Many ways to do it, generator, some powerheads run on 24 volts and have emergency battery back up(Tunze and Vortex Eco's come to mind), there is a plug in air pump that comes on if power goes out. I installed a 75 AMP generator that will run most of the house if power goes out and a tranfer box so I can switch back and forth between TEP and generator with out cross connect and BOOM. Get a small generator and size it to your amps, if you have a 90 gal a 20+ amp will get you by. I would get the biggest I could afford. Ours runs all kitchen, except stove (we can use microwave), all living room, TV, 110 Reef, 54 Discus, Bathroom, Computer room, bedroom and 2 outdoor ponds. Used to run the swamp cooler too before we got central air. If we ever had a long outage in summer, I would just get one of those portable AC units and keep it comfortable. In winter we have portable heaters for the rooms we are in.