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| Glossary
of Solar Energy Terms
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Incandescent
light: an electric lamp which is evacuated or filled
with an inert gas and contains a filament (commonly tungsten). The
filament emits visible light when heated to extreme temperatures
by passage of electric current through it.
Incident light: Light that shines on to the
surface of a PV cell or module.
Independent power system: A power generation
system that is independent of the mains grid.
Insolation: The amount of sunlight reaching
an area, usually expressed in Watt hours per square meter per day.
Installer: Usually a retailer and installer
of PV Systems
Insulation: A material used to prevent the
flow of electricity. Normally used on electrical wires to prevent electric shock.
Typical materials used include plastics such as PVC and polypropylene.
Integrator: Integrates PV components in to
a complete PV System
Interconnect: A conductor within a module
or other means of connection which provides an electrical interconnection between
the solar cells. [UL 1703]
Inverter: An inverter converts DC power from
the PV array/battery to AC power. Used either for stand-alone systems or grid-connected systems.
Irradiance: The solar power incident on a
surface, usually expressed in kilowatts per square meter. Irradiance multiplied
by time gives insolation.
I-V curve: A graph that plots the current
versus the voltage from a PV cell as the electrical load (or resistance) is increased
from short circuit (no load) to open circuit (maximum voltage). The shape of the
curve characterizing cell performance. Three important points on the I-V curve
are the open-circuit voltage, short-circuit current, and peak or maximum power
(operating) point.
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 [ASTM E 1036] |
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Joule
(J): The energy conveyed by one Watt of power for one second, unit of energy equal to 1/3600 kilowatt-hours.
Junction box: A PV junction box is a protective
enclosure on a PV module where PV strings are electrically connected and where
electrical protection devices such as diodes can be fitted.
Junction diode: A semiconductor device, having
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 unit of electrical power, one thousand Watts.
Kilowatt-hour (kWh):
The amount of energy that derives from a power of 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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Langley: Unit of solar
irradiance, one calorie per square centimeter.
1 L = 41.84 kJ/m2.
Lead-acid battery: A type of battery that
consists of plates made of lead, lead-antimony, or lead-calcium and lead-oxide,
surrounded by a sulfuric acid electrolyte. The most common type of battery used
in RAPS systems.
Life: The period during which a system can
operate above a specified performance level.
Life-cycle cost: The estimated cost of owning, operating
and disposing of a system over its useful life.
Light emitting diode: A semi conductor device
composed of a p-n junction designed such that electrons emit visible light during
their migration across the junction.
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.
Light-induced defects: Defects, such as dangling
bonds, induced in an amorphous silicon semiconductor upon initial exposure to
light.
Line wire loss: refers to the voltage or power
lost due to the resistance of any wire or wires in any electrical circuit.
Linear current booster: an electronic circuit
that matches PV output directly to a motor. Used in array direct water pumping.
Liquid electrolyte battery: A battery containing
a liquid solution of an electrolyte in a solvent (e.g. sulfuric acid in water). Also called a flooded battery because
the plates are covered with the electrolyte solution.
Load: The electrical power being consumed
at any given moment or averaged over a specified period. The load that an electric generating system supplies varies
greatly with time of day and to some extent season of year. Also, in an electrical
circuit, the load is any device or appliance that is using power.
Load circuit: The wiring including switches
and fuses
that connects the load to the power source.
Load current: The current required to power the electrical device.
Load resistance: The electrical resistance
of the load.
Low voltage cut-off: The voltage at which
a controller will disconnect the load from the battery.
Low voltage disconnect (LVD): The voltage
at which the charge controller will disconnect the load from the batteries to
prevent over-discharging.
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
the level of the electrolyte solution.
Maximum power point (MPP): Operating a PV
array at that voltage will produce maximum power. 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] This corresponds to the point on an I-V curve that represents
the largest area rectangle that can be drawn under the curve. 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.
Megawatt (MW): A measurement of power equal
to one million Watts.
Megawatt-hour (MWh): A measurement of power
with respect to time (i.e. energy). One megawatt-hour is equal to one megawatt
being used for a period of one hour, or one kilowatt being used for 1000 hours.
Microgroove: A small groove scribed into the
surface of a cell which may be filled with metal for contacts.
Modified sine wave: A waveform with at
least three states (positive, off, and negative) used to simulate a sine wave. It has less harmonic content
than a square wave. This type of waveform is better than a square wave, but not
as suitable for some appliances as a sine wave.
Modularity: The use of
complete sub-assemblies to produce a larger system. Also the use of multiple inverters connected
in parallel to service different loads.
Module: An encapsulated panel containing
a number of electrically connected PV cells.
Module de-rating factor: A factor that lowers
the power output of a module to account for field operating conditions e.g. dirt
build-up on the module.
Monocrystalline solar cell: A form of solar
cell made from a thin slice of a single large crystal of silicon.
Monolithic: Fabricated as a single structure,
as used to describe thin film series interconnected PV cells on a single sheet
substrate.
Multicrystalline: A material that has solidified
at a rate such that many small crystals (crystallites) form. The atoms within
a single crystallite are symmetrically arranged with a particular orientation,
whereas the crystallites themselves are differently oriented. The multitude
of grain boundaries in the material (between the crystallites) reduce the cell
efficiency. Multicrystalline is also referred to as polycrystalline.
Multi-junction device: A PV device containing
two or more cell junctions each of which may be different in nature and optimized
to absorb a particular part of the
solar spectrum in order to achieve higher overall cell efficiency.
Multi-stage controller: A charge controller that allows different charging currents
as the battery approaches full state of charge. |
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NEC: US National Electrical Code which contains
guidelines for all types of electrical installations which should
be followed when installing a PV system.
NEMA: US National Electrical Manufacturers Association, sets standards for some non-electronic products
e.g. junction boxes.
Net metering: The practice of exporting surplus solar power during the
day (to actual
power needs) to the electricity grid, which either causes the home owner electric
meter to (physically) go backwards and/or simply creates a financial credit on
the home owner's electricity bill. (At night, the homeowner draws from the electricity
grid in the normal way).
Nickel-cadmium battery (NiCad): A form of rechargable battery, having higher
storage densities than that of lead-acid batteries, that uses a mixture of nickel
hydroxide and nickel oxide for the anode, and cadmium metal for the cathode. The
electrolyte is potassium hydroxide.
Noise: Unwanted electrical signals produced by electric motors and other
machines that can cause circuits and appliances to malfunction.
Nominal voltage: A rounded voltage value used to describe batteries, modules,
or systems based on their specification (e.g. a 12V, 24V or 48V battery, module, or system).
Normal Operating Cell Temperature (NOCT): The estimated temperature of
a solar PV module when it is operating under 800 W/m2 irradiance, 20°C ambient temperature
and a wind speed of 1 meter per second. NOCT is used to estimate the nominal operating
temperature of a module in the field.
N-type semiconductor: A semiconductor produced by the doping of an intrinsic
semiconductor with an electron-donor impurity, for example phosphorous in silicon.
N-Type silicon: Silicon doped with an element that
has more electrons in its atomic structure than does silicon
(e.g. phosphorus).
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Ohm:
The resistance between two points of a conductor when a constant potential
difference of one Volt applied between these points produces in the conductor
a current of one Amp.
Ohm's Law: A simple mathematical formula that allows
either voltage, current or resistance to be calculated when the other two values
are known. The formula is: V = I x R, where V is the voltage, I is the current,
and R is the resistance.
One-axis tracking:
A PV System structure that is capable of rotating on a single axis in order to
track the movement of the sun.
Open
circuit voltage:
The maximum voltage produced by an illuminated solar PV cell, module, or array
when no load is connected. OCV increases as the temperature of the PV
material decreases.
Operating
point: Defined
by the current and voltage that a module or array produces when connected to a load.
It is dependent on the load or the batteries connected to the
output terminals.
Orientation: Position with respect to the
cardinal directions, N, S, E, W.
Overcharge:
Applying current to a fully charged battery. This can damage the
battery. |
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Panel:
Used interchangeably with "module".
Parallel connected: A method of connection
in which positive terminals are connected together and negative terminals are
connected together. Current output adds and voltage remains the same.
Passive solar home: A house that utilizes
part of the building as a solar collector, as opposed to active solar, such as
PV.
Peak load: The maximum usage of electrical
power occurring in a given period of time, typically a day. The electrical
supply must be able to be meet the peak load if it is to be reliable.
Peak power current: Current in Amperes produced
by a module or array operating at the voltage on the I-V curve that will produce
its maximum power.
Peak sun hours: The equivalent number of hours
per day when solar irradiance averages 1000 W/m2.
Peak Watt: The amount of power a solar PV
cell or module will produce under standard test conditions (normally 1000 W/m2
and 25°C cell temperature, AM 1.5 spectrum).
Photon: Light is composed of energy particles
called photons which have variable energy but constant speed.
Photovoltaic (PV) array: A number of PV modules
connected together in a single structure.
Photovoltaic (PV) cell: The smallest discrete
element in a PV module that performs the conversion of light into electrical energy
to produce a DC current and voltage.
Photovoltaic (PV) conversion efficiency: The
ratio of the electrical power generated by a PV device to the power of the light
incident on it. This is typically in the range 5% to 15% for commercially available
modules.
Photovoltaic (PV) generator: The total of
all PV strings of a PV power supply system, which are electrically interconnected.
Photovoltaic (PV) module: A single assembly
of solar cells and ancillary parts, such as interconnections, terminals, (and
protective devices such as diodes) intended to generate DC power under un-concentrated
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: a term often used
interchangeably with PV module (especially in single module systems).
Photovoltaic (PV): refers to any device which
produces free electrons when exposed to light.
Photovoltaic system: All the parts connected
together that are required to produce solar electricity.
Photovoltaic cell: The semiconductor device
that converts solar irradiance (light) into dc electricity.
Photovoltaic effect: The effect that causes
a voltage to be developed across the junction of two different materials when
they are exposed to light.
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.
Plates: The electrodes in a battery, usually
take the form of metal plates.
Polycrystalline cell: a wafer of silicon with
a multi-grained structure. All grains have the same atomic crystal lattice, however,
each grain has a unique orientation in space thereby producing a unique reflection
of light.
Polycrystalline silicon: A material used to
make solar PV cells which consists of many crystals, compared to single crystal
silicon.
Poly-vinyl chloride (PVC): A plastic used as an insulator on electrical
cables. A toxic material, which is being replaced with alternatives made from
more benign chemicals
Power (Watts): Basic unit of electricity equal
to the product of current and voltage (in DC circuits).
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 e.g. of an inverter.
Power density: The ratio of the power available
from a battery to its volume (Watts per liter) or weight (Watts per kilogram).
Power factor: The cosine of the phase angle between the voltage and the
current waveforms in an AC circuit. A measure of inverter performance.
Power: The rate of doing work. Expressed as
Watts (W). For example, a generator rated at 800 watts can provide that amount
of power continuously. 1 Watt = 1 joule/sec.
Primary battery: A battery that cannot be
re-charged.
PV array: two or more photovoltaic panels wired in series and or parallel.
PV: Short hand for Photovoltaics.
PV components: The individual parts of a PV
System. Individual items like Batteries, Inverters, Regulators, Wiring
PV system: All the parts in combination required to generate solar electricity
Pyranometer: 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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Qualification
test (PV): A testing procedure for PV modules relating to electrical,
mechanical, or thermal stress.
Quasi sine-wave: A description of the type
of waveform produced by some Inverters. |
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RAPS
(Remote Area Power Supply): A power generation
system used to provide electricity to remote and rural homes, usually incorporating
power generated from renewable sources such as solar panels and wind generators,
as well as non-renewable sources such as petrol-powered generators.
Rated battery capacity (Ah): Term used by battery
manufacturers to indicate the maximum amount of energy that can be withdrawn from
a battery at a specified discharge rate and temperature.
Rated module current (A): The current output
of a PV module measured under standard test conditions of 1000 W/m2 and 25°C cell
temperature.
Rated power: Nominal power output of an
inverter, some units cannot produce rated power continuously.
Reactive power: The sine of the phase angle
between the current and voltage waveforms in an AC system.
Rechargeable battery: A type of battery that
uses a reversible chemical reaction to produce electricity, allowing it to be
re-used many times. The chemical reaction is reversed by forcing electricity through
the battery in the opposite direction to normal discharge.
Rectifier: A device that converts ac to dc,
as in a battery charger or converter.
Regulator: A device used to limit the current
and voltage in a circuit, normally to allow the correct charging of batteries
from power sources such as solar panels and wind generators.
Remote site: A site with no electrical
utility grid connection.
Renewable energy: Energy that is produced
from a renewable source.
Resistance (R): The property of a material
which resists the flow of electric current when a potential difference is
applied across it, measured in Ohms.
Resistive voltage drop: The voltage developed
across a cell by the current flow through the resistance of the cell which may
result from the bulk resistance of the materials in the cell and at interfaces
between them.
Resistor: An electronic component used to
restrict the flow of current in a circuit. Sometimes used specifically to produce
heat, such as in a water heater element.
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.
Reverse current protection: Any means of
preventing current flow from the battery to the solar PV array (e.g. at night)
that would discharge the battery.
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