How the calculation works
kWh per year = Wp ÷ 1,000 × specific yield (kWh/kWp/yr) × share ÷ 100
A worked example
880 Wp in Germany at 950 kWh per kWp make about 836 kWh a year (70 kWh a month); hung vertically on a balcony at about 70 %, roughly 585 kWh.
What specific yield means
Specific yield is the energy one kilowatt-peak of modules delivers in a year at a site: about 950 kWh in Germany, 1,100 in France and Italy and 1,400 in Spain for a well-placed, unshaded module. Multiply by your modules' kilowatt-peak to get the yearly yield. Solar irradiation maps and your grid operator give local figures; enter yours to replace the default.
Balconies, shade and the inverter
A module hanging vertically on a balcony railing catches less sun than one tilted at 30°, so enter a lower share. Shade from a neighbouring building or a tree cuts the yield of the whole module. A balcony set's 800 W inverter caps the output on bright days; with 880 Wp of modules that loss is small.
Common questions
How much does an 800 W balcony set produce?
With 880 Wp of modules, about 600–850 kWh a year in Germany depending on the position, and more further south. The inverter's 800 W limit matters only around sunny middays.
Why not use the module's watts × hours of sun?
Modules rarely work at their STC rating: heat, angle, clouds and the inverter all reduce the output. Specific yield already includes those losses, averaged over a year.
Method: arithmetic from the label values you enter. Reviewed .