Energy, Innovation

Small-scale geothermal systems

10.17.07 | 2 Comments

Chena Hot Springs Geothermal Power Plant - chiller, turbine, generator, and pump.

At the GRC Annual Meeting earlier this month, the Chena Hot Springs project was discussed again. Chena is in central Alaska, about 65 miles northeast of Fairbanks and is home to a resort as well as a 400kw geothermal plant. At heart, the Chena geothermal power plant is no different than any other binary geothermal power plant. But in detail, there are some interesting aspects of the project that make it worthy of note:

  • Low resource temperature – The production temperature from the wells at Chena is 165F (74C). Production from this low temperature is possible because of the ample supply of 40F (4C) cooling water that enables a consistent 120+F (49+C) difference in temperature at the harvest point. Location, location, and location matter in this instance.
  • Commercial chiller harvest – Chena elected to go with a commercial, off-the-shelf power conversion unit from UTC. These 280kw gross, 225kw net units are relatively cheap and are essentially industrial chillers being run in reverse. UTC has been producing these units for decades, their performance characteristics and failure modes are well known and understood. This is a departure from the Ormat approach which is to fit a custom harvest system to the resource which makes implementation much cheaper and faster.
  • Shallow resource depth – The production and injection wells at Chena aren’t very deep by conventional geothermal harvest standards. This reduces the cost and complexity of implementing the systems. The wells at Chena range from 100 to 1000 feet (30-300m) deep.
  • Time to production – Unlike most geothermal projects at utility scale, this project was implemented in less than a year real time, and less than 2 years elapsed time (due to the seasons – it’s tough to work in -40F weather.) The world land speed record for other plants appears to be 5 years elapsed time.
  • Government sponsorship – The US Department of Energy and the State of Alaska worked with the project to support exploration, drilling, and development activities. This is not always the case, but in this instance, the public/private partnership seemed to work.

Before the geothermal power plant went live, Chena’s power was provided by diesel generators at a cost of around $0.30/kwh. Now, the cost has dropped to $0.07/kwh and the resort has less ambient noise and particulate matter in the near vicinity because the diesels aren’t running. That’s a real economic benefit coupled with a synergistic effect that is beneficial to the primary business of the resort, a clean, quiet environment. Not every project can be like this, but one has to wonder how many other small scale geothermal systems could be tapped and harvested. Over the lifetime of the plant (if it’s running at full capacity of 400kw for 30 years), the economic benefit just in difference of cost/kwh will be on the order of $23.7M – impressive.