Dirt cheap solar + storage

Daily & weekly load shape in different seasons
Demand peaks between 3 and 5 on hot days, and is highest in summer
(Source)

From IEEFA:

U.S. utilities seeking new sources of peak power are turning to solar farms integrated with battery storage systems that save energy for later use, offsetting their reliance on conventional fossil fuel-fired generators, often at lower prices.

This trend is most apparent in Hawaii and the western U.S., where multiplying solar-plus-storage power purchase agreements, or PPAs, reflect a maturing class of competitively priced peak-power assets, according to an S&P Global Market Intelligence review of state regulatory filings, publicly available contracts and independent analysis.

Though project configurations and contract conditions vary, prices for large-scale solar farms coupled with big lithium-ion batteries, typically offering four hours of energy storage, have fallen to between $30/MWh and $40/MWh in several recent deals and contracts under negotiation.

Contracting activity for what one project developer, AES Corp., has called “PV peakers” has taken off in the southwestern U.S., for both PPAs and utility-owned projects.

“These types of arrangements are repeatable…despite people telling me storage was not cost-effective yet,” Monterey Bay Community Power CEO Tom Habashi said in an interview. The competitively priced projects help reduce the public agency’s exposure to expensive short-term peak-power purchases, he added, and the energy storage component represents less than $10/MWh of the total contract price.

[Read more here]

4 hours of storage for $10/MWh?   Very cheap.  And way below other estimates.  That would imply $30/MWh for 12 hours of storage, enough to take us to 90% renewables, if the grid is a mixture of wind and solar (wind blows at night when it's dark, solar peaks during the day when demand peaks, so the average requires less storage than either individually)  The remaining 10% could be hydro, legacy nuclear, biomass, wave power or some combination of these.  And there will likely be a need for seasonal storage, though for much of the US (for example) demand peaks in summer/hot days, when solar is also producing peak output.  By comparison, the average total cost of new coal is $102/MWh, and the average operating cost of existing coal is $36.