[s1artibartfast]

we went discussing if it can make a difference. spending a billion dollars on hamster wheels for renewable power could make a difference.

The point is that rooftop solar is grossly inefficient and terribly expensive compared to just about anything else someone could do.

[ben_w]

Your point is false. Rooftop PV saves (if your roof is suitable) significant amounts on a domestic energy bill even in the UK. I know this from having lived in two houses in the UK that had them, and the calculations that went into deciding to install the first of those, and that panels/inverters etc. have become much cheaper since then. Also, last time I was living in the UK, the grid cost looked like it was billed as a separate line item to the per-unit (kWh) cost, so this really is about the domestic price itself and not just funky billing hiding the cost of the grid like you wrote in another comment: https://news.ycombinator.com/item?id=38158442

The grid scale alternatives — solar farms, wind farms, hydroelectric — can be better or worse in different ways and different times of year, but normal people can't put full size ones on their own property and such wind and hydro scale non-linearly anyway so small ones aren't as cost effective[0].

Furthermore, the reason for the link under which this is being discussed, is that the UK has land area constraints. Suitable areas in the UK for grid scale PV are basically all farms and/or designed National Parks or AONBs and/or designated green belt, and the exceptions (like disused military bases and airfields) have people clamouring over them to build new towns. Sometimes people can get grid scale PV past planning permission, but it's hard work and upsets people with power who want the countryside to look like farmland. Rooftop PV circumvents that.

[0] Except possibly geothermal/ground source heat pump. Those still provide cost effective benefit when you can do them, but the wide price range means I'm not sure which is better.