Solar Glossary


AC-Coupled System An AC-coupled system combines non-battery-based and battery-based inverters into one system. One or more grid-tied inverters can work with certain battery based inverters to disconnect from the utility grid and continue to supply electricity for critical loads when the utility power fails. Special battery-based inverters are required.
AC Module An inverter that's permanently attached to and an integral part of a photovoltaic module. All DC wiring is completely internal to an ac-module inverter. For that reason, unlike "micro-inverters", ac module inverters are not required to have DC-side ground-fault detection.
Albedo The fraction of solar radiation reflected from the ground, ground cover, and bodies of water on the surface of the earth.
Alternating Current (AC)  Electric current that reverses direction 50 or 60 times per second (depending on the country).  
Amorphous Photovoltaic Amorphous photovoltaic modules are commonly made from a special form of silicon that's applied like other "thin-film" materials. Typically brownish in color. Often found used in calculators and similar applications.
Ampere The quantity of electrical current flowing through a circuit
Amperage Interrupt Capability (AIC) Direct current fuses should be rated with a sufficient AIC to interrupt the highest possible current
Amp-hour Often abbreviated "A-H" or "AH". A measure of the amount (quantity) of electrical current flowing for a given period of time. Typical time unit is "hours", thus "amp-hours".
Array Two or more photovoltaic modules connected together.
Array Operating Voltage The voltage produced by a photovoltaic array when exposed to sunlight and connected to a load.
Azimuth The angle (to the equator) at which a solar panel points. In the northern hemisphere, it should almost always be due south.


Balance of Systems ‘BOS’; all components of a PV system excluding the PV panels. One side of the balance holds the DC generation (solar array) while the other side holds the AC load (utility-grid, household).
Base Load The average minimum amount of electricity a utility company must supply to meet consumer electricity demand.
Baseload Capacity The generating equipment normally operated to serve loads on an around-the-clock basis.
Battery Storage A system that stores electrical energy from a solar PV system, making the electricity available for later use.  These systems are common in Off-Grid Systems and Hybrid Systems.
Building-Integrated Photovoltaics (BIPV) An SED that integrates Solar PV modules into the building envelope, where the solar panels themselves act as a building material (roof shingles) or structural element (i.e., façade). These are becoming more common as prices begin to drop with technology improvements, and they save some costs during installation.


California Energy Commission (CEC) The California Energy Commission ("CEC") is the State of California's primary energy policy and planning agency. Among their missions is supporting renewable energy by providing market support to existing, new, and emerging renewable technologies; providing incentives for small wind and fuel cell electricity systems; and providing incentives for solar electricity systems in new home construction. The CEC requires independent performance certification on renewable energy products sold within the state of California. Certification tests are conducted under more real-world conditions.
Capacity Factor The ratio of the electrical energy produced by a generating unit for a given period of time to the electrical energy that could have been produced at continuous full power operation during the same period.
Cell A solar cell is the basic component of solar modules. Cells are manufactured from wafers.
Conversion Efficiency A measure that gauges the percentage of solar energy reaching a module that in turn is converted into electrical power.
Crystalline Modules (c-Si) Photovoltaic cells made from thinly-sliced silicon. See also "Monocrystalline" and "Polycrystalline".


Direct Current Electricity (DC) Electricity that flows only in one direction. Direct Current is the type of electricity supplied by batteries.
Downtime Time when the photovoltaic system cannot provide power for the load. Usually expressed in hours per year or that percentage.


Energy Payback (Time) The amount of time required for a solar panel to generate the amount of energy it took to manufacture it. Modern PV panels have an energy payback of 1 to 3 years depending on where they’re installed; over a 30+ year life, a PV system will return 10 to 30 times the energy that went into making them.
ERCOT The Electric Reliability Council of Texas ("ERCOT") manages the flow of electric power to 23 million Texas customers representing 85 percent of the state's electric load. As the independent system operator for the region, ERCOT schedules power on an electric grid that connects 40,500 miles of transmission lines and more than 550 generating stations


Feed-in-Tariff (FIT) Money paid to a customer by a power company for excess electricity generated by a renewable energy source. The renewable energy source is most often either solar or wind generated electricity. This excess is connected to the power lines at the customer's residence, and most commonly on the customer's side of the electric meter. For example, if you had a solar electric system installed on your home, and had signed a feed-in-tariff agreement ("FIT") with your power company, you could find the power company selling electricity to you at one price per kilowatt-hour, but BUYING the excess from you for more than they sell it to you at retail. Feed-in-tariffs are implemented to encourage end users to install renewable energy equipment and sell excess renewable energy back to the utility company.
Flat-Plate Collector A solar power collector that absorbs the sun's energy on a flat surface without concentrating or refocusing it


Generation The total amount of electric energy produced by generating units and measured at the generating terminal in kilowatt-hours (kWh) or megawatt-hours (MWh).
Grid-Connected System (Grid-Interactive) A solar electric system that's connected to the utility power grid and uses the utility grid as a backup source of power. If more energy is needed than is being generated by the solar electric system, the difference is supplied to the customer by the utility company. If more energy is being produced than needed, the excess electrical power flows backwards through the electrical meter to the utility company, where it is then used by others.
Grid-Tied Inverter An inverter that converts direct current (DC) into alternating current (AC) and feeds the power into the utility grid of homes and businesses on the customer's side of the meter. This has the effect of reducing the amount of power purchased from the utility company. In certain cases, more power may be produced by the system, in which case the utility meter may run "backwards", which at the discretion of the power company, may provide credit to the customer for the back-fed power. The most common source for the DC energy are photovoltaic modules or small wind turbines. Also commonly called "grid-interactive" inverter(s).
Ground-Mounted Solar Energy System Devices which are freestanding, or not mounted on existing structures. Ground-mounted devices can be static or tracked, meaning they have a mechanism that enables them to maintain tilt toward the sun as it moves across the sky.


HELOC Home equity line of credit. In certain states, a HELOC can be used to pay for a solar installation.
HOA Homeowner’s Association. Can sometimes be a barrier to putting solar on your roof.


Illuminance Solar radiation in the visible region of the solar spectrum to which the human eye responds.
Insolation A measure of the solar radiation energy reaching the earth in a given region over a specific period of time. Not to be confused with "insulation" - material that slows the movement of heat toward cold (such as in attics). Insolation is related to irradiance in a manner similar to how miles-per-hour are related to miles-per-day. Irradiance is the amount of solar energy falling on the earth's surface at any given moment. Insolation relates to the amount of energy over a longer period of time.

Device that changes the direct current (DC) to alternating current (AC) for use.

IRR Internal Rate of Return. Used to show the relative performance of an investment. Allows you to compare the potential return on solar to other investments.
ITC The Investment Tax Credit. Federal tax policy to give homeowners a 30% tax credit on the purchase and installation costs of installing renewable energy generation.






Levelized Cost of Energy (LCOE) The cost of energy of a solar system that is based on the system's installed price, its total lifetime cost, and its lifetime electricity production
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.


Modified Accelerated Cost Recovery System (MACRS) Officially, the Federal Modified Accelerated Cost Recovery System. Under this system, a businesses may recover investments in certain property through rapid depreciation deductions. The MACRS establishes a set of classes for various types of property, ranging from three to 50 years, over which the property may be depreciated. A number of renewable energy technologies are classified as five-year property (26 USC § 168(e)(3)(B)(vi)) under the MACRS, which refers to 26 USC § 48(a)(3)(A), often known as the "Energy Investment Tax Credit" (or "ITC") to define eligible property.
Module Commonly called a “solar panel,” a PV module is composed of multiple solar cells that are electrically connected to increase the total power output and are encapsulated in tempered glass for weather protection and ease of handling.
Monocrystalline Cells Monocrystalline photovoltaic ("PV") cells are cut from cylindrical ingots that resemble a large round salami. They tend to convert more sunlight energy to electricity than other types of photovoltaic cells, but they are also the most expensive. Crystalline PV cells are made from silicon, the same material we use to make window glass, and typically have a very dark-to-black appearance over the entire surface of each cell.
Megawatt (MW) A unit of power or capacity of a generator. 1 MW = 1,000 kW = 1,000,000 W.


North American Board of Certified Energy Practitioners (NABCEP) NABCEP is a volunteer board of renewable energy stakeholder representatives whose mission is to support, and work with the renewable energy and energy efficiency industries, professionals, and stakeholders to develop and implement quality credentialing and certification programs for practitioners (better known as solar energy installers).
Nameplate Rating Also known as STC, or Standard Test Conditions. Nameplate rating refers to the performance of a piece of electricity-generating equipment under ideal laboratory conditions.
Net Metering Net metering allows utility customers to apply the electricity generated by their own devices against their electric bills. If they produce more than they consume, the utility pays or credits them for the excess. Texas does not currently require that utilities offer net metering.
Net Zero Energy credit balances energy consumed.
Normal Operating Cell Temperature (NOCT) The estimated temperature of a photovoltaic module when operating under 800 w/m2 irradiance, 20°C ambient temperature and wind speed of 1 meter per second. NOCT is used to estimate the nominal operating temperature of a module in its working environment.
NREL Abbreviation for the National Renewable Energy Laboratory in Golden, Colorado. NREL is a United States National Laboratory specializing in developing technologies and procedures for using renewable energy sources


OCPD An abbreviation for "over-current protection device". In plain language, this would be a circuit breaker, a fuse, or other device that opens an electrical circuit in the event too much current is flowing, such as too large of a load for the wiring
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.
Off-the-grid (Off-Grid) On-grid/Grid Connected/Grid-tied; An energy device connected to the electric utility provider. More than 90% of solar energy devices installed in the US are grid-tied.
Open Circuit A break in an electrical wire or other path where electricity would normally flow. An open circuit prevents any electrical current from flowing. Examples of an "open circuit" would be a broken wire, or even something like a wall or other switch that's "open" such that no current flows.
Overcharge Forcing current into a fully charged battery. The battery will be damaged if overcharged for a long period.


PACE Loan Property-Assessed Clean Energy financing. A PACE loan is for homeowners who don’t have the capital to finance solar on their own, but to whom leases
Panelboard The official National Electric Code term for "breaker panel", "breaker box", or similar terms. An electrical distribution board that houses electrical circuit breakers. A panelboard is the main point at which electricity is distributed throughout a building. In commercial installations, it's often termed "electrical cabinet".
Parity Occurs when an alternative energy source can generate power at a levelized cost of electricity (LCOE) that is less than or equal to the price of purchasing power from the electricity grid.
Passive Solar Technology for using sunlight to illuminate and heat buildings directly, with no circulating fluid or energy conversion system, and usually no moving parts. Sunlight admitted into your home in the winter that helps to heat the house is a considered a "passive" energy source.
Photovoltaic Array  One or more solar cells connected in one unit is known as a PV module. Multiple PV modules are connected to each other become an array.
Photovoltaic Module Multiple solar cells connected in one unit.An assembly of interconnected photovoltaic cells enclosed in a protective assembly (usually glass and plastic).
Power Purchase Agreement (PPA) A contract between a power producer and a power consumer, which states that the customer will purchase a certain amount of power at a certain price from the producer.
PV Photovoltaic; Electricity generated by light.




Racking Solar energy systems are attached securely and anchored to structural sections of the roof-mounted or pole-mounted systems. Specially designed metal plates called flashings prevent leaks and are placed under shingles and over bolts to create a water-tight seal. 
R-value Resistance value. Used specifically for insulating materials to indicated its effectiveness against the movement of heat toward cold. The higher the number, the greater the slowing of the flow of energy. Three inches of fiberglass insulation has an R value of 7.5.
Retail Electric Provider (REP) Sells electric energy to retail customers in the areas of Texas where the sale of electricity is open to retail competition. A REP buys wholesale electricity, delivery service, and related services, prices electricity for customers, and seeks customers to buy electricity at retail.
Renewable Energy Credits (RECs) Renewable energy credits, or RECs, are tradable commodities that represent the green attributes associated with energy generated from renewable energy resources. One "REC" is generated every time one megawatt-hour (MWh) of renewable electricity is produced. Solar renewable energy credits, or "SRECs" are RECs generated from solar power sources.
Renewable Portfolio Standard (RPS) A renewable portfolio standard (RPS) requires that energy suppliers in a certain state produce a proportion of their energy from renewable energy. To meet these RPS requirements, energy suppliers can: 1) Develop their own renewable energy facilities such as solar energy power plants or wind farms to produce RECS, or; 2) Purchase RECs from others that own renewable energy facilities.All of the components used to convert sunlight into usable electricity. Includes at least one solar cell, panel (multiple connected cells), or array (multiple connected panels), inverter(s) and necessary wiring.


SED Solar Energy Devices; various mechanisms used as active sources of the conversion of sunlight to electrical energy
Short Circuit An unwanted path for electrical current between two points in a circuit. In the case of electrical power, a short-circuit usually allows excessive current to flow (more than the wires are designed to handle), in which case a circuit breaker or fuse will open the circuit, stopping the current flow, and thus preventing damage and/or a fire.
Solar Access The access of a solar energy system to direct sunlight.
Solar Cell Converts sunlight into electricity.A device made of silicon and other materials. Solar cells generate electricity when exposed to sunlight. Multiple solar cells (typically from 36 to 96 cells) are used in the construction of one photovoltaic module.
Solar Collector  Solar Thermal Collector; part of the system which absorbs the sun's energy and converts it into heat, such as a solar collector for a solar hot water system. Solar collectors can convert typically up to 85% of the sun's energy to heat. Not to be confused with a photovoltaic module, sometimes called a "solar panel". The heat collected by the solar collector may be used immediately or stored for later use. Solar collectors are used for space heating; domestic hot water heating; and heating swimming pools, hot tubs, or spas.
Solar Easements Legal agreements that protect access to sunlight on a property.
Solar Energy Radiant energy (direct, diffused, or reflected) received from the sun at wavelengths suitable for conversion into thermal, chemical, or electrical energy.
Solar Energy System A system capable of collecting and converting solar radiation into heat or mechanical or electrical energy and transferring these forms of energy by a separate apparatus to storage or to point of use, including, but not limited to, water heating, space heating or cooling, electric energy generation, or mechanical energy generation. Includes solar thermal, PV, and passive solar systems.
Solar Hot Water System Solar hot water systems use a solar thermal collector to convert the sunlight to thermal energy. Solar hot water systems typically heat water or air. Solar thermal collectors and Solar PV modules utilize the sun, and therefore need to be mounted similarly for sun exposure. Solar energy is also harnessed for space heating and cooling, and other applications, but these are rarer.
Solar Modules Also called solar panels. These are the large collections of solar cells that can produce electricity in a worthwhile quantity.
Solar Renewable Energy Credits  SREC program provides a means for Solar Renewable Energy Certificates (SRECs) to be created for every megawatt-hour of solar electricity created.
Solar Thermal Electric Generation (STEG) Conversion of solar energy to electricity using various technologies to heat a working fluid to power a turbine that drives a generator. Examples of these systems include central receiver systems, parabolic dish, and solar trough.
Stand-alone System Energy generated by these systems is stored in batteries and then subsequently used. Also known as “off-grid,” these systems are not connected to the utility grid.


Thermal Solar The process of deriving or concentrating heat from sunlight. Examples of "derived heat" are: home heating, solar cooking, clothes drying, solar heated water, and so forth. Concentrated solar thermal heat is often used to create steam, from which electric power is generated.
Thin Film Thin-film photovoltaic modules are manufactured using spray-on or print-on techniques, rather than forming cells from ingots or blocks of molten silicon. Thin-film photovoltaic modules are significantly lower in efficiency than crystalline PV, but are also lower in cost per watt of energy generated, and often less affected by heat. Thin-film technologies involve many types of metals including silicon, gallium, cadmium, tellurium, copper, and others.
Time-of-Use Metering (TOU Metering) A utility billing system in which the price of electricity depends upon the hour of day at which it is used. Rates are typically higher during the afternoon when electric demand is at its peak. Rates are lower during at night when electric demand is much less.
TMY Typical Meteorological Year; a typical year of hourly solar and meteorological values which is designed to produce the expected climate of a location throughout a year.
Tracker Mechanical device used in solar electric and solar thermal systems. Follows the movement of the sun (daily and sometimes seasonally) and keeps the energy collection device pointed directly at the sun. Allows for the harvest of the maximum available solar energy.
Tracking Collector Any mechanical structure that that changes its orientation throughout the day in order to follow the path of the sun in the sky. Two-axis trackers continually face the sun throughout the day, changing direction with the time of day and the season. Single-axis trackers rotate on one axis for time-of-day only, and must be manually adjusted for the season.


Uninterruptible Power Supply (UPS) A device (usually containing batteries) that stores power for use when conventional power is unavailable, such as during a power failure.
Utility-Scale PV A utility-scale solar project is not based on the number of panels or energy generated, but on the purpose of the energy. If the power from a solar application’s primary purpose is to be sold for commercial gain, and not for off-setting electric usage at a facility through net metering (i.e., distributed generation), then it can be considered a utility-scale solar application. Energy generated by a utility-scale solar application is typically sold to energy companies, rather than end users. The owners of the utility-scale solar project would need to obtain a permit from the state and are listed by the US Department of Energy as a power generation source.


Volt(s) Unit of electrical pressure


Watt(s) The electrical unit of measure equal to one watt of power for one hour
Watt-hour A watt is a unit of electrical power. Watts = Volts x Amps


Zenith Sun is directly overhead in relation to the observer
Zenith Angle The angle between the direction of interest (of the sun, for example) and the zenith (directly overhead).
Zero Energy Home Energy value produced = value consumed


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For more solar terms, please refer to the North Texas Renewable Energy Group or to the U.S. Department of Energy.