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.

New Hampshire, U.S.A. -- 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. 

This technology was first put to the test in Húsavík, Iceland in July 2000. The Orkuveita Húsavíkur plant uses geothermal resources with a typical temperature of 250°F. The 1.6 MW plant, still in operation today, produces enough reliable energy to power 80 percent of the town, according to the article. Among other benefits, the hot fluid that leaves the plant is used in the town’s heating system, heats greenhouses and the town’s swimming pool and assists in melting snow.

These community benefits have an Oregon community hoping for the same results. In the Klamath Basin Wildlife Refuge, where energy and water are becoming a major issue, experts are testing for Kalina geothermal potential. The refuge has a water shortage problem, and energy price hikes have made water pumping too costly. When drilling for water in 2002, experts found a 200°F geothermal resource — perfect for the Kalina cycle.

“We had a need for cheaper power, they wanted to put this technology to work,” said Ron Cole, refuge manager, to Sustainable Oregon. The $10 million project is said to have investors ready to move forward once the environmental regulations are cleared — construction could start by the end of 2012. If the project is a success, it may influence four other sites in the area, according to Sustainable Oregon.

Is Support For Geothermal Power Waning?

With low-temperature technology advancements, successful projects and a vast resource map, what’s next for the geothermal industry? Many argue that despite technology advancements, much more needs to be done: particularly with policy and funding. Experts argue that the geothermal industry has gotten this far due to strong support from the DOE, and this leads them to question what will happen if this support goes away.

“The DOE has, as part of the stimulus bill, invested a significant amount of money into cost-share demonstrations. Most companies view DOE technology support, in terms of developing ways to reduce the risk of finding and developing resource, critical. We need to have better exploration and drilling technologies because that’s one of the biggest hurdles to geothermal prospects,” said Gawell. “Our hope is that we see a sustained program built upon that stimulus funding and that it’s not just a one-shot deal.”

Many hope that programs like the DOE will be able to generate technology that drove oil and gas resources. According to Gawell, there are some similar promising technologies under development that he believes will significantly help the industry move forward. And many of these improvements focus on low-temperature sources. “Some of the demos looking at low temperature and co-production have been essential because they are at the edge of economics and are showing the potential for low-temperature resources to expand the scope of geothermal significantly,” he said.

Dickey agrees that the DOE program support and others like it have helped the industry along. But he said that the public-private partnerships have also made projects make sense for investors when they might have been on the borderline. “We hope that DOE will continue to be supported by the government with dollars to work on exploration and risk-reduction and reservoir development in finding the resource and then helping support the difficulty in bringing those resources to the surface as well as some of these other advanced technologies,” said Dickey.

In the meantime, the global geothermal project pipeline suggests that in the next couple of years we are going to see significant capacity added to the grid. California alone has more than 2,000 MW in development. How much of that will be low-temperature? It is difficult to determine. With long project development times and uncertain resources, implementing this fairly new technology has its challenges — but the future looks bright.

“Dr. David Blackwell from SMU spoke at a national science foundation briefing on Capitol Hill [recently] and once again pointed out his estimates — there’s something in the range of 3 million megawatts [of geothermal energy] that theoretically can be recovered. So I’d say this industry has a long way to go, and technology is going to be a big part of making that happen,” said Gawell.

http://www.renewableenergyworld.com/rea/news/article/2012/05/low-temperature-geothermal-digging-for-its-vast-opportunity