Natural Gas Fleet Serves as the Grid’s Secret Weapon

The strength of TVA’s diverse portfolio – nuclear, hydro, coal, natural gas and renewable energy – enables the Tennessee Valley Authority to better meet changing conditions such as periods of high power demand.

It involves a successful combination of baseload generation – where assets, such as nuclear units, run 24/7 to provide baseload power – and the quiet power of reserve generation, which are purposely offline units, such as natural gas, that lie in wait, ready to supply power at a moment’s notice.

“A combustion turbine plant responds immediately in an emergency or during high peak demands by turning on available units as needed to provide instant power,” Gallatin Combustion Turbine Plant manager Corey Terry said.  “This keeps uninterrupted power flowing for residents, and when it’s no longer needed, we shut down the units and wait for the next opportunity to serve the region.” 

This is the power of reserve generation.

As TVA looks toward the future of its energy portfolio, natural gas provides flexibility that enables TVA to provide affordable, resilient, reliable and clean energy. The ability to turn generation on and off as needed supports the integration of renewables, such as solar, because natural gas generation can keep power running when the sun isn’t shining.

Ready Mode

At Gallatin Combustion Turbine Plant, located northeast of Nashville, there are eight units available to provide up to 642 megawatts – enough to power 375,570 homes.

“TVA’s investing $100 million in this plant to upgrade exciters, transformer switchgears and a variety of other components to keep these units ready to run,” Terry said. “Much like the challenges of keeping a car up and running if it often sits, we must address the same challenges with these units.”

Periodically, the site will do a test run of the units to ensure they remain available and ready to run. However, their value increases when a unit is offline.

“A combustion turbine natural gas plant is different than other generation because our ideal state is offline but ready to run. This reduces carbon output and saves TVA, and therefore ratepayers, money by having reserve megawatts available so we don’t have to pay for expensive market rate power to fill the gaps or pay the cost of fuel for running the unit,” Terry said.

In contrast, the combined cycle natural gas fleet best serves the region when online.

This makes up more than half of TVA’s natural gas fleet. It serves as a bridge between the baseload power of nuclear and the offline combustion turbine plants by filling the gaps between everyday needs and before power demand rises enough to need reserve generation.

As TVA maintains a focus on delivering a secure energy future for the region, it will depend on its natural gas fleet, TVA Gas Operations general manager Eric Grau said.

“Our combined cycle plants will carry the day-to-day changes in energy demand while our combustion turbines – including our aeroderivatives currently under construction at Johnsonville – stand ready to handle high demand and to provide a firm and dispatchable backstop for our increasing renewable portfolio,” he said.