Depends on your definition of solved, but yes kinda: https://en.m.wikipedia.org/wiki/Power-to-gas https://en.m.wikipedia.org/wiki/Power-to-gas While I don't th

Depends on your definition of solved, but yes kinda: https://en.m.wikipedia.org/wiki/Power-to-gas https://en.m.wikipedia.org/wiki/Power-to-gas While I don't think any large scale P2G installations do currently exist, it is all well proven tech that requires little to no additional research. At least for Germany there exist some studies that suggest that it should be doable (especially financially) on a national scale.