While most tourists visit the Chena Hot Springs Resort to swim in the steaming water of Rock Lake, the locals use the hot springs for another reason: to power their buildings in an attempt to become a self-sufficient community.
Located 60 miles northeast of Fairbanks, Alaska, and many miles from the nearest electric grid, Chena is about isolated as it gets. The resort consists of an ice museum, a greenhouse, and a few tourist buildings - all of which are powered by geothermal energy. The ice museum is the only one of its kind open year-round, and the greenhouse temperatures stay at a tropical 78 degrees F, even when it's -40 outside.
All this is possible because of Chena's 400kW power plant that uses hot water to produce energy for both cooling and heating applications. However, the hot water is not all that hot - just 165 degrees. At first, the United Technologies Corporation (UTC) researchers thought that this was too low of a temperature for power generation. But partly because the air in Chena is so much colder than in most locations, they found a way around this apparent challenge.
The 165-degree water heats and vaporizes refrigerant (like that used in car air conditioners), which has a lower boiling point that water has. The refrigerant vapor then turns a turbine that produces electricity. To restore the refrigerant back to its liquid state, 40-degree water from a nearby creek condenses the vapor back into a liquid so that the process can be repeated. As an article in Popular Mechanics explains, the power plant is similar to refrigeration equipment running backwards. . . even down to the computer read-out, which expresses the power output as a negative number.
To keep the greenhouse warm, the residents use some of the hot water to flow under a radiant concrete floor. This enables the greenhouse to provide lettuce, tomatoes, cucumbers, and herbs for the resort's restaurant, meaning less food needs to be imported from out of state.
Source: www.chenahotsprings.comTo keep the ice museum cool, an absorption chiller pumps out heat from inside the ice museum during warmer summer days. The technology is first of its kind in the world: the water heats ammonia (which has a low boiling point) into a vapor, which in turn is used to circulate a salt brine that pulls heat out from the museum.
In the future, Chena has plans to use geothermal energy to produce hydrogen gas. Electricity generated by the hot water would be used to split water, and then the hydrogen could be mixed with propane that could be added to the fuel used for cooking.
While Chena may be physically unconnected from the outside world, the small resort town is implementing ideas that could be beneficial far beyond its borders. The technology developed by UTC can operate off any heat source, with a minimum of 100°F temperature differential between the heat source and sink.
"Chena Hot Springs is the lowest temperature geothermal resource to be used for commercial power production in the world," according to the Chena power plant's Web site. "We hope this will be the first step toward much greater geothermal development in the state." The site adds that the cost of power production in locations similar to Chena could be reduced from 30 cents to less than 7 cents per kWh with geothermal power.
more information: Chena Geothermal Power Plant Web site
via: Popular Mechanics