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Alternating current (AC): the type of electricity used by most household appliances. An inverter is used in a renewable energy system to convert incoming direct current (DC) into usable alternating current (AC).

Azimuth: degree of deviation from north in orientation of solar panels.
Carbon dioxide (CO2): greenhouse gas linked to global warming.
Charge controller: component of a photovoltaic system that controls the flow of current to and from the battery to regulate the flow to prevent over-charge or over-discharge.
Combiner box: an enclosure that collects wires from multiple arrays and joins them into larger wires to be passed into the system's inverter.
Compact fluorescent lighting (CFL): an energy-efficient form of lighting. CFL bulbs use one-quarter to one-third as much electricity to provide the same light output as a standard incandescent bulb while creating much less heat, and they last up to 10 times as long as a standard incandescent bulb (10,000 vs. 1,000 hours).
Conversion efficiency (%): the percentage of the sunlight incident on a solar panel that is successfully passed to the system as current.
Critical load sub-panel: a secondary load circuit used with a backup power system to isolate the circuits that will receive power from the backup power source.
Cycle: used to refer to the charging and discharging of a battery.
Deep-cycle battery: a battery that can withstand multiple discharges to a low percentage of its capacity.
Direct current (DC): the form of electricity generated by renewable sources.
Disconnect: switch used to turn on or off current between various components of a renewable energy system.
Energy efficiency: technologies and measures that reduce the amount of electricity and/or fuel required to do the same work without reducing the end-use benefits.
Energy management: empowering a customer to monitor and control usage to leverage use with times of peak pricing or demand. Allows visibility into usage and opportunities for conservation measures.
Fossil fuel: examples are oil, coal, and natural gas. Finite resources formed in the ground millions of years ago from plant and animal remains. Fossil fuels are the primary source of power generation. The process of burning fossil fuels produces emissions that are detrimental to the environment, such as carbon dioxide (CO2), nitrous oxides (NOx), and sulfurdioxide (SO2). These emissions are one of the leading causes of global warming, pollution, smog, acid rain, and other negative health effects that result from poor air quality.
Fuel cell: an electrochemical device that converts hydrogen (clean source of fuel) and oxygen (oxidant, key to chemical reaction) directly to electricity. A fuel cell is composed of catalytically activated electrodes for the fuel (anode) and the oxidant (cathode) combined with an electrolyte that functions as a conductor for the ions to move between the opposing electrodes.
Grid-connected system: a renewable energy system that works in conjunction with the utility electrical supply. Utility supply is used to supplement renewable-generated power when demand exceeds production. Conversely, when net metering agreements are in place, renewable-generated power is fed back into the grid, and compensation is provided by the utility. Compare with off-grid (stand-alone) system.
Insulation: the amount of solar power incurred by a surface of a specific area and orientation. Typically expressed as watts per square meter per day.
Interconnection: an agreement made with a utility provider to establish a grid-tied renewable energy system. Allows for energy to flow in both directions from the system.
Inverter: a device that converts direct current (DC) into alternating current (AC).
Irradiance: the direct, diffuse, and reflected solar radiation that strikes a surface. Usually expressed in kilowatts per square meter. Irradiance x time = insulation. Also interpreted as peak sunhours to measure output of solar panel production. Every hour in which their radiance averages 1,000 watts per square meter is considered one peak sunhour.
Junction box: in reference to a solar PV module, an enclosure located on the back of the module where PV strings are electrically connected and protection devices are located.
Kilowatt (kW): standard unit of electrical power equal to 1,000 watts (kilo = 1,000).
Kilowatt-hour (kWh): standard measurement of electricity consumption or production. One thousand watts consumed or produced over the course of one hour. For example, a 100-watt light bulb used for 10 hours would consume 1 kWh of electricity.
Load: the electrical demand of a location. Also, the amount of energy required by a particular piece of equipment. Usually expressed in watts or kilowatts.
Load circuit (electrical panel): the combined wires, switches, fuses, etc. that connect the load to the power source.
Megawatt (MW): 1,000 kilowatts or 1 million watts.(Mega = million). Standard measure of electrical generation capacity at utility-scale facilities.
Megawatt-hour (MWh): 1 megawatt used or produced over the course of one hour.
Monocrystalline silicon cells: refers to the type of technology of a photovoltaic (PV) cell. PV cells are produced by melting highly refined silicon. For a Monocrystalline silicon cell, a "seed" is dipped into molten silicon and allowed to solidify into a silicon "ingot," which is then sliced into wafers. The wafers are laminated between sheets of glass to produce a Monocrystalline silicon cell. Compare with polycrystalline silicon cells.
Nitrogen oxides (NOx): 22% of the nitrogen oxide pollution in the United States comes from power production. Nitrogen oxides are one of the main ingredients in the formation of ozone and smog. It also contributes to the formation of acid rain and global warming.
Off-grid system (stand-alone system): a renewable energy system designed to meet the full electrical requirements of a site. Requires batteries to store energy for use at times of lower production (e.g., nighttime). May also be coupled with a generator to provide additional power supply. Often an economical alternative in locations without direct access to utility lines. Compare with grid-connected system.
Orientation: siting of photovoltaic panels in relation to the cardinal directions (north, south, east, west). South is the optimal orientation in the northern hemisphere, although good production can be realized with panels facing east and west.
Peak demand: the maximum energy demand during particular time period.
Photovoltaic (PV) effect: "photo" = light; "voltaic" =electricity. The process by which photons from the sun's rays knock electrons loose from the atoms that they strike.
Photovoltaic (PV) array: the combination of multiple PVpanels (modules) that function as a single electricity-producing unit.
Photovoltaic (PV) cell: the smallest building block of the solar electrical system. Composed of semiconductor material. Performs the immediate conversion of light into electrical energy in the form of direct current (DC).
Photovoltaic (PV) module/panel: the combination of multiple PV cells laminated between thick sheets of tempered glass, which is then placed in a frame for support. Module production ratings are based on the sum of the production capacity of the cells in the module and typically range from 30 to 300 watts.
Power conversion efficiency (%): in reference to the inverter, the ratio of output power to input power. Typically between91% and 97%.
Polycrystalline silicon cell: refers to the type of technology of a photovoltaic (PV) cell. PV cells are produced by melting highly refined silicon. For a polycrystalline PV cell, the molten silicon is poured into a mold. These processes create silicon ingots, which are then sliced into wafers. The wafers are laminated between thick sheets of tempered glass to produce a polycrystalline silicon cell. Compare with Monocrystalline silicon cell.
Renewable Energy Certificate (REC): also known as green certificates' or green tags.Tradable commodity usually measured in 1MWh (megawatt-hour) of energy from a renewable source. Sold separately from commodity electricity.
Renewable Portfolio Standard (RPS): policy set by federal or state governments requiring that a certain percentage of the area's electricity come from renewable sources.
Secure load sub-panel: see critical load sub-panel.
Semiconductor: any material that has limited ability to conduct an electric current. The most common semiconductor used in photovoltaic applications is silicon. Other semiconductors used for photovoltaic applications include cadmium telluride, copper indium diselenide, and gallium arsenide.
Solar resource: amount of solar insulation a site receives, measured in kilowatt-hours per square meter per day. Equivalent tithe number of peak sun hours.
SO2 (sulfur dioxide): 67% of the sulfur dioxide emissions produced in the United States are from power generation. Sulfur dioxide emissions are one of the main contributors to the production of acid rain.
Standard Test Conditions (STC): controlled conditions under which PV modules are tested in a laboratory. Output rating oaf module is typically based on output measured when subjected to these conditions.
Time-of-use pricing (TOU pricing): a electrical rate structure that uses different rate tiers for different times of day and/or days of the week. Rates are typically divided into peak and off-peak rates (and sometimes even part-peak), with peak rates coinciding with peak demand. Rates are highest during these periods. Solar electric systems are especially beneficial under this pricing structure, as the system's peak production typically coincides with peak rate time periods.
Watt: unit of measure of electricity. The product of voltage and current.

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