| Glossary of Terms |
|
| -A- |
| Absorbers--Dark-colored objects that soak up
heat in thermal solar power collectors used to produce heat energy. |
| Active solar--A solar water or space-heating system
that moves heated air or water using pumps or fans. |
| AGM--Absorbed Glass Mat, a newer type of battery
construction that uses saturated absorbant glass mats rather than gelled or liquid electrolyte.
Somewhat more expensive than flooded (liquid), but offers very good reliability. |
| Alternating Current--Electric current in which the
direction of flow is reversed at frequent intervals--usually 100 or 120 times per second (50 or
60 cycles per second or 50//60 Hz). |
| Amorphous SemiconductorM--A non-crystalline
semiconductor material. Easier and cheaper to make than crystalline, but less efficient and
slowly degrades over time. Also called thin film. |
| Ampere (A) or Amp--The unit for the electric current;
the flow of electrons. One amp is 1 coulomb passing in one second. One amp is produced by an
electric force of 1 volt acting across a resistance of 1 ohm. |
| Ampere-hour (Ah)--Quantity of electricity or measure of
charge. How many amps of flow or which can be provided over a one hour period. Deep cycle
batteries used in solar power systems are rated in Ah (amp-hour). |
| Angle of incidence--Angle between the normal to a
surface and the direction of incident radiation; applies to the aperture plane of a solar
collector. Most modern solar panels have only minor reductions in power output within plus/minus
15 degrees. |
| Antireflective Coating--A thin coating of a material,
which reduces the light reflection and increases light transmission, applied to a photovoltaic
cell surface. |
| Array--Any number of photovoltaic modules connected
together to provide a single electrical output. Arrays are often designed to produce significant
amounts of electricity. |
| Autonomous System--A stand-alone PV system that has no
back-up generating source. May or may not include storage batteries. Most battery systems are
designed for a certain minimum "days of autonomy" - which means that the batteries can supply
sufficient power with no sunlight to charge the batteries. This varies from 3-5 days in the
sunbelt, to 5 to 10 days elsewhere. |
| AWG--American Wire Gauge, a standard system for
designating the size of electrical wire. The higher the number, the smaller the wire. Most house
wiring is #12 or 14. In most other countries, wire is specified by the size in millimeters.
|
| Azimuth--Angle between the north direction and the
projection of the surface normal into the horizontal plane; measured clockwise from north. As
applied to the PV array, 180 degree azimuth means the array faces due south. |
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| -B- |
| Balance of System (BOS)--Represents all components and
costs other than the PV modules. It includes design costs, land, site preparation, system
installation, support structures, power conditioning, operation and maintenance costs,
batteries, indirect storage, and related costs. |
| Baseline Performance Value--Initial values of Isc, Voc,
Pmp, Imp measured by the accredited laboratory and corrected to Standard Test Conditions, used
to validate the manufacturer's performance measurements provided with the qualification modules
per IEEE 1262. |
| Blocking Diode--A diode used to restrict or block
reverse current from flowing backward through a module. [UL 1703] Alternatively, diode connected
in series to a PV string; it protects its modules from a reverse power flow and, thus, against
the risk of thermal destruction of solar cells. |
| British Thermal Unit (BTU)--The amount of heat energy
required to raise the temperature of one pound of water from 60 degrees F to 61 degrees F at one
atmosphere pressure. |
| 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. [UL 1703] Alternatively, diode connected anti-parallel across a part of the solar
cells of a PV module. It protects these solar cells from thermal destruction in case of total or
partial shading, broken cells, or cell string failures of individual solar cells while other
cells are exposed to full light. |
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| : |
| -C- |
| Cathodic Protection--A method of preventing oxidation
(rusting) of exposed metal structures, such as bridges and pipelines, by imposing a small
electrical voltage that opposes the flow of electrons between the structure and the ground that
is greater than the voltage present during oxidation. |
| Cell--The basic unit of a photovoltaic panel or
battery. |
| 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, cell
junction, 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 Controller or Charge Regulator--An
electronic device which regulates the voltage applied to the battery system from the PV
array. Essential for ensuring that batteries obtain maximum state of charge and longest
life. Usually provides protection from current backflow at night. |
| Combined Collector--A photovoltaic device or
module that provides useful heat energy in addition to electricity. |
| Concentrator--A PV module that uses optical
elements to increase the amount of sunlight incident on a PV cell. Concentrating arrays
must track the sun and use only the direct sunlight because the diffuse portion cannot be
focused onto the PV cells. Efficiency is increased, but lifespan is usually decreased due
to the high heat. |
| Concentrator (module, array, or collector)--An
arrangement of photovoltaic cells that includes a lens to concentrate sunlight onto
small-area cells. Concentrators can increase the power flux of sunlight hundreds of
times. |
| Conversion Efficiency (cell or module)--The ratio
of the electric energy produced by a photovoltaic device (under one-sun conditions) to the
energy from sunlight incident upon the cell. |
| Current at Maximum Power (Imp)--The current at
which maximum power is available from a module. [UL 1703] |
| Cycle Life--Number of discharge-charge cycles
that a battery can tolerate under specified conditions before it fails to meet specified
criteria as to performance (e.g., capacity decreases to 80-percent of the nominal
capacity). |
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| -D- |
| DC to DC converter--Electronic circuit to convert
dc voltages (e.g., PV module voltage) into other levels (e.g., load voltage). Can be part
of a maximum power point tracker (MPPT). |
| Deep Discharge--Discharging a battery to 20-percent or
less of its full charge. |
| 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. |
| Direct Current (dc)--Electric current in which
electrons flow in one direction only. Opposite of alternating current. |
| Direct Insolation--Sunlight falling directly upon a
collector. Opposite of diffuse insolation. |
| Discharge Rate--The rate, usually expressed in amperes
or time, at which electrical current is taken from the battery. |
| 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. |
| DOD--'Depth of Discharge,' from 100-percent state of
charge (SOC), in a battery or battery system. |
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| -E- |
| Electric Circuit--Path followed by electrons from a
power source (generator or battery) through an external line (including devices that use the
electricity) and returning through another line to the source. |
| Electric Current--A flow of electrons; electricity,
amps. |
| Electrical Grid--An integrated system of electricity
distribution, usually covering a large area. As in "off the grid". |
| Electrolyte--A liquid conductor of electricity. In
batteries, usualy H2SO4, sulfuric acid, but may be any number of things. Seawater is the
mostcommon electrolyte in the world - and by suspending a zinc and a steel sheet in it, you can
get a little electricity. |
| Energy--The ability to do work. Stored energy becomes
working energy when we use it. |
| Energy Density--The ratio of energy available from a
battery to its volume (Wh/1) or mass (Wh/kg). "watts to weight" ratio. |
| Energy Payback Time--The time required for any energy
producing system or device to produce as much energy as was required in its manufacture. For
solar electric panels, this is about 16-20 months. |
| EVA--(ETHYLENE VINYL ACETATE) An encapsulant used
between the glass cover and the solar cells in PV modules. It is durable, transparent,resistant
to corrosion, and flame retardant. |
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| -F- |
| Flat-Plate PV--Refers to 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--Float charge is the voltage required to
counteract the self-discharge of the battery at a certain temperature. |
| Float Life--Number of years that a battery can keep its
stated capacity when it is kept at float charge (see float charge). |
| Fuel Cell--A device that converts the energy of a fuel
directly to electricity and heat, without combustion. Because there is no combustion, fuel
cells give off few emissions; because there are no moving parts, fuel cells are quiet. |
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| -G- |
| Gel-Type or Gel Cell Battery-—A sealed, Lead-acid
battery in which the electrolyte is composed of a silica gel matrix or infused with another
gelling medium. |
| Grid-Connected (PV system)--A PV system in which the
PV array acts like a central generating plant, supplying power to the grid. |
| Ground Loop--An undesirable feedback condition caused by
two or more circuits sharing a common electrical line, usually a grounded conductor. |
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| -H- |
| Hot Spot--An undesirable phenomenon of PV device
operation whereby one or more cells within a PV module or array act as a resistive load,
resulting in local overheating or melting of the cell(s). Usually appears as a brown or black
spot on the backside of the solar module. |
| Hybrid System--A PV system that includes other sources
of electricity generation, such as wind or fossil fuel generators. |
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| -I- |
| Incident Light--Light that shines onto the face of a
solar cell or module. |
| Insolation--Sunlight, direct or diffuse; from 'incident
solar radiation.' Not to be confused with 'insulation.' Equal to about 1000 watts per square
meter at high noon. |
| Interconnect--A conductor within a module or other
means of connection which provides an electrical interconnection between the solar cells.
[UL 1703] or batteries. |
| Inverters--Devices that convert dc electricity into ac
electricity (single or multiphase), either for stand-alone systems (not connected to the grid) or
for utility-interactive systems. |
| 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
characterized cell performance. |
| I-V Data--The relationship between current and voltage
of a photovoltaic device in the power-producing quadrant, as a set of ordered pairs of current
and voltage readings in a table, or as a curve plotted in a suitable coordinate system (i.e.,
Cartesian). [ASTM E 1036] |
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| -J- |
| Junction Box--A 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. Also referred to as a J-Box. |
| 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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| -K- |
| Kilowatt (kW)--1000 watts. |
| Kilowatt-Hour (kWh)--One thousand watts acting over a
period of 1 hour. The kWh is a unit of energy. 1 kWh=3600 kJ. |
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| -L- |
| 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 dc to ac) is controlled by the
power line, so that, if there is a failure in the power grid, the PV system cannot feed power
into the line. |
| Load--Anything in an electrical circuit that, when the
circuit is turned on, draws power from that circuit. |
| Low Voltage Disconnect (LVD)--A battery protection
function usually incorporated within the PV charge controller or regulator whereby any DC loads
will be disconnected from a battery if the battery voltage falls below a given set point. |
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| -M- |
| 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. [UL 1703] For a typical silicon cell panel, this is about 17 volts for a 36 cell
configuration. |
| Maximum Power Point Tracker (MPPT)--A power
conditioning unit that automatically operates the PV-generator at its MPP under all conditions.
An MPPT will typically increase power delivered to the system by 10% to 40%, depending on
climate conditions and battery state of charge. |
| Microgroove--A small groove scribed into the surface
of a solar cell which is filled with metal for contacts. |
| Modified Sine-Wave--An AC waveform that resembles but
is not identical to a full Sine-wave when viewed using an oscilloscope.
|
| Module--A number of PV cells connected together,
sealed with an encapsulant, and having a standard size and output power; the smallest
building block of the power generating part of a PV array. Also called panel. |
| Monolithic--Fabricated as a single structure. |
| Multicrystalline--Material that is solidified at such
as rate that many small crystals (crystallites) form. The atoms within a single crystallite
are symmetrically arranged, whereas crystallites are jumbled together. These numerous grain
boundaries reduce the device efficiency. A material composed of variously oriented, small
individual crystals. (Sometimes referred to as polycrystalline or semicrystalline). |
| Multijunction Device--A photovoltaic device containing
two or more cell junctions, each of which is optimized for a particular part of the solar
spectrum, to achieve greater overall efficiency. |
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| -N- |
| n-Type Semiconductor--A semiconductor produced by doping
an intrinsic semiconductor with an electron-donor impurity (e.g., phosphorous in
silicon). |
| NOCT--Nominal Operating Cell Temperature. The solar
cell temperature at a reference environment defined as 800 W/m2 irradiance, 20°C ambient air
temperature, and 1 m/s wind speed with the cell or module in an electrically open circuit
state. |
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| -O- |
| Ohm--The unit of resistance to the
flow of an electric current. |
| One-axis tracking--A system capable
of rotating about one axis. |
| Open-Circuit Voltage (Voc)--The
maximum possible voltage across a photovoltaic cell or module; the voltage across the cell
in sunlight when no current is flowing. |
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| -P- |
| Parallel Connection--A way of joining two or more
electricity-producing devices (i.e., PV cells or modules) by connecting positive leads
together and negative leads together; such a configuration increases the current. |
| Passive Solar Home--A house that uses a room or another
part of the building as a solar collector, as opposed to active solar, such as PV. |
| Peak Load; Peak Pemand--The maximum load, or usage, of
electrical power occurring in a given period of time, typically a day. |
| Peak Watts (Wp)--See 'Photovoltaic peak watt.' |
| Photon--A particle of light that acts as an individual
unit of energy. |
| Photovoltaic (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
(dc voltage and current). |
| 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) Efficiency--The ratio of electric
power produced by a cell at any instant to the power of the sunlight striking the cell. This is
typically about 9% to 14% for commercially available cells. |
| 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 dc
power under unconcentrated sunlight. The structural (load carrying) member of a module can
either be the top layer (superstrate) or the back layer (substrate). [UL 1703] |
| 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) Peak Watt--Maximum "rated" output of
a cell, module, or system. Typical rating conditions are 0.645 watts per square inch (1000 watts
per square meter) of sunlight, 68 degrees F (20 degrees C) ambient air temperature and 6.2 x 10-3
mi/s (1 m/s) wind speed. |
| 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. |
| Polycrystalline--See 'Multicrystalline.' |
| 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 Factor--The ratio of the average power and the
apparent volt-amperes. |
| Pulse-Width-Modulated (PWM) Wave Inverter--PWM inverters
are the most expensive, but produce a high quality of output signal at minimum current harmonics.
The output voltage is very close to sinusoidal. |
| PV--Abbreviation for photovoltaic(s). |
| Pyronometer--An instrument for measuring total
hemispherical solar irradiance on a flat surface, or "global" irradiance; thermopile sensors
have been generally identified as pyranometers, however, silicon sensors are also referred to
as pyranometers. |
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| -Q- |
| Qualification Test (PV)--A procedure applied to a
selected set of PV 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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| -R- |
| Rectifier--A device that converts ac to dc, as in a
battery charger or converter. See 'inverter.' |
| Remote Systems--Systems off of the utility
grid. |
| Resistive Voltage Drop--The voltage developed across a
cell by the current flow through the resistance of the cell. |
| Reverse Bias--Condition where the current producing
capability of a PV cell is significantly less than that of other cells in its series string.
This can occur when a cell is shaded, cracked, or otherwise degraded or when it is electrically
poorly matched with other cells in its string. |
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| -S- |
| Schottky Barrier--A cell barrier established as the
interface between a semiconductor, such as silicon, and a sheet of metal. |
| 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. Generally falls between a metal and an insulator
in conductivity. 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 or
batteries by connecting positive leads to negative leads; such a configuration increases the
voltage. |
| Series Regulator--Type of battery charge regulator where
the charging current is controlled by a switch, transistor, or FET connected in series with the
PV 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. |
| 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
from a photovoltaic cell through an external circuit that has no load or resistance; the
maximum current possible. |
| Shunt Regulator--Type of a battery charge regulator
where the charging current is controlled by a switch or transistor connected in parallel with
the PV panel. Overcharging of the battery is prevented by shorting the PV output. Shunt regulators
are common in PV systems as they are relatively cheap to build and simple to design. Series
regulators usually have better control and charge characteristics. |
| Silicon (Si)--A chemical element, atomic number 14,
semimetallic in nature, dark gray, an excellent semiconductor material. A common constituent of
sand and quartz (as the oxide). Crystallizes in face-centered cubic lattice like a diamond. The
most common semiconductor material used in making photovoltaic devices. |
| Sine Wave or Sinusoidal Waveform--A visual representation
of the flow of an AC current, resembling ocean waves with peaks and valleys at regular
intervals. |
| 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. |
| Solar Cell--See 'Photovoltaic cell.' |
| Solar Constant--The strength of sunlight; 1353 watts per
square meter in space and about 1000 watts per square meter at sea level at the equator at
solar noon. |
| Solar Energy--Energy from the sun. The heat that builds
up in your car when it is parked in the sun is an example of solar energy. |
| Solar-Grade Silicon--Intermediate-grade silicon used in
the manufacture of solar cells. Less expensive than electronic-grade silicon. |
| Solar Noon--That moment of the day that divides the
daylight hours for that day exactly in half. To determine solar noon, calculate the length of
the day from the time of sunset and sunrise and divide by two. Solar noon may be quite a bit
different from 'clock' noon. |
| Solar Spectrum--The total distribution of electromagnetic
radiation emanating from the sun. |
| Solar Thermal Electric--Method of producing electricity
from solar energy by using focused sunlight to heat a working fluid, which in turn drives a
turbogenerator. |
| 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.' |
| Square Wave Inverter--The inverter consists of a dc
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. The square wave inverter is the simplest and the least expensive
to purchase, but it produces the lowest quality of power. |
| Stand-Alone System--An autonomous or hybrid energy 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 PV 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 Test Conditions (STC)--Conditions under which a
module is typically tested in a laboratory: (1) Irradiance intensity of 1000 W/square meter
(0.645 watts per square inch), AM1.5 solar reference spectrum, and (3) a cell (module) temperature
of 25 degrees C, plus or minus 2 degrees C (77 degrees F, plus or minus 3.6 degrees F).
[IEC 1215] |
| State of Charge (SOC)--The available capacity remaining
in the battery, expressed as a percentage of the rated capacity. |
| Substrate--The physical material upon which a
photovoltaic cell is made. |
| 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. |
| Superstrate--The covering on the sun side of a 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. |
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| -T- |
| Thermal Electric--Electric energy derived from heat
energy, usually by heating a working fluid, which drives a turbogenerator. See 'solar thermal
electric.' |
| Thermophotovoltaic (TPV) Device--A device that converts
secondary thermal radiation, re-emitted by an absorber or heat source, into electricity; The
device is designed for maximum efficiency at the wavelength of the secondary 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, cadmium telluride, gallium arsenide, or amorphous silicon, a few
microns or less in thickness, used to make photovoltaic cells. Commonly called
amorphous. |
| 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 eventually be absorbed by the semiconductor. |
| Tracking Array--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. Typically, a single axis tracker will give you 15% to 25% more power per day, and dual
axis tracking will add about 5% to that. Depends somewhat on latitude and season. |
| Transformer--Steps AC voltage up or down, depending on
the application. |
| 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 system capable of rotating
independently about two axes (e.g., vertical and horizontal) and following the sun for
maximum efficiency of the solar array. |
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| -U- |
| Utility-Interactive Inverter/Grid Tie 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 PV
system's output is fully synchronized with the utility power. |
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| -V- |
| VAC--Volts ac. |
| VDC--Volts dc. |
| Vmp--Voltage at
maximum power. |
| Voc--Open-circuit voltage. |
| Volt (V)--A unit of measure of the force, or 'push,'
given the electrons in an electric circuit. One volt produces one ampere of current when
acting a resistance of one ohm. |
| Voltage at maximum power (Vmp)--The voltage at which
maximum power is available from a module. [UL 1703] |
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| -W- |
| Wafer--A thin sheet of semiconductor material made
by mechanically sawing it from a single-crystal or multi-crystal ingot or casting. |
| Watt (W)--The unit of electric power, or amount of
work (J), done in a unit of time. One ampere of current flowing at a potential of one volt
produces one watt of power. |
| Watt-hour (Wh)--See 'Kilowatt-hour.' |
| Waveform--The shape of the curve graphically
representing the change in the ac signal voltage and current amplitude, with respect to
time. |
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