Solar Cross e-bike uses Sun's energy to help with the pedaling
By Ben Coxworth
June 29, 2011
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.