Ammonia would make a pretty handy, potentially carbon-free liquid transportation fuel, say engineers, and it could be produced right at gas stations using electricity from the grid, water, and air. 

Researchers at Texas Tech University have developed a new ammonia production system, which makes an end-run around the problems of the so-called "hydrogen economy" — you remember, all those hydrogen-powered "freedom cars" that Bush Jr. said we'd be driving by now. Hydrogen is difficult to store, but this system combines the hydrogen with nitrogen from the atmosphere, turning it into ammonia, which is still a good fuel source but a lot more filling-station-friendly. (For the fossil fuel geeks out there, the process they use is the Haber Bosch process — the very same one used to produce munitions during WWII and fertilizer today.)

Unfortunately, their process doesn't solve the challenge of making the hydrogen in the first place. Hydrogen is produced by splitting it off from water molecules using electricity, and the process is pretty inefficient. But, if we have enough renewables on the grid, the hydrogen production process could be a way to convert extra energy into something useful, thus "storing" it.