Turn Up the Juice: New Flywheel Raises Hopes for Energy Storage Breakthrough

Renewables could be the world's primary source of energy if only someone could solve the storage problem--how to store lots of electricity cheaply on a wide scale? Batteries are too expensive and don't last long enough. Pumped hydro is cheap but not feasible for most locations. Thermal storage is promising but still too expensive or hard to scale. Compressed air is cheap and scalable but not yet efficient enough (although LightSail, a new company backed by Peter Thiel, Vinold Khosla and Bill Gates, hopes to change that). And what about flywheels? The biggest player, Beacon Power, went bankrupt in 2011 .