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.
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
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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