Pi-Pop uses supercapacitors as the energy source for its e-bike.
The supercapacitors are housed in a module mounted to the side of the rear rack, so, in a manner of speaking, it does have a battery. The housing is notably smaller than that of a typical e-bike battery, though. That’s backed up by the Pi-Pop’s weight: just 47 lbs. (21.5kg).
Pi-Pop’s concept works from the same basic concept as regenerative braking. Rather than plugging in the e-bike to charge it up, the supercapacitors charge as you ride. Pi-Pop says that their e-bike will charge on flats, while descending and when braking. They even claim that you can arrive home from a ride with the same level of charge in the supercapacitors as when you left.
Supercapacitors are an interesting technology to use for storing energy. They have several obvious selling points. First, there’s no lithium. Second, they can last 10-15 years, rather than three to five years. Third, they are very energy dense, meaning that 250Wh of supercapacitor storage will weigh less than a 250Wh lithium-ion battery.
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That said, it’s important to bear in mind that there’s no free lunch. The only time it is possible to charge the supercapacitors without seeing a reduction in either speed or momentum is while braking. In order to charge the supercapacitors while pedaling, some of the energy the rider generates as they pedal will have to be diverted to the supercapacitors. Let’s say that a rider is producing 100W as they pedal along at 10 mph. Now, let’s say that 10 percent of the energy they are producing—10W—is diverted to the supercapacitors. That means that they are going to lose 10 percent of their speed. They are now going 9 mph, and after pedaling at 9 mph for an hour, they will have stored 10Wh in the capacitor.
Charging on a downhill means going slower and not coasting as far as a more traditional e-bike. What that does is simply distribute the energy expended to different points in the trip: Go slower on a descent in exchange for a little help on a hill.
Marketing claims aside, a supercapacitor is the same as a lithium-ion battery in that it can only discharge as much energy as goes into it. That it can’t discharge more energy than you put into it isn’t a knock. If they are as energy-dense as it seems, this is a technology that deserves to be further developed. A lighter e-bike has no downsides.
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