There are other sources of backup power besides an engine generator. Both wind and microhydro turbines can be good renewable sources, if the property has consistent winds or a creek. Sometimes multiple sources of energy are available that work well together throughout the seasons. For instance, in the wet Northwest, there are seasonal creeks that can run microhydro turbines in the rainy season, and then in the dry season solar can kick in to make up for a lack of flowing water. Sites in the Midwest often have winter winds, with the PV system augmenting production on sunny, windless, summer days.