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INTERVIEW TO THE EXPERT - Prof. Ennio Macchi from Politecnico di Milano

Exergy talked about the latest trends in ORC research with emeritus professor Ennio Macchi from Politecnico di Milano, taking the cue from a recent study that examines the global trend of ORC research from 2000 to 2016.

EXERGY: The study examines a series of interesting issues regarding ORC technology research worldwide. From 2000 to 2016, 2120 articles have been published from 997 research institutes. In particular the Politecnico di Milano is the 5th most productive institute in the ORC technology research field. After being among the founding fathers of ORC technology, what is happening today at Politecnico di Milano? Where is Politecnico ORC research heading?

Prof. MACCHI: First of all, I am pleased to see that Politecnico di Milano leads this particular ranking of non-Chinese university institutes (the first 4 are Chinese) in this ranking. As we have mentioned several times in the past, research on engines with organic fluids in Italy started with the initiative of three, once young at the time, professors: Gianfranco Angelino, Mario Gaia and I.Mario Gaia consequently founded Turboden, of which he is still honorary chairman, Gianfranco Angelino sadly passed away a few years ago, and I am today still active in the Department of Energy at the Politecnico di Milano, as emeritus professor. There are numerous researchers today in the group of the energy department operating within the ORC sector: there are those who study new working fluids (pure and mixtures), those who develop complex codes to optimize thermodynamic cycles and components for the different energy sources, and those who study fluid-dynamic project methodologies of the fundamental component, the turbine. A new multi-disciplinary laboratory, called CREA (Compressible fluid dynamics for Renewable Energy Applications) has been created and it operates within the fluid dynamics of non-ideal compressible fluids, most of all for renewable resource applications. It is easy to foresee that these researches will continue for many years. I would also like to highlight a renewed interest in CO2 cycles, a sector in which Gianfranco Angelino had published fundamental research, still very relevant today, even if written half a decade ago!

EXERGY: We read that most of ORC research is focusing mainly on the applications (42.15%) and less on the cycle and expander technology itself. Do you think more research would be needed on technical topics or issues (expander, cycle architecture, design and optimization, working fluid) in order to help the ORC technology to advance further? What is more important to study for an effective technology upgrade?

Prof. MACCHI:Whatever the application (the variety is infinite, from micro applications to power plants with dozens of MW, in a wide range of temperatures), the rules for a successful project are always the same: the working fluid must well match with the thermal source characteristics and must allow the expander to have optimal dimensions, high performance, correct sizing of the heat exchanger, etc..In recent decades there has been a revolution of the working fluids: chlorofluorocarbons have disappeared: even if they have excellent characteristics (nontoxic, non-flammable, wide choice of thermodynamic properties, low price) they have defects from the environmental point of view (high ODP and GWP). On the other hand, a perfect replacement has not been found, and its substitutes are under accusation (HCFC, HFC, HFO) for being greenhouse gases. The research of a new class of fluids (pure or mixed) with a low environmental impact (ODP and GWP index), low safety risk (flammable and toxic) and low cost is probably the most fascinating challenge.

EXERGY: Global energy market needs and the compelling energy policies towards sustainable energy models surely influence the direction taken by the ORC technology research. Where is worldwide ORC research heading today?

Prof. MACCHI: In the coming years the global energy need will continue to rise: ORC cycles will play a very important role for a variety of applications, from biomass to geothermal and CSP (concentrated solar power, or thermodynamic solar power). An important sector, with strong development potential, is the waste heat recovery from industrial processes. In emerging countries, biomass (a renewable and predictable resource) using ORC technology will work alongside with wind and photovoltaic applications to create micro and mini isolated grids that will manage to respond to the emerging energy needs of rural villages.

EXERGY: Italy and USA are, for historic reasons, leaders in this technology. However, in the period considered by this study, USA and Italy have been overcome by research in China. How can you explain this interest in a country that today still registers very few ORC installations?

Prof. MACCHI: China nowadays is a global power in almost all sectors. I don’t think we should overrate the importance of such a high number of scientific articles regarding ORC from Chinese authors: in science and in technology the number of publications is not what counts, the quality and the original ideas that each article communicates are important.

EXERGY: In your vision, what is the role of technological research in the product-to-market process for green technologies worldwide?

Prof. MACCHI:The role of technological research must be first of all focused on creating reliable and economically competitive components and plants: the enormous variety of possible applications allows us to predict wide possibilities for new ideas and creations.

EXERGY: After the first research into, and implementation ORC technology in the 1970's, when you worked together with Prof. Angelino and Prof. Gaia at Politecnico di Milano and Ormat was doing the same in Israel, market leaders have accumulated in 40 years of commercialization a portfolio of approximately 2000 MW for Ormat and 560 MW for Turboden. In the last 7 years, the new-comer Exergy was able to gather a portfolio of 400 MW, proving that the ORC market nowadays is booming. Do you see a possible reason in technological advancement or a market change behind this boost? What expectations do you have for the future, regarding key applications and technologies in ORC marketplace?

Prof. MACCHI:The extraordinary success of Exergy is certainly due to many factors (business courage, commercial ability, etc.) but there is no doubt that the main factor is the innovative technology of the turbine: the centrifugal solution, that allows to obtain a very efficient expansion thanks to the possibility to split it in many stages mounted on a single disk. The favourable market conditions for geothermal harnessing for energy production in different countries, beginning with Turkey, have done the rest.