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W

Abbreviation for watt, the unit of (electrical) output

Power output, or work done, (P, measured in W), voltage (U, measured in V) and current (I, measured in A) are the most important values of a photovoltaic system. If two of the values are known, then the third value concerning the performance can easily be figured:

current = power output / voltage (A = W / V)

power output = voltage x current (W = V x A)

voltage = power output x current (V = W x A)

For the calculation of a photovoltaic system’s power output , one may not multiply the short-circuit current (I short) by the open-circuit voltage (U open), but rather only the actual current at the momentary voltage of the device—which is unfortunately always lower. The exact values can be taken from the current-voltage graph.

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