The global demand for energy is increasing and the detrimental consequences of rising greenhouse gas emissions, global warming and environmental degradation present major challenges. Solar energy offers a clean and viable renewable energy source with the potential to alleviate the detrimental consequences normally associated with fossil fuel-based energy generation. However, there are two inherent problems associated with conventional solar thermal energy conversion systems. The first involves low thermal conductivity values of heat transfer fluids, and the second involves the poor optical properties of many absorbers and their coating. Hence, there is an imperative need to improve both thermal and optical properties of current solar conversion systems. Direct solar thermal absorption collectors incorporating a nanofluid offers the opportunity to achieve significant improvements in both optical and thermal performance. Since nanofluids offer much greater heat absorbing and heat transfer properties compared to traditional working fluids. The review summarizes current research in this innovative field. It discusses direct solar absorber collectors and methods for improving their performance. This is followed by a discussion of the various types of nanofluids available and the synthesis techniques used to manufacture them. In closing, a brief discussion of nanofluid property modelling is also presented.

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The demand for high-quality freshwater is increasing due to global population growth, intensifying agricultural practices and expanding industrial development. Additionally, many global regions have low levels of rainfall which makes them arid and incapable of supporting large human populations or agriculture. Currently, large quantities of fossil fuels are used to generate the power needed to drive energy intensive desalination processes that deliver high-quality freshwater to many of these regions. However, the use of fossil fuels has led to high greenhouse gas emissions, environmental degradation and global warming. Solar-thermal desalination is a low-cost, sustainable and eco-friendly strategy for producing high-quality freshwater without using energy derived from fossil fuels. However, in spite of recent developments to advance solar-thermal desalination, the most effective strategies for achieving higher performance levels still remains elusive. To tackle this problem, the present article reviews several solar-thermal still configurations, including materials, system design parameters, influencing factors and operational parameters. Moreover, recent material advances in plasmonic nanoparticle-based volumetric systems, nanomaterial enhanced phase change materials and interfacial solar evaporators are discussed. These new material advances can have the potential to significantly improve the conversion of light-to-heat, enhance vapor generation and promote greater water production rates.

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