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As a homeowner of a solar system, you might want to know these basic terms or at least be able to look up the terms easily.

Alternating Current (AC) Electric current in which the direction of the flow is reversed at frequent intervals–100/120 (50/60Hz) times per second. The opposite of AC is direct current (DC).

Ampere (A) or Amp The unit for the electric current; the flow of electrons. One amp is 1 coulomb passing in one second. One amp is produced by an electric force of 1 volt acting across a resistance of 1 ohm.

Ampere Hour (Ah) Quantity of electricity or measure of charge. How many amps of flow or which can be provided over a one hour period. Deep cycle batteries used in solar power systems are rated in Ah (amp-hour).

Azimuth Angle between the north direction and the projection of the surface normal into the horizontal plane; measured clockwise from north. As applied to the PV array, 180 degree azimuth means the array faces due south.

Balance of Systems (BOS) The parts of the photovoltaic system other than the PV array such as the switches, controls, meters, power-conditioning equipment, supporting structure for the array and storage components, if any. The cost of land may or may not be included when comparing total system cost with the cost of other energy sources.

Battery A battery is used to provide energy storage for off-grid solar systems.

Cell The basic unit of a photovoltaic panel or battery.

Cell Junction The area of immediate contact between two layers (positive and negative) of a photovoltaic cell. The junction lies at the center of the cell barrier or depletion zone.

Charge Controller An electronic device which regulates the voltage applied to the battery system from the PV array. Charge controllers are typically used in off-grid photovoltaic power systems to protect the battery.

Coulomb A unit of electrical charge equal to the amount of charge transferred by a current of 1 ampere in 1 second.

Crystalline Semiconductor A semiconductor that uses a silicon or gallium arsenide substrate composed of a single crystal. Its atomic structure is the same throughout the material.

Cycle Life Number of discharge-charge cycles that a battery can tolerate under specified conditions before it fails to meet specified criteria as to performance (e.g., capacity decreases to 80% of the nominal capacity).

Deep Discharge Discharging a battery to 20-percent or less of its full charge.

Diffuse Insolation Sunlight received indirectly as a result of scattering due to clouds, fog, haze, dust, or other obstructions in the atmosphere. It is the opposite of direct insolation.

Direct Current (DC) Electric current in which electrons are flowing in one direction only. The opposite of DC is alternating current (AC.).

Direct Insolation Sunlight falling directly upon a collector. It is the opposite of diffuse insolation.

Distributed System A residential photovoltaic system is a distributed system. It is a system that is installed at or near the location where the electricity is used, as opposed to central systems that supply electricity to grids.

Doping The process of adding another element to silicon is called doping.

Discharge Rate The rate at which electrical current is taken from the battery, usually expressed in amperes or time.

Electric Circuit The 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 A flow of electrons; electricity, amps.

Embodied Energy The quantity of energy required to manufacture a product and supply it to the point of use. It is the sum total of energy necessary from the raw material extraction to the manufacture to the transportation and installation of a product or service

Final Annual Yield Total photovoltaic energy delivered to the load during one year per kilowatt of power installed. Unit is kWh per kW installed.

Grid: Network of transmission lines, substations, distribution lines and transformers used by central power systems. In other countries, often called mains electricity.

Grid-Connected PV Power Systems aka On-the-Grid This is a system installed on the consumer’s premises and connected to the utility grid Grid- Installed power: Power delivered by a photovoltaic module or a photovoltaic array, under standard test conditions (irradiance of 1000 W/m², cell junction temperature of 25°C, AM1,5 solar spectrum). Also said STC output power. Unit: W.

Insolation This is a measure of solar radiation energy received on a given surface area in a given time. Insolation is the solar radiation striking Earth or another planet. It is commonly expressed as average irradiance in watts per square meter (W/m²) or kilowatt-hours per square meter per day (kW·h/(m²·day)) (or hours/day). In the case of photovoltaics it is commonly measured as kWh/kWp•y (kilowatt hours per year per kilowatt peak rating). Do not confuse with insulation.

Inverter A device that converts direct current (DC) into alternating current (AC).

I-V Curve: A graphical presentation of the current versus the voltage from a photovoltaic cell as the load is increased from the short circuit (no load) condition to the open circuit (maximum voltage) condition. The shape of the curve characterizes cell performance.

Joule The work done to produce power of one watt continuously for one second; or one watt second (compare kilowatt hour), with the symbol W·s. Thus a kilowatt hour is 3,600,000 joules or 3.6 megajoules. The work required to move an electric charge of one coulomb through an electrical potential difference of one volt; or one coulomb volt, with the symbol C·V.

kilowatt (kW) 1000 watts.

kWh: Symbol of kilowatt-hour. The kWh is a unit of energy. One thousand watts acting over a period of 1 hour. 1 kWh=3600 kJ.

kWh/m2/day KiloWatt hours per square meter per day.

Lifetime of Battery The lifetime of a battery varies. It depends on many factors such as method of use, maintenance, method of charging, and temperature. It is typically between 5 and 10 years.

Load: The amount of electric power being consumed at any given moment. Also, in an electrical circuit, any device or appliance that is using power.

Maximum Power Point Tracking (MPPT) An electronic DC to DC converter that optimizes the match between the solar array or PV panels and the battery bank, utility power, DC motor, or DC pump. An MPPT will typically increase power delivered to the system by 10% to 40%, depending on climate conditions and battery state of charge. It is often called a power tracker for short.

Module A number of PV cells connected together, sealed with an encapsulant, and having a standard size and output power. The smallest building block of the power generating part of a PV array. Also called panel.

Monocrystalline Monocrystalline structures are composed of a single crystal throughout. One crystal

Multicrystalline Material that is solidified at such a rate that many small crystals (crystallites) form. The atoms within a single crystallite are symmetrically arranged, whereas crystallites are jumbled together. These numerous grain boundaries reduce the device efficiency. A material composed of variously oriented, small individual crystals. (Sometimes referred to as polycrystalline or semicrystalline).

Net Metering Net metering is the ability to receive energy credit for excess solar energy you generate that is sent back to your utility company. Energy credits vary in each state and between electric retailers in the State of Texas. Net Metering allows residential and business customers to generate excess solar power during the day and use it at night, without the need for an energy storage system or generator.

Ohm A unit of electrical resistance equal to the resistance between two points on a conductor when a potential difference of one volt between them. A unit of measurement that indicates how much something resists or impedes the flow of electricity.

Open-Circuit Voltage (Voc) The voltage across a photovoltaic cell or module in sunlight when no current is flowing; the maximum possible voltage.

Peak Load or Peak Demand The maximum load, or usage, of electrical power occurring in a given period of time, typically a day.

Peak Power PV modules are rated by their total power output. The peak power is the amount of power output a PV modules produces at Standard test conditions (STC)

Performance Ratio Ratio of the final annual (monthly, daily) yield to the reference annual (monthly, daily) yield, where the reference annual (monthly, daily) yield is the theoretically annual (monthly, daily) available energy per kilowatt of installed power.

Photovoltaic Array A mechanically integrated assembly of modules and panels together with support structure to form a DC power producing unit.

Photovoltaic Cell aka Solar Cell A basic photovoltaic device, which generates DC electricity when, exposed to a light such as the solar radiation.

Photovoltaic Module The smallest complete environmentally protected assembly of interconnected photovoltaic cells.

Photovoltaic Panel A group of modules fastened together, pre-assembled and wired, designed to serve as an installable unit in a photovoltaic array.

Photovoltaic Power System Set of interconnected elements such as photovoltaic modules andl installation and control components with a photovoltaic power capacity of 40 W or more.

Photovoltaics The process that produces electricity from sunlight. "Photo" refers to light and "voltaic" to voltage.

Polycrystalline Polycrystalline structures are composed of many different crystals. Many crystals.

PV: Abbreviation of photovoltaic or photovoltaics .

PVPS: Abbreviation of photovoltaic power system(s).

Semiconductor Any material that has a limited capacity for conducting an electric current. Generally falls between a metal and an insulator in conductivity. Certain semiconductors, including silicon, gallium arsenide, copper indium diselenide, and cadmium telluride, are uniquely suited to the photovoltaic conversion process.

Short Circuit Current (Isc) The current flowing freely from a photovoltaic cell or module through an external circuit that has no load or resistance; the maximum current possible

Silicon (Si) A chemical element, atomic number 14. Silicon is semimetallic in nature, dark gray in color, and an excellent semiconductor material. It is a common constituent of sand and quartz (as the oxide) and crystallizes in face-centered cubic lattice like a diamond. It is the most common semiconductor material used in making photovoltaic devices.

Sine Wave inverter An inverter that produces utility-quality, sine wave power forms.

Solar Cell aka Photovoltaic Cell A basic photovoltaic device, which generates DC electricity when, exposed to a light such as the solar radiation.

Solar Constant The strength of sunlight; 1353 watts per square meter in space and about 1000 watts per square meter at sea level at the equator at solar noon.

Solar Energy IEnergy from the sun. The heat that builds up in your car when it is parked in the sun is an example of solar energy.

Solar-Grade Silicon Intermediate-grade silicon used in the manufacture of solar cells. Less expensive than electronic-grade silicon.

Solar Noon That moment of the day that 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 Spectrum The total distribution of electromagnetic radiation emanating from the sun.

Solar Thermal Electric A method of producing electricity from solar energy by using focused sunlight to heat a working fluid, which in turn drives a turbogenerator.

Square Wave inverter The inverter consists of a DC source, four switches, and the load. The switches are power semiconductors that can carry a large current and withstand a high voltage rating. The switches are turned on and off at a correct sequence, at a certain frequency. The square wave inverter is the simplest and the least expensive to purchase, but it produces the lowest quality of power.

Stand-Alone PV Power Systems aka Off-the-Grid This is a system that is not connected to the utility grid and must use a means to store the electricity produced.

Standard Test Conditions (STC) Conditions under which a module is typically tested in a laboratory: (1) Irradiance intensity of 1000 W/square meter (0.645 watts per square inch), AM1.5 solar reference spectrum, and (3) a cell (module) temperature of 25 degrees C, plus or minus 2 degrees C (77 degrees F, plus or minus 3.6 degrees F

State of Charge (SOC) The available capacity remaining in the battery, expressed as a percentage of the rated capacity.

Substrate The physical material upon which a photovoltaic cell is made.

Superstrate The covering on the sun side of a PV module. It provides protection for the PV materials from impact and environmental degradation while allowing maximum transmission of the appropriate wavelengths of the solar spectrum.

Thin Film A layer of semiconductor material, such as copper indium diselenide, cadmium telluride, gallium arsenide, or amorphous silicon, a few microns or less in thickness, used to make photovoltaic cells. Commonly called amorphous.

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 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. Typically, a single axis tracker will give you 15% to 25% more power per day, and dual axis tracking will add about 5% to that. Depends somewhat on latitude and season.

Transformer Steps AC voltage up or down, depending on the application.

VAC Volts alternating current (AC0

VDC Volts direct current (DC)

Vmp Voltage at maximum power

Voc Open-circuit voltage

Volt (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) The unit of electric power, or amount of work (J), done in a unit of time. One ampere of current flowing at a potential of one volt produces one watt of power.

Watt-hour (Wh) See Kilowatt-hour.

Waveform The shape of the curve graphically representing the change in the AC signal voltage and current amplitude, with respect to time.

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