Utility-scale batteries can revolutionize how we harness renewable power. Coupled with wind and solar, these batteries could increase the reliability of green energy by storing excess energy during times of high generation and low demand. Then, utilities can tap the stored energy when demand increases.
Hydropower accounts for 29% of renewable energy generated in the United States. Despite that, researchers have published few studies about the benefits of hydro-hybrids, hydropower plants that use utility-scale batteries. Renewable energy producers are interested in hydro-hybrids, but there's no clear understanding of the benefits or profitability.
"There's a lot of environmental constraints and procedures that go into building a new dam," said Venkat Durvasulu, a power systems engineer at Idaho National Laboratory (INL). "Hydropower is not growing as quickly as wind and solar, and most of the hydropower studies are about expanding existing infrastructure. We believe coupling battery storage with hydroelectric plants should be studied more because water is so important, and we want to use it sustainably. Adding batteries helps with that."
Durvasulu and his colleagues, with funding from the Department of Energy's Water Power Technologies Office, recently looked at the benefits of hydro-hybrids.
"Batteries offer all kinds of benefits like reduced cost of maintenance, increased production, and investment and production tax benefits," said Hill Balliet, a power systems engineer at INL and contributor to the paper.
Hydro-hybrids also offer a variety of advantages over wind and solar power, namely their predictability. Solar power operators have no control over how much sunlight their panels receive. On cloudy days, for example, solar panels can see up to a 70% decrease in output. In contrast, hydropower plant operators, especially ones with access to reservoirs, can control their outflow.
"With solar and wind, you're tied to the forecast, which isn't always predictable," Durvasulu said. "With hydropower, it's possible to calculate a few days out roughly how much water will be coming downstream, and hydropower owners can get a good idea of how much power they can generate."
The predictability of hydropower means the utility-scale batteries attached to them can make better use of the plant's interconnection headroom, increasing the profitability and grid benefit of hydro-hybrids.
Headroom is the difference between what a power plant produces versus what its connection to the grid is rated for. Operating a plant within headroom avoids costly interconnection upgrades and regulatory studies.
"Hydro-hybrids store excess power when headroom goes down and put more into the grid when it goes up," Balliet said. "Not only that but adding batteries can make relicensing much easier."
Another major advantage of hydro-hybrids is that they're able to restart a grid after a blackout.
"If you add a battery to a hydropower plant, you can start up from a blackout and supply power to critical services, like police, fire stations and hospitals, which isn't feasible with solar and wind," Balliet said.
Hydropower plant operators must consider the needs of everyone and everything downstream. This includes other hydropower plants; anyone that relies on the water for drinking, recreation or irrigation; indigenous populations; and local wildlife.
"Rivers are essential to life and are associated with the heritage of many indigenous populations," Durvasulu said. "Federal agencies need to ensure the river ecology is preserved. If not properly maintained, hydropower plants can affect the oxygen content and temperature of water downstream, which can contribute to ecological damage."
Managing these requirements and needs can be expensive for hydropower plant owners, accounting for an average of 5% to 10% percent of electricity costs. By adding utility-scale batteries, hydropower operators can make up for some of the lost revenue. When they can't fully use the river during peak demand, having batteries that charged during a low demand period means they can still supply power to the grid.
"Batteries add a level of flexibility that can help hydropower operators meet the needs of all the various groups that rely on water," Balliet said.
A major barrier to hydro-hybrid research is that existing models don't account for avoided costs, like reduced maintenance, wear and tear, power grid stability, voltage regulation, production tax credits, carbon credits, and more.
As part of the study, Durvasulu, Balliet and their colleagues developed Hydro + Storage Sizing, an online tool that gives users an estimate of how profitable different battery sizes might be, taking avoided costs into account.
"There are other untapped values and opportunities too," Balliet said, "more jobs, improved load-carrying capacity, lower operational and environmental costs, better water management, and greater profits."
Without this tool or others like it, hydropower hybridization decisions are likely to be one-off assessments, which will result in missed opportunities to increase the value of hydropower plants to owners, the grid, stakeholders and the environment.
"At the end of the day, it's about the ecology and management of water," Durvasulu said. "You have to make money to stay in business, but you have to balance that with all the other living things that rely on the water, and batteries help with that. We want to ignite that idea; it's important to think about those kinds of things."