Roof Inclination
Electric Current Output and Inclination Angle
Graphic: Yearly Electric Current Output Dependent Upon the Roof Inclination Angle in % (At 0° South Orientation).

When asked about a roof’s inclination while planning a solar energy system (i.e. using an online-calculation), it is the inclination of the collector that counts rather than the inclination of the roof itself. By using the correct mountings and stands collectors can be ideally positioned even when a roof’s inclination or orientation is less than ideal.

In order for the solar radiation to be used most efficiently, it must strike the collector at a right angle. The optimal inclination or mounting angle depends on the geographical latitude of a given site. Freiburg, Germany is at 48 degrees latitude and Lübeck, Germany is at 54 degrees latitude. Because the sun is higher in the summer and lower in winter, it also depends on which time of year the solar energy system will mostly be used. Photovoltaic systems, for example, produce the most output on long, summer days while thermal solar systems used to support heating needs are best used in winter months. As a rule of thumb for determining the mounting angle, for summer use subtract 10º from the latitude and for winter use add 10º to the latitude.

The orientation (azimuth angle) towards the south is not to be confused with the angle of inclination. In practice, small deviations from the optimal angles of inclination or orientation cause only small reductions in output, but an occasional shadow over the collector causes a greater loss of output.

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