CleanTech: Sacto Preps Pumped

By Published On: May 15, 2014

For the past several months, the Sacramento Municipal Utility District has been deeply—deeply being the operative concept—involved in a project that adds a whole new dimension to the concept of recycling water. The muni’s been studying the feasibility of a proposed pumped-storage hydroelectricity project called Iowa Hill. It would be built about 50 miles east of Sacramento. Pumped-storage hydroelectricity is used for electricity storage and load balancing. According to Scott Flake, the muni’s director of power generation and project development, three long bores have been drilled—two horizontal and one vertical—of between 1,500 feet and 2,000 feet in length. After drilling, pieces of rock core were pulled out for analysis to make sure the rock is strong enough to support the proposed structures. “We want to understand the geology,” Flake said. “This is primarily an underground construction project, so we want to understand the geology of the area very thoroughly.” “We did all that work and the results were favorable for the project,” he said. Next, the muni plans to conduct geotechnical investigations in October, Flake said, including boring another small tunnel. Under the pumped-storage concept, when electricity demand is high to cool homes and businesses on summer afternoons, water would be released from an upper reservoir and gravity would pull the water down to an underground cavern. Inside the cavern, the rushing water would spin turbines that create electricity. The water would then flow out of the cavern and into the lower reservoir. During the night, when generation at the muni’s wind farms is high and electricity demand is low, the underground turbines would run in reverse and pump water from the lower reservoir back up to the top of Iowa Hill. The cycle could be repeated using the same water over and over again, and Iowa Hill could potentially help manage renewable energy provided by both the wind and sun. The water being used and reused would come from Slab Creek Reservoir. The project would require a new off-stream reservoir to be built 1,200 feet above Slab Creek Reservoir, plus a new underground powerhouse and tunnels connecting the two reservoirs. Sacramento says the project, which would be located in El Dorado County near the town of Camino, would add 400 MW of generating capacity to its hydroelectric system. Although feasibility work only began last fall, the Iowa Hill project’s been well over a decade in the making. Since 2001, the muni began community outreach. In 2007, El Dorado County agencies, recreational advocates and other stakeholders participated in a collaborative process that led to a comprehensive agreement on how the public utility should operate its hydro system in the decades to come. Although an Environmental Impact Report was completed in 2008, the project didn’t get off the ground until last year due to uncertainty over cost and value. A geological investigation is next. After that comes the final design, then a cost estimate based on design, and lastly a proposal document for board approval. “We would try to get the proposal out for bidders in 2016,” Flake said. “And then we would look to award a contract in 2017, and then look at start of construction in 2018.” Construction’s expected to take about four-and-a-half years and is estimated to cost $700-800 million. The cost range is uncertain partly because SMUD doesn’t yet know the cost of some required transmission upgrades, Flake said. “As we get further along in the engineering, we’ll have a better cost estimate.” Helping out the muni’s bottom line was that in 2011 it received $5 million in Department of Energy grant funding for geotechnical evaluation and analysis. The use of pumped storage technology dates back to the 1890s in Europe. At present there are two such facilities in California—the Los Angeles Department of Water & Power’s 1,500 MW Castaic Power Plant and Pacific Gas & Electric’s 1,200 MW Helms Pumped Storage Plant near Fresno. Also currently in development are Eagle Mountain, a $2 billion, 1,300 MW development near Joshua Tree that received State Water Resources Control Board approval in July of 2013; and Swan Lake, a 600 MW, 837-acre project which is set to be located north of the California-Oregon border. Although in PacifiCorp territory, Swan Lake would have access to the California Independent System Operator’s grid.

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