by Jill Cliburn
At this turn of the year, a lot of us who work in renewable energy feel a nice sense of accomplishment, and also the press of a challenge to follow through on great expectations. The list of states that are aiming for 100 percent clean energy by 2050 has grown to nine, plus the District of Columbia and Puerto Rico, and more than 150 local governments nationwide have issued similar goals. We love the vote of confidence, but now we—and I include in our circle researchers, local utility leaders, upstream utility counterparts, engineers, program designers, policy wonks, citizen-advocates and business folks--we all have to move fast and think big.
Energy storage was always the missing puzzle piece. The growth of affordable battery storage is changing that—but we also need to look beyond batteries. The list of viable alternatives is growing; we could not list them all. But we decided to cast our eye on a sleeping giant: pumped-hydro energy storage, reconfigured for communities in nearly all geographies. Read on; you might be surprised.
Pumped hydro relies on moving water between an upper reservoir and another reservoir at a lower elevation. When electricity is needed—even in a quick response mode—it may be generated by releasing the stored water through turbines in an operation that is similar to conventional hydropower. Then, during periods of low demand, the upper reservoir is recharged by using lower-cost electricity from the grid or from co-located renewables to pump the water back up. The technology is well-established and used by (among others) our nation’s federal hydropower providers. Altogether, the U.S. has about 22 GW of pumped hydro storage today. According to Mark Gabriel, Administrator of the Western Area Power Administration, “It’s the best storage you can get.”
However, it may be no surprise that most existing pumped storage projects are big—averaging over 600 MW—and that they have not always met high environmental standards. The question is whether pumped hydro could be cost-effective on a much smaller scale, using modular designs, that would be acceptable and directly beneficial to the communities nearby.
According to Timmons, pumped hydro storage came in cheaper than today’s battery storage costs, especially for longer duration operations. (Timmons modeled his economics using 2018 Lazard data.) The surprise was that the pumped hydro system could be accomplished on a relatively small scale. Modeling targeted a reservoir that also provides drinking water and irrigation for the island’s 1.2 million residents. The cost—especially for longer-duration storage—beat batteries, even considering likely battery cost reductions. Timmons believes that relatively small-scale pumped hydro can help balance the costs and more importantly, the environmental impacts of lithium-ion and other battery products. Where reservoir evaporation might be a an issue, floating PV could be developed to serve a dual, high-value purpose.
We checked the facts and found reasons for cautious optimism. Most small pumped hydro storage projects take a hit on economies of scale, but the designs and the dollars are improving. In 2017, U.S. DOE funded nine projects, including one with Shell that is just 5 MW. The DOE’s Hydropower Vision summarizes a range of new designs, including smaller scale pumped hydro projects.
We also found a recent study from researchers in Australia, employing a mapping tool that identified more than a half-million suitable sites for pumped hydro projects worldwide. Altogether, they would provide more than 22 million GWH of energy storage capacity. An article in PV Magazine quoted one of the authors, saying, “Only a small fraction of (these sites) would be needed to support a 100% renewable global electricity system. We identified so many potential sites that much less than the best 1% will be required.” The team’s approach included identifying sites where dry gullies could be adapted to create pumped hydro stations with less environmental impact than the classic approach, which focuses on damming river ecosystems. The team published a smaller study in 2017, focusing on Australia before going global.
Most likely, even the 1% target for developing potential pumped hydro sites will prove difficult, but from Timmons’ view, it is worth thinking about stored hydropower on the community scale—even using even municipal water reservoirs or charging new systems, as the Aussies envision. According to Timmons, it is entirely possible to see more projects that deploy storage in a front-line integrated-DER strategy, which could provide renewables integration and greater rewards close to home.
We are still betting on batteries for the near term, but looking ahead, we would love to see alternative storage solutions on future SEPA “Top 10” lists, which recognize the top providers of annual watt-hours of storage, per customer.
In parting, Timmons reminded me of the professors who were my mentors years ago, working in relative isolation but thinking freely and a bit wildly. Not all, but most of their renewable-energy innovations eventually came true. And that inspires my holiday wish: keep fueling our future with bold thinking. And here’s to abundant energy for 2020 and the decade beyond.