But that should not keep us from ramping up solar and wind. These details are important only if we want to go 100% CO2-free. I am not sure that is a requirement, if we can achieve 90% soon enough, that should be fine. And in no case it should stop us going all the way to 90%. What the right answer is to go to 100%, depends on the region. In most regions, solar and wind are good for a seasonal balance. This greatly reduces the need for long-term storage.

If not run 0-100%, lithium ion batteries can have thousands of cycles. For stationary storage one can optimize the chemistry for long-term stability rather than weight and volume. A lithium battery doesn't just fail, rather it continuously uses capacity over the cycles used. So the rated number of cycles marks the point where it has 75% of its capacity left, for storage it can be used far beyond that.

On the grid scale, beyond large batteries, one can of course used pumped water storage - still the most efficient mass grid storage available. If really long-term storage is desired, synthesizing methane could be considered, which can easily be stored and then used to drive high efficient gas power plants.