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Session: New applications: Solar
Session starts: Monday 07 October, 11:10
Presentation starts: 11:30
Room: Willem Burger Zaal

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George Kosmadakis (Agricultural University of Athens)
Dimitris Manolakos (Agricultural University of Athens)
Kostas Bouzianas (Hellas Energy K. Bouzianas P. Moschovitis & Co.)
George Papadakis (Agricultural University of Athens)

Abstract:
In low-concentrating PV/Thermal units the heat produced is of low-temperature and should be effectively removed. The motivation of the present work is to recover this low-grade heat and then feed it to a supercritical organic Rankine cycle (SCORC) for additional electricity production. Such bottoming engine can operate with acceptable efficiency at temperature of around 80-90 oC, showing an efficiency higher than around 10% in comparison to a similar subcritical cycle, due to the better thermal match and specific thermodynamic properties. The key parameter of such system design is the temperature of the heat transfer fluid in the CPV/T circuit, transferring heat from the solar collectors to the SCORC unit, through the supercritical heat exchanger. This temperature has a major effect on the performance of both the PV cells and the SCORC engine. For higher temperature, the PV cells’ efficiency decreases linearly, according to their temperature coefficient, while the SCORC efficiency is radically improved [1]. This process can be optimized, resulting to a total higher electric efficiency, and a significant higher productivity. The system includes a CPV/T field of 10 kWp producing 41 kWth, feeding the SCORC engine, which shows a thermal efficiency of 6-7%, and producing almost 3 kW. The total maximum power production is 10 kW, making such system appropriate for installation on buildings and for decentralised applications. The combined system is currently designed through extensive simulation and optimization studies. The so far calculated results are very promising, showing that the proposed system can be competitive to both PV and CPV systems in terms of productivity and specific cost (€/kWh), while the supercritical cycle shows some interesting features, as already mentioned. This integrated system is to be constructed and tested under real conditions by the end of 2013, and then evaluated. Acknowledgement: The research leading to these results has received funding from the European Union's Seventh Framework Programme managed by REA-Research Executive Agency, http://ec.europa.eu/research/rea ([FP7/2007-2013] [FP7/2007-2011]) under grant agreement n° 315049 [CPV/RANKINE], FP7-SME-2012. REFERENCES [1] G. Kosmadakis, D. Manolakos and G. Papadakis, “Simulation and economic analysis of a CPV/thermal system coupled with an organic Rankine cycle for increased power generation”, Solar Energy, Vol. 85, pp. 308–24, (2011).