wrote

A couple of web sites quote a 170 W BP solar panel at around $850. In
full sun this would take about four and a half hours to recharge the
battery. A 115 watt panel would take about six and a half hours and
cost $650. Add another $200 for a charge controller, wiring, etc and
another $100-$200 for the battery.

Well, it looks like they are out there and available as you've pointed out.
When I looked at websites that offered them as battery chargers I only found
the smaller ones meant to keep an already charged battery at full charge.

Still, this is much more expensive than a small generator would be, and
depends on things like sunny days and being kept clear of ice and snow. The
small generator is the way I'd go if it were me.

There's a guy with a solar-power setup on the ramp but I've never been
able to run into him to pick his brain. A friend heard that he has his
thing patented so I might get little info other than a price...

I am not an attorney and this is not legal advice.

I'm not an attorney either but I don't think you would get into any trouble
building one for yourself for your own use - who is going to hire an
attorney to sue you for $1,000 (the cost of pursuing it would be orders of
magnitude higher than that) and what attorney would be interested in such a
case? If you started manufacturing them and selling them, that would be a
different story.

BDS