Generators convert mechanical energy into electrical energy. In most home, commercial, portable, and vehicle generators, an internal combustion engine that runs on liquid or gaseous fuel provides the mechanical energy that turns the generating unit.
Fuel choices for generator engines are somewhat limited and the fuel chosen can impact how much energy the machine is capable of producing. Fuel freshness can also affect performance, and keeping enough fuel on hand is another issue that anyone operating a generator must address when making choices.
Standby generators start and run automatically without human intervention. They are permanently installed for use during a power outage and for regular exercise cycles. An uninterrupted supply of fuel is necessary, making natural gas and LP gas the most common fuel for standby generators. Generators large enough to supply hospitals and other large institutions may use diesel fuel.
Portable generators require manual fueling and starting. They are dependent on their operators to keep them running with a continuous supply of fresh fuel, and for their exercise cycles. Gasoline is the most common fuel, but LP gas and diesel also fuel some portables.
Marine and RV generators usually draw on the fuel type the vehicle uses for their own supply, with the exception of trailered RVs that commonly power their generators with LP gas.
Natural gas is a clean burning fuel often used for heating homes and businesses. It is delivered through a network of natural gas lines that supply communities and the customers that live and operate within those communities. Typically, it is not available to rural areas or where earthquakes make interruption of service likely. Of the four most common fuels, natural gas carries the least amount of energy. In many areas, it is the most convenient and easiest to use for a standby generator because it offers a continuous and interrupted supply of fuel.
LP Gas or Propane
Liquefied Petroleum Gas, often called propane, is another clean burning fuel in homes, is the second fuel of choice for a standby generator, and has slightly more energy than natural gas. Homeowners and businesses store LP gas for use in large tanks ranging from 250 to 1000 gallons. The tank size represents the volume of liquid it may hold. However, space is needed for the liquid fuel to evaporate into the gas that appliances and generators use, so the tanks are never filled completely full. An LP gas supplier would only fill a 500 gallon tank with about 400 gallons of fuel to leave space in the tank for 100 gallons of evaporated gas. The LP tank may require periodic filling during an extended power outage.
Gasoline is a readily available fuel and is commonly used for automobile engines. It stores about 20 percent more energy than a similar amount of natural gas. Safe storage of gasoline is more difficult than LP gas and many communities limit quantities of stored gasoline. It is a good fuel choice for portable, RV, and marine generators, but long-term storage of the fuel is troublesome. Stabilizers can extend the useful life from a few months to a year or more, but rotation of supplies is still required. In a widespread power outage, buying gasoline to power a portable generator is often difficult.
Diesel is another commonly available fuel, but use in generators is usually restricted to very large portables, RV generators, and marine generators. Diesel engines rely on the heat generated by compression to ignite the fuel, which makes it incompatible with engines that rely on spark plug ignition. Diesel engines cannot be easily switched or converted to other fuel types. Stored diesel has a longer shelf life than gasoline, but will absorb moisture from the air which can render it useless for use as a fuel. Of the four most common generator fuel types, it has the most energy.
Generator manufacturers design and build generator engines to run on one or more types of fuel. LP gas and natural gas are similar, so it is fairly easy to compromise and build an engine that will run on both, and some can also run on gasoline.