Yes, you can run a 12 volt roof cleaning pump all day long w/o using any battery, if you have a generator and one of these http://www.12voltpowersupplies.us/ Simply order the 36 amp unit for under 75.00 shipped, plug it into your generator, and go clean some roofs! Be sure and  waterproof this power supply, if you leave it outside. These little power supplies are awesome!  They are rated for 30 amps sustained, and 36 amp peaks!