Avista Utilities has listed in a new long-term plan three potential major hydroelectric upgrades at its Long Lake and Cabinet Gorge dams that would add 144 megawatts of generating capacity to its system, or more than the 125 megawatts of combined capacity at all six of its Spokane River dams.

The three upgrades would cost a total of $316 million, says the company's 2009 Electric Integrated Resource Plan, which it filed Aug. 31. Avista says it's too early for it to provide further specifics about the potential projects or to talk further about the likelihood that they might be built.

One megawatt of electricity is enough to serve 750 homes on Avista's system, so 144 megawatts would meet the needs of 108,000 homes. Avista has 353,000 residential and commercial electrical customers and 1,768 megawatts of generating capacity of all kinds now.

Asked whether Avista's hydroelectric staff could talk in greater detail about the major hydropower upgrades included in the 2009 resource plan, company spokesman Hugh Imhof says, "They still don't have anything specific, beyond what's in the IRP (integrated resource plan)."

Yet, the plan, which is updated every two years and covers a 20-year period, says Avista has done a considerable amount of work—including some design work—on the three potential major upgrades.

After listing smaller upgrades with which the company will go ahead, the plan says, "Avista designed and studied other larger potential upgrades at Long Lake and Cabinet Gorge. These upgrades were too costly in previous studies, but increasing market prices, growing capacity needs, renewable energy incentives, and carbon emission costs may make these resources financially more attractive now."

The plan says the options for major hydro upgrades include:

•A fifth generating unit at Long Lake, which would add 24 megawatts of generating capacity at a capital cost of $69.2 million in 2009 dollars and could be available in 2020.

•A second powerhouse at Long Lake, which would add 60 megawatts of generating capacity at a capital cost of $147.2 million and could be available in 2020.

•A fifth generating unit at Cabinet Gorge, which would add 60 megawatts of generating capacity at a capital cost of $99.6 million and could be available in 2015.

The 2009 resource plan says that Avista engineers also developed "preliminary plans" to replace the powerhouse at Post Falls Dam, which would double that dam's 14.75-megawatt generating capacity. The new plan doesn't provide an estimate of the cost of that project.

"These large hydro upgrade options have attracted attention during this IRP cycle and will be further studied between now and the 2011 IRP," the 2009 plan says.

Initial operation of the 213-foot-high Long Lake Dam began in 1915, the 208-foot-high Cabinet Gorge Dam was completed in 1952, and the 31-foot-high Post Falls Dam began operating in 1906, Avista says.