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lucaspiller

The density/weight needs to be improved a lot for it to be effective compared to existing battery technologies though:

Mazda supercapacitor:

0.007kWh @ 6kg - 857kg/kWh

Prius with nickel-metal hydride batteries:

1.3kWh @ 42kg - 32kg/kWh

Tesla with lithium-ion batteries:

85kWh @ 544 kg - 6.4kg/kWh

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Breaking systems only really need to contain enough energy to stop a car. So, up to 1/2 * 2,000kg * (40m/s)^2 = 1.6e6 J which is a lot of energy, though less than 3.6e+6 J. Going down a mountain is an important edge case, but frankly not something that you really need to use super caps for as these systems still have mechanical breaks for backup, and the lower peaks is more acceptable for battery's.

In an electric car you would then use that energy to speed up again, thus allowing for 10s if not hundreds of charge cycles on a single trip.

Note: 2000kg ~= 4,400lb, 40m/s ~= 90mph.

You forgot to divide by two.

It's actually 1.6 MJ, not 3.2 MJ.

Just edited before seeing your note. But, thanks I always forget about that 1/2.

Just to be pedantic, it is "brakes" for slowing things down, and "breaks" for ruining or damaging something.

Are these figures right ? Gasoline lists on wikipedia [1] as 46.4 MJ/kg which Google gets as 77g/kWh.

[1] https://en.wikipedia.org/wiki/Energy_density

Those figures are right, the best batteries today are still like one percent as good as gasoline at storing energy. Although, you can only get about 20 percent of the energy out of gas while you can get about 90 percent out of a battery.

Right, and ultimately, hydrogen is one of the most (if not THE most) efficient energy storage methods. However, as far a physical storage, actually putting it in a tank, it is not as efficient. Plus, burning it is not as efficient as electricity either.

Electricity and batteries are the way to go. They are around 90% efficient today and will only get better with better cooling methods and recapturing heat loss/preventing heat.

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