Empirical investigation and performance evaluation of flat-plate solar water heating systems: a comparative analysis with and without heat exchangers

Abstract Harnessing solar energy through flat-plate solar water heating systems offers an efficient and sustainable solution for residential water heating needs. This study aims to assess and compare the thermal efficiency of two flat-plate solar water heating systems designed for residential use: one with a heat exchanger and one without. Each system features a flat-plate collector with a dark absorber, a transparent cover to reduce heat losses, and a heat-transport fluid. A thin copper sheet with a selective coating forms the absorber. According to the standards of the Indian Ministry of New and Renewable Energy (MNRE), the evaluation revealed that the system without a heat exchanger achieved a higher efficiency (50 %) compared to the system with a heat exchanger (46 %). This device demonstrated notably lower thermal loss efficiency relative to previous studies, as evidenced by heat loss coefficients of 2.89, 2.66, 1.77, and 2.13 W/m 2 k. Despite the higher efficiency of the system lacking a heat exchanger, the importance of heat exchangers in mitigating issues related to water hardness must be acknowledged. This study offers novel insights into the design and optimization of solar water heating systems, highlighting the trade-offs between efficiency and practical considerations.