# Fewer Dimensions for Higher Thermal Performance: A Review on 2D Nanofluids
## 3 Application of 2D Nanofluids
### PV/T Systems
The operating thermal fluids used were water alone and Gr at 0.05% and 0.15% volume fractions in water nanofluids. The experiments were conducted at flow rates between 20 L and 40 L per minute. An exergy analysis of the performance of the various PV modules, together with the changes in the concentration of the nanofluids and flow rates, was performed. Figure 15 schematically represents the configuration of the experiments for the four studied cases. Considering the experimental results, the authors concluded the following points:  
* The enhancement in the volume fraction of the Gr nanoparticles from 0.1% vol. to 0.15% vol. resulted in a poorer performance of the system because of the agglomeration and settling of the nanoparticles in the distilled water. The agglomeration lowered the heat transfer capability since the Brownian motion of the nanoparticles was restricted. * The exergy losses and entropy generation were decreased by the increasing flow rates in the PV/PCM (phase change material) system. Consequently, the increase in the flow rates of the operating fluid promoted the extraction of energy. Figure 14: Schematic diagram of the Hummer method for the synthesis of GO. Figure 15: Schematic diagram of the configuration of the PV/T system for four different conditions. Adapted from [137]. * The sustainability index increased with increasing flow rate and a maximum of 1.17 was reported for the system with PCM and 0.10% vol. concentration of Gr nanoparticles. The same system presented a minimum improvement potential by demonstrating that this configuration was most efficient. * The electrical exergy contributed more to the overall exergy efficiency than the thermal exergy. This fact can be interpreted based on the inferior thermal energy produced by the PVT/PCM system. Many efforts were undertaken to develop different solar cell technologies, but researchers are still trying to find the best way to enhance the large-scale performance of PV cells. Attention should be paid to the research topics concerning the geometry of the channels, flow pattern configuration and distribution, and maintenance requirements of the PV cells to improve the heat transfer between the solar module and the hybrid nanofluids. The channels with a hexagonal honeycomb geometry demonstrated an 87% thermal efficiency compared with other channel geometries. In addition, the carbon hybrid nanofluids showed a maximum of 63% enhancement in the HTC and a 144% enhancement in the Nusselt number, higher than the other types of hybrid nanofluids. Furthermore, the f-MWCNT/HEG)/water hybrid nanofluids exhibited a 289% increase in heat transfer capability for 0.01 vol% of hybrid nanofluids at a Reynolds number of 15,500 in comparison to the base fluid. It is highly recommended that a detailed review is undertaken to assess the main causes behind the modifications to the heat transfer characteristics induced by hybrid nanofluids. The economic analysis of PV/T systems should incorporate the time value of money for their design and implementation. The cost of factors including maintenance needs, parts warranty, and reduction in electrical performance of the system should be an important feature of the economic analysis. The main point is the payback period, which is expected to be shorter than the PV panel lifetime and less than 14.5 years. The solar energy field and hybrid nanofluids will take advantage of the low carbon content, low initial investment, green methodologies, and the production of non-fossil fuel electricity, which shows a remarkable impact on the environment by limiting the emission of toxic gases and non-renewable resources depletion. In the long run, the use of hybrid nanofluids may enhance the performance of PV/T systems by reducing their overall operating cost. The science and technology associated with hybrid nanofluids will entail economic and environmental profit by enhancing the efficiency of the systems and by reducing the emission of greenhouse gases.