Kent Peterson does it with off-the-self stuff, but it should be easier than this.
Thanks to Kent Peterson of Eugene, Oregon, we have two of our favourite things, together at last: Tiny houses and electric bikes. Well, not really – we have a plastic garden shed. But what's interesting is what Kent has done to make his e-bike "Sparky" solar powered, all for very little money. This is not easy in sunny Oregon, especially when he rides the bike to work so it is only parked there at night, but he pulled it off. Kent writes:
What's lovely about this story is the way Kent explains it so that anyone, including me, can actually understand what the problems are and how he solved them. These were not inconsiderable; the solar panel puts out a maximum of 100 watts at a maximum of 18 volts while the bike needs 42 volts and holds 450 WattHours of electricity.
Five minutes after I installed a solar panel on the roof of my bike shed it began to rain. Since this was April in Oregon, the rain was not an unusual or unforeseen event and in fact the next five days were rainy and mostly cloudy. But even on those damp days my solar system managed to generate enough power to not only charge my e-bike, but also my phone, Android tablet and radio batteries. After that first week, I knew that I had pieced together a workable system. It's not fancy or particularly elegant, but it gets the job done.
Kent first tried what is called a "boost controller" to change the voltage. This is an interesting device which Thomas Edison would have killed for; the reason we all use alternating current instead of direct is that there was no DC device like a transformer that could change voltage. It was hard to set up because of a useless manual, but Kent was able to find videos that explained how to use it. This is fine, except it doesn't store power and won't work at night when he has to charge the bike.
Kent then gets a "power bank," an off-the-shelf combo battery and inverter that holds 220 Wh, about half of what the bike needs, but it is enough. Instead of the boost controller, Kent is now taking the output of the solar panel, storing it in a battery, converting it to 120 volts AC, plugging in the adapter and converting it back to 42 volts with the bike's wall wart, which wastes about 7 percent of the power. But it all works, and gives him enough power to play with all this other stuff.
Kent is a smart guy and gets a charge out of doing this kind of stuff, but in a perfect world this would all be plug and play and anyone could do it. The panel is DC, the stuff plugged into the power bank is all DC and is plugged into the USB ports; just about the whole world is DC now. It's time to get rid of that AC intermediary.
More at Kent's Bike Blog.