Wednesday, 9 December

QGECE signs agreement with US manufacturer to develop next generation power conversion equipment for cheaper geothermal electricity

Readers of this blog will be aware of my belief that much higher geothermal power generation efficiencies are possible and and if they are achieved they will substantially increase the commercial attractiveness of geothermal electricity.

The current industry focus is mainly on minimization of risk and maximization of flow rate. Power generation is seen as mature technology where only marginal improvements are possible. We have been challenging this view. This is an important topic because the proven performance of the mature technology may not be sufficient to ensure EGS project viability, unless high flow rates are achieved, e.g. 100 kg/s from a single well. Almost the entire focus of the geothermal community at the moment is on ways of enhancing the reservoir so as to achieve such higher flow rates.

The question that needs to be asked is if this is the only direction towards commercial viability or if it is more prudent to spread the risk. Achievement of sufficiently high flow rates is certainly of critical importance to the success of an EGS project. But what is "sufficiently high"? A flow rate would be sufficiently high only when it allows the project to deliver electricity at an acceptable cost. For example, it is accepted as common wisdom that high temperatures may compensate for lower flow rates because a higher temperature means higher power conversion efficiency, more power generation, and lower unit cost. The same argument must apply to higher power generation ability.

For example, if 100 kg/s is needed to generate 8 MWe of electricity to make it a commercially viable project with the present power conversion technology, then 75 kg/s would be a "sufficiently high" flow rate if a new generation of power generation equipment can produce the same 8 MW or higher from this lower flow rate.

Is this a realistic aim? Undoubtedly so. There is a theoretical limit that defines what fraction of a heat source can be converted to electricity and this limit is set by the second law of thermodynamics. This theoretical limit is different for different power generation technologies because the temperatures are different. However, one would expect the realised fraction of the theoretical limit to be the same for different technologies.

Less than 40% of the theoretical limit is realised in actual geothermal practice and the ratio is as low as 30% for low reservoir or high ambient temperatures (for air-cooled condensers). In contrast, any other modern power technology is able to enjoy around 70% of its theoretical limit. Clearly, the geothermal energy practice has room to improve.

An agreement signed last week between the University of Queensland and the US-based power plant and turbine manufacturer Verdicorp will help bring the geothermal power conversion efficiencies closer to what are achieved in more mature industries.

With this agreement, QGECE and Verdicorp start a collaborative project to develop not only supercritical turbines and supercritical cycle equipment including supercritical turbines but also heat exchangers and air-cooled condensers for geothermal, solar thermal and waste heat power generation applications and new cycle fluids and fluid mixtures suitable for supercritical cycles. The target technologies have the potential to increase the geothermal productivity by 50%.

A successful conclusion of this project will make geothermal electricity cheaper than the present cost of gas-fired electricity and is expected to make geothermal power cost-competitive even without the motivation of a carbon price. At the first instance, a high-pressure supercritical turbine and cycle testing facility will be built next year on the Pinjarra Hills campus of the University of Queensland. The facility will include a portable test plant for testing and demonstrating the benefits of the new power plant technologies at remote geothermal sites. Watch this space for exciting developments in this area.

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