Low-Temperature Geothermal: Digging for Its Vast Opportunity

Low-temperature geothermal could be just what the industry needs to make a leap forward, but it needs research and technology support to get there.

Meg Cichon, Associate Editor, RenewableEnergyWorld.com
May 09, 2012 | 6 Comments

The geothermal industry recognizes the need for innovation. Halley Dickey of TAS Energy, Karl Gawell of GEA (Geothermal Energy Association), and Doug Glaspey of U.S. Geothermal Inc. expressed the crucial importance of research and development in the geothermal industry during a conference call last month. Most experts have their sights set on the vast potential of and innovative use of low-temperature geothermal resources. Quotes from the conference call follow.

Karl Gawell: “We need to have better exploration and drilling technologies because that’s one of the biggest hurdles to geothermal prospects.”

Doug Glaspey: “We must look at new technologies on all fronts – both exploring for new resources and for developing and operating those new resources — so we would like to see additional funding from the DOE [U.S. Department of Energy] in the geothermal technologies program.”

Halley Dickey: "[We need] a continued focus and expansion of trying to utilize lower-temperature resources so that we can continue to bring what was once thought uneconomical and unattractive for geothermal, but often more abundant. These low-temperature resources actually can produce utility-scale power production."

What’s the Difference between Low-Temp and Traditional Geothermal?

Traditional geothermal technology requires 360+ degrees Fahrenheit sources that are difficult to find, less abundant, and therefore costly to discover and develop. Low-temperature geothermal technology makes it possible to access resources less at than 300°F, even as low as 165°F. According to the SMU Geothermal Laboratory, this innovative technology is a “game-changer” and widely opens doors for the geothermal industry.

The organic Rankine cycle (ORC) is a common energy-producing method that is making low-temperature geothermal possible. It takes advantage of geothermal brine at temperatures ranging from 200 to 300 degrees — brine that was previously considered unusable. The difference from traditional technology is that the brine is mixed with a working fluid that has a low boiling point, rather than water. This fluid is compressed into steam, which creates energy.

A binary geothermal plant uses this technology in a closed loop — the geothermal brine and the working fluid never leave the plant. In this system, the brine is pulled from the earth into an evaporator. Working fluid is held in the evaporator and flashes into steam when the brine enters the chamber. This fluid is usually an oil-based refrigerant or hydrocarbon such as R-22, as it is a nontoxic refrigerant normally used in air conditioners and refrigerators that has a boiling point of -41°F. The working fluid-brine steam then travels to turbines that power a generator.

Success Stories

Despite a mostly quiet 2011, there have been several successful low-temperature projects that went online in the past year. The Beowawe Geothermal Facility in Nevada added 2.5-MW of low-temperature geothermal power capacity to its existing 16.7-MW geothermal plant that went online in 1985 with the help of a DOE loan. Since its inception, Beowawe has been experiencing resource decline, which caused reduced output that was well below its designed intention. To solve this issue, Terra-Gen Power and TAS Energy used a DOE loan to incorporate low-temperature technology at the site.

“An increase in the DOE’s geothermal budget allowed this project to become a reality, which lead to additional jobs and promises more clean renewable energy for the future as this project paves the way for additional low temperature binary projects in Nevada and elsewhere,” said Jim Pagano, CEO of Terra-Gen Power.

With energy created from a 205°F resource, Beowawe confirms the technical and economic feasibility of low-temperature electricity generation. It uses new binary expanders that allow the use of lower resource temperatures for geothermal and waste heat applications. An axial turbine using R134a and R245fa as the primary working fluid, covers gross power output from 500-kW – 5.0-MW output with temperatures from 200 – 500°F (97 - 260°C).

And in 2006, the Chena Hot Springs plant in Alaska set the record for the lowest-temperature production at 165 degrees Fahrenheit – and still holds it today. The 400-kW plant was the first low-temperature geothermal plant in the world and uses United Technologies Company (UTC) generators to produce power. Chena Hot Springs has reduced the cost of power from $0.30 per kWh to $0.05 per kWh and has helped to lift the veil on Alaska’s geothermal potential.

Not So Successful

The Hatch Geothermal Power Plant in Beaver County, Utah has been online since 2009. Developed by Raser Technologies, the 14-MW plant was expected to generate energy from temperatures ranging from 158°F to 176°F. Its UTC-built generators, the same company that produces air conditioners, are able to generate power at 165°F and these generators have been proven under such conditions at the aforementioned Chena Hot Springs plant.

Though expectations were high, the plant has underperformed over the years. According to reports, the geothermal resource temperatures were unexpectedly low, and Hatch was producing 5 MW – less than half of its capacity, and it takes 4 MW to run its operations. Raser has continued drilling to uncover higher-temperature resources and rework its current wells, but has incurred more debt. The DOE granted Raser a $33 million loan in 2010 to help the project along, but its prospects are still uncertain.

A Different Approach

Kalina Cycle success: A look inside the 3.36-MW Unterhaching, Germany geothermal plant, which went online in 2009. Credit: Geothermie Unterhaching

A similar, but innovative method of power generation is gaining interest in the geothermal industry — the Kalina cycle. Developed by Global Geothermal, its major difference when compared to the Rankine cycle is that it uses an ammonia-water working fluid — 82 percent ammonia by weight — that condenses and boils at a wider temperature range. According to the Kalina Cycle website, these attributes can improve the efficiency of the power process by 10 to 50 percent. Henry Mlcak, Mark Mirolli, Hreinn Hjartarson, and Marshall Ralph explain the advantage in an article:

The conspicuous efficiency advantage characteristic of the Kalina cycle is realized from the heat exchange processes of the heat acquisition in the evaporator and the heat rejection in the condenser. Additional efficiency is achieved by the recuperator exchangers. These gains are made possible by the variable boiling and condensing characteristics of the ammonia-water mixture working fluid as it varies in concentration at different points in the cycle.

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6 Comments

Anne van der Bom
May 20, 2012

Philip Haddad,

You derive geothermal potential from the heat flow of geothermal from Earth to space, which is ~40 TW. This is not the correct way to determine geothermal potential. The heat the Earth loses to space is is limited due to the many km's of rock this heat has to traverse, and the ir absorption from atmospheric H2O and CO2.

When harvesting geothermal energy, you drill through this insulating layer of rock to access the heat directly.

OTOH, the earth is losing this heat through every sq m of surface, while drilling for geothermal is only practical in a limited number of locations.

Ann Vole
May 15, 2012

Low temperature electricity production is of great interest to me for use on a small scale for replacing photovoltaic solar and batteries with thermal solar and heat storage. Dry steam requires rather high temperatures and pressures that make small systems unsafe and expensive. If these binary systems can be developed with safer fluids then ammonia or at least at low temperature and pressure so ammonia-containing systems can be made safe, the cost of small independent solar systems can be made low enough to compete with utilities rates. Geothermal is everywhere if the working temperatures can be brought low enough so research and working sites is good news.

edit: just to be clear, I am talking of using the technologies developed for low temperature geothermal for a different purpose: thermal energy storage. Storing energy is expensive but very important to using alternate energy sources that are not available on demand. Thermal storage promises to be the lowest cost alternative. Both geothermal and thermal energy storage seek to create electricity via turbines operating on heat removed from underground stores of heat. The only difference is geothermal is sourced on the earths core and storage is put there by solar thermal collectors.

John Carr
May 11, 2012

The Kalina Cycle is simply a combination of the original ice house ammonia absorption refrigeration from the 1800's and ammonia compression refrigeration from the early 1900's. Not exactly revolutionary. The fear of ammonia's safety has driven companies away from using it over the years. It was a good idea 120 years ago, it still is today.

Philip Haddad
May 10, 2012

Since heat, not CO2 is the cause of global warming, does geothermal energy maintain the total heat emission from the geothermal flow, or does it increase it. If it does mot increase it the limit of geothermal energy is 44TW, still a sizeable potential.

Ron Tolmie
May 10, 2012

Meg:
There is another class of low temperature "geothermal" energy sources that has a much larger near-term potential for large scale applications. I am referring to thermal storage systems that operate at only a few degrees from the normal ambient ground temperature. Although such systems do not generate electricity they can be used to nearly eliminate the consumption of electricity for cooling buildings (and for heating them) so the end supply/consumption consequence is the same.

The city of Toronto uses such storage (employing water as the storage medium) for cooling many of its big downtown buildings. There are over a million buildings world wide that use such storage for space heating. Sometimes natural heating or cooling methods are used to recharge the storage medium but in most cases it is actually more cost effective to utilize the same ground heat exchangers to both store and recover the energy.

Big buildings waste far more energy than they consume. Given a means of storing that energy (including all of the electrical energy that is converted to heat within the building) the surplus energy from big buildings can optionally be used to heat thousands of surrounding homes and smaller buildings. This is by far the biggest, simplest and most cost effective renewable energy source in urban areas but for some reason it is being ignored by publications like Renewable Energy World.

Dornadula Chandrasekharam
May 10, 2012

The potential of Low-Enthalpy geothermal resources has been recongnized way back in 2002 and has been documented in detail in two books:

1. "Geothermal Energy Resources for Developing Countries" Eds: D. Chandrasekharam and Jochen Bundschuh, AA Balkema Pub., The Netherlands, 2002, 412p.

2. D. Chandrasekharam and J. Bundschuh 2008. " Low Enthalpy Geothermal Resources for Power generation" Taylor and Francis Pub., U.K. 169 pp.

The second book is a text book for the graduate students and researchers.

The benifits of developing low enthalpy resources and the savings from carbon emissions and cost have been well documented in the second book.

This book was reviewed by GRC and other leading publishers. This may be brought to the notice of the policy makers who are keen in developing low enthalpy geothermal sources. It is in deed will be very useful and cost effective especially for developing countries trhat has huge such resources.

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Meg Cichon

As associate editor of RenewableEnergyWorld.com, I coordinate and edit feature stories, contributed articles, news stories, opinion pieces and blogs. I also research and write content for RenewableEnergyWorld.com and REW magazine. I manage...