Angle between the normal to a surface and the direction of incident radiation; applies to the aperture plane of a solar panel. Only minor reductions in power output within plus/minus 15 degrees.
Array(solar)
A number of solar modules connected together in a single structure.
Azimuth
The 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.
B
Battery
A system in which stored chemical energy is converted directly into electrical energy. Can be either rechargeable or non-rechargeable. Different from a fuel cell in that it contains a fixed quantity of stored chemical energy rather than a continuous supply of fuel.
British Thermal Unit (BTU)
The amount of heat energy required to raise one pound of water from a temperature of 60 degrees F to 61 degrees F at one atmosphere pressure. One Watt hour equals 3,413 BTU.
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.
C
Current
Current is the flow of electric charge in a conductor between two points having a difference in electrical potential (voltage) and is measured in Amps.
Capacitor
An electronic component used for the temporary storage of electricity, as well for removing unwanted noise in circuits. A capacitor will block Direct Current (DC) but will pass Alternating Current (AC).
Charge
The process of inputting electrical energy to a battery.
D
Diffuse insolation
Incident sunlight received indirectly because of scattering due to clouds, fog, particulates, or other obstructions in the atmosphere. The opposite of direct insolation.
Diffuse radiation
Radiation received from the sun after reflection and scattering by the clouds, fog, haze, dust or other substances in the atmosphere, and the ground.
Direct beam radiation
Radiation received by direct sunlight. Measured by a pyrheliometer with a solar aperture of 5.7.
E
Earth
Refers to physically connecting a part of an electrical system to the ground by means of a conductor embedded in suitable soil. Done as a safety measure.
Electricity
The movement of electrons (a sub-atomic particle), produced by a voltage, through a conductor.
F
Fixed Tilt Array
A photovoltaic array set in at a fixed angle with respect to horizontal.
Frequency
The number of repetitions per unit time of a complete waveform, expressed in Hertz (Hz).
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).
G
Gigawatt (GW)
A unit of power equal to 1 billion Watts; 1 million kilowatts, or 1,000 megawatts.
H
I
Incident Light
Light that shines onto the face of a solar cell or module.
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.
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.
J
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.
K
Kilowatt (kW)
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.
L
Langley
Langley (L) — Unit of solar irradiance. One gram calorie per square centimeter. 1 L = 85.93 kwh/m2.
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.
Lumen
lumen (symbol: lm) is the SI derived unit of luminous flux, a measure of the total "amount" of visible light emitted by a source.
Lux
The lux (symbol: lx) is the SI unit of illuminance and luminous emittance, measuring luminous flux per unit area.[1] It is equal to one lumen per square metre.
M
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.
N
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.
O
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.
Open-Circuit Voltage (Voc)
The maximum possible voltage across a photovoltaic cell; the voltage across the cell in sunlight when no current is flowing.
P
Photovoltaics
A solar cell, or photovoltaic cell (PV), is a device that converts light into electric current using the photovoltaic effect. The first solar cell was constructed by Charles Fritts in the 1880s.[10] The German industrialist Ernst Werner von Siemens was among those who recognized the importance of this discovery.
Q
R
Regulator
Prevents overcharging of batteries by controlling charge cycle-usually adjustable to conform to specific battery needs.
Resistance
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.
S
Solar
Solar is the Latin word for sun—a powerful source of energy.
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.
T
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.
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.
U
Ultraviolet
Electromagnetic radiation in the wavelength range of 4 to 400 nanometers.
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.
V
Volt
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 Regulation
This indicates the variability in the output voltage. Some loads will not tolerate voltage variations greater than a few percent.
W
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).
Z
Zenith Angle
the angle between the direction of interest (of the sun, for example) and the zenith (directly overhead).
