Hi Boris,
the 'Yield reduction due to shading' is calculated as the ratio of the PV Generator Energy (AC) minus the Clipping at the Feed-in Point without shadows and the same number with shadows. So, as example you have the following (the numbers are from one of our example projects).
System 1, without feed-in clipping/export control:
without shadows:
PV Generator Energy (AC) =145,377 kWh
Feed-in Clipping = 0 kWh
with shadows:
PV Generator Energy (AC) =132,972 kWh
Feed-in Clipping = 0 kWh
Yield reduction =1 - (132,972 - 0) / (145,377 - 0) = 8.6 %
System 2, with feed-in clipping/export control:
without shadows:
PV Generator Energy (AC) =145,377 kWh
Feed-in Clipping = 59470 kWh
with shadows:
PV Generator Energy (AC) =132,972 kWh
Feed-in Clipping = 52,822 kWh
Yield reduction =1 - (132,972 - 52,822) / (145,377 - 59470) = 6.8 %
Hope that helps, kind regards,
Martin