Choosing a Backup Generator

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GENERATOR FUELS

Generators run on a wide variety of fuels, including gasoline, diesel, biodiesel, natural gas, propane and—in the case of some fuel cells—hydrogen. Most of the less-expensive models use gasoline. Your choice of fuel and type of generator should be determined by how often you will use the generator and the fuels available in your area.

If you live in a grid-connected house and power failures are infrequent, a gasoline-fueled generator may be best. The challenge is safely storing the gasoline—neither your house or your garage are considered safe because of the fire hazard. A small, fireproof tool shed in the back yard is probably the best strategy. Gasoline has an average shelf life of about six months, so refresh your supply regularly. How much fuel to store, whether gasoline, diesel or biodiesel, depends on the size of your generator—store a useful amount, but not so much that you are constantly replacing large quantities.

If you already have natural gas service to your house, or if propane is readily available in your area, consider a natural gas- or propane-fueled generator. They tend to last longer and burn cleaner than their gasoline counterparts, though they still are powered by fossil fuels. Recently, more people are opting to use natural gas: "The most popular models in the 10- to 12kilowatt range these days are natural gas, followed by propane," says Jim Flowers, director of marketing—residential products at Cummins Power/Onan Generators in Minneapolis, Minnesota.

If your electrical loads are fairly heavy and you live in an area where blackouts are frequent, consider a generator that runs on diesel or biodiesel fuel. Diesel-powered generators are more powerful and generally last longer than gasoline units, but they tend to be more difficult to start in cold weather. This is especially true in northern regions where winters can be brutally cold and utility lines tend to ice over—and come down—with regularity. Keep in mind that diesel fuel has a shelf life of about a year.

Biodiesel, a greener alternative, is made from vegetable oil or recycled restaurant cooking oils. It produces significantly less emissions, is safer to store and has better lubricating properties than petroleum-based diesel. Numerous businesses and municipalities, and some homeowners, use biodiesel fuel or biodiesel blends (a mixture of diesel and biodiesel) to power their diesel generators or furnaces.

In cold weather, full-strength biodiesel (B100) will gel, so it needs to be stored above 32 degrees. Lower percentage biodiesel blends (B20 or less) aren't as prone to freezing. Biodiesel's shelf life is similar to that of gasoline—about six months. Before you use biodiesel, ask your generator's manufacturer if your engine contains any natural or butyl rubber components that could be damaged by biodiesel; generally, diesel generators manufactured after 1993 do not have these parts. Also, make sure using biodiesel will not void your generator's warranty.

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