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


Absorber
In a photovoltaic device, the material that readily absorbs photons to generate charge carriers (free electrons or holes).

AC
see alternating current.

Acceptor
A dopant material, such as boron, which has fewer outer shell electrons than required in an otherwise balanced crystal structure, providing a hole, which can accept a free electron.

Activated Shelf Life
The period of time, at a specified temperature, that a charged battery can be stored before its capacity falls to an unusable level.

Activation Voltage(s)
The voltage(s) at which a charge controller will take action to protect the batteries.

Adjustable Set Point
A feature allowing the user to adjust the voltage levels at which a charge controller will become active.

AIC
See amperage interrupt capability.

Alternating Current (AC)
A type of electrical current, the direction of which is reversed at regular intervals or cycles. In the United States, the standard is 120 reversals or 60 cycles per second. Electricity transmission networks use AC because voltage can be controlled with relative ease.

Ambient Temperature
The temperature of the surrounding area.

Amorphous Semiconductor
A non-crystalline semiconductor material that has no long-range order.

Amorphous Silicon
A thin-film, silicon photovoltaic cell having no crystalline structure. Manufactured by depositing layers of doped silicon on a substrate. See also single-crystal silicon an polycrystalline silicon.

Amperage Interrupt Capability (AIC)
direct current fuses should be rated with a sufficient AIC to interrupt the highest possible current.

Ampere (amp)
A unit of electrical current or rate of flow of electrons. One volt across one ohm of resistance causes a current flow of one ampere.

Ampere Hour Meter
An instrument that monitors current with time. The indication is the product of current (in amperes) and time (in hours).

Ampere-Hour (Ah/AH)
A measure of the flow of current (in amperes) over one hour; used to measure battery capacity.

Angle of Incidence
The angle that a ray of sun makes with a line perpendicular to the surface. For example, a surface that directly faces the sun has a solar angle of incidence of zero, but if the surface is parallel to the sun (for example, sunrise striking a horizontal rooftop), the angle of incidence is 90

Annual Solar Savings
The annual solar savings of a solar building is the energy savings attributable to a solar feature relative to the energy requirements of a non-solar building.

Anode
The positive electrode in an electrochemical cell (battery). Also, the earth or ground in a cathodic protection system. Also, the positive terminal of a diode.

Antireflection Coating
A thin coating of a material applied to a solar cell surface that reduces the light reflection and increases light transmission.

Array
see photovoltaic (PV) array.

Array Current
The electrical current produced by a photovoltaic array when it is exposed to sunlight.

Array Operating Voltage
The voltage produced by a photovoltaic array when exposed to sunlight and connected to a load.

Autonomous System
See stand-alone system.

Availability
The quality or condition of a photovoltaic system being available to provide power to a load. Usually measured in hours per year. One minus availability equals downtime.

Azimuth Angle
The angle between true south and the point on the horizon directly below the sun.

Balance of System
Represents all components and costs other than the photovoltaic modules/array. It includes design costs, land, site preparation, system installation, support structures, power conditioning, operation and maintenance costs, indirect storage, and related costs.

Band Gap
In a semiconductor, the energy difference between the highest valence band and the lowest conduction band.

Band Gap Energy (Eg)
The amount of energy (in electron volts) required to free an outer shell electron from its orbit about the nucleus to a free state, and thus promote it from the valence to the conduction level.

Barrier Energy
The energy given up by an electron in penetrating the cell barrier; a measure of the electrostatic potential of the barrier.

Base Load
The average amount of electric power that a utility must supply in any period.

Battery
Two or more electrochemical cells enclosed in a container and electrically interconnected in an appropriate series/parallel arrangement to provide the required operating voltage and current levels. Under common usage, the term battery also applies to a single cell if it constitutes the entire electrochemical storage system.

Battery Available Capacity
The total maximum charge, expressed in ampere-hours, that can be withdrawn from a cell or battery under a specific set of operating conditions including discharge rate, temperature, initial state of charge, age, and cut-off voltage.

Battery Capacity
The maximum total electrical charge, expressed in ampere-hours, which a battery can deliver to a load under a specific set of conditions.

Battery Cell
The simplest operating unit in a storage battery. It consists of one or more positive electrodes or plates, an electrolyte that permits ionic conduction, one or more negative electrodes or plates, separators between plates of opposite polarity, and a container for all the above.

Battery Cycle Life
The number of cycles, to a specified depth of discharge, that a cell or battery can undergo before failing to meet its specified capacity or efficiency performance criteria.

Battery Energy Capacity
The total energy available, expressed in watt-hours (kilowatt-hours), which can be withdrawn from a fully charged cell or battery. The energy capacity of a given cell varies with temperature, rate, age, and cut-off voltage. This term is more common to system designers than it is to the battery industry where capacity usually refers to ampere-hours.

Battery Energy Storage
Energy storage using electrochemical batteries. The three main applications for battery energy storage systems include spinning reserve at generating stations, load leveling at substations, and peak shaving on the customer side of the meter.

Battery Life
The period during which a cell or battery is capable of operating above a specified capacity or efficiency performance level. Life may be measured in cycles and/or years, depending on the type of service for which the cell or battery is intended.

Blocking Diode
A semiconductor connected in series with a solar cell or cells and a storage battery to keep the battery from discharging through the cell when there is no output, or low output, from the solar cell. It can be thought of as a one-way valve that allows electrons to flow forwards, but not backwards.

Boron (B)
The chemical element commonly used as the dopant in photovoltaic device or cell material.

Boule
A sausage-shaped, synthetic single-crystal mass grown in a special furnace, pulled and turned at a rate necessary to maintain the single-crystal structure during growth.

Btu (British Thermal Unit)
The amount of heat required to raise the temperature of one pound of water one degree Fahrenheit; equal to 252 calories.

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. It protects these solar cells from thermal destruction in case of total or partial shading of individual solar cells while other cells are exposed to full light.

Cadmium (Cd)
A chemical element used in making certain types of solar cells and batteries.

Cadmium Telluride (CdTe)
A polycrystalline thin-film photovoltaic material.

Capacity (C)
See battery capacity.

Capacity Factor
The ratio of the average load on (or power output of) an electricity generating unit or system to the capacity rating of the unit or system over a specified period of time.

Captive Electrolyte Battery
A battery having an immobilized electrolyte (gelled or absorbed in a material).

Cathode
The negative pole or electrode of an electrolytic cell, vacuum tube, etc., where electrons enter (current leaves) the system; the opposite of an anode.

Cathodic Protection
A method of preventing oxidation of the exposed metal in structures by imposing a small electrical voltage between the structure and the ground.

Cd
see cadmium.

CdTe
see cadmium telluride.

Cell (battery)
A single unit of an electrochemical device capable of producing direct voltage by converting chemical energy into electrical energy. A battery usually consists of several cells electrically connected together to produce higher voltages. (Sometimes the terms cell and battery are used interchangeably). Also see photovoltaic (PV) cell.

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 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
The process of adding electrical energy to a battery.

Charge Carrier
A free and mobile conduction electron or hole in a semiconductor.

Charge Controller
A component of a photovoltaic system that controls the flow of current to and from the battery to protect it from over-charge and over-discharge. The charge controller may also indicate the system operational status.

Charge Factor
A number representing the time in hours during which a battery can be charged at a constant current without damage to the battery. Usually expressed in relation to the total battery capacity, i.e., C/5 indicates a charge factor of 5 hours. Related to charge rate.

Charge Rate
The current applied to a cell or battery to restore its available capacity. This rate is commonly normalized by a charge control device with respect to the rated capacity of the cell or battery.

Chemical Vapor Deposition (CVD)
A method of depositing thin semiconductor films used to make certain types of photovoltaic devices. With this method, a substrate is exposed to one or more vaporized compounds, one or more of which contain desirable constituents. A chemical reaction is initiated, at or near the substrate surface, to produce the desired material that will condense on the substrate.

Cloud Enhancement
The increase in solar intensity caused by reflected irradiance from nearby clouds.

Combined Collector
A photovoltaic device or module that provides useful heat energy in addition to electricity.

Concentrator
A photovoltaic module, which includes optical components such as lenses (Fresnel lens) to direct and concentrate sunlight onto a solar cell of smaller area. Most concentrator arrays must directly face or track the sun. They can increase the power flux of sunlight hundreds of times.

Conductor
The material through which electricity is transmitted, such as an electrical wire, or transmission or distribution line.

Contact Resistance
The resistance between metallic contacts and the semiconductor.

Conversion Efficiency
See photovoltaic (conversion) efficiency.

Converter
A unit that converts a direct current (dc) voltage to another dc voltage.

Crystalline Silicon
A type of photovoltaic cell made from a slice of single-crystal silicon or polycrystalline silicon.

Current
See electric current.

Current at Maximum Power (Imp)
The current at which maximum power is available from a module.

Cutoff Voltage
The voltage levels (activation) at which the charge controller disconnects the photovoltaic array from the battery or the load from the battery.

Cycle
The discharge and subsequent charge of a battery.

Czochralski Process
A method of growing large size, high quality semiconductor crystal by slowly lifting a seed crystal from a molten bath of the material under careful cooling conditions.

Dangling Bonds
A chemical bond associated with an atom on the surface layer of a crystal. The bond does not join with another atom of the crystal, but extends in the direction of exterior of the surface.

Days of Storage
The number of consecutive days the stand-alone system will meet a defined load without solar energy input. This term is related to system availability.

DC
See direct current.

DC-to-DC Converter
Electronic circuit to convert direct current voltages (e.g., photovoltaic module voltage) into other levels (e.g., load voltage). Can be part of a maximum power point tracker.

Deep Discharge
Discharging a battery to 20% or less of its full charge capacity.

Deep-Cycle Battery
A battery with large plates that can withstand many discharges to a low state-of-charge.

Dendrite
A slender threadlike spike of pure crystalline material, such as silicon.

Dendritic Web Technique
A method for making sheets of polycrystalline silicon in which silicon dendrites are slowly withdrawn from a melt of silicon whereupon a web of silicon forms between the dendrites and solidifies as it rises from the melt and cools.

Depletion Zone
Same as cell barrier. The term derives from the fact that this microscopically thin region is depleted of charge carriers (free electrons and hole).

Depth of Discharge (DOD)
The ampere-hours removed from a fully charged cell or battery, expressed as a percentage of rated capacity. For example, the removal of 25 ampere-hours from a fully charged 100 ampere-hours rated cell results in a 25% depth of discharge. Under certain conditions, such as discharge rates lower than that used to rate the cell, depth of discharge can exceed 100%.

Design Month
The month having the combination of insolation and load that requires the maximum energy from the photovoltaic array.

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.

Diffuse Radiation
Radiation received from the sun after reflection and scattering by the atmosphere and ground.

Diffusion Furnace
Furnace used to make junctions in semiconductors by diffusing dopant atoms into the surface of the material.

Diffusion Length
The mean distance a free electron or hole moves before recombining with another hole or electron.

Diode
An electronic device that allows current to flow in one direction only. See blocking diode and bypass diode.

Direct Beam Radiation
Radiation received by direct solar rays. Measured by a pyrheliometer with a solar aperture of 5.7

Direct Current (DC)
A type of electricity transmission and distribution by which electricity flows in one direction through the conductor, usually relatively low voltage and high current. To be used for typical 120 volt or 220 volt household appliances, DC must be converted to alternating current, its opposite.

Direct Insolation
Sunlight falling directly upon a collector. Opposite of diffuse insolation.

Discharge
The withdrawal of electrical energy from a battery.

Discharge Factor
A number equivalent to the time in hours during which a battery is discharged at constant current usually expressed as a percentage of the total battery capacity, i.e., C/5 indicates a discharge factor of 5 hours. Related to discharge rate.

Discharge Rate
The rate, usually expressed in amperes or time, at which electrical current is taken from the battery.

Disconnect
Switch gear used to connect or disconnect components in a photovoltaic system.

Distributed Energy Resources (DER)
A variety of small, modular power-generating technologies that can be combined with energy management and storage systems and used to improve the operation of the electricity delivery system, whether or not those technologies are connected to an electricity grid.

Distributed Generation
A popular term for localized or on-site power generation.

Distributed Power
Generic term for any power supply located near the point where the power is used. Opposite of central power. See stand-alone systems.