Natural gas serves an increasingly important role in TVA’s mission to provide clean, reliable energy to the people and businesses of the Tennessee Valley. Natural gas produces far lower levels of emissions than coal, helping TVA to improve air quality while meeting the growing demand for power in our region.
While these plants can cost more to operate than other power sources, their fast start times and flexibility make them a vital element in our power mix, helping us:
- Quickly meet demand during peak periods such as hot summer afternoons or cold winter nights. Many units can reach full power in as little as 17 minutes and are used only during peak demand.
- Reduce the need to purchase higher-priced power from external sources during peak periods.
- Control costs while reliably meeting energy demands because of their ability to quickly start up and shut down as needed.
Our Changing Portfolio
TVA operates 101 natural gas- and fuel oil-fired generators at 17 sites—nine in Tennessee, five in Mississippi, one in Alabama and two in Kentucky. Together, they have a generation capacity of over 12,000 megawatts—enough to about 7 million homes.
TVA’s Integrated Resource Plan suggests that natural gas will play an important role in TVA’s future generation portfolio to ensure reliability and grid stability. Already, it has changed the face of TVA: In 2017, natural gas accounted for 20 percent of our generation portfolio, as compared to 10 percent in 2007. Looking ahead to 2020, natural gas will account for 23 percent of our total generation. Meanwhile, coal-fired generation will drop to only 22 percent; by contrast, coal made up 58 percent of total generation in 2007.
About Gas Plants
There are two types of gas generators: combustion turbines and combined cycle units.
Combustion turbines work like jet engines to power our generators. They draw in air, compress it, mix it with fuel and ignite it. The hot combustion gases then expand through turbine blades connected to a generator to produce electricity. Find out more about how combustion turbines work.
At some sites, we use combined cycle units that generate 50 percent more power from the same amount of fuel. These units initially operate the same as traditional combustion turbines. But they capture the exhaust heat from the gas turbines, convert it to steam, and use it to drive steam turbines to produce additional power. Find out more about how a combined cycle plant works.
Air Quality Improvements
By replacing older coal-fired plants with natural gas-fired generators, we work to improve air quality in the Tennessee Valley. Compared to coal, natural gas plants dramatically reduce emissions, including:
- Sulfur dioxide by nearly 100 percent
- Nitrogen oxide by more than 90 percent
- Carbon by more than 60 percent
The location provides additional benefits as well. The new plant recycles water from a nearby wastewater treatment plant rather than drawing water from a lake. The wastewater treatment plant also captures methane gas that we can then use along with natural gas at the new plant to create additional energy. Read more about our efforts in Memphis.
While natural gas and low-sulfur fuel oil are far cleaner than coal, we still take significant strides to reduce emissions as much as possible.
We equip many of our plants with state-of-the-art emission control technologies that reduce harmful nitrogen oxide emissions 10 to 20 percent below the levels emitted 30 years ago.
A few plants have implemented additional measures as part of the $5.9 billion TVA has invested in reducing air emissions since the 1970s. A selective catalytic reduction system at the Caledonia plant and a heat recovery steam generator at Southaven, for example, each reduce nitrogen oxide emissions by 60 percent compared to similar plants.