Glossary of Solar Terms
Accelerated Depreciation- Depreciation of an asset for tax purposes over a period of years less than their normal life.
Alternating Current (AC)- The movement (or flow) of an electric charge that periodically reverses direction. The direction of flow is reversed at frequent intervals--usually 100 or 120 times per second (50 or 60 cycles per second or 50//60 Hz). Households and businesses use AC power as the norm.
Alternative Electricity Supplier- A company or organization other than the utility, that sells electricity to homes and businesses.
Amorphous semiconductor- A non-crystalline semiconductor. Thin film is an example of a solar module made out of amorphous semiconductors. Easier and cheaper to make than crystalline, but less efficient.
Ampere Hour (amp hr. or AH)- A measurement of the amount of Amps that flow for one hour. Batteries are often measured using this designation. A current source that delivers one amp-hour can deliver one amp for an hour or two amps for half an hour or sixty amps for one minute.
Ampere Hour Meter- A device that measures the current over a span of time.
Ampere or Amp (SI)- The unit of electrical current flowing through a wire; a measure of electrons passing through a point per unit time; a unit of measurement of the quantity of electric current.
Angle of Incidence- a measure of deviation of something from "straight on". In the solar industry it is the angle of the sun’s rays to that of 90 degrees.
Anti-reflection- coating A thin coating of a material, which reduces the light reflection and increases light transmission, applied to a photovoltaic cell surface.
Array- A group of PV modules connected together that provide a single electrical output.
Autonomous system- A PV system that is not connected to the grid. These types of systems are usually connected to a battery. An example of this type of system is a traffic sign.
AWG or American Wire Gauge- A standard system for designating the size of electrical wire. The higher the gauge number, the smaller the diameter of the wire. Most house wiring is #12 or 14.
Azimuth- The direction that an object is in regards to a compass. Generally referred to in degrees with 180 degrees representing due south.
Balance of system (BOS)- Usually understood to mean the racking, mounting, wiring, conduit etc. for a solar electric system.
Ballasted Mount- A racking system that supports solar panels that is placed on a flat roof. This racking system is held in place by concrete blocks installed inside the rack.
Base load- The minimum amount of power that a utility or distribution company must make available to its customers.
Battery Backup- An array of batteries attached to a solar system that will provide power in the event of a power outage.
Black-on-black- A style of solar panel with an all-black appearance.
Blocking Diode- A diode can be thought of in the same way as a water check valve. It keeps power from flowing in the reverse direction. This feature protects the solar cells from being damaged.
British Thermal Unit (BTU)- A traditional unit of energy equivalent to about 1.06 kilojoules. 1 watt is approximately 3.41214 BTU/h. It can also be understood as the amount of energy required to raise the temperature of one pound of water from 60 degrees F to 61 degrees F at one atmosphere pressure.
Building Integrated Photovoltaic ( BIPV)- When PV is designed to be part of the structure itself. A roof shingle PV is an example. BIPV panels are more expensive and somewhat less efficient than traditional solar panels, but many consumers consider them to be the best-looking option on the market.
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, broken cells, or cell string failures of individual solar cells while other cells are exposed to full light.
Capital Lease- A lease considered to have the economic characteristics of asset ownership. A capital lease would be considered a purchased asset for accounting purposes.
Cathodic Protection- A process that protects buried metal from rusting by running electrical currents through the metal.
Cell- The individual units that make up a photovoltaic module.
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 cell junction.
Cell Junction- See “Cell Barrier”
Charge Controller- A piece of equipment between the solar panels and the batteries that regulates the voltage and current (amperage) coming from the solar panels and going to the batteries.
Combined Collector- A solar module or other solar photovoltaic device that provides useful heat energy in addition to electricity.
Concentrator- The use of a lens to focus more of the sun on a smaller area thus increasing the energy harvested from a smaller PV area. A dual axis tracker is usually needed for this type of PV system.
Current at Maximum Power (Imp)- The current at which maximum power is available from a module.
Delivery Service- The portion of your electricity bill for the delivery of electricity to your home or business. Your utility always provides delivery service.
Demand- The rate of use of energy during a specific time period.
Diffuse Insolation- The solar radiation received indirectly due to scattering or reflection by atmospheric components (clouds, for example).
Direct Current (DC)- The flow of electric charge in a constant direction. Power generated by solar panels is direct current.
Direct Insolation- The solar irradiance measured at a given location on Earth with a surface element perpendicular to the Sun's rays, excluding diffuse insolation.
Distributed system- A power generating system that is installed where the energy is needed. A solar electric system is considered a distributed system since the owner uses the electricity produced right there at the site.
Efficiency- The ratio of power output of a Photovoltaic cell to the incident power from the sun or simulated sun sources under specified standard insolation conditions.
Electric Circuit Path- followed by electrons from a power source (generator or battery) through an external line (including devices that use the electricity) and returning through another line to the source.
Electric Current- The rate at which electricity flows through an electrical conductor, usually measured in amperes (amps).
Electric Meter- The meter installed by the electricity utility to measure electricity consumption.
Electric Panel- The panel installed in your home or business that distributes the power throughout the building.
Electrical Grid- The overall system in which electricity is delivered from the generation plant to the end user.
Electrons- A negatively charged particle. The movement of electrons in an electrical conductor constitutes an electric current.
Energy Payback- Time The amount of time needed for the energy saved on a product to offset the energy it took to build the product.
Federal Tax Credit- A dollar-for-dollar reduction of your tax burden for installing solar.
Fuel Cell- A device that converts the energy of a fuel directly to electricity and heat, without combustion. Because there is no combustion, fuel cells give off few emissions.
Full Sun- The amount of energy that is received at the surface of the earth at noon on a clear day, which is approx. 1000 watts per square meter.
Gigawatt (GW)- One billion watts
Grid Lines Metallic- contacts fused to the surface of the solar cell to provide a low resistance path for electrons to flow out of the cell.
Grid Tied/Grid Connected- A solar electric system that is interconnected to the electrical grid. Generally these systems do not use battery back-up as electricity from the grid supplements the system.
Ground Loop- A condition caused by two or more circuits sharing a common electrical line, usually a grounded conductor.
Ground Mount- A solar electrical system that is mounted on the ground.
Hybrid System- A power system that consists of more than two power generating devices. An example would be a diesel generator coupled with a PV system.
Incident Light- The incident light is the amount of light reaching an object. It is the measure of light falling on an object rather than that reflected from it.
Insolation- A measure of solar radiation energy received on a given surface area in a given time.
Interconnection- An agreement with or approval by the utility and the distributed power generator (solar array owner), for the distributed power generator to connect their renewable energy system (solar array) to the electric utility system or grid.
Interconnection/Interconnected- The process of hooking up a solar electrical system to the power grid. Interconnection (and related standards) refers to the technical and practical aspects of connecting the solar generator to the grid.
Inverter- An electrical device that converts direct current (DC) electricity into alternating current (AC) electricity.
Junction box- An electrical box designed to be a safe enclosure in which to make proper electrical connections.
Junction Diode- A diode that conducts an electric current in one direction and blocks it in the other.
Kilowatt (kW)- One thousand watts
Kilowatt hour (kWh)- A common unit of electric power consumption. One kilowatt-hour equals 1000 watt-hours and can be used to define the amount of energy used over a one-hour period. This is one of the units of measure that utilities use when billing a customer.
Load Usually- expressed in terms of amperes or watts; refers to the amount of power that equipment is using that is powered by electricity.
Magnetic South- The direction toward which the south-seeking arrow of a compass points. In this region, magnetic south varies from true south by approximately 12 degrees.
Maximum Power- The power at the point on the current-voltage characteristic where the product of current and voltage is a maximum (measured in watts).
Maximum Power Point (MPP)- The point on the I-V curve where the current and the voltage are at their highest levels.
Maximum Power Point Tracker (MPPT)- A power conditioning unit that automatically operates the PV-generator at its MPP under all conditions.
Megawatt- One million watts
Microgroove- A small groove scribed into the surface of a cell which is filled with metal for contacts.
Microinverter- Small inverters typically installed behind each solar panel that converts the DC power from the panel to AC.
Module- See Photovoltaic (PV) Panel.
Monocrystalline- A single silicon crystal. In the context of solar, a type of PV panel with cells made with monocrystalline silicone.
Monocrystalline Panel- A PV module that is made from a single silicon crystal. These panels are usually more efficient and more expensive than multi-crystalline panels.
Mounting System- The method of securing solar panels. See ballasted mount, ground mount, and roof mount.
Multicrystalline Panel (also polycrystalline)- A solar panel that is made from small silicon crystals oriented in multiple directions. Multicrystalline panels are less expensive and less efficient than monocrystalline panels.
Net metering- A policy set by states, for renewable energy generators to receive credit for overproduction of electricity. Both overproduction and consumption are measured by the utility, allowing renewable energy generators to pay for only the power consumed after their production is accounted for.
Off Grid- A distributive energy system that is not attached to the electrical grid.
Ohm- The unit of resistance to the flow of an electric current.
One-Axis Tracking- A system capable of rotating about a single axis
Online Monitoring- A system that allows you to monitor the production of your solar array from any Internet-connected device.
Open Circuit Voltage (VOC)- The maximum possible voltage across a photovoltaic cell or module; the voltage across the cell in sunlight when no current is flowing; measured with a voltmeter.
Operating Lease- A contract that allows for the use of an asset, but does not convey rights of ownership of the asset. This method of financing is known as "off balance sheet financing" and do not result in assets or liabilities being recorded on the lessee's balance sheet, which can improve the lessee's financial ratios.
Orientation- The direction your solar panels face, in relation to true south.
Panel- See Photovoltaic (PV) Panel.
Parallel Connection- A wiring configuration used to increase current (amperage); A way of joining two or more electricity-producing devices (i.e., PV cells or modules) by connecting positive leads together and negative leads together.
Passive solar home- When a house uses the warmth of the sun to supplement the heating of a home. An example would be having southern facing windows which would allow the sun to stream into a home.
Peak Load/Peak Demand- The maximum load, or usage, of electrical power occurring in a given period of time, typically a day.
Peak Power Point- Operating point of the I-V (current-voltage) curve for a Photovoltaic cell or module where the product of the current value times the voltage value is a maximum.
Peak Watts- The amount of electricity that is produced at 12 noon on a cloudless day.
Photon- A particle of light
Photovoltaic (PV)- Able to generate a current or voltage when exposed to visible light or other electromagnetic radiation.
Photovoltaic (PV) array- A number of PV modules that are interconnected so as to act as a single unit.
Photovoltaic (PV) Cell- A device composed of specially prepared semiconductor material or material combinations exhibiting the ability to convert incident solar energy directly into electrical energy. The smallest semiconductor element within a module that converts sunlight in DC electricity.
Photovoltaic (PV) Efficiency- The amount of electricity produced compared to the amount of sunlight. This amount is expressed as a percentage.
Photovoltaic (PV) Panel- Often used interchangeably with PV module, but more accurately used to refer to a physically connected collection of PV cells in series, in parallel, or in series- parallel combination to provide greater voltage, current, or power. A large panel consisting of solar cells that convert the sun’s radiation into electricity.
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.
PJM Interconnection, LLC (PJM)- The independent system operator that operates and controls the bulk electric power system throughout the majority of the Mid-Atlantic region. PJM manages electricity distribution; local utilities manage electricity delivery.
Polycrystalline- A material consisting of small silicon crystals. In the context of solar, a type of PV panel with cells made with polycrystalline silicone.
Power Purchase Agreement (PPA)- An agreement between an electricity producer and an electricity consumer or delivery company for the purchase of electricity. Owners of solar arrays can use PPAs to realize their return on investment in solar.
Procurement Cost Adjustment (PCA)- The adjustment made to your electric bill in order to true-up your electricity rates to the utility’s actual cost of providing electricity.
Production- The amount of electricity produced in a year, based upon your array’s tilt and orientation.
PV- Short for photovoltaic(s)
PV Watts- A calculator from the National Renewable Energy Laboratory (NREL) that models the estimated annual energy production from solar PV systems.
Racking System -The support system for solar panels. See ballasted mounting, ground mount, and roof mount.
Remote Systems- Systems off of the utility grid.
Renewable Energy- Sources of energy that are regenerative or virtually inexhaustible. Most commonly includes solar (electric and thermal), biomass, geothermal, wind, tidal, wave, and hydro power sources.
Renewable Portfolio Standard- A law that requires utilities to deliver a certain portion of their power from renewable resources.
Reverse Bias- Condition where the current producing capability of a PV cell is significantly less than that of other cells in its series string. This can occur when a cell is shaded, cracked, or otherwise degraded or when it is electrically poorly matched with other cells in its string.
Roof Mount- The installation of solar panels parallel to a building’s roof, utilizing a racking system consisting of brackets to connect the array to the roof, and rails to support and connect the solar panels.
Series Connection- A wiring configuration used to increase voltage. Series wiring is positive to negative (+ to -) or negative to positive (- to +), such a configuration increases the voltage. This is opposite of a parallel connection.
Short-Circuit Current (Isc)- The current flowing freely from a photovoltaic cell through an external circuit that has no load or resistance; the maximum current possible in a cell.
Silicon- The raw material used to manufacture most photovoltaic cell. A chemical element, semi metallic in nature, and an excellent semiconductor material. When specially treated, it is sensitive to light and capable of transforming light into electricity.
Single-Crystal Structure- A material having a crystalline structure such that a repeatable or periodic molecular pattern exists in all three dimensions.
Solar Cell- See Photovoltaic (PV) Cell.
Solar Noon- The time of day when the sun reaches its highest point in the sky. This time divides the daylight hours for that day exactly in half. To determine solar noon, calculate the length of the day from the time of sunset and sunrise and divide by two; solar noon may be quite a bit different from 'clock' noon.
Solar Panel- See Photovoltaic (PV) Panel.
Solar Renewable Energy Certificate (SREC)- A legislatively-created commodity equivalent to one megawatt hour (1,000 kWh) of solar electricity production. The green attribute of the electricity produced, and not the actual electricity created by the solar array. These commodities can be sold a variety of ways, turning them into cash for the solar owner.
Solar Renewable Energy Credit- An alternative phrase for Solar Renewable Energy Certificate.
Solar Spectrum- The total distribution of electromagnetic radiation emanating from the sun.
Solar Thermal Electric- Method of producing electricity from solar energy by using focused sunlight to heat a working fluid, which in turn drives a turbo generator.
Solar-Grade Silicon- Intermediate-grade silicon used in the manufacture of solar cells.
Stand-off Mounting- Technique for mounting a PV array on a sloped roof, which involves mounting the modules a short distance above the pitched roof and tilting them to the optimum angle.
State Grant- A payment made to you by the division of your state that administers renewable energy grants after you install a solar array. Your state grant availability and eligibility is determined by which utility you use.
Substrate- The physical material upon which a photovoltaic cell is attached.
Supply Service- The portion of your electricity bill for the supply of power to your home or business. In states with electricity choice, this may be supplied by the company that delivers electricity (the utility), or by an alternative electricity supplier.
Thick-Crystalline Materials- Semiconductor material, typically measuring from 200-400 microns thick, which is cut from ingots or ribbons.
Thin film panel- A solar panel that is thin and flexible. The term refers to both amorphous photovoltaic solar panels, which use silicon as their semiconductor, and panels that use other semiconductors like cadmium telluride and copper indium gallium diselenide.
Tilt- The orientation of solar panels in relation to true horizontal.
Tilt Angle- A fixed angle measured from the horizontal to which a solar array is tilted. The tilt angle is chosen to maximize the array output. Depending upon latitude, season and time of day this angle will vary.
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 eventually be absorbed by the semiconductor.
Tracking Array- A PV array that follows the path of the sun to maximize the amount of energy that the array can produce.
True South- The direction towards the southern end of the axis (the South Pole) about which the earth rotates. In this region, magnetic south varies from true south by approximately 12 degrees.
Utility- The company or organization that delivers power to your home or business. This is based upon the location of your home or business.
VAC- Volts ac
VDC- Volts dc
Vmp- Voltage at maximum power
Voc- Open-circuit voltage
Volt/Voltage (V)- A unit of measure of the force, or 'push,' given the electrons in an electric circuit. One volt produces one ampere of current when acting a resistance of one ohm.
Voltage at Maximum Power (Vmp)- The voltage at which maximum power is available from a module.
Wafer- A thin sheet of semiconductor material made by mechanically sawing it from a single-crystal or multi-crystal ingot or casting.
Watt (W)- A unit of power, equivalent to one joule per second. Watts are calculated by multiplying volts by amps.