But not easily storable.

Not entirely true. There's all sorts of mechanical storage systems, the most common being artificial hydroelectric and flywheels - spin something really fast and than extract energy from its rotational velocity later.

But a practical issue here is that there hasn't really been much motivation to develop this industry, because there's been relatively little critical necessity for high capacity at-scale energy storage.

Just store it by selling it to your neighbor state or country and buying it back when their renewables are at peak :)

It is very easily storable, and in energy markets that are driven by free markets (rather than utility biases or legislative mandates), storage is one of the biggest investments on the grid:

> Installed battery capacity increased from 153 MW in 2019 to 3,518 MW in 2023. Interconnection agreements have been signed for an additional 7,945 MW of battery storage through 2024, allowing batteries to play a growing role in daily power needs in the near future.

https://www.dallasfed.org/research/economics/2023/1017