Thermo-economic analysis and optimization of a high concentration photovoltaic thermal (HCPVT) integrated system II

This paper presents the results of the semester thesis realized in the frame of the minor in energy and conducted within the IPESE laboratory. This work aims to study the integration of a high concentration photovoltaic thermal system (HCPVT) with a wastewater treatment plant. System modeling and thermo-economic analysis is performed to study the energetic and cost performance of the system. The case of the Martigny wastewater treatment plant (WWTP) is considered in this report based on specific parameters measured on-site. From the energy aspect, it is demonstrated that the high energy demand of the Martigny plant (around 2’260’000 kWhel/year and 635’000 kWhth/year) cannot be fulfilled by a single high concentration photovoltaic thermal tracker system which can only supply less than 1% of the electrical need and 6% of the thermal need. However, by installation of several HCPVT units the fraction solar energy supply would be increased. Therefore the addition of a cogeneration system, fueled by the methane produced on-site through the use of an anaerobic digester, and the electrical grid is studied to satisfy the electrical energy balance. These two systems were found to supply 13% and 86% of the electrical demand respectively under the current assumptions. Due to the insufficient methane production, the cogeneration system can only produce 59% of the heat used by the wastewater treatment plant resulting in an energy gap. External natural gas resources used to run the cogeneration engine is studied as an option to fulfill the heat demand. The Martigny plant has much higher (>3) electrical demand with respect to its thermal demand. While the HCPVT trackers deliver twice as much heat as electricity. This indicates despite the lack of a precise cost analysis, which can be part of further work on the topic difficulty for the integration of the concentration photovoltaic thermal system with a wastewater treatment plant.