At the moment, we have one solar panel (not currently working - Dylan says it's the battery, or the connections there, and that the panel itself is fine) and we're still using some mains power.

The burn would be a good source for small-scale hydro, possibly in several places.

The wind seems pretty usefully consistent in summer at least, since it blows straight off the firth (and therefore the North Sea). One thing I wondered about when I was there was the possibility of an old-fashioned windpowered water pump to feed a header tank for the sand filter.