Generators are always recommended and often a necessary part of a Renewable Energy System. In an off-grid application, a generator may be the only source of power to charge your batteries if the sun doesn't shine or the wind doesn't blow. They can also be used as the primary charging source when solar panels or wind generators can not be purchased immediately. Because gasoline storage can be a problem, consider a propane generator. Be sure to get a generator with enough wattage to run your biggest loads.