There are a few technologies on the horizon. Using excess energy during the summer to produce a fuel, like you said, is one option. Hydrogen has been considered, but storing it long term is difficult. Another option is ammonia, although it’s toxic and corrosive, and although it produces no CO2 when burned, it still produces NOx, a potent greenhouse gas.

There are technologies on the horizon that could fill the long term storage needs for winter power. Lithium Ion, although great for mobile technologies, is not ideal for grid scale storage. It can’t store power for long. But other chemistries such as vanadium flow batteries and iron air batteries can discharge longer, and they can store power for far longer.