Solar Glossary

Array — An interconnected system of photovoltaic modules that function as a single electricity-producing unit. The modules are assembled as a discrete structure, with common support or mounting.

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

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

Cell — The smallest semiconductor element within a PV module to perform the immediate conversion of light into electrical energy.

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.

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

Joule — A metric unit of energy or work; 1 joule per second equals 1 watt or 0.737 foot-pounds; 1 Btu equals 1,055 joules.

Junction Box — A PV generator junction box is an enclosure on the module where PV strings are electrically connected and where protection devices can be located, if necessary.

Kilowatt — A standard unit of electrical power equal to 1000 watts, or to the energy consumption at a rate of 1000 joules per second.

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).

Panel — often used interchangeably with PV module, but more accurately used to refer to a physically connected collection of modules.

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.

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

Purchase Power Agreement–contracts between two parties, one who generates electricity for the purpose of sale (the seller) and one who is looking to purchase electricity (the buyer). There are various forms of Power Purchase Agreements; these are differentiated by the source of energy harnessed (solar, wind, etc.). Financing for the project is delineated in the contract, which also specifies relevant dates of the project coming into effect, when the project will begin commercial operation, and a termination date for which the contract may be renewed or abandoned.

Renewable Energy Resource — An energy resource that is regenerative or virtually inexhaustible. Typical examples are wind, solar, geothermal, and water.

Solar Energy — Electromagnetic energy transmitted from the sun.

Volt — 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.

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).

Balance of System — Used to describe the AC and DC breakers, fuses and other electrical safety components of a utility or grid tied solar electric system. Components other than the solar modules, mounting structure, and inverter.

Battery Backup — The use of batteries to power your system in case of electrical power outage. Used for emergency back up only of critical loads.

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 in 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.

Electrical Grid — An integrated system of electricity distribution, usually covering a large area.

Grid-Tie System (GTS) — A solar electric or photovoltaic (PV) system in which the PV array acts like a central generating plant, supplying power to the grid. Also called a Grid-Connected System.

Inverter — A device that converts direct current electricity to alternating current either for stand-alone systems or to supply power to an electricity grid.

Kilowatt Hours — 1,000 thousand watts acting over a period of 1 hour. The kWh is a unit of energy. 1 kWh=3600 kJ.

Net Metering — The practice of exporting surplus solar power during the day (to actual power needs) to the electricity grid, which either causes the home owner electric meter to (physically) go backwards and/or simply creates a financial credit on the home owner’s electricity bill. (At night, the homeowner draws from the electricity grid in the normal way).

Rack Mounts — In a rack mount, the photovoltaic modules (solar panels) are supported by a metal framework and are set at a predetermined angle. The rack-mounted solar array is placed above the roof with the rack’s members bolted to the roof’s structural members. Pre-configured rack mounting offered with ASG Power, SunWise and other systems position the solar panels at the roof pitch angle. Additional mounting components are available if panels need to be tilted further (e.g., on flat or low-pitch roofs) in order to maximize the solar array performance. Please don’t hesitate to contact us for consultation if you have related questions.

Series Connection — A way of joining photovoltaic cells by connecting positive leads to negative leads; such a configuration increases the voltage.

Tilt Angle — The angle at which a photovoltaic array is set to face the sun relative to a horizontal position. The tilt angle can be set or adjusted to maximize seasonal or annual energy collection.

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

Battery Energy Capacity — The total energy available, expressed in watt-hours (kilowatt-hours), which can be withdrawn from a fully charged cell or battery. The energy capacity of a given cell varies with temperature, rate, age, and cut-off voltage.

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.

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.

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.

Gel-Type Battery — Lead-acid battery in which the electrolyte is composed of a silica gel matrix.

Hybrid System — A solar electric or photovoltaic system that includes other sources of electricity generation, such as wind or diesel generators.

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.

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

Off-Grid System — An autonomous or hybrid photovoltaic system not connected to a grid. May or may not have storage, but most off-grid systems require batteries or some other form of storage. Also called a stand-alone system.

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

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

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

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.

Tracking Array — A PV array that follows the path of the sun to maximize the solar radiation incident on the PV surface. The two most common orientations are (1) one axis where the array tracks the sun east to west and (2) two-axis tracking where the array points directly at the sun at all times. Tracking arrays use both the direct and diffuse sunlight. Two-axis tracking arrays capture the maximum possible daily energy.

Vented Cell — A battery designed with a vent mechanism to expel gases generated during charging.Adequate Wind Resource — The wind speed you would need to start up your turbine and the average speed needed to produce power. This will vary by manufacturer and model.

Base — The structure below the generator of a wind turbine that supports the turbine, houses the meters and wires, and keeps the turbine high above the ground level to protect the surrounding area and people from the force of the blades. Also, to get the turbine above the surrounding buildings which could otherwise block the wind.

Blades — Usually flat objects connected to a center shaft that converts the push of the wind into a circular motion in a wind turbine.

Dump Load — A machine that uses excess energy being produced to heat air or water.

Free Standing Tower — A structure that is used to support a wind generator, usually high in the air with no supports.

Guyed Tower — A structure that is used to support a wind generator, usually high in the air with wires anchoring it to the ground.

Hybrid System — A system that combines wind and solar energy.

Marine Wind Turbine — A wind turbine that is designed to be used on or near water. It has a painted and sealed body and offers more protection from the elements.

Rated Power Output — Used by wind generator manufacturers to provide a baseline for measuring performance. Rated output will vary by manufacturer.

Tower Kit — Set of hardware that is used to secure the wind generator to the tower. (May or may not include tower pole depending on the brand/model.)

Wind Generator — A machine that is used to produce electricity. Often used interchangeably with wind turbine.

Wind Turbine — A machine that captures the force of the wind and converts it into electricity. Often used interchangeably with wind generator.

Booster Pump — A surface pump used to increase pressure in a water line, or to pull from a storage tank and pressurize a water system.

Centrifugal Pump — A pumping mechanism that spins water in order to push it out by means of centrifugal force.

Check Valve — A valve that allows water to flow one-way but not the other.

Diaphragm Pump — A type of pump in which water is drawn in and forced out of one or more chambers, by a flexible diaphragm. Check valves let water into and out of each chamber.

Dispositive Displacement Pump — Any mechanism that seals water in a chamber, then forces it out by reducing the volume of the chamber. Used for low volume and high lift.

Dry Run Switch — A device that stops the pump when there is no water to pump in the well.

Float Switch — An electrical switch that responds to changes in water level. It may be used to prevent overflow of a tank by turning a pump off, or to prevent a pump from running dry when the source level is low.

Float Valve — A valve that responds to changes in water level. It is used to prevent overflow of a tank by blocking the flow of water.

Foot Valve — A check valve placed in the water source below a surface pump. It prevents water from flowing back down the pipe.

Head — The vertical distance that water is pumped. This determines the pressure that the pump pushes against. Total head = vertical lift from surface of water source up to the discharge in the tank + (in a pressure system) discharge pressure. Also called vertical lift.

Helical Rotor Pump — A pump with a helix-shaped rotor that fits closely into a rubber stator that has a helical groove. It forms sealed cavities that trap water. As the rotor turns, the cavities move toward the outlet.

Impeller — The device that spins inside of a centrifugal pump, in order to develop centrifugal force.

Jet Pump — A surface-mounted centrifugal pump that uses an ejector (venturi) device to augment its suction capacity. In a deep well jet pump, the ejector is down in the well, to assist the pump in overcoming the limitations of suction.

Lift — The distance the water is to be raised.

Linear Current Booster (LCB)– An electronic device, which varies the voltage and current of a PV array to match the needs of an array-direct pump, especially a positive displacement, pump. It allows the pump to start and to run under low sun conditions without stalling. Also called pump controller.

Multi-stage Centrifugal Pump — A centrifugal pump with more than one impeller and chamber, stacked in a sequence to produce higher pressure. Conventional AC deep well submersible pumps and some solar submersibles work this way.

Pounds per Square Inch — vertical lift (head) in Feet / 2.31.

Pressure Switch — An electrical switch actuated by the pressure in a pressure tank. When the pressure drops to a low point (cut-in) it turns a pump on. At a high point (cut-out) it turns the pump off.

Priming — The process of hand-filling the suction pipe and intake of a surface pump. Priming is generally necessary when a pump must be located above the water source. A self-priming pump is able to draw some air suction in order to prime itself, at least in theory.

Pulsation Damper — A device that absorbs and releases pulsations in flow produced by a piston or diaphragm pump. Consists of a chamber with air trapped within it or a length of flexible tube.

Pump Controller — An electronic device that controls or processes the power to a pump. This devise will start and stop the pump.

Pumping — The amount of force applied by water that is either forced by a pump, or by the gravity. Measured in pounds per square inch (PSI).

Pump Jack — A deep well piston pump. The piston and cylinder is submerged in the well water and actuated by a rod inside the drop pipe, powered by a motor at the surface. This is an old-fashioned system that is still used for extremely deep wells.

Submersible Pump — A motor/pump combination that is designed to be placed entirely below the water surface.

Surface Pump —A pump that is not submersible. It must be placed no more than about 20 ft. above the surface of the water in the well.

Tracking Array — A PV array that follows the path of the sun to maximize the solar radiation incident on the PV surface. The two most common orientations are (1) one axis where the array tracks the sun east to west and (2) two-axis tracking where the array points directly at the sun at all times. Tracking arrays use both the direct and diffuse sunlight. Two-axis tracking arrays capture the maximum possible daily energy.