I'm sorry, it was a mistake. You're not counting it twice, it is indeed a figure just for storage, with the assumption of daily cycling. If we use the ratio of

I'm sorry, it was a mistake. You're not counting it twice, it is indeed a figure just for storage, with the assumption of daily cycling. If we use the ratio of the plant (i.e. 200 MWh storage for 720 MWh generation at a 30% capacity factor), that would leave us with (81-140 * 0.27) + 29-38 for the generation, for a total cost of $51-76/MWh. But that's still based around the idea of cycling the storage daily. Solar performs poorly on cloudy days, so you can either overbuild it significantly, build days of storage instead of hours, or keep the old power plants around as backup. Either of the three is going to bump up that cost significantly. It blows coal out of the water if you don't have to worry about days you're not producing power, but you can't build a grid around that. And coal is mostly being eaten by natural gas for price reasons anyway. Did you factor in a discount rate with your back of the napkin math? It might explain why the purchase price looks so high.