So, as an electric car owner, who dutifully left it on charge, I will not know if it will be charged, when I next need it, or if instead it was busy boiling the kettle for Mrs Miggings down the Street!,(reply>), Marcus Gault well you get paid. Charge the car up on cheap electricity overnight, or free at work! Then sell electricity back at peak times for more money.,(reply>), @Steve Ormrod Erm, since most people I know are essentially selfish, why do I imagine that the default setting would be "I need my car 100% charged" every time. I actually agree with the rather neat concept, it is the successful  implementation I have cause to doubt.,(reply>), It would be Smart. So you would decide how much of your battery capacity you'd be happy to sell back to the grid. And it would never take more than that. So if you only needed 50% battery to get to work and back, and your car was 80% charged, then it would only ever take the spare 30%.