Solar Cross e-bike uses Sun's energy to help with the pedaling


June 29, 2011

The Solar Cross is a one-off pedal-electric bicycle, that receives its power from onboard solar panels (Photo: Terry Hope)

The Solar Cross is a one-off pedal-electric bicycle, that receives its power from onboard solar panels (Photo: Terry Hope)

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This March, we reported on the Kinetic Photovoltaic Vehicle (KPV), a one-of-a-kind solar-electric scooter that fits inside a suitcase. Well, it seems that Terry Hope, the Canadian inventor who created the KPV, wasn't content to stop there. He recently contacted us about his latest creation, the Solar Cross ebike. As its name suggests, it's a pedal-electric bicycle that receives its power from the Sun ... and the rider, of course.

Hope started out with a stock 18-speed Specialized FSR mountain bike. While a road bike would have been lighter and offered less rolling resistance, he told us that he needed a double crown suspension fork in order to mount the two front solar panels over the front wheel. The bike also has a third handlebar-mounted panel, along with a 24-volt 1-horsepower motor, a 5000 mah (milli Ampere hour) lithium-ion polymer (LIPO) main battery, two 5000 mah LIPO booster packs wired in series, and a 24-volt controller.

Terry built the solar panels himself, out of eighth-inch polycarbonate sheeting, aluminum, and 18 x 6 x 6-inch (457 x 152 x 152-mm) mono crystalline cells. In order to keep the weight down, he drilled thousands of holes through the aluminum parts. The cells each put out 3.8 to 4 watts, together providing an estimated 8.7 volts of electricity. Using the controller, riders can assign them to charge any two of the three batteries.

Along with that controller, the bike's instrumentation includes a watt analyzer, four voltage meters, two booster switches, and an all-important emergency kill switch.

When activated, the motor directly drives the bicycle's outer 80T (80-tooth) chainring via a short chain. The inner 42T and 22T chainrings use a regular-length bike chain to turn the rear wheel. Riders can pedal without electric assistance using any combination (within reason) of the two inner chainrings and the rear cassette cogs, or they can activate the motor to turn the outer chainring, providing a boost to their pedaling in whatever their chosen gear happens to be.

Hope still plans on augmenting the solar cells by adding solar-energy-capturing fluorinated ethylene propylene (FEP) film to the bike, along with some snazzy nighttime lighting effects.

"I'm very happy with the results so far, and mostly everyone has very positive comments in person," he told us. "What I'd like to eventually accomplish is support from a solar cell manufacturer ... When +15 percent efficiency flexible CIGS solar cells are available within the next 1-2 years, re-engineering the bike for better aerodynamics and lighter weight will be no problem."

The video below shows the Solar Cross' electric assist motor being put through its paces.

About the Author
Ben Coxworth An experienced freelance writer, videographer and television producer, Ben's interest in all forms of innovation is particularly fanatical when it comes to human-powered transportation, film-making gear, environmentally-friendly technologies and anything that's designed to go underwater. He lives in Edmonton, Alberta, where he spends a lot of time going over the handlebars of his mountain bike, hanging out in off-leash parks, and wishing the Pacific Ocean wasn't so far away. All articles by Ben Coxworth

Im looking forward to outfitting the e-bike with full-spectrum CQD solar cells from U of T !

Terry Hope

A nice idea, but a bit behind the times. ;-)

If he\'s using a 1 hp motor (747 watts), with an unmodified frame, that\'s going to put a LOT of strain on the drive train and rear sub-frame, even without the contribution of the rider. And if nothing actually breaks, it\'s still going to wear things out fairly quickly, which would make for a false economy.

Might be better considering a hub motor.

Further, his solar panels are not going to collecting much in the way of sunlight if they are nearly vertical as in the photos. Be much better sitting as horizontal as possible.



I hope the power added by the motor surpasses the extra power required to overcome the huge amount of friction of that panel.. and the weight of the batteries, motor, and controlgear.

but I doubt it.

I\'d really hate to have a truck pass me on the open road on that thing as well. Get blown off and under the wheels. Reduce carbon footprint by early demise.


1hp = 750w, so the motor uses that in 1 hour at 100% duty cycle (uphill). The three 4w solar cells can supply up to 12w total per hour. A 24V5A battery has 120w of capacity. That means the solar cells would charge one of the three batteries in 10 hours, assuming full, direct sunshine, so likely to be at least 15 hours for a full recharge. The 750w motor/controller could use 120w in about 9.5 minutes. This is assuming the stated 1hp actually refers to the motors\' controller output (not the power rating of the motor, as it is above) It could achieve a lot more range if a 200 watt motor controller was used instead, but with less acceleration. But I\'ll stick to my 5000w e-MTB that I can recharge in about 30 mins. I did have a small solar cell on one of my e-bikes once, but that was only used to charge the battery for the lights. Did get a few funny questions, like \"how long does it take to charge?\" \"About 8 weeks... in summer\"

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