I got this INDI 500 bike off the side of the road and put a standard conversion kit on it. This has a small 10W panel cable tied onto the carrier rack that re-charges the 36V lithium ion battery directly. There is no regulator between the panel and battery so electricians will likely tell you that this isn’t ideal but it is certainly the most direct way possible to recharge the battery via photovoltaic. I had the panels specially cut to give a closed circuit voltage of 42.5V (the same as what the chargers put out) and so far it is working as intended. From my testing so far it seems that for each hour I leave it in the sun I can travel 1km. I am also testing another direct charging system using a 100W 48V panel with a custom designed regulator that outputs at 42.5V and that is functioning well too. A 100W panel is too large to put on a bicycle but if you have space to mount it at work or home where the bike can charge directly from it during the day then it can fully charge the battery from flat in about 4 hours.
Matt – Solar Bike