Performance enhancement of solar energy systems using nanofluids: An updated review

There are various techniques used to enhance the conversion of solar energy into useful forms. Use of nanofluids is one of the prominent techniques in the active research of enhancing the energy utilization. In this paper, an updated review is carried out for various recent studies that illustrate the use of nanofluids in different types of solar collectors for improvement of their performance. In addition, some suggestions are made in relation to the future research directions in view of the prevailing challenges using nanofluids in solar energy systems. It has been witnessed that proper dispersion of nanoparticles is a key issue for adequate solar absorption. Improvement of solar collector performance agrees until certain limit of nanofluid volume fraction above which it can end up with adverse results. Proper combination of particle size, pH value and adequate dispersion of nanoparticles results in efficiency increment. Among all possible nanoparticles carbon nanotubes result in larger enhancement when compared to rest, in general. It is also noted that the optical properties of nanoparticles play a key role in absorption, extinction coefficient and the penetration depth of the solar radiation in the nanofluids. (C) 2019 Elsevier Ltd. All rights reserved.