Recent Trends in Applications of Nanofluids for Effective Utilization of Solar Energy

Renewable-energy sources have been explored recently by scientists to fulfill the global energy demand. According to the International Energy Agency (IEA), by 2040, wind and solar power will be the star performers for energy conservation. The annual potential energy received from the sun ranges from 1,575 to 49,800 exajoules (EJ). However, this energy is not being utilized to its potential. Recently, researchers have proven that nanofluids can be used as a working fluid replacing the conventional working fluid for solar collectors and other heat exchange operations. The selection of the nanofluid is not only based on the size and shape of nanoparticles but the pH value and stability of nanofluids are also important parameters. This review paper is mainly focused on the recent trends in nanofluids applications for the capture, conservation, and utilization of solar energy. The present paper reviews the detailed analysis of various forces affecting the nanofluid system and also highlights the important aspects to reduce the frictional energy losses, exergy destruction, entropy generation, effect of the flow properties, and thermo-physical properties of the nanofluids, and other reasons for wastage of the exergy. This study also compares the performance of the direct absorption solar panel, flat plate solar panel, parabolic solar collector, photovoltaic thermal solar collector, linear Fresnel solar collector, solar dish, and evacuated type solar collector. Among these solar collectors, direct absorption solar collectors, flat plate solar collectors, photovoltaic solar collectors, and evacuated type solar collectors are more commonly used solar collectors; thus, the exergy and energy analyses of these collectors are important for their design and application. Stability issues and agglomeration problems are still some major concerns involved in the application of nanofluids. However, the use of nanofluid increases the performance of the solar collector compared to the base fluid as a working fluid. This paper also highlights the recent trends in the application of nanofluids in solar collectors.