If there are, say, ten times a year when the sun gets clouded out for 2+ days in a row the cost of that extra storage would have to be spread over only ten days – some very expensive electricity.

There might be a lot more one cloudy day events. I expect someone has done the math and demonstrated that one day of storage makes sense. Might be that there’s a need to fill in for cloudy mornings along the coast.

The big issue, IMO, is late afternoon/early evening storage. PV solar is going to get very affordable (and later on cheap). But it quits producing once the sun drops lower in the sky. And good wind often does not start up until later at night. I’m betting that down the road these thermal plants are going to be late-peak providers, not adding much to the grid when the sun is shining but storing up for the hours when it starts to set. That is going to be their best paying market.

Other storage systems, flywheels aren’t likely a bulk storage solution, more grid smoothing. Utility scale batteries likely to be major players, but more likely for already generated power from wind. Pump-up is likely to be growing, we’ve got lots of existing dams that could be converted, thousands of them. And more solar/wind means that we can often reserve the hydro we have and use it as backup, rather than ‘base load’.

And I’m really interested in semi-deep ocean CAES. Sticking air bladders at some depth and compressing air into them when we have extra power, pulling it out when we need it. One company now in the testing process is projecting $0.025/kWh for storage. Combine that with wind at less than a nickle and we’ve got some affordable very reliable power. Gas peakers could easily be twice, three, four, or more times as expensive.

A little hard to guess how it will play out. We’re years away from needing significant storage. And when we add EVs to the grid we will need less, put the date off further. Parked, plugged-in EVs will mean a good market for what would otherwise be surplus power which means that it will be more profitable to install more solar and wind than otherwise.

I’m liking the fact that we’re building a few of these thermal plants with storage now. This gives us time to tinker and get costs as low as possible. We need to be putting some money into all types of storage so that when the time comes we have mature technologies ready to go.

The folks in Italy who are doing thermal solar with storage are talking some very inexpensive electricity. It’s going to be interesting to see how things work out.