Lowest energy use per passenger-km, electric bicycle or electric unicycle?

Question

Which uses less electrical energy per passenger-km (pkm) travelled?

• Electric bicycle (with a single rider)
• Electric unicycle (aka. self-balancing personal transporter)

I have heard that a standard bicycle and an electric bicycle are both very efficient modes of transportation for an individual. But I haven't heard much about the energy efficiency of self-balancing personal transportation devices. Are they competitive with an electric bicycle?

(I'm also interested in comparing lifecycle energy use, but that might be too much for one question.)

Answer 1

A two-wheeled electric scooter / bicycle uses less energy. You can take a look at the specifications of two-wheeled electric scooters and electric unicycles. Look at the battery size and the claimed range. An electric bicycle uses less watt-hours per kilometer.

The reason for electric unicycle using more energy is that it needs to continuously stay balanced. The currents in the electric motors can be fairly large and some of that current turns into heat. Of course, it can regenerate electricity while keeping the rider in balance at some times, and then use the energy at other times to keep the rider balanced. However, the mechanical energy -> electricity -> mechanical energy pathway is never 100% efficient.

These considerations of course are very minor. If you need a convenient transport mode that you can carry around at all times and are willing to invest in unicycling skills, it is more sustainable to have an unicycle because you will use it more. An electric bicycle is large, and thus, you will use it less.

Answer 2

The air drag is the biggest force to overcome on flat road. Air drag is growing exponentially with speed increasing. The position of a bike rider seems more economical than the regular position of the e-scooter rider or unicyclist. In case we let those guys also sit down - e-scooter rider on the seat and EUC rider on the wheel cover, the difference should become less significant. It is the function of the area the rider covers with its body facing the air and the aerodynamic position the rider can take and clothing they may use. Somebody may want to invest some time and figure this out. My guess is that the cyclist would still win, whatever way the other two try to position themselves. Losing the air drag game means the whole competition for efficiency is lost.