Recent progress in solar water heaters and solar collectors: A comprehensive review

Solar water heating (SWH) is a clean, reliable, and cost-effective method of harnessing solar energy effectively to satisfy 50–80% of hot water needs. SWH technology is currently employed in many countries to reduce utility bills in both commercial sectors and houses. With the advancement of technology, SWH systems can be operated efficiently in any geographical area and climatic region in the world. However, the installation and overall performance of the system are still questionable. This review aims to provide an overview of the most commonly used solar water heating technologies. This paper seeks to critically analyze and summarise recent advancements in the technology, including storage tank/integrated collector storage solar water heater, solar water heaters (active and passive), solar thermal collectors, including concentrated and non-concentrated collectors and different policies. Substantial experimental studies and research works, including optimal designs, geometric modifications, and simulation works, were carried with respective technologies to enhance the system performance. Besides, the effect of solar collectors, radiation, region, water tank temperature, experimental modelling/simulation and studies conducted in Asia, America and Europe on SWHS improvements are also included. Policy developments of renewable energy heat consumption in different countries by technology from 2012 to 2024 were also included for better understanding. A detailed status on current and ongoing solar power projects based on solar technologies for electricity generation has been provided. The final section introduces the technical advancements of SWH technologies, policies, and future research SWHS.