The hope of generating geothermal power in Snohomish County could take a giant leap forward in the next few months.
Or, it could send the Snohomish County Public Utility District back to the drawing board.
The PUD in the next couple of weeks plans t
o begin drilling an exploratory well for geothermal power.
The PUD will drill a hole nearly a mile into the earth in the Cascades and send down a special thermometer to test the water temperature, said Craig Collar, senior manager for energy resource development for the PUD.
Geothermal power is created when steam, heat or hot water from underground reservoirs is used to spin turbine generators. The water is heated by magma farther below.
If the PUD is able to develop geothermal power, it would be the first utility in the state to do so, officials have said. Geothermal plants are operating elsewhere in the nation, including California, Idaho and Nevada.
The hope is that geothermal electricity could potentially power up to 35,000 homes in Snohomish County by 2020.
The drilling will be done about 15 miles north of Skykomish. The site formerly was accessible on the Index-Galena Road, but that road has been closed for several years starting at a washout about five and a half miles east of Index. Now the site is reached by the Beckler River Road, Collar said.
The new well is the next step of exploration for geothermal power following the drilling of five test wells last year. Four of those wells were located near Skykomish, one near Sultan. The sites, on federal, state and private land, were selected because they were easy to reach.
Those wells, about 700 feet deep, measured the temperature of the soil and groundwater. Only one of the wells produced high enough temperatures to warrant further drilling. The site, located on private property, is referred to as the Garland site.
This fall’s drilling operation will cost about $2.5 million, Collar said. Last year’s test wells cost about $400,000.
Commissioner Toni Olson said it’s worth the expense to generate more home-grown power. The PUD currently buys most of its power from the Bonneville Power Administration.
“A huge portion of our costs are associated with the power supply,” Olson said.
Like the drilling operations last year, this one will be mounted on a truck, Collar said.
The hole will be 4,000 to 5,000 feet deep. It will take about two months to drill the hole, then crews will have to wait another two months for the temperature to equalize between the soil and the groundwater that flows into the hole, Collar said.
The PUD hopes to find that the groundwater warms up by least 50 degrees centigrade per kilometer into the earth, and to see if that difference persists or tapers off, Collar said.
Fractured, permeable rock is preferable to solid stone because it allows the water to move through the rock and pick up the heat, Collar said.
If the water is hot enough and soil conditions are right, the PUD will still have to study the surrounding area to see if it’s suitable for a geothermal plant, Collar said. If the conditions aren’t right, then the PUD will have to look elsewhere in the mountains for possible locations for new test wells, he said.
Ultimately, a 50-megawatt plant — the size needed to generate power for 35,000 homes — would cost between $150 million and $200 million, Collar said. The PUD likely would borrow money and sell bonds to pay off the loans to build a plant.
The earliest a plant would be built is about 2016, officials have said. The plant would likely be built in phases of about 10 megawatts at a time depending on its output.
The PUD’s geothermal plans are part of an ambitious strategy to develop several different types of alternative energy. The PUD is nearing completion of a microdam in the Cascade foothills near Sultan. It’s expected to produce about 7.5 megawatts, enough power for about 5,200 homes.
The PUD also is buying wind power from three different windmill farms — two in Oregon and one near Goldendale, Wash. — is offering incentives for solar power and is about to spend about $20 million trying to generate power from the tides.
Bill Sheets: 425-339-3439; email@example.com.