How efficiently do different vehicles convert stored energy to kinetic energy?

Question

I came across this interesting infographic from the U.S. Department of Energy:

They provide a figure of 12 to 30% efficiency of a gasoline vehicle converting fuel energy into forward motion (or kinetic energy). How does this compare to other vehicle types?

Wikipedia has a detailed table on energy efficiency in transport, but all the numbers are in terms of fuel used per mile traveled, or per passenger mile.

All of these vehicles convert stored energy (whether electric, chemical, or something else) into kinetic energy. How efficient are they at doing this? I'm looking for actual numeric figures (not a discussion or ranking).

Since kinetic energy accounts for mass (KE = 1/2 * mass * (velocity)^2), this should provide for a fair comparison across vehicle types.

Answer 1

The Department of Energy has an equivalent infographic for electric cars here. The bottom line is 60% to 73% efficient, not counting the benefit of regenerative braking, compared with 12% to 30% efficient for gasoline powered cars.

With regenerative braking included, they say 77% to 100% efficient. I don't understand the basis for the 100% figure, and the pop-up description is not helpful, saying

An EV’s electric motor stops when the vehicle stops. The motor doesn't waste energy idling.

The efficiency is clearly much higher, primarily because the extremely inefficient conversion from heat to mechanical power has been eliminated in the car. Of course, electricity has to be generated somewhere to charge the car, so the total system efficiency is lower.

Answer 2

Looks like over 90% for electrical - from caranddriver.com,

Taming the Powertrain

Reducing waste in the powertrain increases range. The more efficient a motor, the more time an EV will stay on the road. Tesla told Car and Driver that the motor in the Model S has gone from 80 percent efficient to 90 percent, with peak efficiency at 94 percent during the EPA test cycles.

I'm trying to get the same figures on Hydrogen Fuel Cells - looks like about twice as efficient as gasoline, but unsure of the exact amount.

Answer 3

We can estimate the efficiency of a hybrid (Toyota RAV4 hybrid, consuming 6 L / 100 km) by noting that a similar purely electric vehicle (Toyota bZ4X) consumes 0.17 kWh / km.

If we set the efficiency of the electric vehicle to 90% (an estimate, including losses in battery, wiring, power electronics and motor), and note that one liter of gasoline contains 9.5 kWh / liter, then the hybrid consumes 0.57 kWh / km.

The estimate for the hybrid is therefore 27% (calculated from 0.17/0.57*90)

A non-hybrid (gasoline engine) would consume about 7.5 L / 100 km, and the efficiency would be therefore 21%.

In reality, an electric vehicle has charging losses too, maybe having a charging efficiency of 93% (the 0.17 kWh / km figure does not have this charging loss included, with the charging loss it would be more like 0.18 kWh / km). The electricity distribution network has maybe an efficiency of 95%. Electricity generation from fossil fuels or nuclear power can have 30%-50% efficiency, but those generation methods are becoming more rare and we are increasingly utilizing wind power and hydropower.

Hydrogen cars are like electric cars so the power electronics, wiring and motor efficiency is about 90% combined, but the fuel cell is running at 50% efficiency and the hydrogen electrolyzer is running at 75% efficiency. Thus, the efficiency from the grid is about 34%. Presumably electrolyzers would be located near the electricity generation so distribution losses don't affect hydrogen. However, an electric vehicle would have efficiency of 0.93 * 0.95 * 0.9 (charging times distribution times vehicle) or 80%.

You can compare hydrogen's efficiency of 34% to electric vehicle total charging, driving and distribution efficiency of 80% and the electricity clearly wins.

Also if calculating well-to-wheels efficiency, you should include oil refining efficiency too in the gasoline models.

All these figures were in warm climates. In cold climates, efficiency of gasoline vehicles suffers only very little because you get waste heat for free, but for electric cars, the efficiency suffers a lot because you need to use a heat pump (typical these days) or even resistive heaters (typical for older Tesla models).