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Alternating current (AC)
Type of current where the flux of electrons changes direction with a regular frequency.
Amorphous silicon (a-Si)
Non-crystalline silicon form. The conversion yield of an amorphous cell is between 5 and 8%.
Angle of incidence
Angle between an incident beam on a surface and its normal (perpendicular to the plane).
In the horizontal plane, the angle between any direction and the South, measured clockwise from the South.
Type of cell where the contacts are not deposed on the active surface of the cells, but integrated at the back of the module. This method presents two advantages: the aspect of the cells is uniform, which facilitates the aesthetic integration of the modules, and the absence of metallic grids augments the yield of the cell.
Balance of system (BOS)
The balance of system is the whole of the electric equipment other than PV modules: cables, switches, inverters, control and measurement systems, batteries and module fastening systems.
BiPV (Building Integrated Photovoltaics)
Acronym of "Building Integrated Photovoltaics", it refers to those photovoltaic elements that are an integral part of a building while they produce also electric energy at the same time.
Characteristics of a cell: IV curve
To obtain them, it is sufficient to connect a load (resistance) and make its value vary from zero to infinite. By measuring the current I and the voltage V, the curve I(V) is obtained for a defined temperature and solar irradiance.
Voc [V]: Open circuit voltage, when the charge is infinite.
Isc [A]: Short circuit current, when the charge is zero. Such as the power is given from the current multiplied by the tension, the curve P(V) is also obtained by the power in function when the charge varies from zero to infinite.
Current-tension curve I(V): As it can be observed, for a constant temperature and solar irradiance, a value of tension (and thus of charge) exists where the cell supplies maximum power. At this point, the MMP (Maximum Power Point), meaning the yield of the cell is at its maximum.
Correlation between the supplied power for a PV element and the received solar power. For example, if a square cell of 0.1m side length receives a 1000W/m2 solar irradiance and supplies a 1.2W electrical power, its conversion yield is: 1.2W / (1000W/m2 x 0.01m2) = 12%. It is important to distinguish the intrinsic conversion yield of the cells used and the one of the PV modules (that depends on the relation between the active surface and the total surface).
Crystalline solar cell
Ii is the most widespread photovoltaic technology (approximately 93% of the market). The cell is the fundamental element of the photovoltaic generation and is consisted of a "wafer" (thin silicon block). Silicon, the semiconductor material that converts the solar radiation in electric energy, can be monocrystalline or multicrystalline.
Electronic device for the collection and the memorization of experimental measurements.
Diffuse solar irradiance
Diffuse solar irradiance is a measure of the rate of incoming solar energy on a horizontal plane at the earth's surface resulting from scattering of the sun's beam due to atmospheric constituents. Is measured by a pyranometer, with its glass dome shaded from the sun's beam.
Direct current (DC)
Electron fluxes always move in teh same direction within a conductor. The unit of measurement of current is the Ampère [A] that corrisponds to the flux of 1 Coulomb (that is 6.2 x 1018 electrons) per second.
Direct solar irradiance
Direct solar irradiance (also referred as direct normal irradiance) is a measure of the rate of solar energy arriving at the earth's surface from the sun's direct beam, on a plane perpendicular to the beam, and is usually measures by a pyrheliometer mounted on a solar tracker.
The whole of the infrastructures that connect all the producers and consumers of electricity. The transport of electric energy is done by alternating current (50Hz in Europe) at high tension so to reduce the losses.
Mechanic or electronic device predesposed to the counting of produced and/or consumed energy.
Glass and/or plastic covering of PV panels, useful for teh protection of the cells and contact grids.
Energy Payback Time (EPBT)
The time, measured in years, necessary for a whole photovoltaic system (modules+cables+electronic devices) to produce the enrgy spent for its production. It depends on the technology and the location.
Energy Return Factor (ERF)
The relation between produced energy by a photovoltaic system during its lifetime and energy used for its production.
Acronym of ethylenvinylacetate. Type of plastic resin used for gluing the encapsulant of the PV cells through lamination.
Ratio between useful energy (at the output of the inverter if there) produced by a given period and the nominal power of this same system. The production index is measured in [kWh/kWp].
External part of the modules that provide protection of the module and is useful for their fixing.
Global solar irradiance
Global solar irradiance is a measure of the rate of total incoming solar energy (both direct and diffuse) on a horizontal plane at the earth's surface. A pyranometer sensor can be used to measure this quantity with limited accuracy. The most accurate measurements are obtained by summing the diffuse and horizontal component of the direct irradiance.
Grid connected PV system
System connected to the electrical net, to aliment it or use it as a storage cell.
Metallic parts of a PV module necessary for the series and parallel connection of the cells.
Height of the sun
In the vertical plan, the angle between the direction of the sun and the horizon, measured positively during the day.
Instrument that is used to convert direct current produced by PV panels into alternating current. It is necessary for the connection of the PV system to the electrical grid.
PV module without frame, the result of lamination. It is a glass-glass sandwich, glass-PVF or insulating glass.
Minimum nominal power
Equivalent to nominal power minus the tolerance.
Mono-crystalline silicon (sc-Si or mono-Si)
Crystalline silicon form composed by a single silicon crystal. The conversion yield of a mono-crystalline cell is between 15 and 22%.
Multi-crystalline silicon (mc-Si or poly-Si)
Crystalline silicon form composed by more silicon crystals. The conversion yield of a multi-crystalline cell is between 10 and 16%.
Peak or nominal power
Nominal power of a photovoltaic system in standard functioning conditions, called STC - Standard Test Conditions (solar irradiance 1000W/m2, temperature 25°C). Peak or nominal power is generally measured in "Watt-peak" [Wp].
Performance Ratio (PR)
Ratio between the production index Yf and the reference index Yr (the energy theoretically available per kWp installed), in [kWh/kWp], during the same period. It is measured in [%].
Quantity of work (or energy) that a system produces (or consumes) per unit of time. It is measured in Watt [W] that corrisponds to 1 Joule per second.
PV panel, module or element
Assembly of PV cells through grids and contacts, laminated and that work as a single PV system.
A whole composed by photovoltaic modules, cables, inverter and electric/energy meters used for the generation of electrical energy.
Acronym of Polyvinyl buthiral. Type of plastic resin used for gluing the encapsulant of PV cells by lamination.
Acronym of Polyvinyl fluoride. Type of plastic resin used for gluing the encapsulant of PV cells by lamination. Tedlar® is a commercial name of PVF.
Obstacle to direct solar irradiance that projects a shadow/shading over the whole or a part of PV cell, module, string or system. It is possible to distinguish: remote shading, distant enough to project shading over the whole system almost instantaneously (horizon effect), and close shading that projects partial shadings over the system.
Partial shading has to be avoided as much as possible because it causes proportionally higher losses of power.
In the case of a system with an inverter per string, the connection has to be done in parallel to the most significant shading: for example, if a tree is projected on a PV facade during theday, the strings have to be connected vertically.
Flat representation in rectangular coordinates of the trajectory of the sun in the sky. The coordinates used are: height and solar azimuth, that define the position of the sun in a precise moment. Representing on the same diagram the trajectories of the sun of different days of the year you obtain a synthesis of annual solar irradiance.
Representation on a solar diagram of the solar path and of the solar trajectorydiagram a specific day of the year. Solar irradiance is the power of the sun per surface unit, in [W/m2], hitting on a set surface (position and orientation). Global solar irradiance is the sum of all solar irradiances, direct and diffuse, that reaches the earth's surface, generally measured in the horizontal plane.
A string is composed by a variable number of cells, modules or panels connected in series to obtain a particular voltage.
Legislative financial benefits suitable for the promotion of PV through the repurchase of the electric energy produced at a higher price than the market price, an aid to compensate the installation expenses or a tax rebate. More information: Swiss Federal Office of Energy (SFOE), www.ufe.admin.ch.
Thin film cell
Second generation cell that takes advantage of the deposition of a very thin layer of semiconductor materials. These cells are characterized by a lower production cost. Different semiconductor materials can be used for this technology: amorphous or micromorphous silicon, CdTe (Cadmium telluride), CIS (Copper-Indium-Diselenide), etc..
The angle that characterizes the inclination of the module over the horizon, measured positively from the horizontal plane upwards. A module laid horizontally has a tilt of zero.
The characteristic of a PV module that defines the quantity of light that it lets through. The supplier offers a degree of transparency: if it is 0%, the module is opaque. The efficiency of a semi-transparent module is always lesser than the efficiency of an opaque module with comparable technology and surface.
Tri-phase alternating current
Transport and use of electricity shift based on three alternating currents with the same frequency but with a phase difference. The advantage is that there are less losses during the transport of the electric energy.
Quantity of energy corresponding to 1W during one hour, or 3600Joule. A kilowatt-hour (kWh) corresponds to 1'000Wh, a megawatt-hour (MWh) to 1'000'000Wh and a gigawatt-hour (GWh) corresponds to 1'000'000'000Wh.