A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

A
AC	See alternating current.
Alternating Current (AC)	A type of electrical current with a directional flow that is reversed at regular intervals or cycles. In the United States, the standard is 60 cycles per second. Electricity transmission networks use AC because voltage can be transformed to different levels with relative ease.
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 (Ah/AH)	A measure of the flow of current (in amperes) over one hour; used to measure battery capacity.
Anti-Islanding Provisions	Measures taken to prevent an isolated generator from feeding power back into the utility grid during a power outage. Most utilities require grid-tied generators to meet specific anti-islanding standards.
Array	See photovoltaic (PV) array.
Automation	See home automation.
Back to Top
B
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.
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 Backup System	An assemblage of batteries and power electronics that protects users in the event of a power outage by providing power from the stored energy in the batteries to pre-chosen secure loads.
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 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.
BIPV (Building-Integrated Photovoltaics)	A term for the design and integration of photovoltaic (PV) technology into the building envelope, typically replacing conventional building materials. This integration may be into vertical facades, replacing view glass, spandrel glass, or other facade material; into semitransparent skylight systems; into roofing systems, replacing traditional roofing materials; into shading "eyebrows" over windows; or other building envelope systems.
Back to Top
C
Charge	The process of adding electrical energy to a battery.
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.
Combiner Box	An enclosure that combines the output of many circuits into an output carried by fewer circuits. In photovoltaic systems, a combiner box often sits on the roof or mounting structure near the panels, collects wires from many arrays, and outputs just two wires to link into the system's inverter.
Compact Fluorescent Light Bulb	A type of light bulb that provides light equivalent to a traditional light bulb while consuming significantly less energy. Though compact fluorescent bulbs cost more than traditional bulbs, they last significantly longer and use less energy, producing significant savings over the course of its lifetime. The ENERGY STAR logo on the bulb package ensures that a bulb is indeed designed to meet efficiency standards.
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.
Back to Top
D
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 percent 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.
Demand Response	Demand Response services empower the customer and/or utility to react to high energy prices or high energy load demands. With these services, customers may opt to control when or how often select appliances in the home may run, and adjust thermostats to reduce energy consumption, avoiding the high price periods. Alternatively a utility, with select programs and services, may opt to control energy demands for participants in their territory by shifting or decreasing energy load demands to avoid costly grid failures or strain. These programs have been created to offset energy demand drains on utilities as well as offset high energy costs for the consumer, and often can eliminate the need for constructing additional power plants.
Demand Side Management (DSM)	A generic term for the ability of a utility to reduce its customers' demand for electricity, normally at peak times. For example, some utilities offer compensation to customers in exchange for the ability to modestly adjust household air conditioning loads when the overall demand for electricity on the grid is high.
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 percent depth of discharge. Under certain conditions, such as discharge rates lower than that used to rate the cell, depth of discharge can exceed 100 percent.
Design Month	The month having the combination of insolation and load that requires the maximum energy from the photovoltaic array.
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.
Discharge	The withdrawal of electrical energy from a battery.
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.
Dispatch, Dispatchability	The ability to call upon energy storage or electricity generation capacity to supply the utility grid with needed power when needed.
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.
Distributed Systems	Systems that are installed at or near the location where the electricity is used, as opposed to central systems that supply electricity to grids. A residential photovoltaic system is a distributed system.
Duty Cycle	The ratio of active time to total time. Used to describe the operating regime of appliances or loads in photovoltaic systems.
Back to Top
E
Efficiency	See energy efficiency.
Electric Current	The flow of electrical energy (electricity) in a conductor, measured in amperes.
Electrical grid	An integrated system of electricity distribution, usually covering a large area.
Electricity	Energy resulting from the flow of charge particles, such as electrons or ions.
Energy	The capability of doing work; different forms of energy can be converted to other forms, but the total amount of energy remains the same.
Energy Audit	A survey that shows how much energy used in a home, which helps determine ways to use less energy.
Energy Density	The ratio of available energy per pound; usually used to compare storage batteries.
Energy Efficiency	The quality of using less energy to perform an action that would otherwise consume more energy. Energy efficiency in lighting and appliances saves money and reduces pollution by cutting demand for electricity.
Energy Policy Act of 2005	A broad energy policy bill signed into law by President George W. Bush. Among many other outcomes, the Act instates a federal tax credit of up to $2,000 for residential solar systems and an uncapped tax credit for 30 percent of the installed cost of commercial solar systems. These credits stand in addition to state and local incentives.
Energy Star	A government-backed program helping businesses and individuals protect the environment through energy efficiency. The program offers energy saving tips and leads a labeling program for energy efficient wares. It may be found on the Web at www.energystar.gov.
Back to Top
F
Feed-in Tariff	A mandated price per kWh paid to generators of renewable energy. Favorable feed-in tariffs encourage the use of renewable energy by guaranteeing a price for renewable generation.
Float Charge	The voltage required to counteract the self-discharge of the battery at a certain temperature.
Float Life	The number of years that a battery can keep its stated capacity when it is kept at float charge.
Float Service	A battery operation in which the battery is normally connected to an external current source; for instance, a battery charger which supplies the battery load under normal conditions, while also providing enough energy input to the battery to make up for its internal quiescent losses, thus keeping the battery always up to full power and ready for service.
Fossil Fuel	A hydrocarbon fuel formed in the ground millions of years ago from plant and animal remains. Fossil fuels can be burned for heat or power, but produce carbon dioxide. Oil, coal and natural gas are all fossil fuels.
Frequency	The number of repetitions per unit time of a complete waveform, expressed in Hertz (Hz).
Frequency Regulation	This indicates the variability in the output frequency. Some loads will switch off or not operate properly if frequency variations exceed 1percent.
Fuel Cell	An electrochemical device that converts the chemical energy of a fuel, such as hydrogen, and an oxidant, such as oxygen, directly to electricity. The principal components of a fuel cell are catalytically activated electrodes for the fuel (anode) and the oxidant (cathode) and an electrolyte to conduct ions between the two electrodes.
Back to Top
G
Generator	A device that generates electricity. At the residential level, usually fueled by diesel or natural gas.
Gigawatt (GW)	A unit of power equal to one billion Watts; one million kilowatts, or 1,000 megawatts.
Green Tags	Another term for renewable energy certificates.
Grid	See electrical grid.
Grid-Connected System	A solar electric or photovoltaic (PV) system in which the PV array acts like a central generating plant, supplying power to the grid.
Grid-Interactive System	Same as grid-connected system.
Ground Fault Protection	A circuit protection device that prevents the flow of electrical current to earth if a short circuit is present.
Back to Top
H
Harmonic Content	The number of frequencies in the output waveform in addition to the primary frequency (50 or 60 Hz.). Energy in these harmonic frequencies is lost and may cause excessive heating of the load.
High Voltage Disconnect	The voltage at which a charge controller will disconnect the photovoltaic array from the batteries to prevent overcharging.
High Voltage Disconnect Hysteresis	The voltage difference between the high voltage disconnect set point and the voltage at which the full photovoltaic array current will be reapplied.
Home Automation	A general term for anything that gives homeowners remote or automatic control of lighting, energy, appliances, security, or HVAC systems around the home.
Hybrid System	A solar electric or photovoltaic system that includes other sources of electricity generation, such as wind or diesel generators.
Back to Top
I
I-V Curve	A graphical presentation of the current versus the voltage from a photovoltaic device 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.
Incentive	Something offered to motivate action. Financial incentives such as tax credits, rebates and feed-in tariffs are offered to varying degrees to the purchase and use of renewable energy systems.
Input Voltage	This is determined by the total power required by the alternating current loads and the voltage of any direct current loads. Generally, the larger the load, the higher the inverter input voltage. This keeps the current at levels where switches and other components are readily available.
Insolation	The solar power density incident on a surface of stated area and orientation, usually expressed as watts per square meter or Btu per square foot per hour. See diffuse insolation and direct insolation.
Interconnect	A conductor within a module or other means of connection that provides an electrical interconnection between the solar cells.
Inverter	A device that converts direct current electricity to alternating current either for stand-alone systems or to supply power to an electricity grid.
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.
Islanding	An instance when an isolated generator feeds power back into the utility grid during a power outage. Most utilities require grid-tied generators to meet specific anti-islanding standards.
Back to Top
J
Joule	The standard unit of energy in electronics and general scientific applications. One joule (pronounced DJOOL) is defined as the amount of energy exerted when a force of one newton is applied over a displacement of one meter. One joule is the equivalent of one watt of power radiated or dissipated for one second.
Junction Box	A photovoltaic (PV) generator junction box is an enclosure on the module where PV strings are electrically connected and protection devices can be located, if necessary.
Back to Top
K
Kilowatt (kW)	A standard unit of electrical power equal to 1,000 watts, or to the energy consumption at a rate of 1,000 joules per second.
Kilowatt-Hour (kWh)	1,000 thousand watts acting over a period of one hour. The kWh is a unit of energy. 1 kWh=3600 kJ.
Back to Top
L
Lead-Acid Battery	A general category that includes batteries with plates made of pure lead, lead-antimony or lead-calcium immersed in an acid electrolyte.
Life-Cycle Cost	The estimated cost of owning and operating a photovoltaic system for the period of its useful life.
Line-Commutated Inverter	An inverter that is tied to a power grid or line. The commutation of power (conversion from direct current to alternating current) is controlled by the power line, so that, if there is a failure in the power grid, the photovoltaic system cannot feed power into the line.
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.
Load Circuit	The wire, switches, fuses, etc. that connect the load to the power source. When installing a backup power system, the load circuit is separated into a distinct set of circuits called the secure load sub-panel.
Load Current	The current required by the electrical device.
Load Panel	Sometimes called a fuse box, the load panel houses breakers or fuses for circuits in an electrical system.
Load Resistance	The resistance presented by the load. See resistance.
Low Voltage Cutoff (LVC)	The voltage level at which a charge controller will disconnect the load from the battery.
Low Voltage Disconnect	The voltage at which a charge controller will disconnect the load from the batteries to prevent over-discharging.
Low Voltage Disconnect Hysteresis	The voltage difference between the low voltage disconnect set point and the voltage at which the load will be reconnected.
Low Voltage Warning	A warning buzzer or light that indicates the low battery voltage set point has been reached.
Back to Top
M
Maintenance-Free Battery	A sealed battery that maintains its electrolyte level on its own and does not require additional water.
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 one million watts; standard measure of electric power plant generating capacity.
Megawatt-Hour	1,000 kilowatt-hours or one million watt-hours.
Million Solar Roof Initiative	A public-private partnership headed by the U.S. Department of Energy and designed to support states and local communities as they develop a strong commitment to the sustained deployment of solar energy technologies. For more information, access www.millionsolarroofs.org.
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.
Back to Top
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.
Negawatt	A term coined by Amory Lovins referring to a unit of reduction in energy demand. Instead of building more power plants to increase supply, Lovins argues, employing energy efficiency technologies reduces demand and meets the same goal with less impact on the environment.
Net Metering	A Net Metering service begins with a utility or other energy providing entity metering or measuring the energy that is produced by a home or business using a renewable energy source against that which is consumed by that same home or business. The ‘net' metered result will enable the customer to realize a ‘retail' value for the energy they produce. If there is a ‘net' excess of energy produced, meaning the home or business did not consume all of the energy produced, the utility or energy provider may opt to spin the meter backwards to reflect a decreased amount of energy purchased or bank the unused energy until needed by that customer. Net metering simply allows an energy customer to use any excess electricity they generate to offset the amount of electricity consumed and purchased during a billing period so that they are only billed for the ‘net' energy consumed.
Nominal Voltage	A reference voltage used to describe batteries, modules or systems (i.e., a 12-volt or 24-volt battery, module or system).
Normal Operating Cell Temperature (NOCT)	The estimated temperature of a photovoltaic module when operating under 800 w/m2 irradiance, 20ºC ambient temperature and wind speed of one meter per second. NOCT is used to estimate the nominal operating temperature of a module in its working environment.
Back to Top
O
Ohm	A measure of the electrical resistance of a material equal to the resistance of a circuit in which the potential difference of one volt produces a current of one 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.
Overcharge	Forcing current into a fully charged battery. The battery will be damaged if overcharged for a long period.
Back to Top
P
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.
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.
Performance Monitoring	A service that tracks the workings of equipment, often remotely, to make sure that a device is working optimally.
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) Conversion Efficiency	The ratio of the electric power produced by a photovoltaic device to the power of the sunlight incident on the device.
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 crystalline, multicrystalline or amorphous forms.
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(s) (PV)	Pertaining to the direct conversion of light into electricity.
Power Conditioning	The process of modifying the characteristics of electrical power (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.
Power Quality	Power quality is a comparison of the electrical wave form to an ideal sine wave. Poor power quality can result in inefficient operation or damage to equipment.
Primary Battery	A battery whose initial capacity cannot be restored by charging.
Protect	See GridPoint Protect
PV	See photovoltaic(s).
Back to Top
Q
Quad	One quadrillion Btu (1,000,000,000,000,000 Btu).
Back to Top
R
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.
Rebate	A sum offered to reduce the total cost of a good or service. Some states, municipalities, and utilities offer rebates for the purchase and installation of renewable energy systems.
REC	See renewable energy certificate.
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 Diagnostics	The ability to monitor and analyze a system from a location distant from the system; often remote diagnostics use a phone line or the internet as a line of communication between the system and the analyzer.
Remote Systems	See stand-alone systems.
Renewable Energy	Generally, any energy generated from a source that does not diminish when consumed. Wind energy, for example, is termed renewable because generating electricity from wind does not diminish the future potential of the wind to blow. Conversely, petroleum in termed a non-renewable resource because consuming a barrel of oil diminishes the future availability of that resource. Since renewable energies are not based on fossil fuels, they generally produce low or no air pollution and do not contribute to global warming.
Renewable Energy Certificate (REC)	A tradable commodity, usually representing one Megawatt hour of energy from a renewable source (wind, solar, biomass, etc.) Where markets are established, RECs can serve as a revenue source for owners of renewable energy systems.
Renewable Portfolio Standard (RPS)	A policy set by federal or state governments mandating that a percentage of the area's electricity be generated from a renewable source.
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.
RPS	See renewable portfolio standard.
Back to Top
S
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 to 90 day period of poor solar insolation. This factor results in a slightly smaller photovoltaic array.
Secondary Battery	A battery that can be recharged.
Secure Load	The circuits connected to the secure load sub-panel and protected with back-up power in the event of a utility power outage.
Secure Load Sub-Panel	A secondary load panel, connected both to the secure load and to the backup power source. Circuits connected to the secure load sub-panel receive backup power from the backup power unit in the event of a utility power outage.
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.
Series Connection	A way of joining photovoltaic cells by connecting positive leads to negative leads; such a configuration increases the voltage.
Short-Circuit Current (Isc)	The current flowing freely through an external circuit that has no load or resistance; the maximum current possible.
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 and is 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.
Smart Grid	A term commonly used for an electricity grid that incorporates information technology with distributed generation, demand side management and supply side management
Solar Cell	See photovoltaic (PV) cell.
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 Panel	See photovoltaic (PV) panel.
Solar Renewable Energy Certificate	A renewable energy certificate designated specifically for solar energy.
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.
Spinning Reserve	Electric power plant or utility capacity on-line and running at low power in excess of actual load.
SREC	See solar renewable energy certificate
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-by Generator	A generator used for backup power purposes, often powered by diesel or gas.
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.
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.
String	A number of photovoltaic modules or panels interconnected electrically in series to produce the operating voltage required by the load.
Superconducting Magnetic Energy Storage (SMES)	SMES technology uses the superconducting characteristics of low-temperature materials to produce intense magnetic fields to store energy. It has been proposed as a storage option to support large-scale use of photovoltaics as a means to smooth out fluctuations in power generation.
Supply Side Management (SSM)	A generic term for the ability of a utility to increase its supply of electricity, normally at peak times. For example, some utilities may dispatch small generators around a grid to augment their baseline power when the overall demand for electricity on the grid is high.
Surge Capacity	The maximum power, usually three to five 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.
Back to Top
T
Time-Based Metering	Time-Based Metering is analogous with Time of Use (TOU) pricing. Time-of-use metering measures an average usage of electricity at certain times of the day over the length of the billing or meter-reading period. A TOU metered rate schedule indicates that the utility will charge varying energy prices based on the hour and day, providing low and high energy price points. Customers may take advantage of this type of metering by shifting high energy consumption patterns to lower priced time periods. Much like a cell phone plan, time based metering provides peak and off peak time periods.
Time of Use Pricing	See Time-Based Metering.
Total AC Load Demand	The sum of the alternating current loads. This value is important when selecting an inverter.
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.
Back to Top
U
Uninterruptible Power Supply (UPS)	The designation of a power supply providing continuous uninterruptible service. The UPS will contain batteries.
Utility	A company that generates, transmits and/or distributes electricity, water and/or gas.
Utility-Interactive Inverter	An inverter that ties 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. Some modern inverters can also operate in standalone mode during power outages.
Back to Top
V
Varistor	A voltage-dependent variable resistor. Normally used to protect sensitive equipment from power spikes or lightning strikes by shunting the energy to ground.
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.
Back to Top
W
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.
Wind turbine	A machine that captures the energy of the wind and transfers the motion to an electric generator shaft. Wind turbines come in many sizes ranging from large utility scale to small residential scale.
Wire Types	See Article 300 of National Electric Code for more information.
Back to Top
Z
ZigBee	A published specification set of high level communication protocols designed to use small, low power digital radios based on the IEEE 802.15.4 standard for wireless personal area networks (WPANs). The technology is designed to be simpler and cheaper than other WPANs such as Bluetooth. For more information, visit the ZigBee Alliance homepage.