Fine-tuning some innovative techniques in geothermal power production led a slight production delay for U.S. Geothermal's 8.6-megawatt power plant near Gerlach.
U.S. Geothermal Chief Executive Officer Dan Kunz says several problems cropped up once the plant went into commercial production on May 25. The main issue, Kunz says, was unwanted vibrations in the turbine gearbox as the turbine cycled up to full operating speed about 4,500 revolutions per minute.
The refrigerant used inside the turbine is slightly heavier and denser than test fluids used when the turbine manufacturer conducted initial spins on the unit at its factory, Kunz says. To correct the vibration, the manufacturer will install larger-sized bearings inside the gearbox.
"The manufacturer has recommended we go to a larger-footprint bearing, from 4-inch to 6-inch," Kunz says. "This is an innovative technology program, and as a result we are working through a few modifications and adjustments to the plant."
The plant shut down July 27 and is expected to come back online later this month. The adjustments also involve adding a "swirl break" behind the turbine wheel that is designed to disrupt an unwanted pressure wave identified by the turbine manufacturer. A problem with the plant's silencer also has been developed and a replacement unit will be installed during the shutdown.
"All of this in some broad way is because of the innovation," Kunz says. "These are super-critical cycles. All those components are proven, but they are in a new assemblage.
"We are very fortunate that our prime contactor is very adept and is responsible for getting the plant through this adjustment period," he adds. "This scenario is not uncommon when you have some innovative element to it."
The shutdown will have a negative impact on revenues, the Boise, Idaho-based geothermal developer cautions, and the company has entered into discussions for a final settlement of the contractual delay issues and refinancing of its construction loan. U.S. Geothermal says it's found a lender to provide a term sheet for long-term financing to replace its existing $30 million construction loan and expects to complete a deal in about 90 days.
"We fully intended to convert our construction loan to a long-term loan that will be a 20-plus year project financing," Kunz says.
U.S. Geothermal has a long-term power purchase agreement with NV Energy subsidiary Sierra Pacific Power Co. The San Emidio power plant replaced an older, smaller plant that was in operation at the site for about 20 years.
Kunz says the company expects to expand on power production capabilities at San Emidio and plans to develop a second geothermal plant at the site.