How To Make A Solar Powered Electric Bike

Solar Powered Electric Bike with Goal Zero Boulder 30  Sherpa 120 and inverter.
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Solar Powered Electric Bike with Goal Zero Boulder 30 panel (battery and inverter are hidden in panniers).
Solar Powered Electric Bike with Goal Zero Boulder 30 panel (battery and inverter are hidden in panniers).
All electric vehicles, bikes, cars, and scooters suffer the same flaw: short range. Of course range is all relative. If you bike two miles a day to the store and back, most electric bikes are just fine. But if, like me, you are trying to make your electric bike replace more and more car trips, you always want more range. With that in mind, I set out to see if I could extend the range of my electric bike using a solar panel.

The Bike


My Trek Valencia+ is the best electric bike I have used (I have tested four so far). It has a range of 7-30 miles depending on how much pedal power you put in. I generally get 15 miles between charges. I can get to work and back no problem (14 mile round trip). But to go to the San Francisco and back is a 30 mile round trip. To do this, I would barely make it one way, then have to recharge.

NOTE: if you are new to electric bikes, range numbers are very subjective. They depend entirely on how you ride the bike and the terrain. It's like a Toyota Prius. I can get 65+ mpg if I hyper-mile on flat terrain. I have a friend who rarely gets more than 40mpg. But in general, I get around 50 in normal driving. The range of electric bikes swings even more.

The Panel

Goal Zero Sherpa 120 Explorer Kit charges a peddle-assist electric bike so that the gear review can get home  West Marin.
Goal Zero Sherpa 120 Explorer Kit charges a peddle-assist electric bike so that the gear review can get home, West Marin.
I have used the Goal Zero Sherpa 120 Kit to charge my bike before as seen in the photo to the right. It works, but the flexible Nomad 27 Panel panel that comes in the kit is too floppy to ride and charge at the same time. So I opted for the Goal Zero Boulder 30 panel. This panel uses less surface area than the Nomad 27 and puts out slightly more power (30 watts vs 27 watts). The downside is that the Boulder 30 is heavier (6.6 lb vs. 3.4 lb). I secured the panel with bungee cords so that I can still reach into the panniers and access the battery and inverter.

The Battery and Inverter


In a perfect world the panel would plug directly to my bike's battery. I have not found a way to easily do this (send me an email if you know how I can). So I have to plug the panel into an inverter that then goes to an inverter which then goes to the bike's inverter and finally to the bike's battery. The power is going from DC to AC to DC. This likely results in a 20 percent-plus efficiency loss. Also, the battery and inverter and bike charger add another six pounds and a lot of cables to the system. Not ideal, but it works.

Did it work?


Yes. The extra Goal Zero Sherpa 120 battery alone (which starts out each day full) gave me another full charge. And in the course of a day, with my bike in the sun five-plus hours, I get another full charge. So I essentially tripled the range of my electric bike! I used to get 15 miles and now I get 45.

That said, there are some major downsides. The Trek Valencia+, which is already very back heavy, is now even worse. The whole system weighs 12.7 pounds. It is also expensive. Here are the costs and weight breakdowns:
Bike charger: 1.5 lb.
Boulder 30 Panel: 6.6 lb. $240-300
Sherpa 120 Battery 3.6 lb. $320-400
Sherpa Inverter 0.8 lb. $43-80


Bottom Line: Should you make a solar electric bike?


This was a fun experiment but the cost will not be worth it to most people. Better to just bring your charger with you everywhere and find a friendly cafe that will let you plug in for a java break.

If there was a way to plug the panel directly into the the bike battery, it would eliminate most of the weight and cost.

More Solar

  • I did a complete Portable Solar Review. The Sherpa 120 kit that was used here won Editors' Choice in 2012.

Chris McNamara at Big Sur  2008
Chris McNamara
About the Author
Chris is the founder of OutdoorGearLab and serves as Editor-in-Chief. Climbing Magazine once computed that three percent of Chris McNamara's life on earth has been spent on the face of El Capitan—an accomplishment that has left friends and family pondering Chris' sanity. He's climbed El Capitan over 70 times and holds nine big wall speed climbing records. In 1998 Chris did the first Girdle Traverse of El Capitan, an epic 75-pitch route that begs the question, "Why?" Outside Magazine has called Chris one of "the world's finest aid climbers." He's the winner of the 1999 Bates Award from the American Alpine Club and founder of the American Safe Climbing Association, a nonprofit group that has replaced over 14,000 dangerous anchor bolts. Chris is also the founder and lead author of the rock climbing guidebooks publisher, SuperTopo. He is a graduate of UC Berkeley. You can follow him on Facebook, Twitter or ChrisMcNamara.com. He also has two Lake Tahoe Vacation Rentals here and here.
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