I would like to know what parts I would need to charge a 36V lithium battery for an ebike? I want to charge the battery while riding the bike for greater range.


Before you worry about charging, consider this: It takes about 85W to propel a 75kg cyclist at 20km/h under ideal conditions. Thin film (i.e. flexible) solar panels have an efficiency of ~9% and when deployed as an overhead canopy would likely deliver no more than 50W/m² in mid-latitudes. To generate the required 85W you thus would need a panel 1.7m² in size. That's a big panel (which turns into a big sail when it gets windy).

If you weigh more than 75kg, or want to ride in the morning or afternoon, or it's windy or cloudy, or you want to ride through even gently undulating hills, or the road conditions are not perfect, or your bike isn't brand new, then the situation gets a lot worse. Small solar panels are almost worthless for the average e-bike — they just don't harvest enough energy in 'typical' conditions to be useful.

If you want longer range then consider a tow-behind trailer with a (more efficient) mono/poly-crystalline solar panel as a lid, and a power coupling to the bike. You can store your gear in it, have extra batteries in it, and unhitch it whenever you don't want or need it.

  • I doubt that the weight of the trailer would cost less energy than it generates. Maybe if you leave the bike parked outside all-day when not riding. But that is a complicated calculation. – user2451 Aug 18 '18 at 10:05
  • 3
    @JanDoggen Solar bike trailers have been viable for years as a way to boost speed or extend range — which is what the OP is looking to do. Search the web for "solar bike trailer" for hundreds of working examples. If you don't want to carry cargo, you can build a functioning trailer that weighs less than 20kg with off-the-shelf parts — and that includes the weight of the panel. Such basic trailers typically only consume ~15–20% of the power they generate to move themselves, with the remaining power used to (help) move the bike and cyclist. – Tim Aug 18 '18 at 11:14

Your Answer

