Perhaps too quick a look.
Oh, and as far as the “battery eneergy density isn’t good enough” mantra, Mr. Goodenough (of Li-Ion fame) has come up with a new chemistry which is sodium based (added benefit – it does not explode). He expects it to have at least 3x the energy density of Li-Ion.
http://pubs.rsc.org/en/Content/ArticleLanding/2017/EE/C6EE02888H#!divAbstract
OK; another factor of 10 to go after that.
Then somebody needs to make nuclear fusion work, to generate the electricity in the first place.
For sure this conversation will be different say 20 years from now, but not yet…
Why another factor 10?
Peter wrote:
Then somebody needs to make nuclear fusion work, to generate the electricity in the first place.
First somebody needs to find a way to actually make nuclear fusion to work (producing net energy), then somebody else needs to find a way to industrialize it. Maybe it will happen, maybe it won’t, but chances are much larger that the whole concept is rendered irrelevant as an energy source in the foreseeable future within only 5-10 years. When looking at the electric grids, one see that it’s tailor made for on demand production. This is easy with all traditional sources (oil, coal, hydro, nuclear etc) because there is no need to store the electric energy, only the fuel (a hydro dam is the storage for hydro power). With wind and solar, production happen at random, thus there is a need collect and store the electricity itself. That is the only problem, there is more than enough wind and solar potential for many times the current world wide electricity consumption.
If each home got it’s own battery, like Elon Musk want, then the storage problem will be solved. That’s a whole bunch of batteries, but this is happening as we speak, and prices of batteries are going down, electric density and capacity is increasing. Converting solar energy to electricity is getting cheaper and more efficient. Solar power has the potential of becoming much cheaper than anything else we can think of also. In 5-10 years we will laugh at our concerns 
Shorrick_Mk2 wrote:
Why another factor 10?
To be on a par with the utility of existing avgas powered aircraft (in other words, similar range) – actually, a factor of 5 would do, but it still shows even the batteries in the lab fall a bit short of what’s needed to be a general replacement for avgas.
Current lithium batteries are 0.875 MJ/kg, avgas is 46.4MJ/kg. If this sodium-ion battery (which will have great benefits in any case, given the abundance of sodium compared to lithium) has 3 times the energy density, the battery is up to 2.625MJ/kg.
Taking efficiency into account, a petrol engine is about 25% efficient, so with avgas you effectively have an energy density of 11.6MJ/kg. A good motor and battery combination has an efficiency of around 90%, so a battery with 2.625MJ/kg would have an effective energy density of about 2.36MJ/kg which is about a fifth of what the avgas plane has. You may get a bit more efficiency in an electric aircraft since the aerodynamics can be better given you don’t have the size and shape constraints of a piston engine (brushless electric motors can be very compact for the power they produce, and more efficient propellers can be used since you’re now freed of the narrow range of RPM that a piston engine forces you to use). Cooling requirements are much less for electric motors too, so cooling drag will be a lot less – but on its own, this won’t be enough.
Such a battery would be perfect for sport aviation (things like self-launching motorgliders, or glider towplanes – how I would love an electric tow plane), and indeed lithium batteries already work for this, but there’s a way to go for electric propulsion for something the equivalent of a TB-20.
For the non engineering crowd on the forum here, for clarity that includes me :-), I have this vision that all of these batteries must be made from extremely polluting material and the lifetime in them (remember the average planes most people in Europe fly are 20+ years old) this whole electrical thing could very well be an even bigger ecological disaster? Is that a wrong assumption?
LFHNflightstudent wrote:
I have this vision that all of these batteries must be made from extremely polluting material and the lifetime in them
The lifetime of a tank of avgas is one long flight, but the lifetime of a battery is many years. Avgas requires extremely polluting material to make and emits polluting material while you burn it and you have to keep doing it again and again.
Current lithium batteries are highly recyclable and don’t contain much that is toxic (no heavy metals, they are basically copper, carbon, some plastic film, a very small quantity of lithium). An aircraft or car lithium battery will have significant core value so people won’t be just throwing them in landfill.
Here is what’s inside a Li battery (Tesla, Panasonic?)
Thanks!
LeSving wrote:
The pressure tanks in Toyota’s hydrogen tanks still store more energy than an equivalent electric battery. It’s also much lighter. For aircraft I think cooling it down is the envisioned way of storage rather than pressure vessels. More or less the same technology is used for storing huge amounts of natural gas, although at higher temperatures than is required for liquid hydrogen. It’s a bit hard to imagine how this is going to work in practice though. All stranded aircraft will “leak” hydrogen that can ignite at any time. Certainly no solution for GA.
The trouble is cooling it down doesn’t work like natural gas, where if you pressurise it a bit it liquifies at quite a high temperature. Liquid hydrogen cannot exist as a liquid above 33K (-240 C) at any pressure, and having to use cryogenic gasses, especially ones cold enough to start freezing oxygen, brings in a galloping herd of new problems that perhaps you can tolerate if you’re sending 3 people to the Moon, but you’re not going to tolerate for an aircraft that is expected to be used day in, day out.
Even liquid hydrogen isn’t volumetrically dense – you get about 0.07kg per litre (compared to avgas – about 0.7kg per litre) so you still need huge amounts of tankage for liquid hydrogen to get the same amount of energy as avgas – and now they have to be cryogenic storage also!
Hydrogen is a complete non-starter for aviation, apart from things that are highly specialised (such as the Apollo service module). Even the Saturn V didn’t use hydrogen for its 1st stage (that was RP1, basically kerosene, and LOX) because liquid hydrogen has such a tragically poor volumetric energy density.
Really, the only practical way to use hydrogen for typical every day transport is to attach the hydrogen atoms to a carbon atom.
