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New PNNL Geothermal Heat Extraction Process Optimizes Low-Temperature Resources; NYU Stern Study Finds Geothermal Most Efficient Renewable and Improving the Fastest

PNNL’s metal-organic heat carrier (MOHC) in the biphasic fluid may help improve thermodynamic efficiency of the heat recovery process. This image represents the molecular makeup of one of several MOHCs. Source: PNNL. Click to enlarge.

Scientists at the US Department of Energy’s Pacific Northwest National Laboratory (PNNL) have developed a new method for capturing significantly more heat from low-temperature geothermal resources.

PNNL’s conversion system exploits the rapid expansion and contraction capabilities of a new biphasic fluid. When exposed to heat brought to the surface from water circulating in moderately hot, underground rock, the thermal-cycling of the biphasic fluid will power a turbine to generate electricity.

“Some novel research on nanomaterials used to capture carbon dioxide from burning fossil fuels actually led us to this discovery. Scientific breakthroughs can come from some very unintuitive connections.”
—Pete McGrail

To aid in efficiency, scientists added nanostructured metal-organic heat carriers, or MOHCs, which boost the power generation capacity to near that of a conventional steam cycle.

The goal of the project is to enable power generation from low-temperature geothermal resources at an economical cost. The research team is targeting the development of a functioning bench-top prototype generating electricity by the end of the year, according to PNNL Laboratory Fellow Pete McGrail.

PNNL’s Pete McGrail on the process.

PNNL is receiving $1.2 million as one of 21 DOE Energy Efficiency and Renewable Energy grants through the Geothermal Technologies Program. Some of the research was conducted in EMSL, DOE’s Environmental Molecular Sciences Laboratory on the PNNL campus.

A 2006 technical and economic analysis conducted by the Massachusetts Institute of Technology estimated that enhanced geothermal systems could provide 10% of the nation’s overall electrical generating capacity by 2050. (Earlier post.)

NYU Stern study. A new study by NYU Stern found that geothermal and wind energy are more efficient, and are yielding greater returns on the R&D invested in them, than most other renewable energy alternatives.

NYU Stern Professor Melissa Schilling found that the cost of generating electricity with geothermal or wind energy is a fraction of the cost of solar energy. Additionally, the performance of both is improving much more per dollar of R&D invested in them than solar technologies. This is the first study to explore the trajectory of performance improvement of renewable energy alternatives.

Examining data on government R&D investment and technological improvement, she found:

  • Geothermal energy is the most efficient renewable energy alternative and is improving the fastest. Wind energy is second.

  • Fossil fuel technologies are no longer improving (in terms of efficiency) much, if at all. These technologies have likely reached their performance limits, though the government still spends far more on them.

  • Geothermal energy could become cheaper than fossil fuels with R&D spending of as little as $3.3 billion.

  • Both geothermal and wind energy technologies have been underfunded by national governments relative to funding for solar technologies, and government funding of fossil fuel technologies might be excessive given their diminishing performance.


  • Melissa A. Schilling, Melissa Esmundo (2009) Technology S-curves in renewable energy alternatives: Analysis and implications for industry and government. Energy Policy 37 1767–1781 doi: 10.1016/j.enpol.2009.01.004

  • Praveen K. Thallapally, Jian Tia, Motkuri Radha Kishan, Carlos A. Fernandez, Scott J. Dalgarno, Peter B. McGrail, John E. Warren and Jerry L. Atwood (2008) Flexible (Breathing) Interpenetrated Metal-Organic Frameworks for CO2 Separation Applications. J. Am. Chem. Soc., 130 (50), pp 16842–16843 doi: 10.1021/ja806391k



Yup, as I keep saying on here, this is the century of the organic rankine cycle!


Drilling the earth quite risky issue. You never know what you are going to find. Besides it is major part of investment.


Out west we have lots of geothermal, but if you go down far enough you can find heat almost everywhere. It is the cost and heat extraction methods that limit its use.


Geothermal (indirect sun energy) can be a clean STEADY source of e-energy for future e-vehicles.

Production cost, over 25+ years, is very close to interuptable wind and cheaper than direct interuptable Sun power. It could also compete with nuclear and dirty coal if the cost of fixing all the pollution created in considered.

Geothermal is steady and does not require back-up power sources.

It can be installed in many places in USA and should be a major contributor into the energy mix.


I wouldn't consider Geothermal as indirect sun energy. The vast majority of the heat in Earth's interior [up to 90 percent] is fueled by the decay of radioactive isotopes like Potassium 40, Uranium 238, 235, and Thorium 232 contained within the mantle. So really Geothermal is indirect nuclear energy.


ai_vin is right, it is the decay that produces the heat. Solar thermal is a good way to harvest solar energy efficiently. It can be used to heat, cool and provide power for buildings and homes.


This sounds like the link above. I think Raser technology might be doing similar things.



Organic Rankine heat engines are good, but Carnot states the maximum efficiency. You still have to cool and condense with ambient air temperature, unless you have another cool heat sink.


We can put a halt go GHG emissions growth within 2-3 years using the organic rankine cycle and waste heat from industrial process (first) and waste heat from existing power plants. This would be a stop gap measure until the geothermal is a bit more mature. This could be put into effect worldwide with a forceful push by the current administration, since they would have no problems getting the Europeans to go along with it.


Waste heat recovery does make a lot of sense, but when fuel prices are low most do not even bother. This is where incentives come in. If you make it more cost effective to use heat recovery than using more fossil fuels, some may be interested and then we all benefit.

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