You definitely have to convert AC to DC, for battery charging.
At mains voltages, and with a reasonably high DC output voltage, say 50V, a multi-kW converter can be done with an efficiency of around 90-95% depending on how much you want to spend. I would guess an absolute state of the art design could reach 98% or so but it would be very expensive.
I have done this (switching power supplies) for a living for much of my life 
If you have a three phase input, the job is a easier because the full wave rectified input never drops to zero so no input capacitor is needed. Also the EU-mandated power factor correction is easier to do.
I wonder an electric motor shouldn’t loose any power as it gains altitude right?
Once someone sorts out the battery problem, isn’t that the biggest advantage of going electric?
You definitely have to convert AC to DC, for battery charging.
Also motor power conditioning and its loss in controlling the motor, whether DC or AC, from a battery.
Motor power density itself isn’t typically the problem. Taking it to an extreme, you might design a very power dense motor, let’s say to power a turbo-machine without a low (i.e. aircraft propeller) rpm limit. The power supply and control hardware is then much bigger than the motor and the cooling system likewise.
Charging technology is great. The longest time I had to wait was 42 min to charge my car from 5% to full on a fast charger. Usually I have 10% to 99% in 25 mins. I love my car. It is the best way to travel on a day to day basis.
I did longer trips as well with a few breaks.
What is the issue for a training flight to land after an hr and charge for 5 mins and give the student a break.
For the long trips I rent an ICE car, which I did previously as my Smart Roadster was too small.
90% of my driving is covered by my car. You don’t need to have a solution for 100%. Would you buy a 40t lorry and drive it to work on an every day basis, because you might need it once?
Most recreational pilots have a mission profile with less an hr flight. For the big trip once a year, they can rent a plane. For the bacon buttie run to the next airfield 20NM away an electric will do.
People will learn how to use it and they will enjoy it.
We all put our mobile phones on charge every night, the same goes for a car.
It is not a big issue as long as you are not driving 500 miles a day every day.
I had my first service. Break fluid change, some greasing, a software update and 50 quid. Once a year. Not bad.
@ mdoerr – What car is it?
90% of my driving is covered by my car. You don’t need to have a solution for 100%.
My solution to that particular problem is to own and use twelve vehicles in the US, including two aircraft, and two vehicles in the EU. Fuel efficiency varies between them by a factor of about eight. I’m not of favor of limiting myself.
PS Edited due to forgetting one
it is a Renault Zoe
I wonder why they don’t use solar cells on the wings to produce power in flight and to recharge on the ground. Granted, they won’t be able to keep the plane airborne alone (the Solar Impulse Project shows what is required for this) but it will produce some electricity which will in one way or the other make the battery discharge less and, on the ground, will provide free charge when parked over a longer time.
I did ask the same question for cars as well. They have so many surfaes which could house solar cells. I have been using a solar phone charger for a while and it worked just fine. Ok, granted, these are different dimensions but still.
If I see how extremely energy saving has had an impact in the last years on things like light bulbs. Not 5 years ago an average living room had some 500-1000 W lights installed, today, with LED technology there are 10-20. If anyone had told us 10 years ago that the average light bulb would decrease it’s power need from 60W to first 7 and now 1-2, who would have believed them? Not me. Now however I use LED lights wherever I can and my home electricity bill has gone massively down in recent years. I’ve seen the same in Bulgaria, where people had price increases at over 800% in recent years in electric power costs.I there had to convince some people who resisted the normal energy saving lights (100/11W) kicking and screaming, but those who stormed the nearest IKEA and spent a salary or so for new lamps very quickly learned that their bills would collapse to half or less with immediate effect. Personally, I have not a single Edison lamp left in my house.
That is one tiny bit which had a huge impact. I can imagine that it must have been much more extreme in Skandinavia where they have if any 1-2 hours daylight in Winter.
Personally I think the Airbus project will be the first of many and people will sooner or later ask questions and become curious. Certainly for the UL or TMG scene, there is huge potential in this. And I am also watching the car scene with a lot of interest.
I wonder why they don’t use solar cells on the wings to produce power in flight and to recharge on the ground.
It is too much weight. Not only the solar cells, but the supporting stucture and the covering clear resin.
The gain is minimal compared to the weight penalty. Solar cells are only effective if you point them to the light source (sun). A difficult thing to do in a mobile application. I haven’t seen any solar cells on a northern roof.
The other problem is a partial shadowed panel. There is a huge loss, because the shadowed cell acts like a diode.
Also batteries have a lower threshold below they won’t accept any charge.
Think of a big water barrel and someone opening the tap. Would it make much of a difference if you would stand there with a heavy syringe and let a few drops of water in.
