A review on the approaches employed for cooling PV cells
Introduction
Considering the limited sources of fossil fuels and their environmental polluting impact, the development of renewable energy systems is necessary (Ahmadi et al., 2018a, Ramezanizadeh et al., 2019b). When compared with fossil fuels, using renewable energy sources for power generation has lower greenhouse gas (GHG) emission (Dehghani Madvar et al., 2018). In addition, the Levelized Cost of Electricity (LCOE) produced by renewable sources has shown a steady declining trend in the recent decades due to the advancements in the corresponding technologies which has lead to a gradual decrease of their cost (Dehghani Madvar et al., 2018, Perkins, 2018). Accordingly, the conventional power generation systems that utilize fossil fuels will be replaced with renewable energy-based power plants. Solar energy is among the most attractive types of renewable energy sources energy policy makers due to its several advantages such as predictability, availability and its capability of being employed for small-scale power generation (Alhuyi Nazari et al., 2018, Guangqian et al., 2018; Maleki et al., 2020). As PV technologies advance further, their cost of production and operation will continue to plunge in the near future. According to a report published by U.S. Energy Information Administration (EIA), PV’s LCOE will reach values as low as 33.12 USD/MWh in 2025, which would be lower in comparison with other renewable sources, as presented in Table 1. In addition to prospective cost effectiveness of PV panels, solar energy is significantly more ubiquitous and available compared to other renewable sources, see Table 2. An additional benefit of PV panels is the absence of moving components in their design which leads to their easy maintenance on top of their smooth and noiseless operation. Furthermore, solar energy has uses other than mere energy production and it can be incorporated in applications with cooling, heating and desalination processes (Ghorab et al., 2017, Kabeel and El-Said, 2013). The above-mentioned superiorities of solar energy makes it an attractive choice of renewable clean energy. In addition to PV panels, solar thermal technologies are applicable for producing electricity. Depending on the required capacity and climate of a region, the specific solar technology for power generation can be selected. In 2017, the share of solar energy capacity surpassed other types of technologies installed as shown in Fig. 1.
There are specific advantages to each of the solar technologies used for electricity generation (Ahmadi et al., 2018b, Ahmadi et al., 2018c). For instance, Awan et al. (2019), compared concentrated solar power (CSP) and PV technologies, with 100 MW capacity, for electricity generation in Saudi Arabia by considering technical and economical criteria. According to their results, by employing CSP technology, approximately 33.3% higher electricity was generated in comparison with PV modules in the best case; however, net capital cost of CSP was about 4.5 times greater compared with PV. Vergura and Lameira (Vergura and Lameira, 2011), evaluated these technologies based on technical-financial criteria. They concluded that under the same environmental conditions, using CSP leads to higher power generation in comparison with PV plant, while the initial cost for installing CSP is much higher than PV plants. In addition, it was indicated that annual maintenance costs of CSP and PV technologies were 2% and 1% of their investment costs, respectively. Higher maintenance cost of CSP technology was attributed to its more complex structure in comparison with PV panels. Based on a report published by the International Energy Agency (IEA), solar energy harvesting technologies are expected to provide 11% of the world’s generated electricity in 2050 based on the BLUE Map scenario (Frankl et al., 2014). PV panels have a higher share (6%) in this scenario compared to solar thermal technologies (5%). Despite of the fact that the majority of installed PV panels are on-grid, it is possible to use them for off-grid electricity generation as well (Pillot et al., 2019). For instance, Maleki et al. (Maleki et al., 2017b) studied a stand-alone PV system for supplying electricity in a remote location in eastern Iran. They optimized the size of this system for improved reliability and reduced cost of the power production. When PV modules are used to generate electricity in distant areas, an storage unit or another feature must be applied to enhance the reliability of the systems at night hours (Maleki and Askarzadeh, 2014). In a study represented by Maleki et al. (Maleki and Askarzadeh, 2014), a hybrid system composed of diesel generator, PV, wind and battery was used to supply off-grid electricity. Moreover, Hybrid systems with PV modules are useful for grid-connected electricity production (Maleki et al., 2017a).
The electricity produced by PV cells can be applied in various systems (Clarke et al., 2009, Maleki, 2018). Martin et al. (Gutiérrez-Martín et al., 2020), studied a system composed of PV cells, electrolyzers, hydrogen storage and fuel cells. In the proposed configuration, the power produced by PV cells was used to drive the electrolyzer (direct utilization). The main advantage of the proposed system is its ability to store the surplus generated electricity in a separate cell in the form of hydrogen. In another study (Ghribi et al., 2013), a 60 W PV module was coupled with a PEM electrloyzer (50 W) to produce hydrogen. They reported production of 20 to 29 of hydrogen through presenting a case study in Algeria which implemented their proposed system. The required electrical energy of pumps in reverse osmosis desalination systems can be provided by renewable energy technologies. Solar PV modules are applicable in regions with high solar irradiation for supplying power for these systems. Mainly, the produced power is used to run the water pump in reverse osmosis desalination units (Chen et al., 2019). The performance and feasibility of PV-desalination systems can be influenced by many factors such as the system size, whether a storage unit is implemented and also the operating conditions (Ahmed et al., 2019). For instance, Clarke et al. (2013), used PV panels to provide the required power for a reverse osmosis desalination unit and evaluated the effect of using a storage unit on the overall performance, and came to the conclusion that the benefits of using batteries is more remarkable in systems of smaller scales. Moreover, systems composed of PV modules can be integrated with earth-air heat exchangers to produce cooling effects (Mahdavi et al., 2019). Finally, solar PV modules can be used to supply the required electricity for cooling systems such as heat pumps and compression chillers (Lazzarin, 2014).
Due to PV panels significant share in the world’s future electricity generation, it is crucial to discover systematic approaches to improve their efficiency and generated power. Enhancement in the efficiency of power generation systems is one of the main concerns of several studies (Pakatchian et al., 2019). Researches have demonstrated that the efficiency of the PV panels will be increased by reducing their temperature (Teo et al., 2012, Vasel and Iakovidis, 2017). The increase in temperature of the PV panel will cause a huge drop in voltage and a little increase in the current, which will cause reduction in the electric power generated by PV (Abdolzadeh and Ameri, 2009, Akbarzadeh and Wadowski, 1996, Ndiaye et al., 2014). In addition to the technical benefits of improving the efficiency of the PV cells, the LCOE and payback period of the PV projects can be reduced by enhancing their performance (Peng et al., 2017). Due to the temperature-dependent performance of the PV panels, several approaches such as using water as cooling fluid and inserting heat pipes are suggested to improve their efficiency. In recent years, some review studies on the PV cooling technologies have been published; however, the majority of them have focused on the PV/T systems (Lupu et al., 2018) while there are some approaches which are used for PV systems without any thermal accessories. These types of cooling methods, such as pulsating heat pipes and wick structures, are employed for improving the electrical efficiency of the panels without aiming for thermal energy extraction for other purposes. Moreover, some novel ideas have been introduced in recent years such as air precooling and liquid cooling with various nanofluids and channel shapes which have not been covered in the previous studies (Siecker et al., 2017).
In this article, different methods employed for cooling PV panels are reviewed. Firstly, the active methods applicable in PV thermal management are represented. Afterwards, the passive approaches such as wick structure and heat pipes are discussed. Finally, according to the reviewed methods and their effect on the efficiency of PV panels, some suggestions are presented to achieve further enhancement in their efficiency and reducing their operating temperature.
Section snippets
Factors influencing the performance of PV cells
As previously mentioned, there are different factors that control the performance of PV cells. These parameters are usually specific to the cell type and the operating conditions and are explained in detail in the previously published literature (Fouad et al., 2017). In this section, the most important ones are presented:
PV cooling approaches
As previously indicated, the performance of the PV modules are temperature-dependent (Brinkworth, 2000, Hasanuzzaman et al., 2016). Nordmann et al. (Nordmann and Clavadetscher, 2003) evaluated the efficiency of PV modules with different mountings. The highest reduction in the performance was observed when the cells were inside an insulating glass located in the roof with slight slope. In this case, the highest measured temperature was 85 °C. This increment in the temperature of the modules led
Recommendations for future studies
In the previous section, the conventional strategies of PV thermal management were reviewed and discussed. According to the performed literature survey, several suggestions are proposed here for future studies. The configuration of air cooling systems affect their performance and efficiency (De las Heras et al., 2018); therefore, different configurations should be tested to find the most appropriate type. In addition, since the shape of channels affect the heat transfer in forced convection
Conclusion
The effectiveness of solar PV cells is affected by various factors such as their material, the ambient conditions and operating temperature. Amongst these parameters, the temperature plays a key role on the performance of the cell and is preferred to be maintained at low as feasible. As it is importance to employ a suitable thermal management solution, various passive and active approaches in the literature are comprehensively reviewed in this study. The key findings are summarized as follows:
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Declaration of Competing Interest
The authors declared that there is no conflict of interest.
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