Closed-loop pumped-storage hydropower

An example from the U.S. Department of Energy of a closed-loop pumped-storage hydropower system similar to one that the Rocklin-based company Trane Technologies wants to deploy in Tuolumne County, which would include a 50-foot-tall roofed water tank on top of Bald Mountain, with pipelines down the slope and two roofed tanks at the bottom designed to create hydropower using gravity and to pump water back up slope using solar-photovoltaic cells.

The Tuolumne County Board of Supervisors voted 3-2 a week ago to bet on new technology and move forward on a $147,000 commitment to a closed-loop-pumped-hydropower research project with the Rocklin-based company Trane Technologies.

The project — if completed as planned — would result in a 50-foot-tall roofed tank that would be 320 feet across and could hold up to 35 million gallons of water on top of Bald Mountain, with pipelines down the slope and two roofed tanks at the bottom designed to create hydropower using gravity and to pump water back up slope using solar-photovoltaic cells.

It’s supposed to be a way to harness gravity to create hydropower and generate revenue, while using solar power to push the water back up the hill. Even the people selling the idea are challenged when it comes to explaining and talking about the concept, which is also called a “firemain linked auxiliary supply hydraulic energy storage system.”

Regardless of its complexity, the majority of the board voted on Nov. 9 to move forward. County supervisors Ryan Campbell, Anaiah Kirk, and Jaron Brandon voted in favor, while David Goldemberg and Kathleen Haff were opposed.

The move by the board was a step in a process that began back in June when the board signed a letter of agreement with Trane that authorized Trane to conduct a preliminary review on a speculative basis to find projects of interest and benefit to the county. 

Cole Przybyla, the county’s innovation and business assistance director, brought the Trane option to the county board at the board’s request.

County staff call the plan a microgrid and revenue-generating project. Up until last Tuesday, Trane was bearing all the costs for the project. Now the county is on the hook for $147,000 if the county decides to back out.

The project is a proposal to create a system that combines “enormous new water storage on hills” with solar photovoltaic generation to produce benefits including: water tanks and pipelines equipped with hydro turbines to create and store energy, as well as to store water for firefighting; energy revenues up to $250,000 a year over 40 years for the county; shared risk for the county with private investors; and creation of what energy wonks call a microgrid for part of the county that would keep communities and critical infrastructure energized during power outages and shutoffs.

Przybyla favored the Trane project and emphasized in his report to the board that the letter of commitment with a $147,000 price tag “relates to the twin threats of catastrophic wildfires and regular loss of electricity.”

“Both threats are huge impediments to economic development in Tuolumne County and even when the events do not occur, the threat of them occurring is a constant drag on the lives and livelihood of all of those who live in the communities where these threats are present,” Przybyla said in his report.

Michael Day described himself as “the advanced energy development lead” for Trane Comprehensive Solutions when he introduced himself to the board.

Goldemberg and Haff both balked at approving the $147,000 commitment because they wanted to see more sales pitches to the public from Trane, so that they as elected leaders could observe and gauge public input on the overall scope and scale of the proposed project.

Day said the tank on top of Bald Mountain would be “about the size of a high school football stadium” and visible from space.

Przybyla told the board the Trane project is viable in terms of the first steps, while the letter of commitment would be the next step. He also said he was looking for new technologies to benefit the county, and Trane signed up to do initial research while bearing the costs of exploring individual projects and their viability.

“Our job in this first phase was to go out and find several options,” Day said. “We did find multiple options. This is one. The risk to the county going forward is the county could face liquidated damages for a portion of expenses. If we move forward and something comes up, like a new endangered species, or if the project collapses for any reason, there’s inflation and interest rate risk, or problems with PG&E infrastructure, if any of those things come along and kill the project, that risk is on Trane.”

In the next predevelopment phase, the county’s breakup fee paid to Trane would be $147,000. That backout fee or breakup fee would increase to up to half a million dollars if the county cuts bait in a subsequent phase, Day said.

“I have seen this whole project, but for the public’s benefit you’re putting all the questions before explaining what the project is,” Haff said. “I’d appreciate it if you would explain what the project is.”

Brandon asked Day who would own the project plans, to which Day replied that they would belong to Trane. 

“We put the money up, and we own that, and as part of this, we’re asking for exclusivity,” he said.

Trane has already spent $50,000 to $75,000 on preliminary engineering studies, endangered species identification, hydraulics, soils analysis, studying the fair market value of electricity, and other parts of their screening process, Day said.

The development phase of the project could cost $1.5 million to $3 million, and the county’s phase three commitment has not been determined yet, Day said.

“I gotta see what the county would be obligated with,” Goldemberg said.

Trane can’t tell the board yet what a phase three termination fee would be until Trane gets a little bit further into phase two, Day said. A phase three breakup fee could be in excess of a half-million dollars, Day added.

Explaining the basics of the project, Day said, “The idea is we put a large tank on Bald Mountain, and two smaller tanks at the bottom of the hill, water flows downhill to two tanks. It’s an enclosed system with roofed tanks and limited evaporation. Photovoltaic cells power off the sun and push water up the hill.”

Closed-loop-pumped-hydropower may be complicated to explain, but it is common across the U.S., Day said.

“We’re going to put a reservoir at the top of the hill and another reservoir at the bottom of the hill,” Day said. “The benefits include there’s no dam on a waterway. Instead of reservoirs we use roofed tanks. Less evaporation.”

Haff emphasized again she believes it’s an exciting project, but she wanted to address the “big elephant in the room” — a lack of public outreach about the proposal up to this point.

“You’re asking for a big commitment and there’s been no public outreach,” she said. “This is something that is going to sit above Sonora, and I don’t want to find out there’s a huge public outcry... I sincerely believe we need to get the public’s buy-in before we can vote on this.”

Goldemberg agreed and said he has concerns about how much fire protection might be provided or not by the Trane project.

Ray Longeway, 37, a Hetch Hetchy senior power generator technician at Moccasin, came up during public comment and said, “This is definitely where the industry is going, energy storage and demand response. The only question I have is how is this project sized? For example, why don’t we build this twice as big or half as big?”

Day answered, “There is a sweet spot, and the smaller you get the more it can cost. This is the sweet spot.”

Campbell summarized why he likes the Trane proposal so far and why he believes it’s worth the risk.

“What natural resources do we have here?” he asked. “We don’t have natural gas. We don’t have oil. We do have a lot of hills, and if we’re looking say 20 years in the past, if we had built some electrical regeneration 20 years ago, would we want to go back in time, having built that? My answer is yes. Electricity is getting more expensive, more things are going electric, and it’s an obvious need in the future. If we’re able to take a bit of a risk and be one of the front runners for this, I think it would put our county in a really good position.”

According to a memo to the board from Przybyla, Trane is now through an initial screening and has been invited to apply on Dec. 1 for a federal grant to subsidize deployment of the tank-pipelines-hydropower-water storage project. 

The county’s letter of commitment is necessary to move forward on the federal grant application.

Contact Guy McCarthy at or 770-0405. Follow him on Twitter at @GuyMcCarthy.

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