a container and electrically interconnected
in an appropriate series/parallel arrangement to provide the
required operating voltage and current
levels. Under common usage, the term battery also applies
to a single cell if it constitutes the entire electrochemical
storage system.
Battery Available Capacity : The total maximum charge,
expressed in ampere-hours, that
can be withdrawn from a cell or battery
under a specific set of operating conditions including discharge
rate, temperature, initial state
of charge, age, and cut-off voltage.
Battery Capacity : The
maximum total electrical charge, expressed in ampere-hours,
which a battery can deliver to a load
under a specific set of conditions.
Battery Cell : The simplest operating unit in a storage
battery. It consists of one or more
positive electrodes or plates, an
electrolyte that permits ionic
conduction, one or more negative electrodes or plates, separators
between plates of opposite polarity, and a container for all
the above.
Battery Cycle Life : The number of cycles, to a specified
depth of discharge, that
a cell or battery can undergo before
failing to meet its specified capacity or efficiency performance
criteria.
Battery Energy Capacity : The total energy available,
expressed in watt-hours (kilowatt-hours),
which can be withdrawn from a fully charged cell or battery.
The energy capacity of a given cell varies
with temperature, rate, age, and cut-off voltage.
This term is more common to system designers than it is to
the battery industry where capacity
usually refers to ampere-hours.
Battery Energy Storage : Energy storage using electrochemical
batteries. The three main applications
for battery energy storage systems include spinning reserve
at generating stations, load leveling
at substations, and peak shaving on the customer side of the
meter.
Battery Life : The period during which a cell
or battery is capable of operating
above a specified capacity or efficiency performance level.
Life may be measured in cycles and/or years, depending on
the type of service for which the cell or battery is intended.
BIPV (Building-Integrated Photovoltaics) : A term
for the design and integration of photovoltaic
(PV) technology into the building envelope, typically replacing
conventional building materials. This integration may be in
vertical facades, replacing view glass, spandrel glass, or
other facade material; into semitransparent skylight systems;
into roofing systems, replacing traditional roofing materials;
into shading "eyebrows" over windows; or other building envelope
systems.
Blocking Diode : A semiconductor
connected in series with a solar
cell or cells and a storage battery
to keep the battery from discharging
through the cell when there is no output,
or low output, from the solar
cell. It can be thought of as a one-way valve that allows
electrons to flow forwards, but not
backwards.
Boron (B) : The chemical element
commonly used as the dopant in photovoltaic
device or cell material.
Boule : A sausage-shaped, synthetic single-crystal
mass grown in a special furnace, pulled and turned at a rate
necessary to maintain the single-crystal structure during
growth.
Btu (British Thermal Unit) : The amount
of heat required to raise the temperature of one pound of
water one degree Fahrenheit; equal to 252 calories.
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.
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Cadmium (Cd) : A chemical
element used in making certain types of solar
cells and batteries.
Cadmium Telluride (CdTe)
: A polycrystalline thin-film photovoltaic material.
Capacity (C) : See battery
capacity.
Capacity Factor : The ratio of the average load on
(or power output of) an electricity generating unit or system
to the capacity rating of the unit or system over a specified
period of time.
Captive Electrolyte Battery : A battery having an
immobilized electrolyte (gelled
or absorbed in a material).
Cathode : The negative pole or
electrode of an electrolytic cell,
vacuum tube, etc., where electrons
enter (current leaves) the
system; the opposite of an anode.
Cathodic Protection
: A method of preventing oxidation of the exposed metal in
structures by imposing a small electrical voltage between
the structure and the ground.
Cd : see cadmium.
CdTe : see cadmium telluride.
Cell (battery) : A single unit of
an electrochemical device capable of producing direct voltage
by converting chemical energy into electrical energy. A battery
usually consists of several cells electrically connected together
to produce higher voltages. (Sometimes the terms cell and
battery are used interchangeably).
Also see photovoltaic (PV) cell.
Cell Barrier : A very thin
region of static electric charge along the interface of the
positive and negative layers in a photovoltaic
cell. The barrier inhibits the movement of electrons
from one layer to the other, so that higher-energy electrons
from one side diffuse preferentially through it in one direction,
creating a current and thus a voltage
across the cell. Also called depletion
zone or space charge.
Cell Junction : The area
of immediate contact between two layers (positive and negative)
of a photovoltaic cell. The
junction lies at the center of the cell
barrier or depletion zone.
Charge : The process of adding electrical energy to
a battery.
Charge Carrier : A free
and mobile conduction electron or
hole in a semiconductor.
Charge Controller :
A component of a photovoltaic
system that controls the flow of current
to and from the battery to protect
it from over-charge and over-discharge. The charge controller
may also indicate the system operational status.
Charge Factor : A number representing the time in
hours during which a battery can be
charged at a constant current without damage to the battery.
Usually expressed in relation to the total battery
capacity, i.e., C/5 indicates a charge factor of 5 hours.
Related to charge rate.
Charge Rate : The current
applied to a cell or battery
to restore its available capacity.
This rate is commonly normalized by a charge control device
with respect to the rated capacity of the cell
or battery.
Chemical Vapor Deposition (CVD) : A method of depositing
thin semiconductor films used to
make certain types of photovoltaic
devices. With this method, a substrate
is exposed to one or more vaporized compounds, one or more
of which contain desirable constituents. A chemical reaction
is initiated, at or near the substrate surface, to produce
the desired material that will condense on the substrate.
Cleavage of Lateral Epitaxial Films for Transfer (CLEFT)
: A process for making inexpensive Gallium Arsenide (GaAs)
photovoltaic cells in which
a thin film of GaAs is grown atop a thick, single-crystal
GaAs (or other suitable material) substrate
and then is cleaved from the substrate and incorporated into
a cell, allowing the substrate to be reused to grow more thin-film
GaAs.
Cloud Enhancement : The increase in solar intensity
caused by reflected irradiance from
nearby clouds.
Combined Collector : A photovoltaic
device or module that
provides useful heat energy in addition to electricity.
Concentrator : A photovoltaic
module, which includes optical components such as lenses
(Fresnel lens) to direct and concentrate
sunlight onto a solar cell
of smaller area. Most concentrator arrays
must directly face or track the sun. They can increase the
power flux of sunlight hundreds of times.
Conduction Band (or conduction
level) : An energy band in a semiconductor
in which electrons can move freely
in a solid, producing a net transport of charge.
Conductor : The material through
which electricity is transmitted, such as an electrical wire,
or transmission or distribution line.
Contact Resistance : The resistance between metallic
contacts and the semiconductor.
Conversion Efficiency : See photovoltaic
(conversion) efficiency.
Converter : A unit that converts a direct
current (dc) voltage to another dc voltage.
Copper Indium Diselenide (CuInSe2,
or CIS) : A polycrystalline
thin-film photovoltaic material (sometimes
incorporating gallium (CIGS) and/or
sulfur).
Crystalline Silicon : A type of photovoltaic
cell made from a slice of single-crystal
silicon or polycrystalline
silicon.
Current : See electric
current.
Current at Maximum Power (Imp) : The current
at which maximum power is available from a module.
Cutoff Voltage : The voltage
levels (activation) at which the charge
controller disconnects the photovoltaic
array from the battery or the load
from the battery.
Cycle : The discharge and subsequent charge of a battery.
Czochralski Process : A method of growing large size,
high quality semiconductor crystal
by slowly lifting a seed crystal from a molten bath of the
material under careful cooling conditions.
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Dangling Bonds
: A chemical bond associated with an atom on the surface layer
of a crystal. The bond does not join with another atom of
the crystal, but extends in the direction of exterior of the
surface.
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.
DC : See direct current.
DC-to-DC Converter : Electronic circuit to convert
direct current voltages
(e.g., photovoltaic module voltage)
into other levels (e.g., load voltage).
Can be part of a maximum power point tracker.
Deep-Cycle Battery : A battery with large plates that
can withstand many discharges to a low state-of-charge.
Deep Discharge : Discharging a battery to 20% or less
of its full charge capacity.
Depth of Discharge (DOD)
: The ampere-hours removed from
a fully charged cell or battery,
expressed as a percentage of rated capacity. For example,
the removal of 25 ampere-hours from a fully charged 100 ampere-hours
rated cell results in a 25% depth of discharge. Under certain
conditions, such as discharge rates lower than that used to
rate the cell, depth of discharge can exceed 100%.
Dendrite : A slender threadlike
spike of pure crystalline material, such as silicon.
Dendritic Web Technique : A method for making sheets
of polycrystalline silicon
in which silicon dendrites are slowly
withdrawn from a melt of silicon whereupon a web of silicon
forms between the dendrites and solidifies as it rises from
the melt and cools.
Depletion Zone : Same as
cell barrier. The term derives
from the fact that this microscopically thin region is depleted
of charge carriers (free electrons
and hole).
Design Month : The month having the combination of
insolation and load
that requires the maximum energy from the photovoltaic
array.
Diffuse Insolation
: Sunlight received indirectly as a result of scattering due
to clouds, fog, haze, dust, or other obstructions in the atmosphere.
Opposite of direct insolation.
Diffuse Radiation : Radiation received from the sun
after reflection and scattering by the atmosphere and ground.
Diffusion Furnace : Furnace used to make junctions
in semiconductors by diffusing
dopant atoms into the surface of the material.
Diffusion Length : The mean distance a free electron
or hole moves before recombining with
another hole or electron.
Diode : An electronic device that
allows current to flow in one direction only. See blocking
diode and bypass
diode.
Direct Beam Radiation : Radiation
received by direct solar rays. Measured by a pyrheliometer
with a solar aperture of 5.7° to transcribe the solar disc.
Direct Current (DC) : A
type of electricity transmission and distribution by which
electricity flows in one direction through the conductor,
usually relatively low voltage and
high current. To be used for typical 120 volt or 220 volt
household appliances, DC must be converted to alternating
current, its opposite.
Direct Insolation :
Sunlight falling directly upon a collector. Opposite of diffuse
insolation.
Discharge : The withdrawal of
electrical energy from a battery.
Discharge Factor : A
number equivalent to the time in hours during which a battery
is discharged at constant current usually expressed as a percentage
of the total battery capacity, i.e., C/5 indicates a discharge
factor of 5 hours. Related to discharge
rate.
Discharge Rate : The rate,
usually expressed in amperes or time,
at which electrical current
is taken from the battery.
Disconnect : Switch gear used to connect or disconnect
components in a photovoltaic
system.
Distributed Energy Resources (DER) : A variety of
small, modular power-generating technologies that can be combined
with energy management and storage systems and used to improve
the operation of the electricity delivery system, whether
or not those technologies are connected to an electricity
grid.
Distributed Generation : A popular term for localized
or on-site power generation.
Distributed Power : Generic term for any power supply
located near the point where the power is used. Opposite of
central power. See stand-alone
systems.
Distributed Systems : Systems that are installed at
or near the location where the electricity is used, as opposed
to central systems that supply electricity to grids.
A residential photovoltaic
system is a distributed system.
Donor : In a photovoltaic
device, an n-type dopant,
such as phosphorus, that puts an
additional electron into an energy
level very near the conduction
band; this electron is easily exited into the conduction
band where it increases the electrical conductivity over than
of an undoped semiconductor.
Donor Level : The level that donates conduction
electrons to the system.
Dopant : A chemical element (impurity)
added in small amounts to an otherwise pure semiconductor
material to modify the electrical properties of the material.
An n-dopant introduces more electrons. A p-dopant creates
electron vacancies (holes).
Doping : The addition of dopants
to a semiconductor.
Downtime : Time when the photovoltaic system cannot
provide power for the load. Usually expressed
in hours per year or that percentage.
Dry Cell : A cell (battery) with
a captive electrolyte. A primary
battery that cannot be recharged.
Duty Cycle : The ratio of active time to total time.
Used to describe the operating regime of appliances or loads
in photovoltaic systems.
Duty Rating : The amount of
time an inverter (power conditioning
unit) can produce at full rated power.
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Edge-Defined Film-Fed Growth (EFG) : A
method for making sheets of polycrystalline
silicon for photovoltaic
devices in which molten silicon is drawn upward by capillary
action through a mold.
Electric Circuit : The path followed by electrons
from a power source (generator or battery), through an electrical
system, and returning to the source.
Electric Current : The
flow of electrical energy (electricity) in a conductor,
measured in amperes.
Electrical grid : An integrated system
of electricity distribution, usually covering a large area.
Electricity : Energy resulting from the flow of charge
particles, such as electrons or ions.
Electrochemical Cell :
A device containing two conducting electrodes,
one positive and the other negative, made of dissimilar materials
(usually metals) that are immersed in a chemical solution
(electrolyte) that transmits positive
ions from the negative to the positive
electrode and thus forms an electrical charge. One or more
cells constitute a battery.
Electrode : A conductor that
is brought in conducting contact with a ground.
Electrodeposition : Electrolytic process in which
a metal is deposited at the cathode
from a solution of its ions.
Electrolyte : A nonmetallic
(liquid or solid) conductor that carries current
by the movement of ions (instead of electrons)
with the liberation of matter at the electrodes
of an electrochemical cell.
Electron : An elementary particle
of an atom with a negative electrical charge and a mass of
1/1837 of a proton; electrons surround the positively charged
nucleus of an atom and determine the chemical properties of
an atom. The movement of electrons in an electrical conductor
constitutes an electric current.
Electron Volt (eV) : The
amount of kinetic energy gained by an electron when accelerated
through an electric potential difference of 1 Volt; equivalent
to 1.603 x 10^-19; a unit of energy or work.
Energy : The capability of doing work; different forms
of energy can be converted to other forms, but the total amount
of energy remains the same.
Energy Audit : A survey that shows how much energy
used in a home, which helps find ways to use less energy.
Energy Contribution Potential : Recombination
occurring in the emitter region of a photovoltaic
cell.
Energy Density : The ratio of available energy per
pound; usually used to compare storage batteries.
Energy Levels : The energy represented by an electron
in the band model of a substance.
Epitaxial Growth : The growth of one crystal on the
surface of another crystal. The growth of the deposited crystal
is oriented by the lattice structure
of the original crystal.
Equalization : The process
of restoring all cells in a battery
to an equal state-of-charge.
Some battery types may require a complete discharge as a part
of the equalization process.
Equalization Charge : The process of mixing the electrolyte
in batteries by periodically overcharging the batteries for
a short time.
Equalizing Charge : A continuation of normal battery
charging, at a voltage level slightly
higher than the normal end-of-charge voltage, in order to
provide cell equalization within
a battery.
Equinox : The two times of the year when the sun crosses
the equator and night and day are of equal length; usually
occurs on March 21st (spring equinox) and September 23 (fall
equinox).
Extrinsic Semiconductor : The product of doping
a pure semiconductor.
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Fermi Level :
Energy level at which the probability of finding an electron
is one-half. In a metal, the Fermi level is very near the
top of the filled levels in the partially filled valence
band. In a semiconductor,
the Fermi level is in the band gap.
Fill Factor : The ratio of a photovoltaic
cell's actual power to its power if both current and voltage
were at their maxima. A key characteristic in evaluating cell
performance.
Fixed Tilt Array : A photovoltaic
array set in at a fixed angle with respect to horizontal.
Flat-Plate
Array : A photovoltaic
(PV) array that consists of non-concentrating PV
modules.
Flat-Plate Module :
An arrangement of photovoltaic
cells or material mounted on a rigid flat surface with
the cells exposed freely to incoming sunlight.
Flat-Plate Photovoltaics (PV) : A PV array or module
that consists of nonconcentrating elements. Flat-plate arrays
and modules use direct and
diffuse sunlight, but if the array is fixed in position, some
portion of the direct sunlight is lost because of oblique
sun-angles in relation to the array.
Float Charge : The voltage
required to counteract the self-discharge
of the battery at a certain temperature.
Float Life : The number of years that a battery
can keep its stated capacity when it is kept at float charge.
Float Service : A battery operation in which the battery
is normally connected to an external current source; for instance,
a battery charger which supplies the battery load< under
normal conditions, while also providing enough energy input
to the battery to make up for its internal quiescent losses,
thus keeping the battery always up to full power and ready
for service.
Float-Zone Process : A method of growing a large-size,
high-quality crystal whereby coils heat a polycrystalline
ingot placed atop a single-crystal seed. As the coils are
slowly raised the molten interface beneath the coils becomes
single crystal.
Float-Zone Process : In reference to solar photovoltaic
cell manufacture, a method of growing a large-size, high-quality
crystal whereby coils heat a polycrystalline ingot placed
atop a single-crystal seed. As the coils are slowly raised
the molten interface beneath the coils becomes a single crystal.
Frequency : The number of repetitions
per unit time of a complete waveform, expressed in Hertz (Hz).
Frequency Regulation : This indicates the variability
in the output frequency. Some loads
will switch off or not operate properly if frequency variations
exceed 1%.
Fresnel Lens : An optical
device that focuses light like a magnifying glass; concentric
rings are faced at slightly different angles so that light
falling on any ring is focused to the same point.
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).
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Ga : See gallium.
GaAs : See gallium arsenide.
Gallium (Ga) : A chemical element,
metallic in nature, used in making certain kinds of solar
cells and semiconductor devices.
Gallium Arsenide (GaAs)
: A crystalline, high-efficiency compound used to make certain
types of solar cells and
semiconductor material.
Gassing : The evolution of gas
from one or more of the electrodes
in the cells of a battery.
Gassing commonly results from local action self-discharge
or from the electrolysis of water in the electrolyte
during charging.
Gassing Current : The portion of charge current
that goes into electrolytical production of hydrogen and oxygen
from the electrolytic liquid. This current increases with
increasing voltage and temperature.
Gel-Type Battery : Lead-acid battery
in which the electrolyte is composed
of a silica gel matrix.
Gigawatt (GW) : A unit of power equal to 1 billion
Watts; 1 million kilowatts, or 1,000 megawatts.
Grid : See electrical grid.
Grid-Connected System
: A solar electric or photovoltaic
(PV) system in which the PV
array acts like a central generating plant, supplying
power to the grid.
Grid-Interactive System : Same as grid-connected
system.
Grid Lines : Metallic contacts fused to the surface
of the solar cell to provide
a low resistance path for electrons
to flow out to the cell interconnect wires.
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Harmonic Content
: The number of frequencies in the output waveform
in addition to the primary frequency
(50 or 60 Hz.). Energy in these harmonic frequencies is lost
and may cause excessive heating of the load.
Heterojunction : A region
of electrical contact between two different materials.
High Voltage Disconnect
: The voltage at which a charge
controller will disconnect the photovoltaic
array from the batteries to prevent overcharging.
High Voltage Disconnect Hysteresis : The voltage
difference between the high
voltag disconnect set point and the voltage at which the
full photovoltaic array
current will be reapplied.
Hole : The vacancy where an electron
would normally exist in a solid; behaves like a positively
charged particle.
Homojunction : The region between an n-layer and a
p-layer in a single material, photovoltaic cell.
Hybrid System : A solar electric
or photovoltaic system
that includes other sources of electricity generation, such
as wind or diesel generators.
Hydrogenated Amorphous Silicon : Amorphous
silicon with a small amount of incorporated hydrogen.
The hydrogen neutralizes dangling bonds in the amorphous silicon,
allowing charge carriers to
flow more freely.
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Incident Light : Light that shines onto
the face of a solar cell
or module.
Indium Oxide : A wide band
gap semiconductor that can be
heavily doped with tin to make a highly
conductive, transparent thin film.
Often used as a front contact or one component of a heterojunction
solar cell.
Infrared Radiation : Electromagnetic radiation whose
wavelengths lie in the range from 0.75 micrometer to 1000
micrometers; invisible long wavelength radiation (heat) capable
of producing a thermal or photovoltaic
effect, though less effective than visible light.
Input Voltage : This is determined by the total power
required by the alternating
current loads and the voltage of any direct
current loads. Generally, the larger the load,
the higher the inverter input voltage.
This keeps the current at
levels where switches and other components are readily available.
Insolation : The solar power
density incident on a surface of stated area and orientation,
usually expressed as Watts per square
meter or Btu per square foot per hour.
See diffuse insolation and
direct insolation.
Interconnect : A conductor
within a module or other
means of connection that provides an electrical interconnection
between the solar cells.
Intrinsic Layer : A layer of semiconductor
material, used in a photovoltaic
device, whose properties are essentially those of the
pure, undoped, material.
Intrinsic Semiconductor
: An undoped semiconductor.
Inverter : A device that converts
direct current electricity to
alternating current either
for stand-alone systems or to supply power to an electricity
grid.
Ion : An electrically charged atom
or group of atoms that has lost or gained electrons;
a loss makes the resulting particle positively charged; a
gain makes the particle negatively charged.
Irradiance : The direct, diffuse,
and reflected solar radiation that strikes a surface. Usually
expressed in kilowatts per square
meter. Irradiance multiplied by time equals insolation.
ISPRA Guidelines : Guidelines for the assessment of
photovoltaic power plants, published
by the Joint Research Centre of the Commission of the European
Communities, Ispra, Italy.
I-Type Semiconductor : Semiconductor
material that is left intrinsic, or undoped so that the concentration
of charge carriers is characteristic of the material itself
rather than of added impurities.
I-V Curve : 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.
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Joule : A metric unit
of energy or work; 1 joule per second equals 1 watt
or 0.737 foot-pounds; 1 Btu equals 1,055
joules.
Junction : A region
of transition between semiconductor
layers, such as a p/n junction, which goes from a region that
has a high concentration of acceptors (p-type) to one that
has a high concentration of donors (n-type).
Junction Box : A photovoltaic
(PV) generator junction box is an enclosure on the module
where PV strings are electrically connected and where protection
devices can be located, if necessary.
Junction Diode : A semiconductor
device with a junction and a built-in potential that passes
current better in one direction than the other. All solar
cells are junction diodes.
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Kilowatt (kW) : A
standard unit of electrical power equal to 1000 watts,
or to the energy consumption at a rate of 1000 joules
per second.
Kilowatt-Hour (kWh) : 1,000
thousand watts acting over a period of 1 hour. The kWh is
a unit of energy. 1 kWh=3600 kJ.
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Langley (L) : Unit of solar irradiance.
One gram calorie per square centimeter. 1 L = 85.93 kwh/m2.
Lattice : The regular periodic
arrangement of atoms or molecules in a crystal of semiconductor
material.
Lead-Acid Battery : A general category that includes
batteries with plates made of pure lead, lead-antimony, or
lead-calcium immersed in an acid electrolyte.
Life : The period during which a system is capable
of operating above a specified performance level.
Life-Cycle Cost : The estimated cost of owning and
operating a photovoltaic system
for the period of its useful life.
Light-Induced Defects : Defects, such as dangling
bonds, induced in an amorphous
silicon semiconductor upon initial exposure to light.
Light Trapping : The trapping of light inside a semiconductor
material by refracting and reflecting the light at critical
angles; trapped light will travel further in the material,
greatly increasing the probability of absorption and hence
of producing charge carriers.
Line-Commutated Inverter : An inverter that is tied
to a power grid or line. The commutation
of power (conversion from direct
current to alternating
current) is controlled by the power line, so that, if
there is a failure in the power grid, the photovoltaic
system cannot feed power into the line.
Liquid Electrolyte Battery : A battery containing
a liquid solution of acid and water. Distilled water may be
added to these batteries to replenish the electrolyte
as necessary. Also called a flooded battery because the plates
are covered with the electrolyte.
Load : The demand on an energy producing
system; the energy consumption or requirement of a piece or
group of equipment. Usually expressed in terms of amperes
or watts in reference to electricity.
Load Circuit : The wire, switches, fuses, etc. that
connect the load to the power source.
Load Current (A) : The current required by the electrical
device.
Load Resistance : The resistance presented by the
load. See resistance.
Low Voltage Cutoff (LVC) : The voltage
level at which a charge controller
will disconnect the load from the battery.
Low Voltage Disconnect : The voltage
at which a charge controller
will disconnect the load from the batteries
to prevent over-discharging.
Low Voltage Disconnect Hysteresis : The voltage
difference between the low voltage disconnect set point and
the voltage at which the load will be
reconnected.
Low Voltage Warning : A warning buzzer or light that
indicates the low battery voltage set
point has been reached.
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Maintenance-Free Battery : A sealed battery
to which water cannot be added to maintain electrolyte
level.
Majority Carrier : Current carriers (either free electrons
or holes) that are in excess in a specific
layer of a semiconductor material
(electrons in the n-layer, holes in the p-layer) of a cell.
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)
: Means of a power conditioning unit that automatically operates
the photovoltaic generator at its maximum power
point under all conditions.
Maximum Power Tracking : Operating a photovoltaic
array at the peak power point
of the array's I-V curve where maximum power
is obtained. Also called peak power tracking.
Megawatt (MW) : 1,000 kilowatts,
or 1 million watts; standard measure of
electric power plant generating capacity.
Megawatt-Hour : 1,000 kilowatt-hours
or 1 million watt-hours.
Microgroove : A small groove scribed into the surface
of a solar cell, which is
filled with metal for contacts.
Minority Carrier : A
current carrier, either an electron
or a hole, that is in the minority in
a specific layer of a semiconductor
material; the diffusion of minority carriers under the action
of the cell junction voltage
is the current in a photovoltaic
device.
Minority Carrier Lifetime : The average time a minority
carrier exists before recombination.
Modified Sine Wave : A waveform
that has at least three states (i.e., positive, off, and negative).
Has less harmonic content
than a square wave.
Modularity : The use of multiple inverters
connected in parallel to service different loads.
Module : See photovoltaic
(PV) module.
Module Derate Factor : A factor that lowers the photovoltaic
module current to account
for field operating conditions such as dirt accumulation on
the module.
Monolithic : Fabricated as a single structure.
Movistor : Metal Oxide Varistor. Used to protect electronic
circuits from surge currents such as those produced by lightning.
Multicrystalline : A
semiconductor (photovoltaic)
material composed of variously oriented, small, individual
crystals. Sometimes referred to as polycrystalline or semicrystalline.
Multijunction Device
: A high-efficiency photovoltaic
device containing two or more cell junctions,
each of which is optimized for a particular part of the solar
spectrum.
Multi-Stage Controller : A charging
controller unit that allows different charging currents
as the battery nears full state_of_charge.
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National Electrical Code (NEC)
: Contains guidelines for all types of electrical installations.
The 1984 and later editions of the NEC contain Article 690,
"Solar Photovoltaic Systems" which should be followed when
installing a PV system.
National Electrical Manufacturers Association
(NEMA) : This organization sets standards for some
non-electronic products like junction boxes.
NEC : See National Electrical Code.
NEMA : See National Electrical Manufacturers
Association.
Nickel Cadmium Battery : A battery containing nickel
and cadmium plates and an alkaline electrolyte.
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.
N-Type : Negative semiconductor
material in which there are more electrons
than holes; current
is carried through it by the flow of electrons.
N-Type Semiconductor
: A semiconductor produced by
doping an intrinsic
semiconductor with an electron-donor
impurity (e.g., phosphorus in silicon).
N-Type Silicon : Silicon material
that has been doped with a material
that has more electrons in its atomic
structure than does silicon.
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Ohm : A measure of the
electrical resistance of a material equal to the resistance
of a circuit in which the potential difference of 1 volt produces
a current of 1 ampere.
One-Axis Tracking : A system capable of rotating about
one axis.
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.
Orientation : Placement with respect to the cardinal
directions, N, S, E, W; azimuth is
the measure of orientation from north.
Outgas : See gassing.
Overcharge : Forcing current
into a fully charged battery. The battery
will be damaged if overcharged for a long period.
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Packing Factor : The ratio of array
area to actual land area or building envelope area for a system;
or, the ratio of total solar
cell area to the total module
area, for a module.
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.
Passivation : A chemical reaction that eliminates
the detrimental effect of electrically reactive atoms on a
solar cell's surface.
Peak Demand/Load : The maximum
energy demand or load in a specified time period.
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 Power Tracking : see maximum power
tracking.
Peak Sun Hours : The equivalent
number of hours per day when solar irradiance
averages 1,000 w/m2. For example, six peak sun hours means
that the energy received during total daylight hours equals
the energy that would have been received had the irradiance
for six hours been 1,000 w/m2.
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.
Phosphorous (P) : A chemical
element used as a dopant in making n-type
semiconductor layers.
Photocurrent : An electric current induced by radiant
energy.
Photoelectric Cell : A device for measuring light
intensity that works by converting light falling on, or reach
it, to electricity, and then measuring the current; used in
photometers.
Photoelectrochemical Cell : A type of photovoltaic
device in which the electricity induced in the cell is
used immediately within the cell to produce a chemical, such
as hydrogen, which can then be withdrawn for use.
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.
Photovoltaic-Thermal (PV/T) System : A photovoltaic
system that, in addition to converting sunlight into electricity,
collects the residual heat energy and delivers both heat and
electricity in usable form. Also called a total energy system.
Physical Vapor Deposition
: A method of depositing thin semiconductor
photovoltaic films. With this method, physical processes,
such as thermal evaporation or bombardment of ions, are used
to deposit elemental semiconductor
material on a substrate.
P-I-N : A semiconductor photovoltaic
(PV) device structure that layers an intrinsic semiconductor
between a p-type semiconductor and an n-type
semiconductor; this structure is most often used with
amorphous silicon PV devices.
Plates : A metal plate, usually lead or lead compound,
immersed in the electrolyte in
a battery.
P/N : A semiconductor
photovoltaic device structure
in which the junction is formed between
a p-type layer and an n-type layer.
Pocket Plate : A plate for a battery
in which active materials are held in a perforated metal pocket.
Point-Contact Cell : A high efficiency silicon
photovoltaic concentrator cell
that employs light trapping techniques and point-diffused
contacts on the rear surface for current collection.
Polycrystalline : See Multicrystalline.
Polycrystalline Silicon
: A material used to make photovoltaic
cells, which consist of many crystals unlike single-crystal
silicon.
Power Conditioning : The process of modifying the
characteristics of electrical power (for e.g., inverting direct
current to alternating
current).
Power Conditioning Equipment : Electrical equipment,
or power electronics, used to convert power from a photovoltaic
array into a form suitable for subsequent use. A collective
term for inverter, converter, battery
charge regulator, and blocking diode.
Power Conversion Efficiency : The ratio of output
power to input power of the inverter.
Power Density : The ratio of the power available from
a battery to its mass (W/kg) or volume (W/l).
Power Factor (PF) : The ratio
of actual power being used in a circuit, expressed in watts
or kilowatts, to the power that is
apparently being drawn from a power source, expressed in volt-amperes
or kilovolt-amperes.
Primary Battery : A battery
whose initial capacity cannot be restored
by charging.
Projected Area : The net south-facing glazing area
projected on a vertical plane.
P-Type Semiconductor : A semiconductor in which holes
carry the current; produced by doping
an intrinsic semiconductor
with an electron acceptor
impurity (e.g., boron in silicon).
Pulse-Width-Modulated (PWM) Wave Inverter : A type
of power inverter that produce a high
quality (nearly sinusoidal) voltage, at minimum current harmonics.
PV : See photovoltaic(s).
Pyranometer : An instrument used for measuring global
solar irradiance.
Pyrheliometer : An instrument used for measuring direct
beam solar irradiance. Uses
an aperture of 5.7° to transcribe the solar disc.
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Quad : One quadrillion Btu
(1,000,000,000,000,000 Btu).
Qualification Test : A procedure applied to a selected
set of photovoltaic modules
involving the application of defined electrical, mechanical,
or thermal stress in a prescribed manner and amount. Test
results are subject to a list of defined requirements.
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Rated Battery Capacity : The term used
by battery manufacturers to indicate the maximum amount of
energy that can be withdrawn from a battery under specified
discharge rate and temperature. See battery
capacity.
Rated Module Current (A) : The current output of a
photovoltaic module measured
at standard test conditions of 1,000 w/m2
and 25�C cell temperature.
Rated Power : Rated power of the inverter.
However, some units can not produce rated power continuously.
See duty rating.
Reactive Power : The sine of the phase angle between
the current and voltage
waveforms in an alternating
current system. See power factor.
Recombination : The action
of a free electron falling back into a hole.
Recombination processes are either radiative, where the energy
of recombination results in the emission of a photon, or nonradiative,
where the energy of recombination is given to a second electron
which then relaxes back to its original energy by emitting
phonons. Recombination can take place in the bulk of the semiconductor,
at the surfaces, in the junction region, at defects, or between
interfaces.
Rectifier : A device that converts alternating
current to direct current.
See inverter.
Regulator : Prevents overcharging of batteries by
controlling charge cycle-usually adjustable to conform to
specific battery needs.
Remote Systems : See stand-alone
systems.
Reserve Capacity : The amount of generating capacity
a central power system must maintain to meet peak
loads.
Resistance (R) : The property
of a conductor, which opposes the
flow of an electric current
resulting in the generation of heat in the conducting material.
The measure of the resistance of a given conductor is the
electromotive force needed for a unit current flow. The unit
of resistance is ohms.
Resistive Voltage Drop : The voltage developed across
a cell by the current
flow through the resistance of the cell.
Reverse Current Protection : Any method of preventing
unwanted current flow from
the battery to the photovoltaic
array (usually at night). See blocking
diode.
Ribbon (Photovoltaic) Cells : A type of photovoltaic
device made in a continuous process of pulling material
from a molten bath of photovoltaic material, such as silicon,
to form a thin sheet of material.
RMS : See root mean square.
Root Mean Square (RMS) : The square
root of the average square of the instantaneous values of
an ac output. For a sine wave the RMS value is 0.707 times
the peak value. The equivalent value of alternating
current, I, that will produce the same heating in a conductor
with resistance, R, as a dc current of value I.
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Sacrificial Anode : A piece of metal buried
near a structure that is to be protected from corrosion. The
metal of the sacrificial anode is intended
to corrode and reduce the corrosion of the protected structure.
Satellite Power System (SPS) : Concept for providing
large amounts of electricity for use on the Earth from one
or more satellites in geosynchronous Earth orbit. A very large
array of solar cells on each satellite would provide electricity,
which would be converted to microwave energy and beamed to
a receiving antenna on the ground. There, it would be reconverted
into electricity and distributed the same as any other centrally
generated power, through a grid.
Schottky Barrier : A cell
barrier established as the interface between a semiconductor,
such as silicon, and a sheet of metal.
Scribing : The cutting of a grid pattern of grooves
in a semiconductor material, generally for the purpose of
making interconnections.
Sealed Battery : A battery with a captive electrolyte
and a resealing vent cap, also called a valve-regulated battery.
Electrolyte cannot be added.
Seasonal Depth of Discharge : An adjustment factor
used in some system sizing procedures which "allows" the battery
to be gradually discharged over a 30-90 day period of poor
solar insolation. This factor results
in a slightly smaller photovoltaic
array.
Secondary Battery : A battery
that can be recharged.
Self-Discharge : The rate
at which a battery, without a load,
will lose its charge.
Semiconductor : Any material
that has a limited capacity for conducting an electric current.
Certain semiconductors, including silicon,
gallium arsenide, copper
indium diselenide, and cadmium
telluride, are uniquely suited to the photovoltaic
conversion process.
Semicrystalline : See Multicrystalline.
Series Connection : A way of joining photovoltaic
cells by connecting positive leads to negative leads;
such a configuration increases the voltage.
Series Controller : A charge
controller that interrupts the charging current by open-circuiting
the photovoltaic (PV) array.
The control element is in series with the PV array and battery.
Series Regulator : Type of battery
charge regulator where the charging current
is controlled by a switch connected in series with the photovoltaic
module or array.
Series Resistance : Parasitic resistance to current
flow in a cell due to mechanisms such
as resistance from the bulk of the semiconductor
material, metallic contacts, and interconnections.
Shallow-Cycle Battery : A battery with small plates
that cannot withstand many discharges to a low state-of-charge.
Shelf Life of Batteries : The length of time, under
specified conditions, that a battery
can be stored so that it keeps its guaranteed capacity.
Short-Circuit Current (Isc) : The current
flowing freely through an external circuit that has no load
or resistance; the maximum current possible.
Shunt Controller : A charge
controller that redirects or shunts the charging current
away from the battery. The controller requires a large heat
sink to dissipate the current from the short-circuited photovoltaic
array. Most shunt controllers are for smaller systems
producing 30 amperes or less.
Shunt Regulator : Type of a battery
charge regulator where the charging current is controlled
by a switch connected in parallel with the photovoltaic
(PV) generator. Shorting the PV generator prevents overcharging
of the battery.
Siemens Process : A commercial method of making purified
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).
Sine Wave : A waveform
corresponding to a single-frequency periodic oscillation that
can be mathematically represented as a function of amplitude
versus angle in which the value of the curve at any point
is equal to the sine of that angle.
Sine Wave Inverter : An inverter that produces utility-quality,
sine wave power forms.
Single-Crystal Material
: A material that is composed of a single crystal or a few
large crystals.
Single-Crystal Silicon : Material with a single crystalline
formation. Many photovoltaic
cells are made from single-crystal silicon.
Single-Stage Controller : A charge
controller that redirects all charging current as the
battery nears full state-of-charge.
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 Cooling : The use of solar thermal energy or
solar electricity to power a cooling appliance. Photovoltaic
systems can power evaporative coolers ("swamp" coolers),
heat-pumps, and air conditioners.
Solar Energy : Electromagnetic energy transmitted
from the sun (solar radiation). The amount that reaches the
earth is equal to one billionth of total solar energy generated,
or the equivalent of about 420 trillion kilowatt-hours.
Solar-Grade Silicon : Intermediate-grade silicon
used in the manufacture of solar
cells. Less expensive than electronic-grade silicon.
Solar Insolation : See insolation.
Solar Irradiance : See irradiance.
Solar Noon : The time of the day, at a specific location,
when the sun reaches its highest, apparent point in the sky;
equal to true or due, geographic south.
Solar Panel : See photovoltaic
(PV) panel.
Solar Resource : The amount of solar insolation
a site receives, usually measured in kWh/m2/day, which is
equivalent to the number of peak
sun hours.
Solar Spectrum : The total
distribution of electromagnetic radiation emanating from the
sun. The different regions of the solar spectrum are described
by their wavelength range. The visible region extends from
about 390 to 780 nanometers (a nanometer is one billionth
of one meter). About 99 percent of solar radiation is contained
in a wavelength region from 300 nm (ultraviolet) to 3,000
nm (near-infrared). The combined radiation in the wavelength
region from 280 nm to 4,000 nm is called the broadband, or
total, solar radiation.
Solar Thermal Electric Systems : Solar energy conversion
technologies that convert solar energy to electricity, by
heating a working fluid to power a turbine that drives a generator.
Examples of these systems include central receiver systems,
parabolic dish, and solar trough.
Space Charge : See cell barrier.
Specific Gravity : The ratio of the weight of the
solution to the weight of an equal volume of water at a specified
temperature. Used as an indicator of battery state-of-charge.
Spinning Reserve : Electric power plant or utility
capacity on-line and running at low power in excess of actual
load.
Split-Spectrum Cell : A
compound photovoltaic device
in which sunlight is first divided into spectral regions by
optical means. Each region is then directed to a different
photovoltaic cell optimized
for converting that portion of the spectrum into electricity.
Such a device achieves significantly greater overall conversion
of incident sunlight into electricity. See mulitjunction
device.
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.
Square Wave : A waveform
that has only two states, (i.e., positive or negative). A
square wave contains a large number of harmonics.
Square Wave Inverter : A type of inverter that produces
square wave output. It consists
of a direct current source,
four switches, and the load. The switches
are power semiconductors that
can carry a large current
and withstand a high voltage rating.
The switches are turned on and off at a correct sequence,
at a certain frequency.
Staebler-Wronski Effect : The tendency of the sunlight
to electricity conversion efficiency of amorphous
silicon photovoltaic devices
to degrade (drop) upon initial exposure to light.
Stand-Alone System
: An autonomous or hybrid photovoltaic system
not connected to a grid. May or may not
have storage, but most stand-alone systems require batteries
or some other form of storage.
Stand-Off Mounting : Technique for mounting a photovoltaic
array on a sloped roof, which involves mounting the modules
a short distance above the pitched roof and tilting them to
the optimum angle.
Standard Reporting Conditions (SRC) : A fixed set
of conditions (including meteorological) to which the electrical
performance data of a photovoltaic
module are translated from the set of actual test conditions.
Standard Test Conditions (STC) : Conditions
under which a module is
typically tested in a laboratory.
Standby Current : This is the amount of current (power)
used by the inverter when no load
is active (lost power). The efficiency of the inverter is
lowest when the load demand is low.
Starved Electrolyte Cell : A battery
containing little or no free fluid electrolyte.
State-of-Charge (SOC)
: The available capacity remaining in the battery,
expressed as a percentage of the rated capacity.
Storage Battery : A device capable of transforming
energy from electric to chemical form and vice versa. The
reactions are almost completely reversible. During discharge,
chemical energy is converted to electric energy and is consumed
in an external circuit or apparatus.
Stratification : A condition that occurs when the
acid concentration varies from top to bottom in the battery
electrolyte. Periodic, controlled
charging at voltages that produce gassing
will mix the electrolyte. See equalization.
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.
Subsystem : Any one of several components in a photovoltaic
system (i.e., array, controller,
batteries, inverter,
load).
Sulfation : A condition that afflicts unused and discharged
batteries; large crystals of lead sulfate
grow on the plate, instead of the usual tiny crystals, making
the battery extremely difficult to recharge.
Superconducting Magnetic Energy Storage (SMES) : SMES
technology uses the superconducting characteristics of low-temperature
materials to produce intense magnetic fields to store energy.
It has been proposed as a storage option to support large-scale
use of photovoltaics as a means
to smooth out fluctuations in power generation.
Superconductivity : The abrupt and large increase
in electrical conductivity exhibited by some metals as the
temperature approaches absolute zero.
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.
Surge Capacity : The maximum power, usually 3-5 times
the rated power, that can be provided over a short time.
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.
System Storage : See battery
capacity.
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Tare Loss : Loss caused by a charge
controller. One minus tare loss, expressed as a percentage,
is equal to the controller efficiency.
Temperature Compensation : A circuit that adjusts
the charge controller activation
points depending on battery temperature. This feature is recommended
if the battery temperature is expected to vary more than ±5°C
from ambient temperature.
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.
Thermophotovoltaic Cell (TPV) : A device where sunlight
concentrated onto a absorber heats
it to a high temperature, and the thermal radiation emitted
by the absorber is used as the energy source for a photovoltaic
cell that is designed to maximize conversion
efficiency at the wavelength of the thermal radiation.
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.
Tin Oxide : A wide band-gap semiconductor
similar to indium oxide; used
in heterojunction solar cells
or to make a transparent conductive film, called NESA glass
when deposited on glass.
Total AC Load Demand : The sum of the alternating
current loads. This value is important when selecting
an inverter.
Total Harmonic Distortion : The measure of closeness
in shape between a waveform and it's fundamental component.
Total Internal Reflection : The trapping of light
by refraction and reflection at critical angles inside a semiconductor
device so that it cannot escape the device and must be eventually
absorbed by the semiconductor.
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.
Transformer : An electromagnetic device that changes
the voltage of alternating
current electricity.
Tray Cable (TC) - may be used for interconnecting
balance-of-systems.
Trickle Charge : A charge at a low rate, balancing
through self-discharge losses,
to maintain a cell or battery
in a fully charged condition.
Two-Axis Tracking : A photovoltaic
array tracking system capable of rotating independently
about two axes (e.g., vertical and horizontal).
Tunneling : Quantum mechanical concept whereby an
electron is found on the opposite
side of an insulating barrier without having passed through
or around the barrier.
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Ultraviolet : Electromagnetic radiation
in the wavelength range of 4 to 400 nanometers.
Underground Feeder (UF) : May be used for photovoltaic
array wiring if sunlight resistant coating is specified;
can be used for interconnecting balance-of-system
components but not recommended for use within battery enclosures.
Underground Service Entrance (USE) : May be used within
battery enclosures and for interconnecting balance-of-systems.
Uninterruptible Power Supply (UPS) : The designation
of a power supply providing continuous uninterruptible service.
The UPS will contain batteries.
Utility-Interactive Inverter : An inverter
that can function only when tied to the utility grid,
and uses the prevailing line-voltage frequency on the utility
line as a control parameter to ensure that the photovoltaic
system's output is fully synchronized with the utility power.
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Vacuum Evaporation - The deposition of
thin films of semiconductor
material by the evaporation of elemental sources in a vacuum.
Vacuum Zero : The energy of
an electron at rest in empty space;
used as a reference level in energy band diagrams.
Valence Band : The highest
energy band in a semiconductor
that can be filled with electrons.
Valence Level Energy/Valence State : Energy content
of an electron in orbit about an
atomic nucleus. Also called bound state.
Varistor : A voltage-dependent variable resistor.
Normally used to protect sensitive equipment from power spikes
or lightning strikes by shunting the energy to ground.
Vented Cell : A battery designed
with a vent mechanism to expel gases generated during charging.
Vertical Multijunction (VMJ) Cell : A compound cell
made of different semiconductor
materials in layers, one above the other. Sunlight entering
the top passes through successive cell barriers, each of which
converts a separate portion of the spectrum into electricity,
thus achieving greater total conversion efficiency of the
incident light. Also called a multiple junction cell. See
multijunction device and
split-spectrum cell.
Volt (V) : A unit of electrical force
equal to that amount of electromotive force that will cause
a steady current of one ampere
to flow through a resistance of one ohm.
Voltage : The amount of electromotive
force, measured in volts, that exists
between two points.
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.
Voltage Regulation : This indicates the variability
in the output voltage. Some loads
will not tolerate voltage variations greater than a few percent.
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Wafer : A thin sheet of semiconductor
(photovoltaic material) made by cutting it from a single crystal
or ingot.
Watt : The rate of energy transfer
equivalent to one ampere under an electrical
pressure of one volt. One watt equals
1/746 horsepower, or one joule per second.
It is the product of voltage and current
(amperage).
Waveform : The shape of the phase
power at a certain frequency and amplitude.
Wet Shelf Life : The period of time that a charged
battery, when filled with electrolyte,
can remain unused before dropping below a specified level
of performance.
Window : A wide band gap material
chosen for its transparency to light. Generally used as the
top layer of a photovoltaic
device, the window allows almost all of the light to reach
the semiconductor layers beneath.
Wire Types : See Article 300 of National
Electric Code for more information.
Work Function : The energy difference between the
Fermi level and vacuum
zero. The minimum amount of energy it takes to remove
an electron from a substance into
the vacuum.
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Zenith Angle
: the angle between the direction of interest (of the sun,
for example) and the zenith (directly overhead).
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