Comparative Performance Analysis of Flat Plate and Evacuated Tube Solar Water Heating Collectors

Solar water heating is one of the most mature and cost-effective applications of solar thermal energy, widely adopted for domestic and commercial hot water requirements. This paper presents a comparative performance analysis of two commonly used solar collector types: the Flat Plate Collector (FPC) and the Evacuated Tube Collector (ETC). Both collector types were studied for water temperature rise, thermal efficiency, and heat loss characteristics under similar solar radiation and ambient conditions representative of Karad, Maharashtra. Hourly measurements of solar radiation, ambient temperature, and water outlet temperature were recorded over a full sunny day. Results show that the evacuated tube collector achieves higher water outlet temperatures (up to 70.6°C) compared to the flat plate collector (up to 61.2°C) under identical conditions, owing to reduced convective heat loss from the vacuum-insulated tube design. However, flat plate collectors offer lower initial cost and simpler maintenance, making them more suitable for low-temperature domestic applications, while evacuated tube collectors are preferable where higher temperature output or operation under low ambient temperature conditions is required.