## 1 Introduction  
Solar energy can be directly utilized in the form of either photovoltaic or thermal energy. The conversion efficiency of solar photovoltaic energy from solar cells using polysilicon materials has reached 24%, which, when compared with the maximum theoretical conversion efficiency for solar photovoltaics of 29%, suggests that the photovoltaic conversion efficiency has reached its maximum. Solar thermal energy, in contrast, has received comparatively little attention. The utilization of solar thermal energy can be divided into low-, medium-, and high-temperature areas. Low-temperature systems (below 100 \({}^{\circ}\)C) generally use a small flat-plate collector to collect and accumulate thermal energy for heating and supplying hot water to buildings, mainly small households [1]. Mid-temperature systems (300 \({}^{\circ}\)C or less) serve as an auxiliary heat source for the heating and cooling of buildings, as well as industrial manufacturing processes using a vacuum tube or trough collector. High-temperature systems (above 300 \({}^{\circ}\)C) serve as solar power plants. Basically, this power generation method drives a steam turbine that in turn drives multiple generators up to 25 kW in capacity in the form of distributed generation [2]. Thermal solar energy depends strongly on the surrounding environment, making it difficult to obtain precise amounts of energy or sufficient amounts when needed, and thus, supplementary devices are necessary. A thermal solar power plant requires three basic facilities: a heat collecting unit, heat storage unit, and utilization unit. The heat collecting unit increases the temperature of the working fluid by collecting solar thermal energy; the heat storage unit collects and stores the thermal energy from the high-temperature working fluid; and the utilization unit converts the heat energy into useable energy. All thermal solar systems require a working fluid to transport and utilize the heat energy absorbed from the sun; air, water, steam, and molten salt are current examples of working fluids [3]. The nanofluid theoretically suggested by [PERSON] [4] in 1873 was not viable at the time due to the absence of nanoparticle fabrication technology, but today, research on and fabrication of various nanofluids are ongoing. In 1975, [PERSON] [5] reported that a fluid with a micrometer-sized particle dispersion showed promising thermal properties but could not be applied to actual cooking systems due to blockage and corrosion of pipes from particle precipitation. In 1995, [PERSON] [6] of the Argonne National Laboratory research team in the United States first introduced the term \"nanofluid,\" which was defined as a fluid in which nanoparticles less than 100 nm in size are dispersed. The authors reported that the thermal conductivity of nanofluids is significantly higher than that of conventional heat transfer fluids. In particular, it has since been reported that the thermal conductivity of nanofluids is more than 10% higher than that of other fluids, even at a small nanoparticle volume ratio, and the heat transfer properties are greatly improved compared with those of conventional fluids [7]. [PERSON] et al. [1] studied the energy and emission duration of solar collector systems in South Korea and suggested the need for heat energy storage based on the theoretical results. [PERSON] et al. [8] and [PERSON] et al. [9] demonstrated the feasibility of a lightweight adsorption refrigeration system that is efficiently driven by a combination of a solar parabolic trough collector (PTC) and heat pipes; they also proved that the PTC is useful for improving solar adsorption refrigeration systems. Additionally, the authors concluded that this technology meets the requirements for not only cooling, freezing, ice manufacturing, and condensing purposes but also for energy and environmental conservation. [PERSON] et al.