Thought experiment of rigging solar panel to electric bike, questions about LiFePO4

[jflorey2]

Another question which came to me (And that should have been my first one) is that can a battery be safely used to power a motor while also simultaneously being charged by the panel?

Yes. You still need a charge controller to prevent overcharge when stationary though.

The specific panel I had in mind was a 45 Watt 24V panel. It's measurements are 22x27x3 inches. However; the bike would not operate on the panel's power alone.

Well, give it a try if you want. I suspect you won't see much contribution from the panel but it probably won't hurt anything. I would advise mounting the panel VERY well to the rack; the panel will see a lot of force on it on bumpy roads.

[HarperHurst]

The math I've done is like this:

45 Watt Panel with operational voltage of 36V going into an MPPT controller that perhaps isn't even the most efficient one. Say 85% efficiency, even though most of them are >90%. Converting 45W & 36V to say the battery's voltage of ~29V with 85% efficiency is about 1.3 amps at the panel's peak performance. The charger that comes for the battery is a 24V 8A charger, which they claim can charge the battery in 4 hours from a near-dead state. Would my reasoning of saying an average solar charging amperage of 1A vs the 8A of the official charger is 1/8th as fast?

Mind you, whilst riding the bike I would not be using the motor 100% of the time. Perhaps it would be used with pedal assist to get to around top speed where I take over with just pedaling to keep it at top speed. Once the bike is parked the panel could charge the battery at its fastest possible rate (which would be dependent on parking position, angle of panel and how much sunlight it would receive.) so hopefully it would be back near a full charge by the time I got back to it. (Provided the initial journey wasn't too long and I didn't use up that much of the battery's juice whilst traveling.)