[belorn]

If we are talking about the US and not like places like northern Europe, then they have a lot of existing capacity for fossil fuel production. The cheapest way to produce energy would be to just add more renewables and use that fossil fuel whenever that weather isn't optimal. Batteries might be competitive to fossil fuel in places such situation as highlighted by the financial advisor, ie when they can discharge fully each day of the year at the maximum price point.

[epistasis]

The batteries can often be cheaper than fossil fuels, especially when colocated with existing solar. Most solar designs currently under size the inverters compared to maximum solar power output, to get the cost optimal balance. Batteries on-site allow storage of that extra DC energy, and then reuse of the same inverters outside normal solar generation hours to discharge the batteries.

This means that hitting the cost peak is really easy for batteries.

As this cheapest form of energy begins to dominate, and the "baseload" generators like coal or combined cycle gas become more expensive than solar, then it becomes less economical to run the "baseload generators because they don't have sufficient price support during the peak solar output times. This will raise the night time prices of energy, as the daytime prices decrease, and eventually storage plus solar becomes cheaper than new "baseload" facilities, and then cheaper than continuing to run existing "baseload" facilities.

I put "baseload" in quotes because on the past baseload meant cheapest energy, in addition to slow and expensive dispatchability. That is all changing.

[belorn]

> and then reuse of the same inverters outside normal solar generation hours to discharge the batteries.

Yes, if we are talking about hours of capacity then batteries can be very cost competitive to fossil fuels. That is exactly what the financial advisor stated in their report.

In areas where solar + batteries can reliable handle all year round demands for energy, those technologies should just replace fossil fuels. There will likely be some natural gas plants that get subsidies to exist as reserve in case there is a sudden weather change, but nuclear wouldn't be a great option in such places.