S
Self-discharge
In an electrochemical accumulator it corresponds to the leak of energy due to the passing of time. It can depend on direct reactions between active material and electrolyte, caused by leaks of the device.
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.
Series connection
A way of joining photovoltaic cells or batteries by connecting positive leads to negative leads; such a configuration increases the voltage.
Shadow band pyranometer
An instrument for measuring diffused solar irradiance. It measures the global irradiance excluding the direct component thanks to the shadow band.
Short-circuit current Isc [A]
The current flowing freely from a photovoltaic cell through an external circuit that has no load or resistance; the maximum current possible.
Silicon (Si)
A chemical element, atomic number 14, semimetallic in nature, dark grey, 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.
Sine wave
Waveform having a periodic oscillation that can be graphically expressed as a sine curve; it continues for all time with a single constant frequency and amplitude.
Solar grade silicon
Silicon of intermediate grade between the electronic one and the metallurgical one, produced specifically for the photovoltaic industry.
Solar radiation [kWh/m²]
It's the electromagnetic power produced by the sun as a result of the processes of nuclear fusion.
Specific gravity
Relationship between the weight of the solution in the accumulator and the weight of an amount of water of the same volume. Specific gravity usually represents an indicator of the battery SOC.
Sputtering
Procedure to value the depth of ion penetration on the silicon surface. See also: Ion accelerator.
Square wave
Waveform having only two significant conditions (i.e. positive and negative). Square waves usually have a high number of harmonics.
Stand-alone (PV system)
An autonomous or hybrid photovoltaic system not connected to a grid. May or may not have storage, but most stand-alone systems require batteries or some other form of storage.
Standard conditions of functioning
A PV device works in “standard conditions” with a 25 °C cell junction temperature, 1.000 W/m² radiation and standard radiation spectral distribution (AM 1.5).
State of charge (SOC)
The available capacity remaining in the battery, expressed as a percentage of the rated capacity.
Steam barrier
Any project element, structural or not, preventing condensation steam on bodies at different temperatures.
Stratification
It takes place when the concentration of acid in an accumulator is different in the upper part from the one in the lower part. It can be solved through an equalization recharge or by blowing air inside the accumulator.
String
Collection of series-connected modules with the aim of reaching the working voltage of the PV array.
Subarray
Electrical parallel-connection of several strings. The subarrays taken together form the PV array.
Substrate
The physical material upon which a photovoltaic cell is made.
Subsystem
Any of the components of a PV system (string, controller, inverter, etc.).
Sulphation
A condition that afflicts unused and discharged batteries; large crystals of lead sulphate grow on the plate, instead of the usual tiny crystals, making the battery extremely difficult to recharge.
Sunseeker
Supporting structure of the solar panel maintaining a constant sun-facing orientation through an electro assisted device. It can be moved along the horizontal axis, or the horizontal and vertical ones at the same time.
Sunseeker array
Array following the path of the sun. The tracking can be on one or both axles.
