Shawn Ryan is neither an engineer nor a professional cyclist, just someone who wanted to know how far an electric-assist bicycle can go when the sun is its only fuel tank. The answer, it turns out, is more than a thousand kilometers of French tarmac and numerous Alpine mountain passes.
Ryan built his solar-powered e-bike from scratch. Solar panels bolted to a cargo bike, a mid-drive motor, and a battery management system he designed himself. After weeks of testing in Nottingham, UK, he took the machine to the Sun Trip, the international solar bike competition.
The Sun Trip was founded in France in 2013 by adventurer Florian Bailly, who three years earlier had ridden a solar e-bike solo from France to Japan. That personal expedition snowballed into an association, The Sun Trip, dedicated to promoting renewable energy, sustainable transport, and grassroots engineering through long-distance cycling expeditions.
Unlike a professional bike race, the Sun Trip has no support vehicles and no safety net. Riders navigate, camp, repair their own machines, and manage their own power budgets, either picking their own route between mandatory checkpoints or following a route through designated regions. Since its founding, the event has run editions across Europe, Central Asia, China, and North Africa, alongside shorter regional versions confined to France and the Alps. We previously featured a unique semi-enclosed solar ebike that took part in a Sun Trip race which went from Lyon, France to Morocco and back.
You can see some highlights from Ryan's race in the following video.
This year's Alpine edition, based in the Auvergne-Rhône-Alpes region, sent riders over brutal climbs including the Col du Galibier (2,642 m/8,668 ft) and the Col de l'Iseran – which at roughly 2,770 m (9,088 ft) is the highest paved pass in the Alps – before finishing in Albertville. There's a points system based on distance and checkpoints, but one rule underpins the whole event: touch grid electricity, and you're out of the solar-only competition.
"Once you used mains electricity, you were effectively out of the solar-only points competition," Ryan tells me via email. "So after plugging in, I could continue the rally, but I was no longer eligible in the competition."
Building a cargo bike that runs on sunlight
Ryan started with an existing cargo bike, the Omnium from Paradise Cycles, whose front rack gave him a stable platform for solar panels while still working as a normal daily-use bike once the panels came off.
He fitted a 250W Tongsheng TSDZ2B mid-drive motor from Varstrom, plus two 36-volt batteries – one from EM3-EV, one from Infinit. For the solar side, Ryan wired the solar panels straight into a single charge controller – a Genasun GVB-8 boost MPPT (Maximum Power Point Tracking) unit – which then fed directly into the battery. The controller takes the panel's fluctuating voltage and converts it into the steady voltage the battery needs to charge properly, so the whole setup runs solar panel → charge controller → battery, with only a small energy loss along the way.
His original design called for three 100W panels covering the whole front cargo platform. They produced more power, but testing showed the bike became too long and bulky in traffic or tight spaces. Ryan cut the array down to 200 W, suspecting it was close to the bare minimum he'd need for the distances and climbs ahead.
That call proved both risky and decisive. Fully loaded – camping gear, camera equipment, and all – the bike weighed 61 kg (134 lb) in total. During UK testing it consumed 10 to 12 Wh per mile (about 6 to 7.5 Wh per km), while the panels, rated for 200 W, actually produced between 70 and 100 W depending on weather and sun angle.
On his toughest day of the Sun Trip – 130 km (81 mi) through heavily mountainous terrain – the MPPT controller logged 985 Wh of usable solar energy delivered to the bike's electrical system, working out to roughly 7.58 Wh per km (12.2 Wh per mile), at an average speed of 21 to 22 km/h (13 to 14 mph).
The trip's biggest crisis arrived during a heatwave that pushed French temperatures to 41 °C (106 °F) and sparked wildfires near Lyon. The heat went straight for one of Ryan's batteries. "Unfortunately, during the extreme heat one of my batteries, an Infinit modular battery, began refusing incoming solar charge because its BMS was overheating," he says, referring to the battery management system (BMS), the electronics that monitor and protect a battery pack. "The BMS was essentially doing its job and protecting the battery, but it meant that for periods of the day I couldn't store all the solar energy the panels were producing."
Looking back, Ryan has a clear fix in mind. "In retrospect, I should simply have mounted the battery somewhere completely shaded and protected from the heat." He also points to a possible design quirk: the Infinit is a rebuildable battery whose cells are held together mechanically rather than permanently spot-welded, as in a conventional pack.
"After discussing the problem with people with more battery expertise than me, one possibility is that contact resistance within that arrangement contributed additional heat under the combination of discharge and incoming solar charging," he says. "I can't say definitively that this was the cause, but it may have contributed."
That thermal problem, layered on top of an already razor-thin energy budget, forced Ryan to plug into the mains twice during the trip – around 1 kWh in total – and it cost him his place in the solar-only competition. "I had deliberately reduced the solar array to 200W to make the bike more maneuverable, and in hindsight that was probably right on the limit for the distances and terrain we were covering," he admits. "The bike itself proved remarkably efficient, and on good days 200W came very close to providing all the energy I needed, but there wasn't much margin for anything to go wrong."
Would a perfectly behaved battery have kept him fully solar the whole way? "I genuinely don't know. I think it would have been very close," Ryan says. "There were days when 200W was enough, but over an Alpine route with variable weather and significant climbing, it left very little reserve."
The other suspect component was the motor. Before the event, Ryan worried the 250-W Tongsheng mid-drive would be the weakest link on long climbs in extreme heat – and to some extent, he was right. "The 250W Tongsheng did struggle thermally on some of the really long climbs, although I think 'struggle' needs putting into perspective," he says. This was the smallest 250-W version of the motor, tasked with hauling a heavily loaded cargo bike up some of the longest, highest climbs in the Alps.
"Initially I hadn't appreciated how much heat a mid-drive could build up under those conditions," Ryan tells me. When the motor overheated, the fix was simple: stop, and let it cool. A few times, he poured water directly onto the motor casing.
He found the trick was keeping the motor spinning fast rather than grinding along under heavy load. "It was much happier at high RPM in a low gear, so on the big climbs I'd select a very low gear and spin slowly up the mountain. It wasn't fast, but it worked." That's one advantage a mid-drive motor has over hub-motor systems – it can use the bike's own gears to stay in a more efficient RPM range on steep gradients. "Considering it was a nominally 250W motor, I thought it did an impressive job."
Next up: France to China
Ryan isn't claiming everyone needs a solar bicycle. "For somebody riding a few miles to work and charging at home, it probably doesn't make much sense," he says. Where the concept clicked for him was cycle touring. "The route was extremely mountainous, so on flatter long-distance touring I think the concept becomes even more compelling," he says.
But for Ryan, the Alps bike was only a prototype. He's already redesigning the concept for a far bigger target: the Sun Trip from France to China in 2028. The provisional route would cover around 15,000 km (9,320 mi) through the Balkans, Turkey, the Caucasus, Central Asia, and western China, skirting Russia and crossing the Caspian Sea, with roughly 40 riders expected – though both the route and rules remain subject to change.
Tackling a distance like that will need considerably more solar area, but Ryan has ruled out the obvious fix of simply widening his current upright bike and plastering it with panels. "I've realized that I'll probably need substantially more solar area, but simply making the existing upright bike wider and covering it with panels isn't necessarily the answer," he says. "Aerodynamics and rider comfort become increasingly important when you're riding very long distances day after day."
Instead, he's exploring a shift from a cargo bike layout to a semi-recumbent, long-wheelbase design, with the rider seated toward the front of the current cargo platform under a wider solar canopy. "That could improve aerodynamics, increase solar area, and, importantly, make the riding position much more comfortable over multi-day distances."
It's a significant departure from the simplicity that made his first build work. "One thing I liked about the Alps setup was its simplicity: essentially a normal cargo bike, a 250W mid-drive, one solar charge controller, and 200W of panels. It demonstrated that you don't necessarily need to build an exotic solar vehicle for the basic idea to work." The China bike, he says, will inevitably be a far more specialized machine – but everything learned from that first, simple version is already feeding into what comes next.
Source: Shawn Ryan
