A friend of a friend is putting in a loft extension, with new dormer windows. The new window will cast a shadow on part his neighbour's photo-voltaic array.
The neighbour seems to know his stuff, but part of what he is saying sounds strange.

As best as I can remember, the panel nearest the dormer will drop in efficiency, by say 20%. This bit I understand, due to the shade. (The neighbour has built a model and used a torch to help his estimates).

However, according to the neighbour, this is not the end of his losses. Because one panel is at 80% efficiency, the others have to drop their efficiencies too.

The neighbour is taking his loss on the chin and not hassling, but how can shade on one panel effect the efficiency of every panel?
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