Converting electric power to and from a battery requires an electrochemical reaction to occur. That is a conversion just the same - I don't really buy this "no

Converting electric power to and from a battery requires an electrochemical reaction to occur. That is a conversion just the same - I don't really buy this "no conversion required" argument, just because you started and ended with direct current. Flywheels aren't some hypothetical means of storing power, either - they've seen a lot of exciting R&D over the last 15 years, and there are operators of grid-scale flywheels. e.g. http://beaconpower.com/ http://beaconpower.com/ http://en.wikipedia.org/wiki/Flywheel_energy_storage http://en.wikipedia.org/wiki/Flywheel_energy_storage