Glossary

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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.

Sensor
A device that translates a condition (temperature, sunlight) or event (kWh production) into electronic signals interpreted by a datalogger.

Series Connection
A way of joining photovoltaic cells or batteries by connecting positive leads to negative leads; such a configuration increases the voltage.

Short-Circuit Current (Isc)
The current flowing freely from a PV cell through an external circuit that has no load or resistance; the highest current possible.

Silicon (Si)
A chemical element, atomic number 14, semi-metallic 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-Crystal Material
A material that is composed of a single crystal or a few large crystals.

Solar Cell
See 'Photovoltaic cell.'

Solar Energy
Energy from the sun.

Solar Radiation
Radiant energy deriving from the sun. Measured in watts per square meter.

Stand-alone (PV system)
A photovoltaic system not connected to a main electric grid. May be solar-only or hybrid. May or may not have storage batteries, but most stand-alone systems require batteries or some other form of storage (e.g. water reservoir for pumping).

Stand-off Mounting
Technique for mounting a PV array on a sloped roof, which involves mounting the modules a short distance above the pitched roof and tilting them to the optimum angle.

Standard Operating Conditions (SOC)
A standard set of conditions used for comparing PV module performance. The conditions are: ambient air temperature of 20oC, solar irradiation of 800 W/m2, and wind speed of 1 m/s.

Standard Test Conditions (STC)
A standard set of conditions used for comparing PV module performance. The conditions are: solar irradiation of 1,000 W/m2 and cell temperature of 25oC. Abbreviated as "STC", as in "Module Rating (DCstc)".

Substrate
The physical material upon which a photovoltaic cell is made.

Superstrate
The covering on the sun side of a PV module, providing protection for the PV materials from impact and environmental degradation while allowing maximum transmission of the appropriate wavelengths of the solar spectrum.

System
All equipment used to generate electricity whose output is metered at a single point.

System KWac (KWac)
A rating of the AC electricity generating capacity of a system. This approximates the maximum expected AC output (peaking power) of a PV system under ideal conditions. Although there are many ways to calculate an AC system rating, for simplicity and consistency we multiply the System KWdc (the sum of the DCstc ratings of all the PV modules in a system) by 0.90 to obtain System KWac. This method is based on estimated wire and mismatch losses of about 4% and inverter losses of about 6%. Other factors, such as high temperatures, could also degrade the actual system KWac. For example, modules are rated at 20 degrees C, but experience a degradation of about 0.5% for every degree C above 20. In hot climates, modules can operate at very high temperatures and the effect of this temperature degradation can be quite high.

System KWdc
A rating of the DC electricity generating capacity of a system. In the case of PV systems, it is the sum of the rated module DC capacity (module Wdc) of all modules deployed in the system.