Techno-economic analysis of a hybrid district heating with borehole thermal storage for various solar collectors and climate zones in Pakistan

Abstract

Fossil fuels are being used to accommodate domestic heating needs all over the world, and the alarming rise in carbon footprint is demanding the world to shift towards renewable energy technologies. A key strategy to lessen household fossil fuel consumption is a solar hybrid district heating network integrated with seasonal thermal energy storage (TES). The objective of this study was to analyze and compare the thermo-economic performance of solar hybrid district heating systems integrated with borehole TES systems in ' 'Pakistan's five climate zones and identify the best suitable solar thermal collector technology. Based on the solar energy incident on different types of thermal collectors, a validated TRNSYS model was used to investigate the dynamic performance indices i.e., solar fraction, system efficiency, and thermal storage efficiency. The heat demand model and weather-related data were changed as input to the system. Based on mentioned performance indices, out of 5 different cities having different climates, climate Zone-C(Quetta), having a continental semi-arid climate, is selected as the most suitable, and Zone-E(Karachi) has tropical desert climate as the least favorable among five different zones with a seasonal storage efficiency of 61% and 19% respectively. The solar fraction is about 91%, also up to the mark as the proposed system utilizes both solar energy and auxiliary systems. Further, the implementation of different thermal collector technologies Parabolic Trough Collector, Evacuated Tube Collector & Flat Plate Collector, revealed that the thermal efficiency of ETC is best among all, with the highest value of 65%, followed by PTC at 44%, and FPC shows the least efficiency of 36%. The economic analysis shows that the model embedded with ETC has a minimum payback period of 6.90 years, followed by an FPC of 7.22 years and a maximum for PTC of 7.38 years. The analysis presented in the current study provides guidelines for researchers and policymakers to identify acceptable location-based best solar thermal collector technologies coupled with seasonal thermal storage for district space heating.