Generac sells them. They basically use their high quality portable home generators (the best around in my opinion) and package them with a metal shed, battery start and automatic transfer switch etc. You can see them at: http://www.generac.com/guardian/ep_sys.cfm These systems cost between 3 - 13 thousand dollars, depending on capacity etc. Pretty expensive. If you are going to go with a battery powered backup then I would definately read this: http://www.yachtsurvey.com/bilge_pumps.htm Granted, it is about boats, but the same principles apply. I think the batteries are key. YOu could probably spend $200 on two large, heavy marine batteries. I don't know how long it would go without recharge.