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Session: Poster session & Sponsor Exhibition
Session starts: Monday 07 October, 14:00

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Stephan Paredes (IBM Research - Zurich)
Patrick Ruch (IBM Research - Zurich)
Chin Lee Ong (IBM Research - Zurich)
Brian Burg (IBM Research - Zurich)
Bruno Michel (IBM Research - Zurich)

Abstract:
Waste heat is recovered from high concentration photovoltaic thermal (HCPVT) systems with the aim to enable multi-generation of electricity, cooling, and fresh water. This concept involves 80–90°C waste heat recovery from a low thermal resistance multi PV chip receiver package, 120°C from the optics, and thermal energy storage. The system recovers ~80% of the solar irradiation comprising ~30% as electrical energy and ~50% as heat. HCPVT systems provide a higher exergetic output than concentrated solar power installations due to the good conversion efficiency of triple junction photovoltaic cells (up to 44% in laboratory demonstrations) and their low thermal coefficient. A >25% system-level electrical efficiency can be reached while still having 50% medium grade heat. Conversion of the heat into cooling and desalinated water has been demonstrated using adsorption chillers and multi-effect vacuum membrane distillation systems, respectively [1]. We have estimated the economic value of heat with regard to its consumer and observed that this may differ markedly from its thermodynamic value depending on the system location. Using the generated heat in addition to the electricity boosts the economic value of the overall generated output by more than 20% [2]. Conversion of the heat into additional electrical output, however, is lacking an efficient low grade heat conversion process e.g. an organic Rankine process. Exergetic yields are compared between photovoltaic systems, concentrated solar power (CSP) systems, and HCPVT systems with medium grade heat output. From an exergy point of view, direct heat utilization from HCPVT systems for cooling and desalination is beneficial for key locations. Overall exergetic yields, flexibility, optimal plant size, and cost are neither optimal in photovoltaic nor CSP systems but HCPVT systems can compensate the disadvantages of both pure systems. For a successful power station application HCPVT systems require the conversion of low grade heat to electricity with an efficiency of >10%. With this combination an overall electrical system efficiency of >35% becomes possible – more than with any other solar installation. Combinations of HCPVT systems with Rankine processes using different working fluids are modelled. Since electrical power and cooling are in high demand in areas with high direct normal irradiance a combination of power generation and cooling has also been studied (Kalina and Goswami cycles). Finally, economic and technical modelling is carried out to determine the optimal size for HCPVT plants and match them to available heat conversion devices for high-efficiency multi-generation. REFERENCES [1] C.L. Ong, W. Escher, S. Paredes, A.S.G. Khalil, and B. Michel, “A novel concept of energy reuse from high concentration photovoltaic thermal (HCPVT) system for desalination”, Desalination 295, 70-81 (2012). [2] W. Escher, S. Paredes, S. Zimmermann, C.L. Ong, P. Ruch, B. Michel. Thermal management and overall performance of a high concentration PV. Proc. 8th Intl. Conference on Concentrating Photovoltaic Systems CPV8, 11477 (2012) 239-243.