Poking through the Northern Tool catolog yielded this:
Smart Vent 300
It's a 9" dia. x 4"tall solar
powered vent/fan, with a rechargable battery
backup for up to 100 minutes of vent time at night or overcast conditions. I've run out of luck searching for more info, might try again when I get home and have more time, but I thought I'd bring this up.
Might be just the ticket for those of us who don't have no steeenkin hookups