I am far from an expert, but owning one of the few electric powered aircraft (my self-sustaining glider) in the UK, having worked in the car industry mostly at the R&D end and in financial control of same, and general reading plus input from abgd and others, my opinion FWIW is this:
Electrics for gliders (get you home, or even self launch) – fine. Limited range is needed, payload is only one or at most two people, and it’s in a very efficient airframe (L/D say 50 for a modern glider in which these systems are becoming available, compared with 7 for a Cessna 162 say, and somewhat better but nothing like a glider for modern composite spamcan equivalents). For my glider, a one-off battery set specially shipped from Korea would cost about £5000 when it gets here. Some reduction in cost if greater volumes are sold. I guess the write-off/replacement cost is at most £10 per hour of use or per flight, and my use for gliding (to save an outlanding and a road retrieve, or to extend flight for various reasons) would only be as much as an hour (my system’s maximum – though there are others with greater duration) on a few flights per year out of the 50-100 I would expect to do. That is adequate capability for me. The capital cost of the modification is about the same as for an internal combustion engine self-sustaining set up which has greater range/duration (on at least some gliders) but is otherwise disadvantageous in several ways by comparison.
I think electrics for at least some power flying schools could also be viable, where mostly short details are required, and several battery packs per aircraft could be on charge. There is up front cash flow for multiple packs, but the amortised cost per flight is the same as for only one dedicated pack . With only one pack, and recharging taking however long it would, there would be consequent downtime and low utilisation. Even so, I doubt it would be profitable compared with conventional flying school aircraft.
For touring, I think only specialised aircraft, glider-like in performance etc., would be viable until there is a big advance in battery technology. I don’t know where that would come from.
From what I have seen of cars, electrics are hopelessly expensive in total cost of ownership and use, compared with petrol or diesel, and will be for decades. Hybrids are a bit better and may be worth what they really cost to some users. More, if governments skew the cost/benefit ratio by incentives such as traffic charging, tax etc. Otherwise, there too, a breakthrough in battery technology and cost is needed.
As to the general question of electric power generation, IMHO the world in general and the UK in particular are pursuing idiotic policies. Wind farms are generally a rubbish idea, grossly expensive, stupidly subsidised. We should be going nuclear and spend what it takes to ensure safety and long-term disposition of spent fuel. But that is a whole different ball game, and the government will not come to its senses for a decade or several.
Chris N