PACIFIC NORTHWEST NATIONAL LABORATORY
Adding Batteries to Hydropower Facilities Could Increase Dam Lifespan, Potential Revenue

In its current form, the nation's electric grid largely doesn't store energy. The vast majority of electricity generated by fossil fuels, hydropower, and other sources flows into the grid and is immediately used by consumers. But as battery energy storage becomes cheaper and more powerful, researchers have been investigating new ways to use it to support the power grid. 

Recently, a team led by the Department of Energy's (DOE's) Pacific Northwest National Laboratory (PNNL) found that pairing batteries with hydropower can support the grid by both extending the lifespan of hydropower equipment and creating new avenues for hydropower operators to earn revenue. It also has the potential to improve environmental flows downstream of facilities.

"Hydropower has traditionally acted as the battery of the grid, with water stored in reservoirs ready to spin turbines when needed," said Vishvas Chalishazar, a senior power systems research engineer at PNNL. "But now our grid battery' has the opportunity to have batteries of its own." 

Chalishazar and his colleagues modeled the operation of a real hydropower plant paired, hypothetically, with a 60-megawatt, 2-hour battery system. The researchers found that the added battery could help the hydropower plant generate $6 million more in revenue every year while reducing wear and tear on its turbines.

"With battery energy storage systems costing in the tens of millions, dam operators would recoup their investment in less than a decade," Chalishazar said. 

Converting rushing water to energy

The researchers looked at a specific problem dam operators deal with when hydropower isn't being tapped for grid services, and how adding a battery could help.

When hydropower operators want to generate electricity, they divert water to flow through the dam's powerhouse, which spins massive turbines. Those turbines, in turn, spin the generators and produce electricity.

But hydropower isn't needed all the time. Although hydropower operators can easily stop and start turbines, repeated stops and starts wear down a turbine's mechanical parts. Moreover, repeated stop/start cycles can lead to hundreds of thousands of dollars of operating costs and production loss.

To keep the turbines spinning without generating electricity, dam operators employ a process called "synchronous condensing." Using electricity, compressed air is injected through the turbines to keep them spinning and synchronized with the grid frequency. That way, when the grid does need hydropower, operators don't have to start the turbines spinning from scratch. Demand for electricity can change in an instant, so it's imperative for dam operators to start or stop generating as quickly as possible, Chalishazar said.

But sometimes, physical conditions of the dam's surroundings bar operators from synchronous condensing. If the tailwater or the water on the downstream side of the dam is too high, air injection into the turbines can cause a dangerously high-pressure environment and lead to equipment damage. 

In these rare cases, hydropower operators must shut a turbine down completely until electricity is needed once again. It takes some time for a turbine to restart spinning and synchronize with the grid, so operators end up missing out on opportunities to contribute electricity to the grid and earn revenue.

Economic benefits of energy storage

To investigate the economic benefits of pairing batteries with hydropower, the researchers teamed up with Ameren, the owner and operator of Bagnell dam in Missouri. The half-mile long dam stretches across the Osage River, creating the Lake of the Ozarks. With eight hydropower turbines, the facility can generate 240 MW of electricity at any given time, powering 42,000 homes with more than 500 million kilowatt-hours every year. 

Using real-life operation data for past years from the dam, the researchers created a model to investigate how adding batteries would affect operations and revenue. 

In their models, the researchers added a 2-hour, 60 MW battery system and optimally paired its operations to that of the dam. In times when hydropower isn't needed on the grid, the dam operators would not have to stop the turbines. They could keep water flowing through and spinning the turbines to generate energy, which then would be stored in the batteries. Once the batteries are fully recharged, the operators could then condense the units to still avoid a stop. When operators don't have to stop a unit, they can focus instead on responding to quickly changing power needs thus earning more revenue.

Ultimately, the researchers found that with the battery, the number of stop/start cycles would drop to below just five times per turbine per year. In contrast, in a normal year without batteries, Bagnell dam operators stop and start each turbine 201 times, with each cycle costing them approximately $500. This equates to approximately $100,000 of savings annually.

Raising revenue with increased flexibility 

Incorporating a battery also opens new avenues for dam operators to participate in evolving energy markets. Every time someone turns up their air conditioning on a hot day, that demand needs to be met in real time. Energy demand will also rise as more communities add data centers. 

And while hydropower can be ramped up and down relatively quickly (by diverting water to turbines or stopping the turbines altogether), supporting the minute-by-minute changes required by today's variable energy demands causes more wear and tear on the machinery. With energy in a battery that can be dispatched almost instantaneously, the potential for hydropower dams changes immensely. 

"Adding a battery enables these large, heavy machines to respond at a timescale that they weren't built to respond at," Chalishazar said.

The researchers found that because their model battery-supplemented dam could participate in more variable energy markets, it increased revenue by approximately $6 million annually. 

More analyses to come

Keeping the turbines running constantly provides an additional benefit, the researchers note. Repeated turbine stops and starts create a choppy environment in the river, making it harder for fish to pass through dams. With the turbines constantly spinning, smoother water allows for easier fish passage. 

Chalishazar and the team are now considering more real-life factors that dam operators might consider when thinking about incorporating battery energy storage. They've partnered with two more utilities: Grant Public Utility District and Energy Northwest in Washington State. For both utilities, the PNNL team will analyze how adding energy storage to hydropower facilities in their regions affects operations and revenue. 

Grant PUD operates many hydropower facilities along the Columbia River, and the PNNL team will focus on two of their facilities one that has a reservoir behind it and one located downstream that's known as a "run-of-the-river" facility, which has a very limited amount of water stored behind it.

For Energy Northwest, the team will look at a small, one-turbine hydropower facility located between Packwood Lake and the Cowlitz River.

In both projects, the team will also look at how adding energy storage to those facilities can support the durability of their local grids.

This work was funded by DOE's Water Power Technologies Office.