Located in a mountain valley immediately southwest of Mount Spurr on the west side of Alaska’s Cook Inlet, the 14-mile long Chakachamna Lake presents a spectacular vista to pilots flying the Merrill Pass route through the Alaska Range. But could this large body of water at a relatively high elevation provide a viable source of hydrothermal energy for the Alaska Railbelt? The eastern end of the lake is about 80 miles from Anchorage and only just over 40 miles from the nearest point on the Railbelt electricity grid.
Seeing an opportunity for a new power source for the Railbelt, TDX Power, a subsidiary of the Tanadgusix Native Corp. and operator of electricity utilities at Sand Point and Prudhoe Bay, has shaken the dust off a 1980s study into a potential Chakachamna hydro project. Carried out by Bechtel for the Alaska Power Authority and the U.S. Bureau of Reclamation, that study lay in the shadow of a grandiose and ill-fated scheme that surfaced at about the same time for a Susitna River hydroelectric power plant.
But, whereas the scale of the Susitna proposal proved way too big for the regional electricity supply requirements, a 300-megawatt Chakachamna plant would make optimum use of the hydro resource while also scaling well with Railbelt electricity usage, Nick Goodman, CEO of TDX, told the 2007 Mount Spurr Geothermal Workshop, on Aug. 27. And a stable source of electricity from a hydropower plant could provide a reliable base load supply.
“The (Chakachamna) base load would provide a lot of stability for the grid, but it’s not going to overwhelm the grid,” Goodman said.
And Goodman cited the success of the 1991 Bradley Lake hydropower project on the Kenai Peninsula as evidence that hydropower can make sense as part of the mix of electrical power sources for the Alaska Railbelt. Bradley Lake was an expensive project but it worked out very well, Goodman said.
10-mile tunnel
The TDX Chakachamna Lake proposal is based on the 1980s design concept. That design envisages constructing a 24-foot diameter inclined power tunnel to carry water southeast through the mountains at the east end of the lake down to an underground power plant on the north side of McArthur River, near the toe of the Blockade Glacier. The resulting 938-foot head of water would drive four vertical-shaft 82.5-watt turbines connected to electricity generators.
The turbines and generators would be located in a 250-foot long underground cavern, connected to separate underground chambers housing transformers. Water discharged through the powerhouse would flow into the McArthur River (the Chakachatna River that flows from Chakachamna Lake is a tributary of the McArthur River).
The design involves raising the water level in Chakachamna Lake from its present elevation of 1,142 feet to the lake’s historic maximum elevation of 1,155 feet. That elevation increase would be achieved by constructing a 46-foot high, 600-foot long rock-fill dike at the eastern end of the lake. A spillway and associated water release structure would control the lake level.
The overall design of the proposed system presents a somewhat expensive construction option but a reasonable compromise between cost and minimizing environmental impacts, Goodman said.
“The feeling was at the time that this configuration would allow for the least environmental impact to the Chakachamna Lake,” he said. “… To date I’m pleased to report that we’ve had nothing but positive discussions with the environment community here in Alaska.”
And with fish passage through the system of rivers and lakes of the area a major environmental concern, the design involves fish ladders and a tunnel at the natural outlet of the lake to allow fish migration past the dike and spillway structures. In fact, the first design in the 1980s was scaled back to accommodate fish migration, Goodman said.
FERC license
TDX has obtained a preliminary permit for the Chakachamna project from the Federal Energy Regulatory Commission and has embarked on some initial scoping and information gathering for the project. There is a great deal of engineering to be done to flesh out the concepts in the 1980s preliminary design, Goodman emphasized.
“The preliminary work back in the 1980s was very, very high level,” Goodman said.
And, although TDX is basing its project on the 1980s design, the company is not wedded to the specifics of that design. It’s now a question of determining what makes sense in terms of environmental concerns, costs and today’s engineering standards.
“We will be conducting some geotechnical investigations to look at some of the original designs, to make sure that they’re applicable to today’s construction best practices,” Goodman said.
Specific issues that a more detailed design would need to take into account include the potential for avalanches into the lake and the stability of the glacier that dams the outlet end of the lake, for example.
There is also a major requirement for environmental studies and permitting.
“We’ve engaged some consultants and we’re moving along. … We’ve got environmental surveys under way, trying to update a lot of the permitting requirements from the initial studies in the 1980s,” Goodman said.
Costs and economics
The 1980s study estimated the total cost of the project at around $1 billion. In today’s dollars that would translate to about $2 billion and the project is likely still 10 years out, Goodman said. That estimated current cost translates to a cost of electricity of about 10 cents per kilowatt-hour, a figure that at first blush looks high in comparison to current Railbelt rates.
But TDX thinks that the 1980s cost estimates are significantly high and the company says that FERC has used a lower cost figure in its economic viability analysis of the project.
The high cost estimate stems from the fact that the very limited funding of about $300,000 for the 1980s study prevented an exhaustive evaluation of design options, Goodman said. So, where there was insufficient time to fully investigate a design issue, the analysts would over-engineer a solution, he said.
As an example, the design concept includes lining the whole of the power tunnel with concrete, a very expensive proposition. That may not be necessary, Goodman said.
There’s also a possibility of sharing some of the access and power transmission network with a geothermal power station at nearby Mount Spurr, if someone finds a viable geothermal source there. And there’s a proposal for a wind farm at North Foreland, on the west side of the Cook Inlet to the east of the proposed Chakachamna power station.
“Wind and hydro interact very well together,” Goodman said.
Detailed study
But determining whether the Chakachamna project is viable is going to take some significant detailed study.
“We don’t know if it’s economic,” Goodman said. “… We suspect it could be and we suspect it’s worth spending the $15 million to $20 million we’ll spend over the next three to five years to prove that out.”
And to move forward through that period TDX wants to partner with an international utility company with large-scale hydro experience.
“A big target for us as a company right now is to find the right strategic partner,” Goodman said. “… We’re in discussion with three right now that look very promising. … We’d like to make sure that at the end of the three to four-year period we’ve got a good project.”
Ultimately, there are great benefits from the use of hydropower, Goodman said.
“It’s beautiful, long-term base load power,” he said.
