TL;DR - Saving Energy for Later

    Scientific American, March 2012 -- "Gather the Wind," Davide Castelvecchi

    Renewable energy is definitely the future, but there are still many problems to be worked out before it can take over from fossil fuels.  One major concern is the reliability of energy sources; what happens when the wind calms, or the sun goes down?  Modern energy usage demands consistency, which renewables often lack.  Storing energy for later is the obvious way around this, and Castelvecchi reviews five different proposed solutions, each receiving ratings from an expert panel on measures of scalability, cost-effectiveness, and efficiency. 
    Pumped hydro (pumping water uphill for potential energy) and compressed air (pumping air into rock formations and caverns for later extraction) are two methods that are currently in use, and which show significant promise, though certain limitations, such as geological and geographical considerations, hinder their large-scale deployment.  Battery technology is advancing strongly, as well, though it will inevitably be costly.  I'd heard about thermal storage--storing heat in molten salt--before, though it, too has some technological hurdles to jump.  Finally, home hydrogen conversion (using small-scale systems to break down water into hydrogen at off-peak rates) is an interesting idea, though it is the one that has furthest to go before it's a practical solution.