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


Low Voltage Warning
A warning buzzer or light that indicates the low battery voltage set point has been reached.

Maintenance-Free Battery
A sealed battery to which water cannot be added to maintain electrolyte level.

Majority Carrier
Current carriers (either free electrons or holes) that are in excess in a specific layer of a semiconductor material (electrons in the n-layer, holes in the p-layer) of a cell.

Maximum Power Point (MPP)
The point on the current-voltage (I-V) curve of a module under illumination, where the product of current and voltage is maximum. For a typical silicon cell, this is at about 0.45 volts.

Maximum Power Point Tracker (MPPT)
Means of a power conditioning unit that automatically operates the photovoltaic generator at its maximum power point under all conditions.

Maximum Power Tracking
Operating a photovoltaic array at the peak power point of the array's I-V curve where maximum power is obtained. Also called peak power tracking.

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.

Microgroove
A small groove scribed into the surface of a solar cell, which is filled with metal for contacts.

Minority Carrier
A current carrier, either an electron or a hole, that is in the minority in a specific layer of a semiconductor material; the diffusion of minority carriers under the action of the cell junction voltage is the current in a photovoltaic device.

Minority Carrier Lifetime
The average time a minority carrier exists before recombination.

Modified Sine Wave
A waveform that has at least three states (i.e., positive, off, and negative). Has less harmonic content than a square wave.

Modularity
The use of multiple inverters connected in parallel to service different loads.

Module
See photovoltaic (PV) module.

Module Derate Factor
A factor that lowers the photovoltaic module current to account for field operating conditions such as dirt accumulation on the module.

Monolithic
Fabricated as a single structure.

Movistor
Metal Oxide Varistor. Used to protect electronic circuits from surge currents such as those produced by lightning.

Multi-Stage Controller
A charging controller unit that allows different charging currents as the battery nears full state_of_charge.

Multicrystalline
A semiconductor (photovoltaic) material composed of variously oriented, small, individual crystals. Sometimes referred to as polycrystalline or semicrystalline.

Multijunction Device
A high-efficiency photovoltaic device containing two or more cell junctions, each of which is optimized for a particular part of the solar spectrum.

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.

NEC
See National Electrical Code.

NEMA
See National Electrical Manufacturers Association.

Nickel Cadmium Battery
A battery containing nickel and cadmium plates and an alkaline electrolyte.

Nominal Voltage
A reference voltage used to describe batteries, modules, or systems (i.e., a 12-volt or 24-volt battery, module, or system).

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.

One-Axis Tracking
A system capable of rotating about one axis.

Open-Circuit Voltage (Voc)
The maximum possible voltage across a photovoltaic cell; the voltage across the cell in sunlight when no current is flowing.

Operating Point
The current and voltage that a photovoltaic module or array produces when connected to a load. The operating point is dependent on the load or the batteries connected to the output terminals of the array.

Orientation
Placement with respect to the cardinal directions, N, S, E, W; azimuth is the measure of orientation from north.

Outgas
See gassing.

Overcharge
Forcing current into a fully charged battery. The battery will be damaged if overcharged for a long period.

Packing Factor
The ratio of array area to actual land area or building envelope area for a system; or, the ratio of total solar cell area to the total module area, for a module.

Panel
See photovoltaic (PV) panel.

Parallel Connection
A way of joining solar cells or photovoltaic modules by connecting positive leads together and negative leads together; such a configuration increases the current, but not the voltage.

Passivation
A chemical reaction that eliminates the detrimental effect of electrically reactive atoms on a solar cell's surface.

Peak Demand/Load
The maximum energy demand or load in a specified time period.

Peak Power Current
Amperes produced by a photovoltaic module or array operating at the voltage of the I-V curve that will produce maximum power from the module.

Peak Power Point
Operating point of the I-V (current-voltage) curve for a solar cell or photovoltaic module where the product of the current value times the voltage value is a maximum.

Peak Power Tracking
see maximum power tracking.

Peak Sun Hours
The equivalent number of hours per day when solar irradiance averages 1,000 w/m2. For example, six peak sun hours means that the energy received during total daylight hours equals the energy that would have been received had the irradiance for six hours been 1,000 w/m2.

Peak Watt
A unit used to rate the performance of solar cells, modules, or arrays; the maximum nominal output of a photovoltaic device, in watts (Wp) under standardized test conditions, usually 1,000 watts per square meter of sunlight with other conditions, such as temperature specified.

Phosphorous (P)
A chemical element used as a dopant in making n-type semiconductor layers.

Photocurrent
An electric current induced by radiant energy.

Photoelectric Cell
A device for measuring light intensity that works by converting light falling on, or reach it, to electricity, and then measuring the current; used in photometers.

Photoelectrochemical Cell
A type of photovoltaic device in which the electricity induced in the cell is used immediately within the cell to produce a chemical, such as hydrogen, which can then be withdrawn for use.

Photon
A particle of light that acts as an individual unit of energy.

Photovoltaic (PV) Array
An interconnected system of PV modules that function as a single electricity-producing unit. The modules are assembled as a discrete structure, with common support or mounting. In smaller systems, an array can consist of a single module.

Photovoltaic (PV) Cell
The smallest semiconductor element within a PV module to perform the immediate conversion of light into electrical energy (direct current voltage and current). Also called a solar cell.

Photovoltaic (PV) Device
A solid-state electrical device that converts light directly into direct current electricity of voltage-current characteristics that are a function of the characteristics of the light source and the materials in and design of the device. Solar photovoltaic devices are made of various semiconductor materials including silicon, cadmium sulfide, cadmium telluride, and gallium arsenide, and in single ...

Photovoltaic (PV) Effect
The phenomenon that occurs when photons, the "particles" in a beam of light, knock electrons loose from the atoms they strike. When this property of light is combined with the properties of semiconductors, electrons flow in one direction across a junction, setting up a voltage. With the addition of circuitry, current will flow and electric power will be available.

Photovoltaic (PV) Generator
The total of all PV strings of a PV power supply system, which are electrically interconnected.

Photovoltaic (PV) Module
The smallest environmentally protected, essentially planar assembly of solar cells and ancillary parts, such as interconnections, terminals, [and protective devices such as diodes] intended to generate direct current power under unconcentrated sunlight. The structural (load carrying) member of a module can either be the top layer (superstrate) or the back layer (substrate).

Photovoltaic (PV) Panel
often used interchangeably with PV module (especially in one-module systems), but more accurately used to refer to a physically connected collection of modules (i.e., a laminate string of modules used to achieve a required voltage and current).

Photovoltaic (PV) System
A complete set of components for converting sunlight into electricity by the photovoltaic process, including the array and balance of system components.

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.

Photovoltaic(s) (PV)
Pertaining to the direct conversion of light into electricity.

Physical Vapor Deposition
A method of depositing thin semiconductor photovoltaic films. With this method, physical processes, such as thermal evaporation or bombardment of ions, are used to deposit elemental semiconductor material on a substrate.

Plates
A metal plate, usually lead or lead compound, immersed in the electrolyte in a battery.

Pocket Plate
A plate for a battery in which active materials are held in a perforated metal pocket.

Point-Contact Cell
A high efficiency silicon photovoltaic concentrator cell that employs light trapping techniques and point-diffused contacts on the rear surface for current collection.

Polycrystalline
See Multicrystalline.

Polycrystalline Silicon
A material used to make photovoltaic cells, which consist of many crystals unlike single-crystal silicon.

Power Conditioning
The process of modifying the characteristics of electrical power (for e.g., inverting direct current to alternating current).

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 of the inverter.

Power Density
The ratio of the power available from a battery to its mass (W/kg) or volume (W/l).

Power Factor (PF)
The ratio of actual power being used in a circuit, expressed in watts or kilowatts, to the power that is apparently being drawn from a power source, expressed in volt-amperes or kilovolt-amperes.

Primary Battery
A battery whose initial capacity cannot be restored by charging.

Projected Area
The net south-facing glazing area projected on a vertical plane.

PV
See photovoltaic(s).

Pyranometer
An instrument used for measuring global solar irradiance.

Pyrheliometer
An instrument used for measuring direct beam solar irradiance. Uses an aperture of 5.7

Quad
One quadrillion Btu (1,000,000,000,000,000 Btu).

Qualification Test
A procedure applied to a selected set of photovoltaic modules involving the application of defined electrical, mechanical, or thermal stress in a prescribed manner and amount. Test results are subject to a list of defined requirements.

Rated Battery Capacity
The term used by battery manufacturers to indicate the maximum amount of energy that can be withdrawn from a battery under specified discharge rate and temperature. See battery capacity.

Rated Module Current (A)
The current output of a photovoltaic module measured at standard test conditions of 1,000 w/m2 and 25�C cell temperature.

Rated Power
Rated power of the inverter. However, some units can not produce rated power continuously. See duty rating.

Reactive Power
The sine of the phase angle between the current and voltage waveforms in an alternating current system. See power factor.

Recombination
The action of a free electron falling back into a hole. Recombination processes are either radiative, where the energy of recombination results in the emission of a photon, or nonradiative, where the energy of recombination is given to a second electron which then relaxes back to its original energy by emitting phonons. Recombination can take place in the bulk of the semiconductor, at the surfaces...

Rectifier
A device that converts alternating current to direct current. See inverter.

Regulator
Prevents overcharging of batteries by controlling charge cycle-usually adjustable to conform to specific battery needs.

Remote Systems
See stand-alone systems.

Reserve Capacity
The amount of generating capacity a central power system must maintain to meet peak loads.

Resistance (R)
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.

Resistive Voltage Drop
The voltage developed across a cell by the current flow through the resistance of the cell.

Reverse Current Protection
Any method of preventing unwanted current flow from the battery to the photovoltaic array (usually at night). See blocking diode.

Ribbon (Photovoltaic) Cells
A type of photovoltaic device made in a continuous process of pulling material from a molten bath of photovoltaic material, such as silicon, to form a thin sheet of material.

RMS
See root mean square.

Root Mean Square (RMS)
The square root of the average square of the instantaneous values of an ac output. For a sine wave the RMS value is 0.707 times the peak value. The equivalent value of alternating current, I, that will produce the same heating in a conductor with resistance, R, as a dc current of value I.

Sacrificial Anode
A piece of metal buried near a structure that is to be protected from corrosion. The metal of the sacrificial anode is intended to corrode and reduce the corrosion of the protected structure.

Satellite Power System (SPS)
Concept for providing large amounts of electricity for use on the Earth from one or more satellites in geosynchronous Earth orbit. A very large array of solar cells on each satellite would provide electricity, which would be converted to microwave energy and beamed to a receiving antenna on the ground. There, it would be reconverted into electricity and distributed the same as any other centrally ...

Schottky Barrier
A cell barrier established as the interface between a semiconductor, such as silicon, and a sheet of metal.

Scribing
The cutting of a grid pattern of grooves in a semiconductor material, generally for the purpose of making interconnections.

Sealed Battery
A battery with a captive electrolyte and a resealing vent cap, also called a valve-regulated battery. Electrolyte cannot be added.

Seasonal Depth of Discharge
An adjustment factor used in some system sizing procedures which "allows" the battery to be gradually discharged over a 30-90 day period of poor solar insolation. This factor results in a slightly smaller photovoltaic array.

Secondary Battery
A battery that can be recharged.

Self-Discharge
The rate at which a battery, without a load, will lose its charge.

Semiconductor
Any material that has a limited capacity for conducting an electric current. Certain semiconductors, including silicon, gallium arsenide, copper indium diselenide, and cadmium telluride, are uniquely suited to the photovoltaic conversion process.

Semicrystalline
See Multicrystalline.