Alternative fuel! BtL (bio to liquid) like bioethanol. We have an increasing number of petrol stations selling E85 (and I use it, see several threads), it's really now and not only future.
If you generate electricity by solar or wind, store it in synthesized methan or hydrogen, and burn it again to generate electricity, you actually get about 30-40% overall efficiency (in a stationary system). A nice idea to store the occasionally surplass electric energy production.
Our military uses fuel cells since 2002 (i.e. submarine class 212A), the technology is complicated and expensive, but feasible.
Perhaps we see affordable fuel cell cars in the future. The efficieny could improve to 40-50%.
Direct storage of electric energy has physical and chemical limits. I don't epect any outstanding progress in this research field. If there is any idea, the military uses it decades prior to the public.