As a homeowner of a solar system, you might want to
know these basic terms or at least be able to look up the terms easily.
Alternating Current (AC)
Electric current in which the direction of the flow is reversed at
frequent intervals--100/120 (50/60Hz) times per second. The opposite of AC is
direct current (DC).
(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.
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 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.
Balance of Systems (BOS)
The parts of the photovoltaic
system other than the PV array such as the switches, controls, meters,
power-conditioning equipment, supporting structure for the array and
storage components, if any. The cost of land may or may not be included
when comparing total system cost with the cost of other energy sources.\
A battery is used to provide energy storage for off-grid solar systems.
The basic unit of a
photovoltaic panel or battery.
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.
An electronic device which regulates the voltage applied to the battery
system from the PV array. Charge controllers are typically used in
off-grid photovoltaic power systems to protect the battery.
A unit of electrical charge equal to the amount of charge transferred by a
current of 1 ampere in 1 second.
A semiconductor that uses a silicon or gallium arsenide substrate composed of a single crystal. Its atomic structure is the same throughout the material.
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% of the nominal capacity).
Discharging a battery to
20-percent or less of its full charge.
Sunlight received indirectly as a result of scattering due to clouds, fog,
haze, dust, or other obstructions in the atmosphere. It is the opposite of
Direct Current (DC)
Electric current in which
electrons are flowing in one direction only. The opposite of DC is
alternating current (AC.).
Sunlight falling directly upon a collector. It is the opposite of diffuse
A residential photovoltaic system is a distributed system. It is a system
that is installed at or near the location where the electricity is used,
as opposed to central systems that supply electricity to grids.
The process of adding another element to silicon is called doping.
The rate at which electrical current is taken from the battery, usually
expressed in amperes or time.
The 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.
A flow of electrons;
The quantity of energy required
to manufacture a product and supply it to the point of use. It is the sum
total of energy necessary from the raw material extraction to the
manufacture to the transportation and installation of a product or service
Final Annual Yield
Total photovoltaic energy delivered to the load during one year per
kilowatt of power installed. Unit is kWh per kW installed.
Network of transmission lines, substations, distribution lines and
transformers used by central power systems. In
other countries, often called mains electricity.
Grid-Connected PV Power Systems aka
This is a system installed on the consumer's premises and connected to the
Grid- Installed power: Power delivered by a photovoltaic module or
a photovoltaic array, under standard
test conditions (irradiance of 1 000 W/m², cell junction
temperature of 25°C, AM1,5 solar spectrum). Also said STC output power.
This is a measure of solar radiation energy received on a given surface area in a given time.
Insolation is the solar radiation striking Earth or another planet. It is commonly expressed as average irradiance in watts per square meter (W/m²) or kilowatt-hours per square meter per day (kW·h/(m²·day)) (or hours/day). In the case of photovoltaics it is commonly measured as kWh/kWp•y (kilowatt hours per year per kilowatt peak
rating). Do not confuse with insulation.
A device that converts direct current (DC) into alternating current (AC).
A graphical presentation of the current versus the voltage from a
photovoltaic cell 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.
The work done to produce power of one watt continuously for one second; or one watt second (compare kilowatt hour), with the symbol W·s. Thus a kilowatt hour is 3,600,000 joules or 3.6
megajoules. The work required to move an electric charge of one coulomb through an electrical potential difference of one volt; or one coulomb volt, with the symbol C·V.
Symbol of kilowatt-hour. The kWh is a unit of energy. One thousand watts
acting over a period of 1 hour. 1 kWh=3600 kJ.
KiloWatt hours per square meter per day.
The lifetime of a battery varies. It depends on many factors such as
method of use, maintenance, method of charging, and temperature. It is
typically between 5 and 10 years.
The amount of electric power being consumed at any given moment. Also,
in an electrical circuit, any device or appliance that is using power.
Power Point Tracking (MPPT)
An electronic DC to DC converter that optimizes the match between the
solar array or PV panels and the battery bank, utility power, DC motor, or
DC pump. An MPPT will typically increase power delivered to the system by
10% to 40%, depending on climate conditions and battery state of charge.
It is often called a power tracker for short.
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.
are composed of a single crystal throughout. One crystal
Material that is solidified at such a 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).
Net metering is the ability to receive energy credit for excess solar
energy you generate that is sent back to your utility company. Energy
credits vary in each state and between electric retailers in the State of
Texas. Net Metering allows residential and business customers to generate
excess solar power during the day and use it at night, without the need
for an energy storage system or generator.
A unit of electrical resistance equal to the resistance between two points
on a conductor when a potential difference of one volt
between them. A unit of measurement that indicates how much something
resists or impedes the flow of electricity.
Open-Circuit Voltage (Voc)
The voltage across a photovoltaic cell or module in sunlight when no
current is flowing; the maximum possible voltage.
Load or Peak Demand
The maximum load, or usage, of electrical power occurring in a given
period of time, typically a day.
PV modules are rated by their total power output. The peak power is the
amount of power output a PV modules produces at Standard
test conditions (STC)
Ratio of the final annual
(monthly, daily) yield to the reference annual (monthly, daily) yield,
where the reference annual (monthly, daily) yield is the theoretically
annual (monthly, daily) available energy per kilowatt of installed power.
A mechanically integrated assembly of modules and panels together with
support structure to form a DC power producing unit.
Photovoltaic Cell aka Solar Cell
A basic photovoltaic device, which generates DC electricity when, exposed
to a light such as the solar radiation.
The smallest complete environmentally protected assembly of interconnected
A group of modules fastened together, pre-assembled and wired, designed to
serve as an installable unit in a photovoltaic array.
Photovoltaic Power System
Set of interconnected elements such as photovoltaic modules andl
installation and control components with a photovoltaic power capacity of
40 W or more.
The process that produces electricity from sunlight. "Photo"
refers to light and "voltaic" to voltage.
Polycrystalline structures are
composed of many different crystals. Many crystals.
PV: Abbreviation of photovoltaic or photovoltaics .
PVPS: Abbreviation of photovoltaic power
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.
Short Circuit Current (Isc)
The current flowing freely from a photovoltaic cell or module through an
external circuit that has no load or resistance; the maximum current
A chemical element, atomic number 14. Silicon is semimetallic in nature,
dark gray in color, and an excellent semiconductor material. It is a
common constituent of sand and quartz (as the oxide) and crystallizes in
face-centered cubic lattice like a diamond. It is the most common
semiconductor material used in making photovoltaic devices.
An inverter that produces utility-quality, sine wave power forms.
Cell aka Photovoltaic Cell
A basic photovoltaic device, which generates DC electricity when, exposed
to a light such as the solar radiation.
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.
IEnergy from the sun. The heat that builds up in your car when it is
parked in the sun is an example of solar energy.
Intermediate-grade silicon used in the manufacture of solar cells. Less
expensive than electronic-grade silicon.
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.
The total distribution of electromagnetic radiation emanating from the
A method of producing electricity from solar energy by using focused
sunlight to heat a working fluid, which in turn drives a turbogenerator.
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 PV Power Systems aka
is a system that is not connected to the utility
grid and must use a means to store the electricity produced.
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
of Charge (SOC)
The available capacity
remaining in the battery, expressed as a percentage of the rated capacity.
The physical material upon
which a photovoltaic cell is made.
The covering on the sun side of
a PV module. It provides protection for the PV materials from impact and
environmental degradation while allowing maximum transmission of the
appropriate wavelengths of the solar spectrum.
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.
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.
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
Steps AC voltage up or down,
depending on the application.
Volts alternating current (AC0
Volts direct current (DC)
Voltage at maximum power
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.
at Maximum Power (Vmp)
The voltage at which maximum
power is available from a module.
A thin sheet of semiconductor
material made by mechanically sawing it from a single-crystal or
multi-crystal ingot or casting.
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.
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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