Wind and solar power get most of the attention when it comes to renewable energy. But Duke Energy has another alternative - a type of hydroelectric power called pumped storage. WFAE reporter David Boraks visited Bad Creek hydroelectric station in upstate South Carolina, where Duke is getting ready to invest millions of dollars in upgrades.
We're in a giant cave hollowed out of a mountain about 600 feet below Lake Jocassee, in northwest South Carolina. There’s a loud hum from a large turbine that has two functions: It's both a pump and an electrical generator.
“There's four units all arranged in a line … you're beside unit number four, so you go three-two-one," says Preston Pierce, who oversees Duke's western Carolinas hydro plants, including Bad Creek. "What you're seeing right here, one of the pieces of equipment on this level are these big air handling units.”
Think of this as a kind of natural energy storage. When Duke has extra power, like at night during the summer, it pumps water 1,200 feet up into Bad Creek reservoir. When electricity demand goes up, like when we all turn up the A/C on hot summer afternoons, Duke lets that water flow back down through the turbines to generate power.
“This is a very large battery in that sense,” says Duke spokesman Tim Pettit. “It's a way of storing energy on a large scale.”
The plant is a bit of a curiosity. Duke has 33 hydroelectric plants in the Carolinas, but just two like this one. The other pumped storage plant is here, too, at the other end of Lake Jocassee.
The billion-dollar project is named for a very small creek that once flowed into Lake Jocassee, near Salem, S.C. When the dam was finished and the plant opened in 1991, it became a 318-acre reservoir. It stores enough water to produce up to 1200 megawatts of electricity – which can power about 850,000 homes.
Duke is getting ready to spend nearly $200 million to replace the turbines at Bad Creek. That will add 200 megawatts of generating capacity, so the plant can power up to a million homes. The work begins in 2018:
“The big driver behind the upgrade is the fact that the station's been in operation for 25 years and it's time for us to go through and do what we call a major overhaul on the units themselves,” Pierce says.
Workers will take the turbines apart and rebuild them - one a year over four years.
The two pump storage plants - Jocasee and Bad Creek - generate a little under 4 percent of Duke's total electricity every year. In fact, they actually end up using more power than they generate, because it takes energy to pump all that water up into the reservoir. That power comes mainly from Duke’s nuclear, coal and gas fired plants.
But, it’s power available on demand – when power needs surge or Duke’s main “base-load” plants go down.
“Electricity has to be produced the instant customers need it,” Pettit says.
Bad Creek and Jocassee can start generating with the flip of a switch – which starts the water and electricity flowing. Nuclear, coal and gas-fired plants - which provide most of Duke's electricity - take hours to start up.
As utilities use more solar and wind, hydro power – and pumped storage in particular – are becoming more important part of the energy mix, according to Megan Nesbitt of the Electric Power Research Institute.
“So we're seeing the solar and wind, which we refer to it as intermittent generation … the wind blows when it blows, and not necessarily when energy demands are highest. So pump storage plays a huge role in this in absorbing that excess energy from the grid and storing it for later,” she says.
Duke's investment at Bad Creek is part of a global trend. In China and Japan and Europe, utilities are building dozens of new pump storage plants. U.S. utilities are mainly investing in upgrades at existing plants, like Bad Creek.
It all comes back to that idea of a reservoir as an energy storage pond. Right now, Nesbitt says, pump storage plants are the biggest batteries we have.
Duke Energy web page on pumped storage hydro plants, Duke-Energy.com
Map of all Duke Energy plants