Wintertime Efficiency

Here’s why winter’s colder temperatures make energy production at nuclear and fossil plants more efficient. 

Old Man Winter’s frigid temperatures might bring life to a grinding halt for some. But for the Tennessee Valley Authority, cold days make ideal conditions to generate efficient, low-cost electricity.

“You would think the hot summer would be a perfect time to make steam for electricity,” says D.J. Allen, operations shift manager at Watts Bar Nuclear Plant “It’s the winter where we see the most efficiency because of the colder river water we use as a cooling medium.”

Allen explains that steam is a key ingredient when making electricity at nuclear and fossil plants. TVA turns ultra-pure water into super-hot, high-pressure steam that turns massive turbines. The turbines spin generators to make electricity.

“Heat is the blessing and curse at a power plant,” Allen says. “To run a plant at maximum efficiency you have to generate a lot of heat and then you have to remove it quickly so the steam cycle can start all over again.”

illustration of steam cycle

TVA turns ultra-pure water into super-hot, high-pressure steam that turns massive turbines. The turbines spin generators to make electricity.

According to Allen, removing excess heat is easier in the winter because cooling water from the river could be as low as 45 degrees. In the summer, river water temperatures can rise above 80 degrees.  

“Summertime is extremely hard on equipment,” Allen says. “A generating unit might be rated for 500 megawatts, but restricted to only 300 megawatts in the summer because we don’t have the cooling capability that is provided during the winter months.”

Try It at Home

TVA power plants are like supercharged tea kettles that boil water. They need extreme heat to make purified steam, and thousands of gallons of river water for cooling.

Allen explains you can safely replicate what happens in a power plant’s steam cycle in your kitchen—with adult supervision of course.

Step 1: Boil a pot of water on the stovetop. This represents the heat source (coal, natural gas or nuclear) and the ultra-pure, high-pressure steam that would rotate the turbo generator.

Step 2: Carefully hold a glass of ice water above the pot with tongs, long sleeves and oven mitts. The glass acts as the river water moving through the power plant’s giant condenser that turns steam back into water so it can be heated again. Notice how quickly condensation forms on the outside of the cold glass and then drips back into the pot of boiling water—completing the cycle so it can be turned back into steam.

Step 3: Carefully hold a glass of warm water above the pot and repeat the process. Allen says you’ll see that the warm water does not turn the steam back into water as fast as the ice water.

“It’s that simple to see why winter is the best time to generate power,” says Allen. “The colder the cooling water is, the easier it is to deliver more electricity to you at the lowest possible cost.”