Photovoltaic glossary

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Thyssen-Solartec, application example

Thin film solar cells - application examples
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The term photovoltaics derives from the Greek word "phos" meaning light and the word "volt" (named by Alessandro Volta). Photovoltaics is a science, which examines light-electricity conversion, respectively, photon energy-electric current conversion. In other words it stands for light-current conversion. Some important photovoltaic terms are explained below. For detailed explanations additional links are also provided.

Absorption Coefficient - The factor by which photons are absorbed as they travel a unit distance through a material.

Alternating Current - Electric current in which the direction of flow is reversed at frequent intervals.

AM - Airmass; The ratio of the mass of atmosphere in the actual observer-sun path to the mass that would exist if the observer was at sea level, at standard barometric pressure, and the sun was directly overhead. AM0 corresponds to the solar spectrum in outer space, and the reference spectrum for STC was defined to be AM1.5

Amorphous Semiconductor - A non-crystalline semiconductor material that has no long-range order.

Amorphous Silicon - A thin-film PV silicon cell having no crystalline structure. Manufactured by depositing layers of doped silicon on a substrate.

Ampere (A) - Unit of electric current. The rate of flow of electrons in a conductor equal to one coulomb per second.

Ampere Hour (Ah) - The quantity of electrical energy equal to the flow of current of one ampere for one hour. The term is used to quantify the energy stored in a battery.

Anode - The positive electrode in an electrochemical cell (battery). Also, the earth ground in a cathodic protection system. Also, the positive terminal of a diode.

Antireflection Coating - A thin coating of a material, which reduces the light reflection and increases light transmission, applied to a photovoltaic cell surface.

Array - A collection of electrically connected photovoltaic (PV) modules.

Array Current - The electrical current produced by a PV array when it is exposed to sunlight.

Azimuth - Horizontal angle measured clockwise from true north; 180° is true south.

Base Load - The average amount of electric power that a utility must supply in any period.

Battery - A device that converts the chemical energy contained in its active materials directly into electrical energy by means of an electrochemical oxidation-reduction (redox) reaction.

Battery Capacity - The total number of ampere-hours that can be withdrawn from a fully charged battery.

BIPV – Building Integrated Photovoltaics; A term for the design and integration of PV 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, into shading "eyebrows" over windows; or other building envelope systems.

Blocking Diode - A diode used to restrict or block reverse current from flowing backward through a module. Alternatively, diode connected in series to a PV string; it protects its modules from a reverse power flow and, thus, against the risk of thermal destruction of solar cells.

Bypass Diode - A diode connected across one or more solar cells in a photovoltaic module such that the diode will conduct if the cell(s) become reverse biased. Alternatively, diode connected anti-parallel across a part of the solar cells of a PV module. It protects these solar cells from thermal destruction in case of total or partial shading of individual solar cells while other cells are exposed to full light.

Cadmium Telluride (CdTe) - A polycrystalline thin-film photovoltaic material.

Capacity - The total number of ampere-hours that can be withdrawn from a fully charged battery at a specified discharge rate and temperature.

Cathode - The negative electrode in an electrochemical cell. Also, the negative terminal of a diode.

Cathodic Protection - A method of preventing oxidation (rusting) of exposed metal structures, such as bridges and pipelines, by imposing between the structure and the ground a small electrical voltage that opposes the flow of electrons and that is greater than the voltage present during oxidation.

Charge Controller - A device that controls the charging rate and/or state of charge for batteries.

Chemical Vapour Deposition - A method of depositing thin semiconductor films. With this method, a substrate is exposed to one or more vaporized compounds, one or more of which contain desirable constituents. A chemical reaction is initiated, at or near the substrate surface, to produce the desired material that will condense on the substrate.

CIS - Copper-Indium-Diselelide.

Converter - A unit that converts a dc voltage to another dc voltage.

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

Current - The flow of electric charge in a conductor between two points having a difference in potential (voltage).

Cutoff Voltage - The voltage levels (activation) at which the charge controller disconnects the array from the battery or the load from the battery.

Czochralski Process - A method of growing large size, high quality semiconductor crystal by slowly lifting a seed crystal from a molten bath of the material under careful cooling conditions.

Cycle - The discharge and subsequent charge of a battery.

DC to DC Converter - Electronic circuit to convert dc voltages (e.g., PV module voltage) into other levels (e.g., load voltage). Can be part of a maximum power point tracker (MPPT).

Deep Cycle - Type of battery that can be discharged to a large fraction of capacity many times without damaging the battery.

Depth of Discharge - The percent of the rated battery capacity that has been withdrawn.

Diffuse Radiation - Radiation received from the sun after reflection and scattering by the atmosphere and ground.

Diode - Electronic component that allows current flow in one direction only.

Direct Beam Radiation - Radiation received by direct solar rays. Measured by a pyrheliometer with a solar aperture of 5.7° to transcribe the solar disc.

Direct Current - Electric current flowing in only one direction.

Duty Cycle - The ratio of active time to total time. Used to describe the operating regime of appliances or loads in PV systems.

DVM - digital Volt-meter.

Efficiency - The ratio of output power (or energy) to input power (or energy). Expressed in percent.

EFG - Edge definde Film Growth, A method for making sheets of polycrystalline silicon in which molten silicon is drawn upward by capillary action through a mold.

Electrolyte - The medium that provides the ion transport mechanism between the positive and negative electrodes of a battery.

Electric Current - A flow of electrons; electricity.

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

Electron Volt - An energy unit equal to the energy an electron acquires when it passes through a potential difference of one volt; it is equal to 1.602 x 10^-19V.

Equalisation Charge - The process of mixing the electrolyte in batteries by periodically overcharging the batteries for a short time.

EVA - Ethylene-Vinile-Acetate Foil, it will be used by module production for covering the cells.

Fill Factor (FF) - For an I-V curve, the ratio of the maximum power to the product of the open-circuit voltage and the short-circuit current. Fill factor is a measure of the "squareness" of the I-V curve.

Fixed Tild Array - A PV array set in at a fixed angle with respect to horizontal.

Frequency - The number of repetitions per unit time of a complete waveform, expressed in Hertz (Hz).

Gassing - Gas by-products, primarily hydrogen, produced when charging a battery. Also, termed out-gassing.

Gallium Arsenide (GaAs) - A crystalline, high-efficiency semiconductor/photovoltaic material.

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

Grid - Term used to describe an electrical utility distribution network.

Grid Connected PV System - A PV system in which the PV array acts like a central generating plant, supplying power to the grid.

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

I-U Characteristics - The plot of the current versus voltage characteristics of a photovoltaic cell, module, or array. Three important points on the I-V curve are the open-circuit voltage, short-circuit current, and peak power operating point.

Incident Light - Light that shines onto the face of a solar cell or module.

Insolation - The solar radiation incident on an area over time. Equivalent to energy and usually expressed in kilowatt-hours per square meter.

Inverter - (Power Conditioning Unit, PCU, or Power Conditioning System, PCS) In a PV system, an inverter converts dc power from the PV array/battery to ac power compatible with the utility and ac loads.

Irradiance - The solar power incident on a surface. Usually expressed in kilowatts per square meter. Irradiance multiplied by time equals Insolation.

Joule (J) - Unit of energy equal to 1/3600 kilowatt-hours.

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 (kW) - One thousand watts. A unit of power.

Kilowatt Hour (kWh) - One thousand watt-hours. A unit of energy. Power multiplied by time equals energy.

Load - The amount of electric power used by any electrical unit or appliance at any given time.

Load Current - The current required by the electrical device.

Low Voltage Cutoff - The voltage level at which a controller will disconnect the load from the battery.

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

Module - The smallest replaceable unit in a PV array. An integral, encapsulated unit containing a number of PV cells.

MOS-FET - Metal-Oxid-Silicon Field effect transistor; used as semiconductor power switch in charge regulators, inverters etc.

MPP - Maximum Power Point; The point on the current-voltage (I-V) curve of a module under illumination, where the product of current and voltage is maximum. For a typical silicon cell, this is at about 0.45 V.

MPPT - Maximum Power point Tracker; Means of a power conditioning unit that automatically operates the PV-generator at its MPP under all conditions.

N-Type Silicon - Silicon material that has been doped with a material that has more electrons in its atomic structure than does silicon.

NOCT - Nominal Operating Cell temperature; The estimated temperature of a PV module when operating under 800 W/m² irradiance, 20°C ambient temperature and wind speed of 1 meter per second. NOCT is used to estimate the nominal operating temperature of a module in its working environment.

Nominal Voltage - A reference voltage used to describe batteries, modules, or systems.

Ohm (Ω) - The unit of electrical resistance in which an electromotive force of one volt maintains a current of one ampere.

One Axis Tracking - A system capable of rotating about one axis.

Open Cirquit Voltage - The maximum voltage produced by an illuminated photovoltaic cell, module, or array with no load connected. This value will increase as the temperature of the PV material decreases.

Operating Point - The current and voltage that a module or array produces when connected to a load. The operating point is dependent on the load or the batteries connected to the output terminals of the array.

Overcharge - Forcing current into a fully charged battery. The battery will be damaged if overcharged for a long period.

Panel - A designation for a number of PV modules assembled in a single mechanical frame.

Peak Load - The maximum load demand on a system.

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.

Peak Watt (Wp) - The amount of power a photovoltaic module will produce at standard test conditions (normally 1000 W/m² and 25° cell temperature).

Photon -A particle of light that acts as an individual unit of energy. Its energy depends on wavelenght.

Photovoltaic System - An installation of PV modules and other components designed to produce power from sunlight and meet the power demand for a designated load.

Polycrystalline Silicon - A material used to make PV cells which consist of many crystals as contrasted with single crystal silicon.

Power Factor - The cosine of the phase angle between the voltage and the current waveforms in an ac circuit. Used as a designator for inverter performance. A power factor of 1 indicates current and voltage are in phase and power is equal to the product of volt-amperes. (no reactive power).

Primary Battery - A battery whose initial capacity cannot be restored by charging.

Pulse Width Modulated (PWM) - PWM inverters are the most expensive, but produce a high quality of output signal at minimum current harmonics. The output voltage is very close to sinusoidal.

Pyranometer - An instrument used for measuring global solar irradiance.

Pyrheliometer - An instrument used for measuring direct beam solar irradiance. Uses an aperture of 5.7° to transcribe the solar disc.

Rated Module Current - The current output of a PV module measured at standard test conditions of 1,000 w/m2 and 25°C cell temperature.

Reactive Power - The sine of the phase angle between the current and voltage waveforms in an AC system.

Remote Site - A site not serviced by an electrical utility grid.

Resistance - The property of a conductor which opposes the flow of an electric current resulting in the generation of heat in the conducting material. The measure of the resistance of a given conductor is the electromotive force needed for a unit current flow. The unit of resistance is ohms.

Secondary Battery - A battery that can be recharged.

Self Distance - The rate at which a battery, without a load, will lose its charge.

Series Regulator - Type of battery charge regulator where the charging current is controlled by a switch connected in series with the PV module or array.

Short Cirquit Current - The current produced by an illuminated PV cell, module, or array when its output terminals are shorted.

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

Single Crystall Silicon - Material with a single crystalline formation. Many PV cells are made from single crystal silicon.

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.

Stand Alone System - A photovoltaic system that operates independent of the utility grid.

Standard Test Conditions - Conditions under which a module is typically tested in a laboratory: (1) Irradiance intensity of 1000 W/m², AM1.5 solar reference spectrum, and (3) a cell (module) temperature of 25°C, plus or minus 2°C.

String - A number of modules or panels interconnected electrically in series to produce the operating voltage required by the load.

Subsystem - Any one of several components in a PV system (i.e., array, controller, batteries, inverter, load).

Sun Path Diagram - Graphical representation of the Sun's height and azimuth

System Operating Voltage - The array output voltage under load. The system operating voltage is dependent on the load or batteries connected to the output terminals.

Tilt Angle - The angle of inclination of a solar collector measured from the horizontal.

Thin Film PV Module - A PV module constructed with sequential layers of thin film semiconductor materials.

Tracking Array - A PV array that follows the path of the sun. This can mean one-axis, east to west daily tracking, or two-axis tracking where the array follows the sun in azimuth and elevation.

Transformer - Converts the generator's low-voltage electricity to higher voltage levels for transmission to the load center, such as a city or factory.

Trickle Charge - A small charge current intended to maintain a battery in a fully charged condition.

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

Uninterruptible Power Supply (UPS) - The designation of a power supply providing continuous uninterruptible service. The UPS will contain batteries.

Utility Interactive Inverter - An inverter that can function only when tied to the utility grid, and uses the prevailing line-voltage frequency on the utility line as a control parameter to ensure that the PV system's output is fully synchronized with the utility power.

Varistor - A voltage-dependent variable resistor. Normally used to protect sensitive equipment from power spikes or lightning strikes by shunting the energy to ground.

Vented Cell - A battery designed with a vent mechanism to expel gases generated during charging.

Volt - The unit of electromotive force that will force a current of one ampere through a resistance of one ohm.

Voltage at Maximum Power - 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 multicrystal ingot or casting.

Watt - The unit of electrical power. The power developed when a current of one ampere flows through a potential difference of one volt.

Watt Hour (Wh) - A unit of energy equal to one watt of power connected for one hour.

Waveform - The characteristic shape of an AC current or voltage output.

Zenith Angle - The angle between directly overhead and the line intersecting the sun. (90°- zenith) is the elevation angle of the sun above the horizon.

More detailed information

IEC: Solar photovoltaic energy systems - Terms and symbols; IEC/TR2 61836.
Solarserver - Solar Lexicon
Renewable Resource Data Center (RReDC) - Glossary of Solar Radiation Resource Terms