I'm wondering if it should fall back to a more general shading approach when no OSM building footprint is available, to avoid false precision? My street has a gap in the houses on the other side from mine, so picking the right location matters for the calculation.

You could also try Inspire Index polygons instead of OSM? These correspond to actual lease/freehold boundaries.

This is my issue with this sort of thing. Am I going to have this kit in 7 years? Or would I upgrade to better stuff at the technology improves?

"Caveats: - Outside LIDAR coverage (most of Scotland and Wales) it falls back to a synthetic horizon (less accurate)"

So, "any address in the most of the southern half of Britain"?

Very interesting stuff and quite a large undertaking! I'm often impressed by the quality of the UK's open data.

Would be nice to add this as an extra data point when comparing. Are you open to collaborating at all?

Please consider making the source code available. I’d love to make something similar for your friends across the pond (in Canada).

Also do you actually need a balcony or can you hang these out of a window somehow? Very few houses in the UK have balconies.