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Short explantions of the photovoltaic related terms.

Wp Unit of the module performance under standard condition - maximum performance.

Isc Short circuit current, the flowing current when the ends of the cables from a solar module are directly connected together and the panel is iluminated unter standard conditions.

Pmax Rated power, is the under standard conditions measured module performance. The module power must be specified by the manufacturer that way.

Solar modules are measured at 1000W/m² irradiation, vertical incidence, 25°C cell temperature and the color spectrum 1.5. In actual operation, a module can deliver only very rarely this performance. Neither the sunlight falls perpendicular to the module, nor is the cell temperature 25°C when the modules is in the sun.

Following relationship exists between P max, Imax and Umax:
Pmax = Umax * Imax.

Umax the voltage of the module at the point of maximum power. This measurement is carried out under standard conditions.

Imax the current generated by the module at MPP. This measurement is carried out under standard conditions.

Uoc Open-Circuit Voltage, open circuit voltage of the module. The open circuit voltage can be measured when the module is illuminated under standard conditions between the cableends of the module. For an 12V module the open circuit voltage should be greater than 20V and less than 25V.

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