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Geothermal Firms Explore Low-Temperature Technology

Recognising the need for innovation, most experts on geothermal power have their sights set on the vast potential and innovative use of low-temperature geothermal resources. Indeed, speaking to REW recently, Halley Dickey of TAS Energy, Karl Gawell of the Geothermal Energy Association (GEA), and Doug Glaspey of US Geothermal Inc expressed the crucial importance of research and development in the geothermal industry.

Karl Gawell said, ‘We need to have better exploration and drilling technologies because that’s one of the biggest hurdles to geothermal prospects.’ Meanwhile, Doug Glaspey commented, ‘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 US Department of Energy (DOE) in the geothermal technologies programme.’ And, Halley Dickey said, ‘[We need] a continued focus and expansion of trying to utilise 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.’

Low-Temperature vs Traditional Geothermal

Traditional geothermal technology requires more than 180°C sources that are difficult to find and less abundant – and therefore costly to discover and develop. Low-temperature geothermal technology makes it possible to access resources less than 150°C, even as low as 75°C. According to the SMU Geothermal Laboratory, this is a ‘game changer’ and opens doors for the geothermal industry.

The Organic Rankine Cycle (ORC) is a common energy-producing method that’s making low-temperature geothermal possible. It takes advantage of geothermal brine at temperatures ranging from 90°C-150°C – 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. The phase change of this fluid allows energy to be transferred from the low temperature geothermal source into a usable format.

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 vapour when the brine enters the chamber. This fluid is usually an oil-based refrigerant or hydrocarbon. R-22 is commonly used for this purpose, as it is a nontoxic refrigerant and can normally be found in air conditioners and refrigerators with a boiling point of -5°C. 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 on-line in the past year. For example, the Beowawe Geothermal Facility in Nevada added 2.5 MW of low-temperature power to their existing 16.7 MW geothermal plant that went on-line in 1985 with the help of a DOE loan. Since its inception, Beowawe has experienced resource decline, which caused reduced output that was well below its designed intention. To solve this issue, Terra-Gen Power and TAS Energy were able to use 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 led to additional jobs and promises more clean renewable energy for the future,’ said Jim Pagano, CEO of Terra-Gen Power. ‘This project paves the way for additional low temperature binary projects in Nevada and elsewhere,’ he added.

With energy created from a 95°C 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 with temperatures from 97°C-260°C). And in 2006, the Chena Hot Springs plant in Alaska set the record for the lowest-temperature production at 74°C. The 400 kW plant was the first low-temperature geothermal plant in the world and uses United Technologies Company (UTC) ORC generators to produce power. Chena Hot Springs has reduced the cost of power from US$0.30/kWh to $0.5/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 on-line since 2009. Developed by Raser Technologies, the 14 MW plant generates energy from temperatures ranging from 70°C-80°C. However, its UTC-built generators, the same company that produces air conditioners, are able to generate power at 74°C.

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 with the ORC is that it uses an ammonia-water working fluid – 82% 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%-50%. Henry Mlcak, Mark Mirolli, Hreinn Hjartarson, and Marshall Ralph explain the advantage in a POWER Engineers article: ‘The conspicuous efficiency advantage characteristic of the Kalina cycle is realised 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 2000. The Orkuveita Húsavíkur plant uses geothermal resources with a typical temperature of 120°C. The plant, still in operation today, produces 1.6 MW and powers 80% of the town, according to the POWER Engineers article. Among other benefits, the hot fluid that leaves the plant is used in the town’s heating system, to heat greenhouses and the town’s swimming pool and assist in melting snow. These benefits have an Oregon community hoping for the same results. In the Klamath Basin Wildlife Refuge 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 discovered a 90°C geothermal resource – which is 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 at 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.

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. Experts argue that the geothermal industry has got this far due to strong support from the DOE, and this leads them to question what will happen if this support goes away.

‘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 programme built upon that stimulus funding and that it’s not just a one-shot deal.’

Many hope that programmes like the DOE’s will be able to generate technology in the same way that drove the discovery and exploitation of 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.

Dickey agrees that the DOE programme, and others like it, have helped the industry along. But said that the public-private partnerships have also made projects make sense for investors when they might have been on the fence. ‘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,’ said Dickey.

Meanwhile, the global geothermal project pipeline suggests that in the next couple of years we’ll see significant capacity added to the grid. California alone has more than 2000 MW in development. How much of that will be low-temperature? It’s 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 three million MW [of geothermal energy] that theoretically can be recovered. This industry has a long way to go, and technology is going to be a big part of making that happen,’ said Gawell.

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