Current/Voltage curve of a solar cell (current in A; voltage in V).

Abbreviation for kilowatt-peak, a measure of the peak output of a photovoltaic system, for example.

The electric characteristics of Solar Cells, and therefore of the entire Generator, vary with respect to various general conditions, especially the radiation intensity. In Photovoltaics, the maximum possible output of a solar generator operating under standard conditions is defined as its peak output, which is measured in watts or kilowatts and stated as either Wp (watt, peak) or kWp, respectively. An optimal Solar Radiation of 1000 W / m² is defined as the standard condition, and it can be reached early afternoon on a sunny summer day (however, the mean output over the period of a year is only about one thenth of the peak output due to night-time and less than optimal day-time sun conditions). The peak output is so based on measurements under optimal conditions, and, specifically, the peak output (some Manufacturers also designate this as the nominal or rated value: rated power, rated output, nomial power, nominal output) results from the product of the nominal voltage and the nominal current. More enlightening information over the properties of solar cells or generators can be found on the current/voltage curve at the right. When planning a photovoltaic system, its Performance Ratio (conversion Efficiency) is important as it describes which part of the radiation energy is converted into useable electric current.

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