Can e-bike batteries be charged with solar panels?

[fexixav]

Well, if you took apart your ebike charger you'd find a rectifier (that converts wall outlet AC to DC) and some charging logic that makes sure you don't overcharge the battery. If you can match output voltage on the rectifier (what the actual voltage would be depends on the design of the charger and to a lesser extent the voltage of the batteries being charged) you could theoretically connect your solar panels at that point and charge just fine. With the caveat that you certainly are voiding your warranty and I'd want a fuse or DC breaker in the connection from the solar panel to avoid a fire or explosion.

You can't avoid loss from conversion of DC to AC and vice versa. Good, modern inverter designs running close to capacity have efficiencies in the 80 to 90 percent range. So an 8kw inverter can reasonably deliver 7200 watts from an 8kw array. Bigger inverters are generally more efficient. The catch is that you have to do the conversion twice (once from DC to AC and then back again), so that 80 percent efficiency is really around 64 percent in the most optimistic case -- and keep in mind that the people designing your battery charger probably cared very little about the efficiency of the rectifier, as you are probably only talking about pennies worth of electricity anyway. In practice I think you'd be damned lucky to get fifty percent efficiency with an inverter. Again, the small camping inverters are generally quite a bit less efficient than the larger ones for home solar. You also want to be extremely careful charging in the field since the waste heat even from a dinky 500 watt inverter could easily start a fire in pine needles or dry grass.

Another thing to make you paranoid is that the rated output of a solar panel is for a given temperature, usually 20 °C. I’ve seen in some big island solar projects that in colder temperatures a given panel or array will produce more power. Especially for larger panels and larger systems, this can get quite exciting. That is one additional reason you'll need a DC breaker in that circuit.

Yes, you can charge e-bike batteries with portable solar chargers, but you need a solar charger or regulator that matches the battery’s voltage and current requirements. High-wattage panels and a portable battery backup help ensure reliable charging on multi-day trips.