The city of Aspen wants to add a second turbine and generator unit to its hydroelectric plant at the base of Ruedi Dam, which officials say will allow for more power generation during times of high and low flows.
Officials say an additional turbine, which is estimated to cost about $4.6 million, will restore the plant’s power production capacity to its originally intended 5 megawatts and allow the city to maintain its renewable energy goals. Since 2012, increased releases from Ruedi to benefit downstream endangered fish have meant that late summer and early fall flows are too high for the existing turbine to operate efficiently.
Adding another turbine requires amending Aspen’s license for the Ruedi facility with the Federal Energy Regulatory Commission. According to the city’s draft FERC application for an amendment posted on the Aspen Community Voice website, which officials say they plan on filing by the end of the month, the timing and amount of water released from Ruedi Reservoir has changed since the hydro project began operating in 1986. Power production has diminished in recent years to just 68% of what was originally intended.
“After 40 years of reservoir and hydroelectric operations, it is now clear that achieving power output (maximum capacity and energy values) that approximates the original level authorized under the license will require additional generation equipment,” the application reads.
The facility is most efficient at flows between 100 and 225 cfs. But summer and fall flows are often higher than this range and winter flows often lower. Aspen has no control over how much water is released from the reservoir, which is managed by the U.S. Bureau of Reclamation.
According to the city’s application, gross energy production has declined from an average of 18.5 million kilowatt hours annually from 1986 to 2004 to 15 million kWh over the last decade.
“The equipment is kind of mismatched for what’s going on with those releases,” said Phil Overeynder, utilities engineer for the city of Aspen. “So we’re losing all of that energy above 225 cfs. If we have an additional turbine, we’ll be able to hit the sweet spot for the releases and generate the full amount of energy when it’s available.”
Also, an error in the design of the powerplant introduces air into the water column, reducing the efficiency of the turbine. Because of this flawed design, the hydro plant can’t efficiently make power above about 225 cfs. The city looked at options to fix this problem, Overeynder said, including raising the floor of the building, but the least expensive solution is adding another turbine.
A new turbine would be rated for 1.2 megawatts of production and the original turbine would be downgraded to a 3.8 megawatt capacity, for a total of 5 megawatts — the same as the plant’s current rating, but split between two turbines. During periods of higher releases, about 230 cfs would be routed through the existing turbine and 70 cfs would be routed through the new turbine for about 92% efficiency.
The project would also upgrade the hydro plant so it can be operated remotely, and would let the city continue making hydropower with one turbine if the other one is down for maintenance. The total project cost including the new turbine would be around $8.6 million, according to Overeynder.
“The proposed second turbine at Ruedi, together with other planned actions, will enable Aspen to restore the balanced power supply, which will maintain grid reliability and resiliency while continuing to provide 100% renewable energy,” the application reads.
Fish flow
Releases out of Ruedi have changed since the hydro plant began operating, with the reservoir now one of the most important sources of water for the Colorado River Endangered Fish Recovery Program. The program, designed to get water into a chronically de-watered section of the Colorado River near Grand Junction known as the 15-mile reach, has about 15,000 acre-feet of water available most years in Ruedi. Entities that own water in Ruedi such as Garfield County, Caerus Energy, Grand Junction area water provider Ute Water and the Colorado River Water Conservation District have also in recent years leased their water to the recovery program to boost flows beyond the dedicated 15,000 acre-foot pool.
All of the recovery program’s releases are made in July through October, when streamflows naturally are reduced, but irrigation demands in the Grand Valley leave diminished river levels for endangered fish. According to numbers provided by recovery program staff, the Ruedi fish water releases increased from an average of 18,586 acre-feet in the time period from 1998 to 2012, to 20,460 acre-feet in the time period of 2013-2023.
“Ruedi is an essential piece of our ability to manage water for the endangered fish,” said Juile Stahli, director of the Upper Colorado Endangered Fish Recovery Program. “Ruedi has become really critical in helping us affect the ecology downstream.”
According to Tim Miller, a hydrologist with the U.S. Bureau of Reclamation who manages Ruedi, the current reservoir release pattern — higher flows in the late summer and lower flows in the winter — began after 2012 when the water in the reservoir was fully contracted. The owners of this contracted water (like those mentioned above) release it when they need it, and many lease it to the recovery program. Because more contract water is released from Ruedi, Miller said he has to make up that loss to the reservoir by releasing less water over the winter, resulting in low winter flows.
“I can tell you with absolute certainty that since Ruedi has been fully contracted we have released more water for fish augmentation than we did since the program started,” Miller said. “Because we’ve released more contract water, given an average fill, it’s going to take more water to fill the reservoir the next year. So my releases during the winter were lower to recover that.”
According to data from USBR, the average flow out of the reservoir from July to October before the endangered fish recovery program started from 1980 to 1997 was 180 cfs. The average release after the program began in 1998 has been 204 cfs. The number of days releases have exceeded 225 cfs has also been trending upward since the recovery program began.
Aspen’s 100% renewable energy goals
Aspen first achieved its goal of 100% renewable energy in 2015, when a project that retrofit the Ridgway Reservoir dam in the Uncompahgre River basin to generate hydroelectric power came online. The city of Aspen was integral in launching the project, funding a feasibility study in the early 2000s and signing a 10-year contract in 2012 to purchase about 10 million kwh a year from Ridgway once it became available. Ridgway now accounts for about one-seventh of Aspen’s total power portfolio, according to Overeynder. In an effort to continue meeting its 100% renewable goal, the city is also looking to continue and potentially expand its hydroelectric power generation capacity on Maroon Creek.
Aspen has begun the process of relicensing the project with FERC, which is smaller than the Ruedi project and has a capacity of 450 kilowatts. Aspen is also proposing to add additional units on Maroon Creek for a total of 500 kw.
Hydropower, including energy Aspen buys from projects at Ridgway Reservoir and Western Area Power Administration, is supposed to make up about 45% of the city’s energy portfolio. But that percentage has dropped with the declining power production at Ruedi in recent years. The city also buys wind and solar power to achieve 100% renewable energy.
“If we do this (project at Ruedi) plus what we did already at Ridgway and are proposing to do at Maroon Creek, we will get back up to that 45%,” said Justin Forman, Aspen’s Utilities Director. “For us, every megawatt counts and if it’s something local like this, we’re super proud of it and it certainly fits into the values that we have.”
The FERC relicensing process will take several years, with sign-offs also needed from the Colorado Department of Public Health and Environment, the U.S. Army Corps of Engineers and Pitkin County. Overeynder expects the new turbine to be operating sometime in 2027.
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