When I worked with medium-sized scale batteries one of the most surprising use-cases was to use them _together_ with diesel generators. Diesel generators are incredibly wasteful because they don't vary the power output / fuel-consumption very well based on demand.

When you couple a large battery with a diesel generator the generator turns off when the battery is full so the generator always run at optimal efficiency.

The biggest challenge is keeping the energy almost perfectly in phase. US power runs at 60Hz and most grid equipment fails quickly if that changes even a little bit.

If I'm not mistaken, that was what hit Spain when much of their grid went down for hours. The analysis I heard was that they were running entirely on renewables and it fell out of phase causing large scale safety shutdowns.

That is ancillary services. And where all battery implementations started before saturating those marketss.

We've now past that and batteries are actively killing the business case for fossil gas peakers while renewables are doing the same for legacy thermal producers.

I worked at a company for a while trying to make a battery control device that predicts the peak daily demand and discharges the battery to offset it.

It's kind of crazy how much money you can save by shrinking your peak demand during the time of day it's most expensive.

I am still a fan of centrifugal systems. The lifecycle costs of a spinning mass seem more manageable than the complexities of chemical batteries. The mass of a block of concrete and steal isn't going to degrade over time. And bearings/motors are such mature tech that they can last decades, even a century without replacement.

Producing batteries are not expensive and carbon intensive?

I don't think it's a coincidence that China has developed batteries that neuter the advantage that gas had over coal, but I can't stop wondering if we'd already have solved long-term storage if China hated coal as much as oil and gas.