Also, don't forget the gear to capture the electricity isn't free, is more stuff that can break and incur maintenance fees, must contain purified metals and other non-zero carbon emissions, and so on. Trying to break even on all of this off of human labor is a silly game to play when there are so many other better opportunities. And that $18/yr is already inflated by enough factors that $1/yr is probably a much better estimate.

Same for these solar panels on a car, too. Solar panels aren't the nicest things to manufacture right now. Putting them on a platform this poor is silly when you could put them somewhere more effective. If they were dirt cheap and harmless to create, opportunity costs might be less of an issue, but even today, they aren't dirt cheap and the aren't harmless to manufacture. They should be used effectively, not for show or feelings.