Air mass: The air mass relates to the path length of solar radiation through the atmosphere. An air mass of 1.0 means the sun is directly overhead and the radiation travels through one atmosphere thickness. Approximately equal to the secant of the zenith angle, i.e. the angle from directly overhead to a line to the sun.
Alternating current (AC): Electrical current that continually reverses direction of flow. The frequency at which it reverses is measured in cycles-per-second, or Hertz (Hz). The magnitude of the current itself is measured in amps (A).
Amorphous silicon: A thin-film solar PV cell material which has a glassy rather than crystalline structure. Made by depositing layers of doped silicon on a substrate normally using plasma-enhanced chemical vapor deposition of silane.
Amp hour: The quantity of electrical energy corresponding to the flow of current of one ampere for one hour. The term is used to quantify the energy stored in a battery. Most batteries are rated in Ah. Ampere (A) or amp: The unit for the electric current; the flow of electrons. Angle of incidence: Angle between the normal to a surface and the direction of incident radiation; applies to the aperture plane of a solar panel. Only minor reductions in power output within plus/minus 15 degrees.
Array: A number of solar modules connected together in a single structure.
Azimuth: The 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.
Battery: A system in which stored chemical energy is converted directly into electrical energy.
Battery cycle Life: The number of times a battery can undergo a cycle of discharge and recharge before failing. Cycle Life is normally specified as a function of discharge rate and temperature.
Battery state of charge (SOC): Extent of battery charge status as a percentage of full charge. Also 100 per cent minus the Depth of Discharge.
BIPV: Building Integrated Photovoltaics. As the name suggests, this is where PV modules are integrated in to the building construction materials as on integrated unit.
Charge controller: A component that controls the flow of current to and from the battery subsystem to protect the batteries from overcharge and over discharge. Essential for ensuring that batteries obtain maximum state of charge and longest life. The charge controller may also monitor system performance and provide system protection. Charge Controllers are also sometimes called Regulators.
Cloud enhancement: The increase in solar intensity due to reflected light from nearby clouds.
Crystalline silicon: A type of PV cell material made from a single crystal or polycrystalline ingot of silicon. Cycle life: Number of charge-discharge cycles a battery can perform under specified conditions before it fails to meet its specified performance (e.g. capacity decreases to 80% of nominal capacity).
Deep cycle battery: A battery designed to regularly discharge 80% of its capacity before recharging.
Depth of discharge (DOD): the amount of energy withdrawn from a battery expressed as a percentage of its rated capacity. Diffuse insolation: Incident sunlight received indirectly because of scattering due to clouds, fog, particulates, or other obstructions in the atmosphere. Diode: Electronic device that allows current flow only in one direction. Direct current (DC): Electrical current that flows only in one direction, although it may vary in magnitude. Contrasts with alternating current. Direct insolation: Sunlight falling directly upon a collector. Opposite of diffuse insolation.
Discharge factor: A number equivalent to the time in hours during which a battery is discharged at constant current usually expressed as a percentage of the total battery capacity, i.e., C/5 indicates a discharge factor of 5 hours. Discharge rate: A measure of the current withdrawn from a battery over time, expressed as a percentage of battery capacity. A C/5 discharge rate indicates a current of one-fifth of the rated capacity of the battery. Dry cell battery: A battery that uses a solid paste for an electrolyte. Duty cycle: The ratio of active to total time, used to describe the operating regime of loads in PV systems.
Electrolyte: The medium that provides ionic transport between the electrodes of a battery. All common batteries contain an electrolyte, such as the sulfuric acid used in lead-acid batteries.
Energy pay back time: The time required for any energy producing system or device to produce as much energy as was required in its manufacture. For solar electric panels, this is normally in the range 6-36 months. Energy: The capacity or ability to do work .
Equalization charge: Periodical overcharging the batteries for a short time to mix the electrolyte solution in batteries.
Fixed tilt array: A solar PV array set at a fixed angle to the horizontal.
Flat-plate PV: A solar PV array or module that does not contain concentrating devices.
Float charge: A battery charge current that is equal to, or slightly greater than, the self-discharge rate.
Flooded cell battery: A form of rechargeable battery where the plates are completely immersed in a liquid electrolyte. Most cars use flooded-cell batteries.
Fluorescent light: A form of lighting that uses tubes of glass which contain mercury vapor and various phosphor powders (chemicals based on phosphorus) to produce white light. Generally considered to be the most efficient form of home lighting.
Frequency: The number of cycles per unit time of a complete waveform, in electrical applications usually expressed in cycles per second or Hertz (Hz). Fuel cell: An electrochemical device that converts the energy of a fuel directly into electricity and heat and is therefore very energy efficient.
Fuse: A fuse is a device used to protect electrical equipment from short circuits. Fuses are made with metals that are designed to melt, when the current passing through them is high enough. When the fuse melts, the electrical connection is broken, interrupting power to the circuit or device.
Gel-type battery: Lead-acid battery in which the electrolyte is immobilized in a gel. Usually used for mobile installations and when batteries will be subject to high levels of shock or vibration. Gigawatt (GW): A measurement of power equal to a thousand million Watts.
Grid-connected: An energy producing system connected to the utility transmission grid. Also called Grid tied.
Halogen lamp: A special type of incandescent globe made of quartz glass and a tungsten filament, enabling it to run at a much higher temperature than a conventional incandescent globe. Efficiency is better than a normal incandescent, but not as good as a fluorescent light. I
Incandescent light: an electric lamp which is evacuated or filled with an inert gas and contains a filament (commonly tungsten). The filament emits visible light when heated to extreme temperatures by passage of electric current through it.
Incident light: Light that shines on to the surface of a PV cell or module. Insolation: The amount of sunlight reaching an area, usually expressed in Watt hours per square meter per day. Inverter: An inverter converts DC power from the PV array/battery to AC power. Used either for stand-alone systems or grid-connected systems.
Irradiance: The solar power incident on a surface, usually expressed in kilowatts per square meter. Irradiance multiplied by time gives insolation.
Junction box: A PV junction box is a protective enclosure on a PV module where PV strings are electrically connected and where electrical protection devices such as diodes can be fitted.
Kilowatt(kW): A unit of electrical power, one thousand Watts.
Kilowatt-hour (kWh): The amount of energy that derives from a power of one thousand Watts acting over a period of 1 hour. The kWh is a unit of energy. 1 kWh=3600 kJ.
Lead-acid battery: A type of battery that consists of plates made of lead, lead-antimony, or lead-calcium and lead-oxide, surrounded by a sulfuric acid electrolyte. Liquid electrolyte battery: A battery containing a liquid solution of an electrolyte in a solvent (e.g. sulfuric acid in water). Also called a flooded battery because the plates are covered with the electrolyte solution.
Maintenance free battery: A sealed battery to which water cannot be added to maintain the level of the electrolyte solution. Maximum power point (MPP): Operating a PV array at that voltage will produce maximum power. The point on the current-voltage (I-V) curve of a module under illumination, where the product of current and voltage is maximum. [UL 1703] This corresponds to the point on an I-V curve that represents the largest area rectangle that can be drawn under the curve. For a typical silicon cell panel, this is about 17 volts for a 36 cell configuration.
Maximum power point tracker (MPPT): A power conditioning unit that automatically operates the PV generator at its MPP under all conditions. An MPPT will typically increase power delivered to the system by 10% to 40%, depending on climate conditions and battery state of charge.
Megawatt (MW): A measurement of power equal to one million Watts.
Modified sine wave: A waveform with at least three states (positive, off, and negative) used to simulate a sine wave. It has less harmonic content than a square wave. This type of waveform is better than a square wave, but not as suitable for some appliances as a sine wave. Module: An encapsulated panel containing a number of electrically connected PV cells. Monocrystalline solar cell: A form of solar cell made from a thin slice of a single large crystal of silicon. Multicrystalline: A material that has solidified at a rate such that many small crystals (crystallites) form. The atoms within a single crystallite are symmetrically arranged with a particular orientation, whereas the crystallites themselves are differently oriented. The multitude of grain boundaries in the material (between the crystallites) reduce the cell efficiency. Multicrystalline is also referred to as polycrystalline. Multi-stage controller: A charge controller that allows different charging currents as the battery approaches full state of charge.
NEC: US National Electrical Code which contains guidelines for all types of electrical installations which should be followed when installing a PV system.
NEMA:US National Electrical Manufacturers Association, sets standards for some non-electronic products e.g. junction boxes.
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).
N-Type silicon: Silicon doped with an element that has more electrons in its atomic structure than does silicon (e.g. phosphorus).
One-axis tracking: A PV System structure that is capable of rotating on a single axis in order to track the movement of the sun. Open circuit voltage: The maximum voltage produced by an illuminated solar PV cell, module, or array when no load is connected. OCV increases as the temperature of the PV material decreases. Orientation: Position with respect to the cardinal directions, N, S, E, W.
Panel: Used interchangeably with "module". Peak sun hours: The equivalent number of hours per day when solar irradiance averages 1000 W/m2. Photovoltaic (PV) module: A single assembly of solar cells and ancillary parts, such as interconnections, terminals, (and protective devices such as diodes) intended to generate DC power under un-concentrated sunlight Photovoltaic cell: The semiconductor device that converts solar irradiance (light) into dc electricity. Photovoltaic-thermal (PV/T) system: A photovoltaic system that, in addition to converting sunlight into electricity, collects the residual heat energy and delivers both heat and electricity in usable form. Also called a total energy system. Polycrystalline silicon: A material used to make solar PV cells which consists of many crystals, compared to single crystal silicon. Power: The measure of rate of doing work or transferring energy. Electrically expressed as Watts (W). Is calculated by multiplying voltage x amperage.
PV: Short hand for Photovoltaics.
Reverse bias: Condition where the current producing capability of a PV cell is significantly less than that of other cells in its series string. This can occur when a cell is shaded, cracked, or otherwise degraded or when it is electrically poorly matched with other cells in its string.
Sealed battery: A battery with a captive electrolyte and a re-sealing vent cap to which electrolyte cannot be added. Also called a valve-regulated battery.
Self discharge rate: The rate at which a battery will lose its charge when at open circuit (with no load connected).
Semiconductor: A material that has an electrical conductivity in between that of a metal and an insulator. Transistors and other electronic devices are made from semiconducting materials, and are often called semiconductors. Typical semiconductors for PV cells include silicon, gallium arsenide, copper indium diselenide, and cadmium telluride. Short circuit current (Isc) : The current generated by an illuminated solar PV cell, module, or array when its output terminals are shorted; the maximum current possible.
Silicon (Si): A chemical element with atomic number 14, a dark gray semi-metal. Occurs in a wide range of silicate minerals and makes up approximately 28% of the earth's crust (by weight). Silicon has a face-centered cubic lattice structure like diamond. The most common semiconductor material used in making PV cells either traditionally in its crystalline form or more recently as an amorphous thin film. Sine wave inverter: An inverter that produces grid-quality, sine wave AC electricity.
Single-crystal silicon: Silicon material with a single crystal structure. A common material for the construction of solar PV cells. Solar noon: The mid-point between sunrise and sunset; the time when the sun reaches its highest point in its daily arc across the sky. Solar module: A device used to convert light from the sun directly into DC electricity by using the photovoltaic effect. Usually made of multiple solar cells bonded between glass and a backing material.
Square wave inverter: The simplest and the least expensive type of inverter, but which produces the lowest quality of power. The inverter uses switches that can carry a large current and withstand a high voltage that are turned on and off in the correct sequence and at a certain frequency. 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 capacity of a battery at a particular time expressed at a percentage of its rated capacity. String: A number of cells, modules or panels interconnected electrically in series to produce the required operating voltage.
Sulfation: The formation of lead-sulfate crystals on the plates of a lead-acid battery; large crystals of lead sulfate grow on the plate, instead of the usual tiny crystals, making the battery extremely difficult to recharge. If the crystals get large enough, shorting of the cell may occur. Surge capacity: The ability of an inverter or generator to deliver instantaneous high currents when starting motors, for example.
Temperature compensation: Adjustment via the use of electronic circuitry to change the charge controller activation points depending on battery temperature. This is desirable if the battery temperature is expected to vary by more than 5 deg C from the ambient temperature. The temperature coefficient for lead acid batteries is typically -3 to -5 millivolts/deg C per cell. Thin film PV module: A solar PV module constructed with sequential layers of thin film semiconductor materials usually only micrometers thick. Tilt angle: The angle of inclination of a solar collector or solar module measured from the horizontal. Tracking array: A PV array that is moved to follow the path of the sun in order to maintain the maximum incident solar radiation on its surface. The two most common methods are firstly single-axis tracking in which the array tracks the sun from east to west, and secondly, two-axis tracking in which the array points directly at the sun all the time. Two-axis tracking arrays capture the maximum possible daily energy. Typically, a single axis tracker will give 15% to 25% more power per day, and dual axis tracking will add a further 5%. Two-axis tracking: A system capable of rotating independently about two axes (e.g., vertical and horizontal) and following the sun for maximum efficiency of the solar array.
Vmp: The voltage at which a PV device is operating at maximum power.
Voltage:Unit of measurement for the electrical `pressure' of electricity. Measured in Volts (V).
Wafer: A thin sheet of crystalline semiconductor material either made by mechanically sawing it from a single-crystal boule or multicrystalline ingot or block, or made directly by casting.The wafer is "raw material" for the solar cell.
Watt peak : Is the Direct Current Watts output of a Solar Module as measured under an Industry standardized Light Test before the Solar Module leaves the Manufacturers facility.
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