What is the life expectancy of the battery pack? How much is the replacement? And what is the range?
The warranty is 80% capacity after 8 years / 100,000km whichever comes first. The expected degradation is 75% capacity after 20 years. This is not marketing, this is based on actual simulations. The laptop style Tesla batteries have higher energy density but (just like laptops) degrade quickly and are more challenging from a safety point of view.
Lithium Ion cells have around 0.5MJ/kg, Zinc Air is around 3 times higher, but this completely pales to the ~46MJ/kg for fossil fuels.
Out of the 46MJ, let’s say 30% in average are turned into propulsion, that’s 14MJ, about factor 10 compared to the next generation of batteries. Significantly more efficient airframes and a restriction in endurance can yield to marketable products. Not many people do those 7h non stop TB20 flights, 90% of leisure GA is traffic patterns and short trips. That is an achievable goal.
PS: The biggest practical challenge for battery powered cars is the heating. There is no “free” heat available and having to heat the cabin and the batteries at low temperatures costs a lot of energy. The range of my car goes from 160km in deal circumstances to 80km when it’s cold. That will be a major problem for airplane applications.
That will be a major problem for airplane applications.
That can easily be overcome with a little combustion heater, like the “Janitrol” heaters that are installed in most light twins, where ducting hot air away from the exhaust is not an option. They consume about two litres of fuel per hour and a little electricity for a fuel pump and a fan. You could in theory use every flammable liquid to operate them including vegetable oil or other biofuels.
Still, I think that the future of electrically driven transportation by road and air lies with fuel cells. They would be able to turn 40MJ/kg of fuel into propulsion and weigh (together with their fuel) only a fraction of a battery of the same capacity.
The warranty is 80% capacity after 8 years / 100,000km whichever comes first. The expected degradation is 75% capacity after 20 years
Given that no existing battery gets to within one order of magnitude of this, I would think they are taking quite a risk here.
But the downside for them is finite, and they can regard it all as marketing/R&D costs – like Toyota regard the Prius which, they say, doesn’t make them any money.
The worst case for BMW and the others is that they have to scrap every car they have sold (which won’t be many) and refund the money – pro-rated according to the use you got out of it, of course. They can easily afford to underwrite that risk. Somebody has to do this in order to move forward with the concept.
That can easily be overcome with a little combustion heater, like the “Janitrol” heaters that are installed in most light twins, where ducting hot air away from the exhaust is not an option.
There are actually electric cars with a methanol cabin heater (e.g. Renault Twizy). It is far more efficient to burn fossil fuels to heat than to turn a propeller!
Given that no existing battery gets to within one order of magnitude of this, I would think they are taking quite a risk here.
That seems to be rather sound, there have been numerous tests and you can simulate it quite well. The modern electric cars never let the battery go down below 10-20% of their capacity (my car actually stops driving altogether at around 10%, no way to make it continue) and never charge it to 100%. Lithium batteries are happy in the 20-80% SOC range. You are right though, a certain uncertainty remains. Personally I would judge the risk of this new technology lower as for example buying an aircraft with a Thielert engine back when it came out and yet numerous people did that because it was attractive. Talking about electric cars, Renault took riskier bets than BMW in their design and only offer the 22kWh battery at a lease with a guaranteed repair/replacement should it go below 75% SOC. They charge 80€/month in the cheapest variant (max 15 000km/year I think). In aviation such a rent model wouldn’t give anybody assurance unless it’s from Airbus/Boeing or maybe Cessna.
That is a more common point of view in your part of the world. In Europe, many people take a different view on the present and future of fossil fuels. And I have to say that I absolutely love my electric car and cannot imagine ever going back to a ICE car.
You’ll notice I was talking about aircraft (actually light aircraft), for which I think spark ignition engines will remain the best technical solution indefinitely. Electric cars (Teslas mostly) are becoming quite popular in my part of the world, and joining the numerous hybrids. They don’t make much economic sense and weigh a lot, but there is a non-technical energy security issue which recent political events in Europe have highlighted. Electrical energy storage is slowly making headway, driven mostly by military applications: chemical propellant, steam etc aren’t nice stuff to have around when people are shooting at you and have some intrinsic limitations in those applications, regardless of expense.
I think the eventual electrification of ground transport, making its source of energy either natural gas or nuclear, will free up gasoline for light aircraft – which really can use the energy density of gasoline engines to perform well and usefully at reasonable cost.
The energy security aspect of electric vehicles has all but disappeared in the US, as with the advent of shale oil the US will shortly surpass Saudi Arabia as the worlds largest producer of oil, and will be self sufficient in oil by 2020. The US is already the world’s largest natural gas producer.
I believe Tesla is an environmental play, aided by California law. I think that is a worthwhile objective though. Given the state of the atmosphere in China reducing pollution sounds like a good idea.
They don’t make much economic sense and weigh a lot
Agreed, they don’t make much sense today. Weigh a lot, that depends. The Tesla is a very conventionally built car stuffed with an incredible number of laptop cell batteries weighing almost twice as much as the carbon fiber BMW (which has 25% of the battery capacity and needs about 25% less energy). Increasing energy density of batteries is only one of the things you have to do, reducing the weight is as important. Still, those cars are different and require adjustment but they also offer a lot. From the first moment I was in an electric car, I knew that this is it (that was not in a golf cart ;-)
I think the eventual electrification of ground transport, making its source of energy either natural gas or nuclear
We don’t have a lot of natural gas in Europe with the exception of Norway. The UK supplies are beyond peak and the other countries don’t have much. Nuclear is mostly a technology of the past, several countries are already pulling out (Switzerland, Germany) and others have mostly abandoned plans for new plants due to economics (see the financial disaster in Finland). Solar, water and wind are good energy sources, especially the latter on a large scale and a lot is happening over here in that regard.
Fuel cells in combination with wind/water/sun to produce the fuel are probably what is going to make it into GA airplanes instead of rechargeable batteries but the technology is still awfully far away. They can now build fuel cells that last 10 years or longer (they’ve been driving around my town for the last 20 years) but they cost a fortune because one hasn’t been able to replace platinum with a more affordable metal. Toyota’s 2015 announcement is brave but it doubt they’ll make it, at least not more than a symbolic number.
achima, what sort of electric car do you have? Just curious…
BMW i3, didn’t you guess that from my carbon fiber propaganda? 
I bought it because I think it is a very bold move that deserves support. For the first time in a long time, an established car maker (i.e. a company that has the skills and the funds) did something radically different and the result is gorgeous. I am very glad it appears to be more successful than they thought (somebody offered me 7000€ cash on top of the list price if I gave him mine). The last time I felt that I had something truly revolutionary in my hand that is incredibly desirable (talking about products here, not women) was when I got the iPhone on the day it was released in the US.
We don’t have a lot of natural gas in Europe with the exception of Norway.
Economical sea transportation of natural gas is a very interesting technical problem, the solution of which would benefit the world a great deal.
Nuclear is mostly a technology of the past, several countries are already pulling out (Switzerland, Germany) and others have mostly abandoned plans for new plants due to economics (see the financial disaster in Finland). Solar, water and wind are good energy sources, especially the latter on a large scale and a lot is happening over here in that regard.
I am very glad to see new R&D being done to burn existing nuclear ‘waste’ – the energy available there is enough to power the world for a very, very long time. That allows a lot of time to develop renewables that might in time produce a meaningful fraction of the world’s electric power, and an additional motivation to make electric cars available for people who select their cars on a economic, rational basis without security-related punitive taxation driving them. I can certainly see a time when people have an electric car for commuting and a gasoline car for everything else. Unless local governments forbid the use of gasoline to power light aircraft, I can’t see a time when gasoline won’t be the best way to power a light aircraft.
Fuel cell R&D saw a lot of funding a few years ago, but the problems are huge. I’ve been lucky enough to work in most of the energy and power conversion technologies mentioned in this thread, and really enjoy it. Then like most other people, when I get home I look at my budget, my needs, and the real world market, and make my decisions accordingly.
