Glossary

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.

Amorphous Solar Panels — Amorphous solar panels are also referred to as "thin film" solar panels.  In these types of panels the silicon is spread directly on large plates, usually of something like stainless steel. The thin film type of solar cells can also be spread on to more flexible plastic materials to make very flexible solar panels.  These types of solar cells are much cheaper but also much less efficient than mono crystalline or poly-crystalline solar panels.  Therefore in order to provide as many watts as the other types of solar panels they must be much bigger in size.  However, because they can be put on to flexible backings they have proven very valuable in certain types of applications where flexibility is more critical than power.  For example, these types of solar panels are often used in portable products such as solar backpacks and solar bags. Overall efficiency on average is about 5-6%.

Ampere (amp) — A unit of electrical current or rate of flow of electrons.

Blades — The flat panels on a wind turbine that are connected to a center shaft that converts the push of the wind into a circular motion in a wind turbine.

Crystalline Silicon — A type of photovoltaic cell made from a slice of single-crystal silicon or polycrystalline silicon.

Cut-in Speed — The wind speed at which the turbine blades begin to rotate and produce electricity, typically around 10 miles per hour.

Cut-out Speed — The wind speed at which the turbine automatically stops the blades from turning and rotates out of the wind to avoid damage to the turbine, usually around 55 to 65 miles per hour.

Cutoff Voltage — The voltage levels (activation) at which the charge controller disconnects the energy source from the battery or the load from the battery.

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 household appliances, DC must be converted to alternating current, its opposite.

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

Gigawatt (GW) — A unit of power equal to 1 billion Watts; 1 million kilowatts, or 1,000 megawatts.

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 Lines — Metallic contacts fused to the surface of the solar cell to provide a low resistance path for electrons to flow out to the cell interconnect wires.

High Voltage Disconnect — The voltage at which a charge controller will disconnect the photovoltaic array from the batteries to prevent overcharging.

Hub — The central part of the wind turbine, which supports the turbine blades on the outside

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

Interconnect — A conductor within a module or other means of connection that provides an electrical interconnection between the solar cells.

Inter Connect Agreements — Agreements that a (TDSP) Transmission and Distribution Service Provider requires to be signed, in order to connect to its equipment.

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

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.

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

Kilowatt-Hour (kWh) — 1,000 thousand watts acting over a period of 1 hour. The kWh is a unit of energy.

Life-Cycle Cost — The estimated cost of owning and operating a photovoltaic system for the period of its useful life.

Megawatt (MW) — 1,000 kilowatts, or 1 million watts; standard measure of electric power plant generating capacity.

Mono-crystalline Panels —These types of solar panels use solar cells, which are made from a very pure single large crystal, cut from ingots. They are the most efficient type of solar panels but are also the most expensive. Their performance is somewhat better in low light conditions. Overall efficiency on average is 18%. Most panels of this type are warranted for 20-25 years. They are usually blue-grey in color and have a fairly uniform consistency.

Nacelle — The structure at the top of the wind turbine tower just behind (or in some cases, in front of) the wind turbine blades that houses the key components of the wind turbine, including the rotor shaft, gearbox, and generator.

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.

Net Metering — A term used to describe grid connected installations in which the local electrical source such as a wind turbine or solar panels are connected to the electrical meter so that when excess electricity is generated it is passed to the grid causing the meter to run backwards.

Oncor Rebates —The Solar PV Program from Oncor Electric designed to help Oncor customers meet a portion of their electric energy needs with solar photovoltaic (PV) systems. http://www.oncor.com/electricity/teem/consumer/solarpv.aspx

Payback —The period of time required to recoup a capital investment.

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

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

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

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 also called a solar cell.

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.

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.

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.

Polycrystalline Panels —With most poly-crystalline solar panels the silicon in the solar cells is cast from large blocks of silicon which may contain many small crystals. Some manufacturers use a slightly different approach for creating poly-crystalline solar cells.  Currently, poly-crystalline solar panels are the most common.  They are slightly less efficient than mono-crystalline panels. Overall efficiency on average is about 11-13%.

Power Conversion Efficiency — The ratio of output power to input power of the inverter.

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 Generation Company (PGC) —Power Generation Companies own and operate power plants, including plants fueled by coal, nuclear power, natural gas, wind, water, solar power, or other renewable sources. Power Generation Companies sell this power at wholesale to Retail Electric Providers, who package the power with transmission and delivery service for sale to retail customers. Retail Electric Providers are not permitted under Texas law to own power plants; however, they can be affiliated with a power generation company.

Rated Wind Speed — The wind speed at which the turbine is producing its nameplate-rated power production.  For most small wind turbines this is around 30 to 35 miles per hour.

Retail Energy Provider (REP) —With electric competition, retail electric providers (also known as "REPs") sell electricity to you and routinely handle customer service and billing. REPs compete for your business by offering a variety of different pricing options, renewable energy options, added customer service benefits or other incentives. Not all areas of the state are open to competition.  Electrical cooperatives and city owned utilities may decide whether their customers will have a choice of Retail Electric Providers.

Poly-Crystalline String Ribbon — String ribbon photovoltaics use a variation on the polycrystalline production process, using the same molten silicon but slowly drawing a thin strip of crystalline silicon out of the molten form between two strings. These strips of photovoltaic material are then assembled in a panel with the same metal conductor strips attaching each strip to the electrical current. This technology saves on costs over standard polycrystalline panels as it eliminates the sawing process for producing wafers. Some string ribbon technologies also have higher efficiency levels than other polycrystalline technologies. Overall efficiency on average are from 11-14%.

Rotor — Comprises the spinning parts of a wind turbine, including the turbine blades and the hub.

Silicon (Si) — A semi-metallic chemical element that makes an excellent semiconductor material for photovoltaic devices. It's commonly found in sand and quartz.

Solar Cell — A photovoltaic 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 Panel — A panel consisting of multiple solar cells.

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.

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.

Thermophotovoltaic Cell (TPV) — A device where sunlight concentrated onto a absorber heats it to a high temperature, and the thermal radiation emitted by the absorber is used as the energy source for a photovoltaic cell that is designed to maximize conversion efficiency at the wavelength of the thermal radiation.

Tower — The base structure that supports and elevates a wind turbine rotor and nacelle.

Transformer — An electromagnetic device that changes the voltage of alternating current electricity.

Transmission & Distribution Service Provider —Regardless of which Retail Electric Provider you choose, the actual delivery of the electricity ("transmission and distribution") is still provided by your local Transmission and Distribution Service Provider, (also referred to as the "TDSP"). Your TDSP will continue to be responsible for maintaining the poles, wires, and meter that deliver and measure the electricity consumed by your home or business, for reading your meter and providing amount of electricity that you consume to your REP, and for restoring service when there is a power outage.

Two-Axis Tracking — A photovoltaic array tracking system capable of rotating independently about two axes (e.g., vertical and horizontal). 

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.

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).

Wind Monitoring System — Also termed met tower — A group of instruments (including anemometers and wind vanes) that collectively measure various meteorological parameters such as wind speed, wind direction, and temperature at various heights above the ground. met is short for meteorological.

Wind Powering America (WPA) — A U.S. Department of Energy initiative designed to promote the use of wind energy across the country, with the goal of quadrupling U.S. wind capacity by 2010.

Wind Power Class — A system designed to rate the quality of the wind resource in an area, based on the average annual wind speed. The scale ranges from 1 to 7 with 1 being the poorest wind energy resources and 7 representing exceptional wind energy resources

Wind Resource — The wind energy available for use based on historical wind data, topographic features, and other parameters.

Wind Speed — The rate at which air particles move through the atmosphere, commonly measured with an anomometer.

Wind Vane — A device used to measure wind direction.

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