On Monday, 27 May 2019 21:52:59 UTC+1, misterroy wrote:
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).

Another relevant question is whether the PV owner actually has a right to light for his panels. Did he buy an easement when he set up the panels? I am guessing not. In which case I dont' see why it is the dormer-builder's problem.

To cite an obvious example: you can't prevent a building being built simply by setting up an array of panels that will be shaded by it.