Ampere (A) - Unit of measurement for electric current; it is equivalent to a flow of charge in a conductor equal to one Coulomb per second.
Ampere-hour (Ah) - Quantity of electricity equivalent to the energy corresponding to the flow of a current of one ampere for one hour.
Array - V. photovoltaic field.
Accumulator batteries - Devices capable of converting electrical energy into chemical energy and vice versa. During the charging phase, they are used to store electrical energy, which is then released as needed during the discharging phase. Typically, multiple accumulators are connected together (accumulator batteries).
Photovoltaic field - A set of photovoltaic modules electrically connected to each other and mechanically installed at their operating site.
Battery capacity - The amount of electricity stored by a battery and then deliverable by it at a certain rate until a predetermined voltage. It is measured in Ampere-hours (Ah).
Nominal capacity - The capacity declared by the manufacturer for a certain battery. The nominal capacity refers to a discharge rate of 10 hours and a temperature of 25°C: it is indicated with the symbol C10. It is measured in Ampere-hours (Ah).
Electric load - The amount of instantaneous electrical power consumed by any electrical device (W).
Photovoltaic cell - The basic element of photovoltaic generation, consisting of semiconductor material that is appropriately 'doped' and treated, which converts solar radiation into electricity.
Kilowatt (kW) - A multiple of the unit of power, equal to 1,000 Watts.
Kilowatt-hour (kWh) - Unit of measurement for energy. One kilowatt-hour is the energy consumed in one hour by a device using 1 kW.
Life cycle or lifespan of a battery - A conventional value that indicates the number of charge and discharge cycles a battery can perform before it stops functioning. This is usually accompanied by limitations on the methods of charging and discharging cycles.
Photovoltaic conversion - A phenomenon in which the light incident on a solid-state electronic device (photovoltaic cell) generates electrical energy.
AC/DC converter, rectifier - Device that converts alternating current into direct current.
DC/AC converter, inverter - A device that converts direct current into alternating current.
Current - Flow of electric charges in a conductor between two points having a potential difference (voltage). It is measured in A (Ampere).
Photovoltaic device - Cell, module, panel, string, or photovoltaic field.
Efficiency (in %) - The ratio between the output power (or energy) and the input power (or energy).
Conversion efficiency of a photovoltaic device (in %) - The ratio between the electrical energy produced and the solar energy collected by the photovoltaic device.
Energy - In general, it is measured in J (Joules); the electrical energy that is of interest here is measured in Wh (Watt-hour) and is equivalent to the energy made available by a device that delivers one Watt of power for one hour.
- 1 Wh = 3,600 J
- 1 cal = 4.186 J
- 1 Wh = 860 cal
Thin film - It is the product of technology that utilizes the deposition of a very thin layer of semiconductor materials for the creation of the photovoltaic cell.
Photovoltaic - A compound term from "photo," from the Greek "light," and "voltaic," from Alessandro Volta, the Italian scientist who was among the first to study electrical phenomena.
Photovoltaic generator - An electric generator consisting of one or more photovoltaic modules - or panels, or strings.
Grid - Electrical distribution network.
Maximum Power Point Tracker, MPPT - Electronic equipment that interfaces between the user and the photovoltaic generator, ensuring that the photovoltaic generator always "sees" an optimal load to deliver maximum power. As external conditions (temperature, irradiation) change, the tracker adjusts its operating point to continuously extract the maximum available power from the generator and deliver it to the load.
Inverter - See DC/AC converter.
Irradiance - Instantaneous solar radiation (thus a power) incident on a unit of surface area. It is measured in kW/m2. The irradiance detectable at the Equator, at noon and under optimal atmospheric conditions, is approximately 1,000 W/m2.
Maximum Power Point Tracker (MPPT) - See Maximum Power Point Tracker.
Photovoltaic module - A set of photovoltaic cells connected together in series or parallel, in order to achieve voltage and current values suitable for common applications, such as charging a battery. In the module, the cells are protected from weather elements by a glass on the front side and by insulating and plastic materials on the back side.
Photovoltaic panel - A set of multiple modules, connected in series or in parallel, within a rigid structure.
Power - It is the energy produced per unit of time. It is measured in W = J/s (W = Watt; J = Joule; s = second). From an electrical standpoint, a W is the power developed in a circuit by a current of 1 A (Ampere) passing through a potential difference of 1 V (Volt). Therefore, electrical power is given by the product of the current (I) and the voltage (V). Multiples of the W:
- kilowatt: kW = 10^3 W
- megawatt: MW = 10^6 W
- gigawatt: GW = 10^9 W
- terawatt: TW = 10^12 W
Peak Power (Wp) - It is the maximum power produced by a photovoltaic device under standard operating conditions (irradiance 1000 W/m² and temperature 25°C).
Solar radiation - Electromagnetic energy that is emitted by the sun as a result of the nuclear fusion processes occurring within it. Solar radiation (or energy) at the ground level is measured in kWh/m2.
Rectifier - See AC/DC converter.
Charge regulator - A device that controls the charging rate and the charge status of batteries.
Semiconductors - Materials with electrical characteristics intermediate between those of conductors and insulators. Among them is silicon.
Silicon - Semiconductor material used to build photovoltaic cells.
Amorphous silicon - A type of silicon used in photovoltaic cells that does not have a crystalline structure.
Crystalline silicon - A type of silicon with a crystalline structure (monocrystalline or polycrystalline).
Monocrystalline silicon - Silicon composed of a single crystal.
Polycrystalline silicon - Silicon composed of multiple crystals.
Solar silicon - Silicon specifically produced for the photovoltaic industry or as a byproduct of the electronics industry, having a level of purity sufficient for the preparation of solar cells.
Photovoltaic system - A system composed of photovoltaic modules and other components designed to provide electrical power from solar radiation.
Grid-connected photovoltaic system - Photovoltaic system connected to the electricity distribution grid.
Grid-connected photovoltaic system - See network-connected photovoltaic system.
Isolated photovoltaic system - Photovoltaic system not connected to the distribution power grid.
Stand-alone photovoltaic system - See isolated photovoltaic system.
Subfield - Parallel electrical connection of multiple strings. The set of subfields constitutes the photovoltaic field.
Stand-alone - See isolated or off-grid photovoltaic system.
String - A set of modules or panels electrically connected in series to achieve the operating voltage of the photovoltaic field.
Voltage - The difference in electric potential between two bodies or between two points of a conductor or a circuit. It is measured in V (Volts).
Alternating voltage - The voltage between two points in a circuit that varies over time in a sinusoidal manner. It is the typical form of voltage in electrical distribution systems, as well as in domestic and industrial applications.
Direct current (DC) - Voltage between two points in a circuit that does not change in sign or value over time. It is the typical form of voltage in some isolated systems (railways, ships) and in devices powered by batteries.
Tonne of oil equivalent (Toe) - A unit of energy measurement used to quantify large amounts of energy, such as in energy balances and statistical evaluations. It is equivalent to the energy produced by burning one tonne of oil. Given that the calorific value of crude oil is 41,860 kJ/kg, one toe equals 41,860 · 10^3 kJ.
Volt (V) - Unit of measurement for the voltage existing between two points in an electric field. A voltage of about 0.5 Volts is established across a photovoltaic cell; about 17 Volts across a typical photovoltaic module (at the point of maximum power).
Wafer - A silicon slice with a variable thickness of 250-350 micrometers (thousandths of a millimeter) obtained from cutting silicon ingots produced by melting scrap silicon from the electronics industry. After various treatments, the wafer becomes a photovoltaic cell.
Watt (W) - Unit of measurement for electrical power. It is the power developed in a circuit by a current of one Ampere passing through a potential difference of one Volt. It is equivalent to 1/746 of a Horsepower (HP).
Watt peak (Wp) - A unit of measurement used to indicate the power that a photovoltaic device can produce under standard operating conditions (irradiance of 1,000 W/m² and temperature of 25°C).
Watt-hour (Wh) - Unit of energy measurement: equivalent to one Watt for one hour.