There's treasure in trash

What is the role of landfill gas in Green Power Switch?

Landfill gas is a relatively inexpensive resource that can help lower the cost of green power when combined with solar and wind energy.  As TVA's Green Power Switch gets under way, electricity from landfill gas will provide the largest proportion of its power.  That amount will decrease over time as wind and solar energy grow.

What is landfill gas and how is electricity generated from it?

Landfill gas, which consists mainly of methane and carbon dioxide, is produced when organic wastes in landfill sites decay.  Landfills over a certain size are required to flare, or burn, the gas in order to reduce the hazard of gas build-up.  Although landfill gas is primarily a pollutant that needs control, the methane it contains makes it valuable as fuel to power an electric generator.   Landfill gas was first used as a fuel in the U.S. during the late 1970s.   Since then, the technology required for its collection and use has developed steadily.  This method of producing renewable energy is now regarded as one of the most mature and successful in the field of green power.

Does burning landfill gas have other benefits?

If released directly to the atmosphere, methane is a potent greenhouse gas.  In fact, its global-warming potential is some 21 times greater than that of carbon dioxide.  Landfill gas can be flared (the simplest option), but using it to generate energy encourages more efficient collection and thereby reduces emissions into the atmosphere.  For this reason, energy recovery from landfill methane, where economically viable is of considerable benefit to the environment.   Besides reducing global warming, it lessens the use of conventional fuels and reduces regional and local pollution.

How much energy can a landfill produce?

It depends on the size and age of the landfill, but production tends to range from 3 to 8 megawatts.  Generators at landfill-gas sites are very reliable and operate almost year-round with little downtime.  So a 6-megawatt plant would produce approximately 47 million kilowatt-hours per year enough to supply about 3,200 homes.

How long will a landfill continue to produce gas?

Again, the answer depends on the landfill's age and size.   Although gas is produced once anaerobic conditions are established within the landfill, it may be several years before the level of production is sufficient to fuel an electricity generator.  Later, as the site ages, gas production (as well as the quality of the gas) declines to a point at which power generation is no longer economical.   In the case of a typical well-engineered and well-operated landfill, the expected period of gas production may be as long as 50 to 100 years, but power production may be economically feasible for only 10 to 15 years.

Does using landfill gas to produce electricity encourage a throwaway society?

The part landfill gas plays in energy generation will decline over time as more and more waste is reduced, reused, or recycled instead of being added to landfills.  As waste pretreatment becomes more widespread, the biodegradable content of landfill wastes will also drop.  Such changes in waste management, combined with environmental pressures to reduce reliance on landfilling as a disposal method, will eventually lead to a decrease in the use of landfill gas as an energy resource.

How does the cost of landfill gas energy compare to that of traditional electricity?

The technology to use landfill gas to power generators and produce electricity is nearly 30 years old.  Consequently, the generation costs are significantly lower than those of other forms of green power.  But landfill gas electricity is still somewhat more expensive than that produced by common sources like coal.  A typical coal-fired generating unit currently produces electricity for a little more that a penny per kilowatt-hour.  The cost of producing electricity using landfill gas ranges between three and four and a half cents per kilowatt-hour.