At Airventure last week I listened to a talk on an electric motor glider (http://electricmotorglider.com). One of the takeaways that I had was that with current battery technology, for electric motors to make more sense than a gasoline powered motors you have to have a flight time of less than 23 minutes. Above that, the reduced weight of fuel beats out the weight of batteries. We need additional research in the battery technology space before it's going to make sense for aircraft to be electric.