Chena Hot Springs Resort is a privately owned facility located 60 miles northeast of Fairbanks. Chena is located 33 miles from the nearest electric grid and maintains its own generation facility and approximately 3 miles of distribution lines. Prior to 2006, Chena used diesel engines to supply power to the site, with an average load of 180 kW. In 2006, Chena installed a 400 kW geothermal power plant consisting of two 200 kW PureCycle 200 modules designed and manufactured by United Technologies Corporation. Chena is currently in the process of installing a third 280 kW production model PureCycle 200, for a total installed capacity of 680 kW.
The power plant is unique because it was designed to work using geothermal fluids at 165°F, which is a significantly lower temperature than that of the fluids used at other geothermal sites for commercial power generation. The United Technologies equipment is based on refrigeration components from its subsidiary company, Carrier Refrigeration. Originally designed for industrial waste heat applications, the power plant modules were and modified for this geothermal
application. In the winter, the units are air cooled or water cooled (via a cooling pond installed in 2008), and water cooled in the summer. Project capital costs totaled $1,926,962, which was partially offset by a $246,288 grant from the Alaska Energy Authority. This included the drilling of a geothermal production well, but it did not include any exploration costs. Those were partially covered under a Department of Energy grant. The project also used numerous recycled components including 4200 ft of pipeline and a 1.5 MWh UPS system, which reduced the cost of the project significantly.
Data and Analysis
During its first 27 months of operation, the power plant logged 18,722 hours at 99.4% availability, excluding five weeks of repairs after a fire occurred in the building in May 2007. During this repair period, the unit operated with an average capacity factor of 87%, with an average net output of 174 kW per unit. The reduced capacity factor is due to flow rates on the hot water side averaging approximately 60 gpm below the rate for which the system was designed. When both units are online, this flow rate is further reduced per unit for a total plant output of 280 kW (70% capacity factor). The power plant is designed to be dually cooled, using cold water in the summer, and air or water in the winter. During intermediate seasons, unit output has been reduced as a combined effect of less available cooling water flow and inefficient operation of the air-cooled condensers at temperatures above 0 °F-10 °F. This issue should be mitigated by the installation of a cooling pond in 2008.
Installation of the geothermal modules has resulted in a 50% reduction in gallons of fuel purchased at Chena (compared with fuel purchases prior to the installation during times the power plant was operating). Greater fuel savings have not yet been realized, because the generators were designed to be grid connected, they use induction generators that require a stable frequency and voltage to operate properly. A 1.5 MWh UPS system was installed to provide grid stability, but there were initial problems integrating it into the existing power generation system. This resulted in challenges with completely eliminating the diesel engines and operating both power plant modules simultaneously without overpowering the grid. For this reason, in 2007 and the first half of 2008, only one power plant module was typically in service at a time, and thus actual fuel saving were just half of what was expected. This issue has been resolved, and now both units are operating for a total net output of 280 kW. The third unit, a larger 280 kW PureCycle module, is expected to be online by the end of 2008, bringing the total installed capacity to 680 kW.
Overall fuel offset in the first 26 months of operation was 228,000 gallons for a total savings of $650,873.
This takes into account a 116% increase in site load, to an average of 430 kW since installation of the geothermal power plant. This increase is due to the installation of a production greenhouse (75 kW load), the addition of electric appliances in the hotel rooms and restrooms, addition of plug-ins for vehicles, and an increase in site pump loads. Assuming output remains constant, the simple payback at current (2008) fuel prices will be realized in just over 6 years (the end of 2012) from the date of installation. O&M and debt load for the project are currently $73,500 per year. The addition of these values results in a net payback of 8 years from an installation date at the end of 2014. This could be reduced to 5 years if all units are operated simultaneously and greater fuel savings are realized.
Chena is also planning to drill a deeper well in 2009 to access the deeper reservoir to produce higher temperature fluids. This improved efficiency of the power plant will reduce the total volume of water required for operation.
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