I'm a bit more optimistic regarding power station capacity. Whether it saves energy is another matter - the biggest argument for electric cars isn't that they're more efficient but that they're cleaner. This is a much bigger issue at ground level in cities than in the middle of the sky over the countryside. Also, electric power gets a boost in relative efficiency for city driving, because it's much better than petrol when you're stopped at the lights. Not so relevant for aircraft.
My understanding is that the biggest problem for the grid at the moment, is peaks of power consumption - people putting the kettle on at half time of the world cup final etc. So there's actually excess capacity during times of relatively low demand. I don't see why it would inevitably break the grid to charge cars and aircraft overnight or when the wind's blowing and the turbines are whirring.
Some existing, commercially available batteries can be charged at rates of 5c or above (i.e in 12 minutes) so although it may be slower than filling a tank with petrol, charge times can still be perfectly practical.
As for taxing home wind turbines or solar panels on aircraft hangars... I don't think they'll be able to tax it (how much for my solar powered calculator?) but I'd be surprised if it were cost-effective any time soon.
The real cost benefit of electric power, in my view, would lie in the lack of maintenance required. One moving part. No need for a TBO. Battery packs with monitors that tell you how healthy your batteries are and when they need attention...