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Comment by tonymet | Hacker News Reader

Lithium Battery 0.5 kWh/kg

Diesel 12.7 kWh/kg

Diesel is more like 3.175 (25%) due to the inefficiencies of small heat engines. You're throwing away like 3/4 of the energy as waste heat. Electric motors are >95% efficient and lithium batteries are in the high-90s percent efficient.

Electricity is already low-entropy, whereas energy from burning petrol is high entropy and thus contains less useful work.

Also, a kilo of diesel can emit that energy once. A kilo of battery can emit that energy hundreds or even thousands of times

it's not waste half the year

True if you are cogenerating, but few people do that. Only a miniscule fraction of waste heat from a car engine is required to heat a car.

Tangent but: I've always wondered why home cogeneration never took off. Too bad we don't have gas water heaters and gas furnaces that generate electricity and dump the excess onto the grid and heat with the waste heat.

Even a low-efficiency thermoelectric generator would recover some useful energy that is otherwise kind of wasted.

It's still waste, because if you're in a fixed location (which you'd have to be in order to benefit from much of the heat) you'd be better off running a heat pump.

Diesel has efficiency of 40% not 25%.

Taking the numbers from: https://www.sciencedirect.com/science/article/pii/S030626192...

- Diesel has a peak efficiency of 40% but an average efficiency of 20-25% (depending on the type of driving)

- Gasoline has a peak of 35% and an average of 16%–20%

- Battery has a peak of 85% and an average of 80%

Who cares, we need to stop burning fossil fuels, relative energy density in the abstract does not matter in the context of climate change

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