## 1 Introduction  
Cost of electricity produced by solar photovoltaic (PV) systems has seen an 80% decrease over the past 10 years and is currently at 57 USD per MWh [1]. Although 85% of this reduction is attributed to a decrease in panel cost, enhancement in the efficiency of the solar panel can increase the available power and decrease the price of electricity, making it available at a more affordable price, with reduced unfavorable environment effects. Persisting market pressure to reduce the cost per watt boosted the development of efficient renewable energy systems, thereby enhancing their performances and usage [2]. Apart from PV systems, efficiency improvement in renewable energy applications in heating, power generation, and desalination also underwent substantial development [3, 4]. Solar PV technology is adaptable to different types of customers, due to its simple and trouble-free operation and direct end use [5]. Recent studies have established that a linear reduction in the power generation of a photovoltaic panel occurs when the panel temperature increases beyond its normal operating cell temperature, which is attributed to the fact that the voltage of the electrical output reduces due to the inherent material properties, thereby producing an overall decrease in the power output [6]. The heat present in the panel needs to be continuously removed, in order to maintain the optimum operating temperature, which can result in increased power output, efficiency, and extension in the service life of the panel. For this reason, enhancement in the thermal performance of the PV by cooling is focused recently in PV research [7]. Hybridization of the solar PV system is accomplished by coupling a cooling mechanism for simultaneous extraction and utilization of heat from a panel surface for useful end use [8]. Two different hybridization techniques were adopted and tested by researchers. These techniques can be classified as passive methods, in which no additional energy is used and active methods where extra energy is used to achieve forced circulation heat transfer. Passive techniques include the application of fins or extended surfaces to promote heat transfer or involves phase change cooling, heat pipe cooling, and natural circulation cooling using water/air as the heat absorbing medium. Active techniques use forced circulation of air or water on the panel surfaces, with the help of fans or pumps, with possible heat recovery for useful end use. Experimental results indicated that natural and forced convection hybridization methods achieved 10 \({}^{\circ}\)C and 30 \({}^{\circ}\)C decreases in the temperatures of the PV panels, respectively [9]. Numerical studies on panel cooling using heat sinks of different configurations and geometry reported a reduction in the panel temperature of about 10 \({}^{\circ}\)C, with a consequent increase in the power output from 6.97 to 7.55%, compared to the base case without heat sinks [10]. The fins were in the form of ribs at the back of the panel. The optimization of the fins design was investigated for passive cooling of PV panels [11]. Another study presented a novel design of the tracking mechanical structure that was suggested to serve a dual function: mechanical support and heat sink [12]. A numerical study was conducted, and the results were compared to the experimental data. It was concluded that the temperature could be reduced by 6.3 \({}^{\circ}\)C, and the efficiency could be enhanced by 3%. A discontinuous heat sink was proposed and studied numerically and experimentally [13]. A reduction of 5 \({}^{\circ}\)C in the temperature of the PV panels was reported. Heat pipe thermosibhon heat sinks were used to cool the concentrating solar PV system, due to extreme high operating temperatures [14]. Experimental study was conducted on three PCMs: Rubitherm RT-25 H (RT25), Rubitherm RT-35 H (RT35), and Rubitherm RT-44 H (RT44) with heat pipe to cool PV modules, and they found that the best PCM for PV modules cooling was RT35 [15].