A prototype car tailored to its hydrogen power source gets more oomph from its fuel cell than competitors, leading the way to more efficient, cleaner vehicles

Power when you need it Riversimple

HUGO SPOWERS puts his foot down. The car leaps forward, pressing me into the passenger seat. I’m zipping through London in a new kind of vehicle: its motors are in its wheels, it brakes without friction and it can drive 480 kilometres on one tank of the lightest element in the universe.

Spowers is taking me for a spin in the Rasa, a prototype hydrogen car that emits only water vapour. Trying to power a normal car with hydrogen usually requires a bulky fuel cell capable of delivering the same output as a combustion engine – typically around 100 kilowatts. But the Rasa, built by start-up Riversimple in Llandrindod Wells, UK, does things differently.

Rather than making a fuel cell that can power a normal car, Spowers has designed a car around the fuel cell. This means it requires 10 times less power than an ordinary car. But even with the lightweight design, this power is only enough to keep the vehicle cruising. So the Rasa has another trick to generate the bursts of energy needed for acceleration.


The Rasa uses a sort of high-tech electricity trap called a supercapacitor. Because they store energy as electricity, rather than in chemical form, supercapacitors can release large amounts of energy faster than anything else – perfect for giving a car some oomph. The hydrogen fuel cell sends a constant trickle of energy into a supercapicitor, then the whole lot is released when the car needs it.

“Rather than designing a fuel cell for a normal car, Spowers has designed a car around the fuel cell”

I wince the first time Spowers brakes at a pedestrian crossing, because I know how the Rasa’s brakes work. They are entirely electric. Instead of using brake pads and friction, the Rasa slows down by reversing the motor in each wheel. This turns the motors into generators, recapturing the car’s kinetic energy and pushing it into the supercapacitor. Friction-based brakes only come into play for emergency stops.

“In a normal braking event, we will recover about 50 per cent of the kinetic energy of the car,” says Spowers. For comparison, a similar system in the Toyota Prius only recovers 10 per cent of this energy.

Despite the Rasa’s clever tricks, is the use of hydrogen fuel in cars a non-starter? The Tesla Model S has taken the automotive world by storm, suggesting that running cars on lithium-ion batteries is the way forward.

Nick Asselin-Miller of sustainability consultancy Ricardo says it’s not that simple. “The energy density of hydrogen under high pressure is much higher than you can store in batteries,” he says. A hydrogen tank and fuel cell gets you a lot farther than a battery of the same size and weight.

The electricity grid isn’t ready for widespread adoption of electric cars either. “If you converted the entire vehicle fleet to electric, that would place a huge strain on the grid,” says Asselin-Miller. “A doubling in grid capacity is required. Not going to happen soon.” Hydrogen offers an alternative that is likely to have a place alongside battery power.

The Rasa prototype is not a normal car in looks or function. And the infrastructure to support hydrogen cars is embryonic at best. But when we accelerate swiftly and silently, encased in carbon fibre and leaving nothing in our wake but water, I can’t help but feel like I’m sitting in the future.

This article appeared in print under the headline “This car makes a little hydrogen go a long way”