What is the rated output of solar systems?

One and the same solar system does not generate the same amount of electrical energy in Vienna as in a place in the Alps, for example, due to the different radiation output. There are also big differences in the usable global radiation between individual countries in Europe and worldwide.

In order to be able to compare different solar systems with each other nevertheless, international Standard Test Conditions (STC for “Standard Test Conditions”) have been established. For solar systems that meet these test conditions, the so-called “nominal output” can be specified in kilowatts (this is called “kilowatt peak”, often abbreviated to kWp, which is derived from the English term “peak” for “maximum value”). Products can be compared worldwide with this nominal power, and further calculations are also made with this nominal power.

The standard test conditions (STC) are 25 °C module temperature, 1,000 W/m2 irradiance and a path length through the air mass of 1.5. In practice, however, the conditions are usually worse, e.g. because the modules heat up to more than 25 °C and because 1,000 W/m2 is a value which in Central Europe can only be reached as a so-called “instantaneous value”, e.g. only on a bright blue or slightly cloudy summer afternoon.

For a nominal output of 1 kWp, about 8-10 m2 of solar module surface are currently required.

A solar plant with a nominal output of 1 kWp can produce about 900-1,200 kWh per year in Austria. The exact amount of energy depends on factors such as: location, orientation, sunshine hours, temperature.