A consulting company is recommending more than seven million dollars in repair and replacement work in the long-term for Petersburg’s hydroelectric power plant at Blind Slough. The power plant on southern Mitkof Island is nearing the end of its first century but it continues to function as Petersburg’s cheapest source of electricity.
The power plant at Blind Slough was commissioned by the city of Petersburg and construction work started on it in 1921. A newspaper report says the plant was fully operational by January of 1925 for a cost of 115,000 dollars. Prices have gone up a little since then. Last year the Petersburg borough hired a consulting firm for an assessment of the hydro plant for nearly 160,000 dollars.
Don Jarrett is with the company McMillen Jacobs Associates and he reported to the borough assembly this month.
“The project as you know is a bit of an older facility,” Jarrett said. “It’s a bit of a hidden gem for the borough. Our work was to help with basically planning for the future of the facility.”
The plant is about 18 miles south of Petersburg. It drops water from Crystal Lake, at over 1200 feet above sea level to a generator at Blind Slough. Water from the lake is also crucial for operation of the nearby salmon hatchery.
The original wooden pipeline and old generator from the 1920s was replaced in the 1950s with steel pipe, or penstock, and a new generator. Many of the components still operating today date back to 1955. There are a few smaller safety fixes that the consultant says fall into the urgent category and need to be completed in the short-term. Other items are identified needs in the long term.
The consultant is recommending refurbishment of the power house, including replacement of some of the equipment. The current system uses a single jet of water to push a wheel and generate power. Jarrett says a change to two jets of water could make the power plant more efficient.
“It looked like based on our analysis of the water flows over a few years that you could pick up another 10-13 percent energy with a double jet machine,” Jarrett said. “So this looks like a better more cost effective approach to its refurbishment than just doing the minor repairs to keep it operating.”
Upgrading the equipment and refurbishing the power house is estimated to cost 5.3 million dollars. That includes one million for a new generator. It’s more expensive than rewinding the existing generator but Jarrett is recommending the replacement.
“The trouble with rewinds is you’ve got to mobilize people out,” he explained. “Generally you want to do it on site if you can because it’s a shorter time frame than taking stuff out, shipping it somewhere and getting it back. Although they did that at Tyee (Lake). But either way it’s a long haul. So you got a longer outage that you have to coordinate. So, like I say it seemed like, I won’t call it a no brainer, but it’s close to a no-brainer when we saw the equipment package prices.”
Jarrett estimated it could cost around half million dollars for rewinding the existing unit. The plant is one of Petersburg’s three hydro electric sources. The other two are owned by the Southeast Alaska Power Agency (SEAPA) at Tyee and Swan Lake. The cost of electricity from Crystal Lake is a little over a penny a kilowatt hour. That compares to the wholesale rate from SEAPA of 6.8 cents. So Petersburg’s electric utility makes a lot more money on Crystal Lake power than on electricity purchased from SEAPA. The consultant reported that a longer outage at the plant, if equipment failed, could cost the utility hundreds of thousands of dollars.
McMillen Jacobs also looked at replacing the steel penstock used to drop the water down the mountain from the lake. Jarrett told the assembly that replacing that could cost 14 million dollars.
“So we compared that to just doing some repairs,” he said. “Going through and repairing the foundations, fixing and replacing some of the coupling gaskets, doing some other internal assessment work to make sure the condition inside is going to be OK. And that’s more like a two million dollar project. And the two million dollar project, no big surprise, looks to be quite a bit more cost effective than the 14. We believe that even the two million dollar project will give you another 40 years of life.”
That work could include using a remotely operated vehicle to survey the condition of the inside of the penstock. The consultant is not recommending increasing the capacity of the reservoir by drawing the water from deeper in that lake. But they are recommending repairing the penstock and refurbishing the power house together, putting the combined cost at $7.3 million. He did caution that the cost estimates are preliminary and could change with more engineering work. The power plant could be offline for five months or more while the work is being done.
Petersburg’s electric utility could bond for the projects and pay back that debt with electricity revenue over time. Crystal Lake has capacity to generate around two megawatts, typically around a quarter of Petersburg’s energy needs.