Developing Geothermal Energy at Low Temps

Taking a quick look at the low-temperature geothermal developments and prospects in Mexico, Canada, and the U.S.

Leslie Blodgett, Geothermal Energy Association
September 21, 2010 | 6 Comments

A large portion of the world's installed geothermal generation capacity is located in North America. The United States has 3086 MW of installed geothermal capacity and is the world's leading geothermal electricity generator. Mexico ranks fourth with 958 MW and new projects, all across the region, are underway.

A few new high-temperature fields are under development: Blue Mountain in Nevada, which recently came online, is one such project. Additionally, much of the new geothermal power generation that has come online in the past 10 years has been from expansions of geothermal fields already connected to power grids. And while the largest high-temperature geothermal complex in the world, the Geysers in California, boasts 1517 MWof installed capacity, there is quite a bit happening on the lower end of the temperature scale.

Existing geothermal energy fields that have more untapped energy potential in leasable areas can be hard to come by. But this may not hamper the growth of geothermal energy projects. The reason, some experts say, is that low-temperature geothermal projects are becoming more economical through the use of organic rankine cycles (ORCs) and through new technologies like coproduction from oil and gas wells.

Low-temperature geothermal projects are defined as projects that use water temps of up to 300°F to produce power and/or those that have output capacities of just a few megawatts. The U.S. Geological Survey has identified more than 120,000 MW of untapped potential at these temperatures, some of which are conventional hydrothermal operations, where shallow geothermal fields are used because the deeper field lacks permeability.

Recent low-temperature developments have also been made in oil and gas coproduction projects, generating electricity from the warm wastewater byproduct at oil and gas wells – wells that have already been drilled, eliminating the costs of one huge step of the process. We explored oil and gas coproduction products in our most recent article on RenewableEnergyWorld.com.

As a side note, direct use geothermal and heat pump applications can also be classified as low-temperature geothermal projects, but they are generally used for heating and cooling applications as opposed to power generation.

Low-temperature geothermal power projects have been in existence in the U.S. since 1984, when Ormat Technologies deployed a 700-kW net geothermal power unit in Nevada, the first commercial geothermal power plant in the state.

Low-Temperature Geothermal in Mexico and Canada

Mexico has four large geothermal plants in operation and is considered a major geothermal player. The country has plans to expand existing projects and start new ones in the future. A low-to-intermediate-temperature 300-kW binary unit operated in Maguarichic until the national grid reached the village three years ago, according to the Mexican Geothermal Association. Mexican state power company CFE acquired two similar plants to provide electricity to pumps systems at the Los Humeros and Las Tres Vírgenes geothermal fields using residual high-temperature brines.

An article that ran in 2009 in Geotermia magazine by Eduardo R. Iglesias and Rodolfo J. Torres, entitled First assessment of low- to medium-temperature geothermal reserves in 20 Mexican states, gives an assessment of low-to-medium geothermal reserves in Mexico and their aggregate value on a state-by-state basis. “The most likely reservoir temperatures range between 60-180°C [140-356°F] with a mean of 111°C [232°F],” according to the abstract. “Such massive amounts of recoverable energy—and the associated temperatures—are potentially important for the economic development of nearby localities and the nation.”

Although Canada has no current installed geothermal power, two low-temperature geothermal projects are in progress according to the Canadian Geothermal Energy Association. The Alberta Energy Research Institute recently approved “The Borealis Project” for $2.6 million. The ADK/Borealis Geothermal Demonstration Project will deliver a minimum of about 1 MWe of electrical power and about 1 MWth of direct heat to a community in Northern Canada. Another project that was set up to research coproduction from oil and gas wells is located in the Canadian Foothills.

ORCs and Notable Low-Temperature Geothermal Developments

ORCs are often used in low- to moderate-temperature systems. With a range between 200°F and 350°F they are often used when brine is not sufficient for flashing the steam. “It is ideal for vapor power cycles,” according to an article by Josh Nordquist of Ormat Technologies in a Geothermal Resource Council publication titled Use of Small, Sub 1 MW Organic Rankine Cycle Power Systems and Low Temperature Resources (Vol. 33, 2009).

An example of how ORCs in low-temperature projects can extend the life of existing resources was recently reported in another part of the world. In Taiwan, the Yilang Chingshui Geothermal Project will use two UTC PureCycle systems to generate electrical power at an existing geothermal site for the first time in 25 years. With a capacity of 500-kW net using 130°C geothermal resources, power production is expected by the end of the year.

Another application of low-temperature ORC systems is through the use of Solar Ponds. In large lakes with high salt content, much of the salt sinks to the bottom. “The upper layers of [fresh]water act as an insulating blanket and the temperature at the bottom of the pond can reach 90 degrees C. This is a high enough temperature to run an organic rankine cycle (ORC) engine or Stirling engine,” as described on SolarThermalMagazine.com, The first solar pond ORC system in the United States was a 100-kW system that supplied process heat to a commercial manufacturer. It was installed in Texas in 1986 and produced at 85°C [185°F], according to Ormat Technologies, which supplied the unit.

Chena Hot Springs, Alaska, is the site of the lowest temperature commercial geothermal plant to date, though test units of 1-4 kW have run on lower temperatures. Two 210-kW units using 73.3°C [165°F] geothermal fluid as the heat source were installed at Chena in 2006 by United Technologies Corp. The systems replaced on-site diesel generation systems, resulting in substantial cost savings.

Additional projects for analysis and development of low-temperature resources and technology are underway by West Virginia University; the City of Klamath Falls, Oregon; Johnson Controls, Inc; and Oasys Water. Information is available on GTP’s Projects Database.

This article continues with discussions about prospects, challenges and support for low-temperature geothermal applications in the November/December issue of Renewable Energy World North America. Developments in Oil and Gas coproduction will also be covered. Watch for it in November!

6 Comments

Richard Elder
September 30, 2010

Before deciding that low temperature geothermal is the next silver bullet, one should take into account the basic principles of physics. The amount of energy that can be obtained from a geothermal plant is a function of the difference between the ambient air temperature or achievable cooling temperature and the temperature of the geothermal fluid. A geothermal system with 300C plus working fluid temperature will produce many times the energy for a given flow volume and plant cost compared to one drawing from a 73C hot spring. Pursuing low temperature geothermal as a national policy is something like exploring for oil with a 500' water well drill rig.

The second limiting factor for low temperature geothermal has to do with geology. Shallow surface features that produce geothermal hot water are scattered far and wide around the intermountain west, typically with poor or non-existent grid interconnection and limited individual potential capacity.

If we were serious about developing geothermal energy we would go where the energy is.

As the tectonic plates slid past each other a feature known as the Yellowstone Hot Spot, the footprint of the Yellowstone mega-volcano, left its path under what is now the Snake River Plain all the way from Boise to Yellowstone. The basic geology underlying this area consists of a highly permeable lava aquifier overlying an impermeable cap layer. Under that at relatively shallow depths of a mile or so is one of the highest temperature gradient access points to the earth's core heat on the planet.

The heat energy from this single geologic feature is likely sufficient to provide a large portion of the nation's energy needs for thousands of years into the future. Any rational society not driven by short term tunnel vision would be investing sufficient capital to develop the technology to capture this resource.

James Davis
September 30, 2010

It sounds like there is no excuse for America not converting immediately over to Geothermal power production. It takes 10 to 50 billion dollars to build one nuclear power plant. If that funding was transferred to Geothermal, we would be fossil free in less than 10 years and created hundreds of thousands of jobs. Is there anyone getting this information to President Obama and the Energy counsel?

Mark Bertrand
September 28, 2010

Interested in implementing in Guatemala. A lot of hot spots found. How can we get detailed information on setting up a plant for private co-generation?

bob freeston
September 22, 2010

For a variation on the above comments, two projects in central Canada with construction of about 45 houses each have used solar thermal heat,gathered in the summer via roof collectors and then stored in bedrock via a field of bore holes, to heat the houses for the winter. The heat source declines over the winter, so some boost is needed in late winter, but its central Canada after all. Only running cost is pumping.

Mary Saunders
September 22, 2010

I like Angus's ideas.

Heat from the Street was an article that appeared in the Economist some time ago which discussed using natural aquifers to store heat for winter and cold for summer, not only for space heating but for cooling asphalt in summer and removing snow in winter.

The possible efficiency gains from such uses are pretty stunning.

Angus Campbell
September 22, 2010

Is it possible that Low Temperature Geothermal plants could be built in conjunction with Solar Thermal plants whereby the Geothermal side of the operation extracts heat up a medium to a certain temperature and a solar thermal plant heats it up to a higher temperature? This would be a broad application since peak useage on the grid would coincide with the daylight hours when the system would produce at its maximum power output. This type of "marriage" bewtween renewable technologies is something that should be studdied more closely in the future. Another example could be wind turbines that are used to pump water back into hydro damms during low demand hours. This would act as a storage asystem for wind power. I would be cuious to know if these types of systems were studied in more detail and if their costs justify real life applications. Should make for a good article. Thank you.

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Leslie Blodgett

Leslie Blodgett edits the Geothermal Energy Association's weekly newsletter. She has been involved in the production of many of GEA's recent reports and workshops and has written articles for several renewable energy publications. Prior...