The proposal to use electric cars as a buffer has been around for over a decade. It has some technical challenges. For starters, inverting DC to AC isn't as easy as it sounds but transistor technology is improved so much that this is becoming easier to do by the day. I don't understand the part about mass in the turbines... every country over generates electricity to cover these gaps anyway so why would it be an issue? Some countries generate up to 40% more than they need just in case power stations go offline unexpectedly.