In this paper, the performance of a solar still equipped with a heat exchanger using nanofluids has been studied both experimentally and theoretically through three key parameters, i.e., freshwater yield, energy efficiency and exergy efficiency. First, experiments are performed on a set-up, which is mainly composed of two flat plate solar collectors connected in series, and a solar still equipped with a heat exchanger. After heated in the collectors, the nanofluid enters the heat exchanger installed in the solar still basin to exchange heat with brackish water. The research question is to know how much the effect of nanofluids on the evaporation rate inside the solar desalination system is. The experiments are conducted for different nanoparticle volume fractions, two sizes of nanoparticles (7 and 40 nm), two depths of water in the solar still basin (4 and 8 cm), and three mass flow rates of nanofluids during various weather conditions. It is found that the weather conditions (mainly the sun radiation intensity) have a dominant influence on the solar still performance. To discover the effects of nanofluids, a mathematical model is developed and validated by experimental data at given weather conditions. The results reveal that using the heat exchanger at temperatures lower than 60 °C is not advantageous and the corresponding yield is smaller than that of solar still without the heat exchanger; although in such a case, using nanofluids as the working fluid in the heat exchanger can enhance the performance indices about 10%. At higher temperatures (e.g. 70 °C), the use of heat exchanger is beneficial; however, using nanofluids instead of water can augment the performance indices marginally i.e. just around 1%. In addition, it is found that in high temperatures using SiO2/water nanofluids, which have a lower effective thermal conductivity than that of Cu/water nanofluids, provides higher performance indices.

Steam production is essential for a wide range of applications, and currently there is still strong debate if steam could be generated on top of heated nanoparticles in a solar receiver. We performed steam generation experiments for different concentrations of gold nanoparticles dispersions in a cylindrical receiver under focused natural sunlight of 220 Suns. Combined with mathematical modelling, it is found that the initial stage of steam generation is mainly caused by localized boiling and vaporization in the superheated region due to highly non-uniform temperature and radiation energy distribution, albeit the bulk fluid is still subcooled. Such a phenomenon can be well explained by the classical heat transfer theory, and the hypothesized ‘nanobubble’, i.e., steam produced around the heated nanoparticles, is unlikely to occur under normal solar concentrations. For future solar receiver design, attention should be paid to focus and trap more solar energy at the superheated region while minimizing the temperature rise of the bulk fluid.

Improving photovoltaic efficiency is fundamental to the large scale utilization of solar energy and reduction of carbon emission. In this field, reducing the temperature of the Photovoltaic (PV) panel will increase its efficiency and power production. Utilizing hybrid photovoltaic/thermoelectric (PV/TE) systems is an effective way to simultaneously release the excess heat of the PV panel and use this heat to produce power. The cooling method used for the thermoelectric module (TEM) plays an important role in the system efficiency as well as the produced power. A new nanofluid-based cooling method for a hybrid photovoltaic/thermoelectric system is proposed in this work and compared with the conventional cooling methods experimentally. To this end, five different cooling methods were investigated experimentally, namely natural cooling, forced air cooling, water cooling, SiO2/water nanofluid cooling, and Fe3O4/water nanofluid cooling. The results showed the promise of SiO2/water nanofluid cooling, which yielded the highest power and efficiency, showing 54.29% and 3.35% improvement, while Fe3O4/water nanofluid cooling showed 52.40% and 3.13% improvement in power production and efficiency respectively, comparing with the natural cooling method.