Someone mentioned the LED anti-collision light, I know Whelen offers LED nav
lights as well. Perhaps a call to them to find out what the draw would be
for anti-collision and the 3 nav lights to make him legal and safe, then see
what the different scenarios would be (i.e. a fully charged, 15 pound gel
cell battery might run those lights reliably for 3 hours). The light retro
would be a little costly, but it would be a simple system to maintain,
versus introducing an alternator or generator, and a belt or propellor or
whatever else you might need to run the thing.