Battery "Breakthrough"

About a year ago I went to a presentation by an electric vehicle researcher who said the state of the art is a factor 47x, in battery weight versus the weight of the equivalent liquid fuel.

So if somebody has achieved parity, that would be amazing.

I also recently met a vehicle battery specialist who said they had some technologies which improved by a factor of 5x but had a very poor life – of the order of 10 cycles.

They are bound to chip away at this challenge – because there is so much money at the end of it.

You don’t need parity of energy density.
An electric motor delivers power about 2-3 times more efficiently than an internal combustion engine and can also regenerate energy when braking/descending.

The ratio you quote is roughly correct i.e 44MJ/kg for petrol and about 1MJ/kg for lithium cells (include packaging, BMS, inverter etc), but that’s more like 12-15 times heavier in practical terms and improving about 6-8% per year currently.
It’s a giant leap from what has been achieved in small controlled conditions in a lab to a commercially viable product. Maybe there will be a revolutionary breakthrough, but expect to see electric propulsion getting a bigger and bigger share in the near future.

I am as many know a great believer in electric propulsion. I share mr Musk’s prediction that in 17 years time (his prediction was 20 years, but that’s over 3 years ago), there will be no ground transport where the prime mover is not electric. That said, I also read about “revolutionary breakthroughs in batteries” on all the gadget websites all the time. Every week there’s some new science lab at some university who comes up with something. Truth is, until they’re on the market and actually working, it’s all vaporware. Therefore I take with great helpings of salt any new announcement of batteries.

But if, as Mark1 mentioned, we can start to get up to about 1000Wh/kg in storage, which is a 2-4 fold improvement over today, it will be all over for combustion engines. If we can get to 2000-4000Wh/kg, aviation is even going to go electric.

Reading the related thread on avgas viability/availability feels a bit like reading an 80’s electronics mag article on the virtue of Trinitron tubes.

What I can’t quite figure out is whether a 10 x practical increase in battery energy density is a realistic goal or a hard, intractible problem.

Will vehicle engine technology & new light GA run on piston power for the next 50 years?

Airplane are the very last vehicles where switching away from fossil fuel makes sense. We have plenty of oil and it will remain cheap if we make smart use of it. Airplane is what I consider “smart use”. V8 town car NYC taxis is the opposite of “smart use”. We will see more and more of ground transport switch to batteries, already today it makes sense for a certain market and it will gradually become better.

What does make sense in airplanes is a diesel electric cycle like we’ve had for decades in locomotives. Use electric motors with their small form factor to drive propellers and a combination of battery and efficient diesel engine in the fuselage to generate the electricity.

A 1:1 ratio is not even necessary. In ground transportation, most of the energy used is for acceleration, and can be recovered during braking, so the energy cost of carrying 1kg of battery is less than the energy cost of carrying 1kg of fuel in a combustion car. Also, in a typical car the fuel is less than 5% of the total weight, and payload is not much of a consideration.

Compared to aircraft, which don’t accelerate very often, most of the energy goes into drag and cannot be recovered, and fuel is 15% of the total weight or more, this is quite favorable.

Hence Tesla can build a viable “proper” electrical car even with current technology, for which only [en-route] refuelling is currently limiting its utility.

Hodja wrote:

What I can’t quite figure out is whether a 10 x practical increase in battery energy density is a realistic goal or a hard, intractible problem.

I’m not so optimistic. There has not been much new knowledge gained in Electrochemistry since the late 19th century, The latest big improvement in battery technology (factor of 2 to 4 over lead acid) came from the use of Lithium. It’s not that people recently discovered Lithium, but they were reluctant to use it because it is difficult to handle, until the pressure got big enough to start to tackle the issue. And it has been a bumpy road, as reports of burning laptops and the Dreamliner problems show.

The LiIon battery, which gave us some factor 2-4 improvement took about 20 years from research to practical product, and another 20 years from product to large scale use. Given that, there’s no way I will live long enough to see classical battery technology to close the factor 100 gap to Jet A, and not even long enough for the factor 20 gap to a Ham&Cheese sandwich

So more radical ideas are needed. It kind of all points back to the use of organic molecules for energy storage. Not having to carry around the oxidizer (O2) and the waste products (CO2 and water) is hard to ignore.

and the Dreamliner problems show

The Dreamliner incident in LHR was a squished cable with a short on the ELT Battery.

Any battery with a high energy density is going to have potential catch-fire problems – it’s not really limited to lithium (and as the name suggests Li-Ion batteries don’t use metallic lithium which is pretty reactive, but ionic compounds of lithium).

However, battery technology didn’t really move much until Li-Ion batteries became practical. Since starting with the hobby of flying RC helicopters less than 10 years ago, the Li-Poly batteries we used have gone from being rather short lived, with a low charge rate (no greater than 1C – which means if you have a 2Ah battery, the maximum charge current can be 2A) and 15C maximum continuous discharge. Li-Ion batteries before that were much more limited.

Today’s RC batteries are much higher performance – 5C charge rate is usual, and 30C maximum continuous discharge/60C peak is not at all unusual – a pretty significant improvement in under 10 years. For radio control, the writing has already been on the wall for nitro engines for a couple of years now. There are some pretty large models that are electric power. So real improvements are being constantly made in what used to be a pretty stagnant technology area.

I agree that we won’t see electric propulsion in GA planes any time soon, probably the forseeable future, with the exception of some niche applications (such as self-launching gliders, or certain sport aircraft) – but for ground transportation where the constraints are quite a bit lower it’s only a matter of time before it’s mostly battery electric.