Rooftop solar is already oversubsidized by net metering in many places. I would be much more for it if rooftop solar could guarantee capacity (and therefore actually reduce infrastructure costs on the grid) and was paid the wholesale instead of retail costs for electricity but as it is the utility companies are losing money for all the power that goes on the grid and that money is only going to people rich enough to buy dollar panels. I haven't talked to someone recently but last time I checked residential solar was often inefficient compared to commercial solar and a subsidy for the rich
The issue as you say in the beginning is capacity. Part of the solution is certainly energy storage (and here's tons of innovation happening here, ala tesla batteries etc). The other part is smartening the grid to utilize the most power when it's the most available.
I can imagine a desalination plant that cranks during the hottest part of the day when electricity is cheapest, and slumbers during the night.
Of course most of these problems are usually issues of economics. When it becomes cheaper to do it then it will happen.
The problem right now is that if you look at it economically rooftop solar doesn't make a lot of sense and is mainly being driven by subsidies (which are being paid for by everyone else). My guess is that large scale commercial solar will end up generally more economical than rooftop solar.
