Source? For solar heating you'll want one to store excess heat collected during the day. With (grid sourced) electricity as the only energy source for the heat

Source? For solar heating you'll want one to store excess heat collected during the day. With (grid sourced) electricity as the only energy source for the heat - and in absence of a "smart grid" - storing hot water adds losses, compared to heating the water just in time. So I can understand why they might think about some sort of ban. If they go for a ban, I'd expect them to add some conditions.