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US Department of Energy - Solar power glossary
Category: Sciences > Solar power
Date & country: 01/06/2011, US
Words: 396


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 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 com...

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.

Solar-Grade Silicon
Intermediate-grade silicon used in the manufacture of solar cells. Less expensive than electronic-grade silicon.

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.

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.

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

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 p...

Transformer
An electromagnetic device that changes the voltage of alternating current electricity.

Trickle Charge
A charge at a low rate, balancing through self-discharge losses, to maintain a cell or battery in a fully charged condition.

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.

Two-Axis Tracking
A photovoltaic array tracking system capable of rotating independently about two axes (e.g., vertical and horizontal).

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.

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.

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.

Zenith Angle
the angle between the direction of interest (of the sun, for example) and the zenith (directly overhead).