I was looking around for something else and came across this USB powered fan. It might be overkill and too heavy for ultralight types. If I figure it correctly, the fan would run for about 11 hours on a solar battery like this.
My thought would be to hang the fan from the ridge line, charge my battery pack all day and be cool all night. Don't have the weather or money to try it out right now. Anyone see any major issues with a setup like this?