Are Supercapacitor Ebikes More Efficient Than Battery-Powered Ones?

There is a growing number of electric bikes powered by supercapacitors on the European market. Let’s analyze the factors that could promote more widespread adoption of this technology, or limit it to a niche.

What is a supercapacitor?
What is a supercapacitor made of?
Applications of supercapacitors
How supercapacitors work on electric bikes
Reasons to prefer them to lithium-ion batteries
Misinformation about supercapacitors
Three European manufacturers of supercapacitor bikes

What is a supercapacitor or ultracapacitor?

A supercapacitor is a device for storing and delivering electrical energy, similar to a battery. Unlike lithium-ion batteries, they have much less storage capacity, or energy density. Li-ion batteries can deliver 200 Wh per kilogram, compared to only 20 Wh per kilogram for supercapacitors. On the one hand, they can deliver more energy faster than a battery; on the other hand, they discharge very quickly, even when not in use. They are also more expensive, averaging €18 per watt-hour compared to one euro per watt-hour for lithium-ion batteries. On the other hand, they have a much higher power density, also known as specific power, meaning they can deliver up to 10,000 W per kilogram, compared to up to 3,000 W per kilogram for batteries. This translates, for an e-bike, into rapid acceleration from start-up, at intersections, and even on hills.

Reasons for preferring them to lithium-ion batteries: are they sufficient?

1. Ecological impact: no mineral extraction, which pollutes like any mining. In this case, they benefit from misinformation regarding battery pollution, which is often overestimated.
2. No fire risk: although it is very low for quality batteries.
3. Longer lifespan: almost double that of a lithium-ion battery.
4. No need to recharge; they recharge while cycling.
5. They are allowed on ships and aircraft, since they can’t catch fire.

Composition of a supercapacitor

Ultracapacitors are sealed metal containers (steel or aluminum) containing layers of activated carbon saturated with an electrolytic solution. This solution contains a quaternary salt (tetraethylammonium tetrafluoroborate) dissolved in a solvent, acetonitrile. A conventional capacitor consists of two metal plates (electrodes) separated by a dielectric substance. When a voltage is applied, electrons gather on one of the electrodes, storing the electric charge.

Applications of Supercapacitors

Electric vehicles, Cube satellites, Energy harvesting, Barcode scanners, Lasers, Aerospace and defense, Oil and gas, SSDs, IoT, Medical devices, Flight data recorders, etc. The most common application is in start/stop cars with supercapacitors, which restart the engine even after stopping every 20 seconds, without draining the battery. They automatically turn off the engine after 2-3 seconds of stopping, for example at a red light.

How supercapacitors work on electric bikes

They produce electrical energy during braking, downhill riding, and, to a lesser extent, while pedaling on flat terrain, above a certain speed. They release this energy to assist pedaling, calibrating the flow to match the cyclist’s effort, as with battery-powered electric bikes. They can store little energy, about 20 watt-hours per kilogram of weight. Enough to travel a maximum of 5 km with a 3 kg battery.

Misinformation about supercapacitors

Manufacturers of supercapacitor electric bikes, probably to make the information more understandable, compare them to batteries, causing a limitation in the specialized press. The result:

• We often read that supercapacitors recharge much faster than batteries. The comparison doesn’t make much sense, given that the former recharge while braking or going downhill, with no maximum of 60 watt-hours. The latter are recharged via a wall outlet, storing up to 800 Wh.
• Even worse, the enthusiastic comments claiming that these bikes recharge while pedaling. They didn’t invent the perpetual motor; the additional energy they require from your legs to recharge is slightly greater than the energy they will return to you.
• Supercapacitors are said to withstand at least 10 times more charge cycles: of course, except that these cycles charge about 15 times fewer watt-hours than batteries, 60 Wh versus 800 Wh at most.
• Manufacturers and reviewers boast a fairly high range. However, calculating the range is rather random, given that supercapacitors need braking and descents to recharge. Their battery life is much shorter on flat terrain.

Function	Supercapacitor	Lithium-ion battery
Charging time	1 to 10 seconds, but 56 Wh of storage maximum	2 to 3 hours
Electric Bike Life Cycle	20 years on average	10 years on average
Specific Energy (Wh/kg)	5 on average	200 on average
Specific Power (Wh/kg)	up to 10,000	1,000 to 3,000
Average Cost per Watt-hour	€18	€1
Charging Temperature	-40 to 65 C	-0 to 45 C
Operating Temperature	-40 to 65 C	-20 to 60 C

Three European manufacturers of supercapacitor bikes

The Pi-pop

This French bike, see our post, has a hub motor, delivers 45 Newton meters of torque and weighs 21.7 kg. The equipment is rather low-end, with a very minimalist display, low-power disc brakes, battery-powered lights, and a Shimano Altus derailleur at this speed. One-size-fits-all aluminum frame, no shock absorber. For this price of €2,690, a battery-powered electric bike normally also offers shock absorbers, a display with plenty of information, powerful lights connected to the battery, the option to choose the size, and quality tires.

On flat roads, the electric assistance is intermittent. While you can recover energy by braking or going downhill, there is good assistance at start-ups and on hills, but for no more than a few hundred meters. We are rather skeptical about it delivering a sound performance.

The Anod Supercapacitor ebike

We’ve also already written about the Anod. We find it more convincing than the Pi-pop, thanks to its 80 Wh battery, which weighs 650 grams, what at least guarantees a range of five to ten kilometers, and, above all, the ability to store the energy produced by braking or on descents, if it hasn’t all been used up. It weighs 20 kg, has a 45 Newton-meter motor, a lighting system connected to the battery integrated into the frame, and a single-speed drivetrain with a Gates carbon belt. No shock absorber. Price: 3,499 euros. Ostrichoo has a range of three supercapacitor bikes.

The most interesting one seems to be the one that uses Fastcap® high-capacity supercapacitors, which promise to be twice as powerful as the others. What’s more, its bikes are also distributed by Decathlon, currently in the Netherlands and Belgium, which is a guarantee of viability. Ostrichoo claims its bikes use batteries ranging from 180 Wh to 540 Wh, rechargeable via the mains, and all come with a 4-year warranty. This suggests a hybrid supercapacitor/battery system.

Its Lucius model costs just €990, weighs 26 kg, features a Bafang motor with 45 newton meters of torque, a removable battery, rear drum brakes, front rim brakes, smart lighting, a 7-speed derailleur, and a luggage rack.

The Zeno, at €1,299, weighs only 21.3 kg, has disc brakes, and otherwise shares the same specifications as the Lucius.

The Caesar, at €2,599, stands out with its 85 Newton meters of torque, 540 Wh battery, Bafang mid-mounted motor, suspension seatpost, and luggage rack. Its powerful supercapacitor battery weighs 7 kg, bringing its total weight to 33 kg. All Ostrichoo bikes claim a fairly high range, from 80 km to 120 km for the Caesar.

Images: Anod, Pi-pop, ES Components, Ostrichoo