Energy and Exergy Enhancement Study on PV Systems with Phase Change Material

Abstract

A solar photovoltaic (PV) system produces electrical energy from solar energy. This green, sustainable system has low energy conversion efficiency due to the rise in PV temperature throughout the day. In order to keep the temperature of the panels close to ambient, this study examines the usage of hydrated salt (HS36) as a Phase Change Material (PCM) for PV cooling. The primary goal of this experimental study is to cool the PV panel by introducing PCM behind the PV system (PV-PCM), thus increasing its performance. An energy and exergy performance assessment was carried out on PV and PV-PCM systems. The result indicates that placing a PCM over the back of the solar panel’s back reduced the operational temperature by 25.4% and increased the panel’s electrical efficiency by 17.5%. PV-PCM systems’ maximum exergy efficiency increased by 12.57%, and their exergy destruction ratio decreased by 12.49%. The proposed PV-PCM system with HS36 PCM increased the PV panel performance and can be deployed in the PV system.

1. Introduction

Photovoltaic (PV) panels capture a substantial portion of solar energy and partially transform solar energy into electricity. Many different types of solar cells produce electricity directly. The type of solar cell and its operational parameters significantly impact how well solar energy is converted into electric energy. A specific wavelength of the incoming radiation is converted by PV cells, while the remaining light is wasted as heat; some of it contributes to the direct conversion of sunlight into electricity. Only 15–25% of the incident’s solar energy is converted into useful power. The solar cells convert the remaining solar energy into heat, which heats the PV panels. The PV panel’s surface may reach temperatures up to 60 °C above the surrounding temperature [1]. An increase in solar cell temperature reduces a photovoltaic panel’s electrical efficiency. For each degree that the PV cells’ temperature increased, the PV panel’s conversion efficiency was reduced by 0.4% to 0.65% [2]. Every 1 °C over 25 °C causes a 0.08% loss in PV panel electrical efficiency, which also leads to a 0.65% reduction in power production [3]. The PV panel should ideally be cooled to improve efficiency. Active or passive cooling techniques are available for PV panels. A photovoltaic panel is often actively cooled using gases or liquids. A PV system with dynamic cooling includes heat extraction tools such as fans and pumps to bring water to the solar panels to cool them. Some researchers used fins to reduce the PV temperature. Fins increase the contact point between the heat sink and the environment, where the limiting factors are both the convective and radiative heat transfer coefficients [4] and where heat dissipation is restricted in such cooling systems. It increases the system’s maintenance and operating costs, and its economic viability will be of concern. There are many other different passive cooling methods available that have low maintenance and operating costs. The simplest method is the deployment of PCM on the backside of the PV system. Therefore, it is better to utilize PCM to cool the PV panels because it requires no extra energy [5]. The ideal PCM for cooling PV panels must have good thermal conductivity, large latent heat of fusion, chemical stability, and tolerable sub-cooling [6]. It should also be close to the PV panel’s operating temperature. Assuring PCM has a high thermal conductivity from the above qualities is one of the more complicated tasks. One of their alternatives is inserting fins for heat extraction [7]. We could enhance power production and lower the PV cells’ temperature by removing extra heat from the PV panel. PV-T refers to cooled solar panels that utilize the excess heat for other purposes. According to studies, PV-T technology is an emerging technology and has a great deal of potential in the upcoming years since it can be utilized in various systems and the amount of energy produced from renewable resources is increasing every year.

A PCM-based PV temperature management technique has recently attracted much interest from academics. A hybrid technology known as the PV-PCM system combines PCMs and PV panels into a single module to improve solar energy conversion effectiveness. In addition, such a system can provide inexpensive thermal energy if the proper heat extraction techniques are used. It can also absorb latent heat throughout the transition from the solid to the liquid phase, and latent heat can be transferred across a minimal range of temperatures to the liquid phase. Thus, it is believed that the PV-PCM system is a potential substitute for the conventional approach. The first test setup was created, directly linking a PV module to a PCM-filled glass tank. However, temperature stratification developed between the PCM container’s top and bottom portions because of inadequate heat conductivity and little contact surface. In two subsequent experimental setups, the authors employed flat copper tanks and an aluminum absorber, which enhanced the system. To minimize the PV panel’s temperature increase, [8,9,10,11] assessed the integration of a proper PCM computationally and analytically. Their ground-breaking research proved the PV-PCM system’s viability and excellence by evaluating the performance of two potential PCMs with various fin shapes, sizes, and designs. Investigations were conducted on a PV-PCM system with a modified PCM–air combined case that was partitioned into two triangular-shaped metal cells. Evaluations were performed on the impact of crystalline segregation, convection, and the Rayleigh number on the heat transfer efficiency of the PV-PCM system. While investigating flat-plate PV panels, the study was conducted on a variety of PV modules with a V-trough that have PCMs incorporated into the back to dissipate heat. Moreover, there were examinations conducted on the PV modules that use PCMs for thermal management [12]. A passive cooling technique for concentrated solar cells employing PCM thermal storage was investigated. The outcome showed that cooling methods might increase system dependability and electrical power production.

Recent studies on PV panel passive cooling using PCM have demonstrated that the PCM has a large heat storage capacity and maintains a nearly constant temperature when cooling the PV panel. There have been several documented PV-PCM idea designs in the literature. Four distinct types of PV panels cooled by the PCM were employed and evaluated in one study. In the end, the PV panel with the PCM performed more efficiently than a standard PV panel because the cells were heated to a lower temperature and the materials took a long time to degrade [13]. The most widely used system investigated takes into account PCM integration in building integrated photovoltaics [14]. There have also been a few reports of standalone solar collectors with PCM thermal storage. Other authors [15] also looked into how crystalline segregation and convection affected melted PCM, and the outcomes showed that, at a particular fin spacing (12–24 mm), convection had a better influence on the rate of heat transfer and thermal stratification could be reduced, resulting in a PV-PCM system temperature distribution that is more uniform. Compared to the standard PV module, the PV-PCM generated 1.0% to 1.5% more electricity. The PV-PCM module’s efficiency was enhanced by approximately 3.1%, according to studies on electrical power generation and efficiency. In contrast, in other regions of Europe, the increase in energy output is between 2% and 5%, with a maximum of 6% [16]. Other researchers [17] used RT25 and GR40 PCMs to investigate the efficiency of photovoltaic-phase change material systems inside the PCM container, both with and without fins. It has been demonstrated that CeP and CaCl₂.6H₂O may reduce the photovoltaic temperature by a maximum of 18 °C at 1000 W/m². Yellow petroleum jelly was suggested by [18] as the PCM for the operation, and they researched how well the system worked in the Indonesian environment. It has been shown that photovoltaic efficiency increased from 8.3% to 10.1%. Other authors [19] took into account the RT35 PCM and analyzed the Malaysian environment. The findings show that PCM caused the photovoltaic temperature to drop by 10 °C. Another study [20] examined the system’s behavior in Ireland and Pakistan, two contrasting locales. In Pakistan, the system operates more effectively. Moreover, [21] examined the system’s performance in the United Arab Emirates’ scorching heat. The annual generation of power increased by 5.9%. Other authors [22] built integrated concentrated photovoltaic systems using the RT42 phase change material and observed an increase in electrical efficiency of 7.7% at 1000 W/m². Furthermore, another study [23] looked at the efficiency of photovoltaic systems using pure phase change materials and combined phase change materials and found that there was an average improvement in electrical efficiency of 5.8% and 3%, respectively. The behavior of phase change materials with photovoltaics is covered in several publications [24,25,26,27,28]. Most of the research was concentrated on the deployment of organic PCM, i.e., paraffin wax. Only a few researchers used hydrated salt (HS) PCM in PV-PCM systems in hot regions.

This work focused on demonstrating how PCM is used to improve the traditional PV panels’ electrical efficiency and sustain higher daytime temperatures in hot regions. This study aims to demonstrate how latent cooling enhances the performance of a PV panel by utilizing HS36 commercial PCM. In addition, this work compares the PV-PCM system with its reference PV system based on energy and exergy characteristics, i.e., PV cell temperature, electrical efficiency, exergy efficiency, and the exergy destruction ratio.

2. System Description

An experimental setup was devised and built on the top floor of the School of Mechanical Sciences building at Bannari Amman Institute of Technology to examine the effects of the proposed heat dissipation system on the performance of PV cells. The experimental apparatus was installed at a location of 11.5034° N latitude and 77.2444° E longitude, and its tilt angle was fixed at 11.5° based on the latitude location [29]. The following sections will provide an overview of the experimental setup, detailing the components and how they were designed and providing examples of field tests. In this paper, outdoor experiments were used to explore the effect of PCM addition to PV modules and how it affected the modules’ performance. For the purpose of this study, two 260-Watt PV module setups were constructed, one with a traditional PV system and the other with PCM integration. The thermal and electrical performances of the two different designs were tested against one another simultaneously under identical environmental circumstances. The layers and methodology of PV-PCM system preparation are shown in Figure 1. Glass, Si-solar cells, EVA, Tedlar foil, aluminum sheet, thermal paste, PCM, and insulation are among the eight layers that make up the PV-PCM system. Figure 2 represents the PV and PV-PCM systems’ experimental setup.

PCM was added to a typical PV panel for the experimental setup, and measurements can be seen on the left in Figure 2. Olitech’s 260-watt conventional PV panel was used, and polycrystalline silicon was used in solar cells to make PV cells.

Table 1. Specification of PV.

Description	Power (W)	Vm (V)	Im (A)	Voc (V)	Isc (A)	Dimensions (mm)
Values	260	32.0	8.38	38.5	8.93	1661 × 991 × 35

displays the specific electric characteristics of a PV cell in detail. PCM was encased in aluminum foil, which had dimensions of 50 cm × 30 cm × 2 mm, as shown in Figure 2. In total, 9 sets of 1 kg of HS 36 PCM filled the aluminum foil [30]. It was mounted to the PV module’s backside on the module’s aluminum sheet, which was fixed behind the PV Tedlar with thermal paste and grease. The modified PV-PCM panel is a hydrated salt PCM of type HS36, and its properties are listed in

Table 2. PCM Properties.

Description	Melting Temperature (°C)	Freezing Temperature (°C)	Latent Heat (kJ/kg)
Values	37.0	36.0	167

. Since HS36 is a pure PCM, through the phase transition processes between solid and liquid, large volumes of thermal energy may be stored and released at very constant temperatures (melting and congealing). Even when small volumes and temperature changes are present, phase change materials offer a very efficient way to store heat and cold. Therefore, the PCM was chosen based on its melting point, which was suitable for the hot climate conditions. Thermal dissipation between the aluminum sheet and PCM is high if the PCM melting temperature falls between 3 °C and 6 °C higher than the average ambient temperature [31]. The average temperature in the study was 31 °C.

Experiments were carried out on PV and PV-PCM systems simultaneously during April 2022 with many trials. The results obtained throughout the various trials were similar. Hence, a comprehensive analysis carried out on 25 April 2022 is discussed in this work. This day was chosen because the weather was consistent and there was no cloud cover, which made for more accurate measurements. The experiments were carried out each day from 9:00 a.m. to 4:00 p.m. The amount of solar energy absorbed by the inclined surface, the wind speed, and the surrounding air temperature were all measured with the assistance of a Davis Vantage weather station available at the testing location. At predetermined 30-s time intervals, PV analyzers were used to measure the system’s output current and voltage. These readings were then carefully recorded in the PV analyzer DAQ and utilized in calculations. To analyze the thermal dissipation, each panel’s temperature and ambient air temperature were recorded by a K-type thermocouple at various locations, as shown in Figure 2. The Unilog pro plus DAQ was extensively used to measure the temperatures. The thermocouples and other sensors were hardwired into a data logger, which recorded readings every thirty seconds. The measurement output data were saved to a laptop for further processing.

Table 3. Details of Sensors.

Instruments	Data Logger	Pyranometer	PV Analyzer	Thermocouple
Range	Universal Channel, Sampling rate 30 s	0–2000 W/m2	0–50 V & 0–20 A	0–1000 °C
Accuracy	±0.26%	±7%	±6%	±0.6

includes a list of the measuring items and equipment.

2.1. Thermodynamic Analysis

The output energy ratio of a PV system is determined by the system’s input energy (solar radiation on the photovoltaic surface). As specified in the first law, the efficiency of solar systems was calculated using Equation (1) [32],

$${\eta }_{Iele}=\frac{P_{max}}{I_{s}A}$$

(1)

The photovoltaic system’s electric power aims to transform available energy into usable energy. Therefore, energy capacity or quality is taken into account during exergy analysis. Equation (2) expresses the photovoltaic (PV) system’s total exergy balance [33].

$${\displaystyle \sum }{\dot{E}}_{in}={\displaystyle \sum }{\dot{E}}_{out}$$

(2)

The PV module’s total output energy ratio to its total input energy is referred to as its exergy efficiency, and it is calculated using Equation (3). Only solar radiation intensity exergy is included in a PV system’s input exergy, as shown in Equation (4) [34].

$${\eta }_{ex}=\frac{E{x}_{out}}{E{x}_{in}}$$

(3)

$$\dot{E}{x}_{in}=\left(1-\frac{T_a}{T_s}\right)I_{s}A$$

(4)

A PV system’s exergy production may be computed as shown in Equations (5)–(7) [35,36]. Ts is the assumed value of 5777 K for the sun’s temperature, where v is the wind speed and hca is the heat transfer coefficient. Equation (8) indicates the exergy destruction ratio (EDR).

$$\dot{E}{x}_{out}=P_{max}-\left(1-\frac{T_a}{T_c}\right)h_{ca}A\left(T_c-T_a\right)$$

(5)

$$\dot{Q}=h_{ca}A\left(T_c-T_a\right)$$

(6)

$$h_{ca}=5.7+3.8v$$

(7)

$$EDR=\frac{1}{\left({\eta }_{ex}\right)}-1$$

(8)

2.2. Uncertainty Analysis

Experimental investigations lack a clear understanding of the accuracy of the data provided. Hence, an examination of the devices’ uncertainty should be carried out to show that the information used in experimental testing was accurate. For computed and independent variables, the error is 3.2% for electrical efficiency and 3.82% for temperature. It was calculated using Equation (9) [37].

$$W_R={\left[{\left(\frac{\partial R}{\partial x_1}{W}_1\right)}^2+{\left(\frac{\partial R}{\partial x_2}{W}_2\right)}^2+\dots +{\left(\frac{\partial R}{\partial x_n}{W}_n\right)}^2\right]}^{1/2}$$

(9)

3. Result and Discussion

An experiment was carried out on the terrace of the Faculty of Mechanical Engineering at Bannari Amman Institute of Technology, Tamil Nadu, India, on 25 April 2022. The ambient conditions are shown in Figure 3. The PV/PCM and traditional PV panels had their temperatures monitored during the trial. The temperature was sampled every thirty seconds between 9.00 and 16.00. During the experiment, the ambient air temperature rose and varied from 30.2 °C to 35.7 °C. The most significant diffuse solar irradiation was 916 W/m² at 1.15 p.m. as a result of the clear-sky weather measurement output data displayed in

Table 4. Environmental conditions and measurement output data.

Radiation (W/m2)	Power PV (W)	Power PV PCM (W)	Electrical Efficiency—PV (%)	Electrical Efficiency—PV PCM (%)	PV Cell Temp (°C)	PV-PCM Cell Temp (°C)	Ambient Temp (°C)	Exergy Efficiency—PV (%)	Exergy Efficiency—PV-PCM (%)	EDR-PV	EDR-PV PCM
225	42.3	48.7	11.33	13.04	39.4	33.3	30.2	13.04	14.79	6.67	5.76
262	46.2	54.2	10.62	12.46	42.1	33.8	30.5	12.46	14.13	7.03	6.08
332	55.8	60.2	10.12	10.92	43.5	34.5	31	10.92	12.37	8.16	7.09
363	59.6	64.5	9.89	10.7	48.2	34.9	31.4	10.7	12.15	8.35	7.23
398	65.2	69.8	9.87	10.56	49.4	35.2	32	10.56	12	8.47	7.33
420	68.2	73.5	9.78	10.54	51.8	36.6	32.1	10.54	11.89	8.49	7.41
486	73.9	83.2	9.16	10.31	54.8	37.8	32.8	10.31	11.58	8.7	7.63
453	70.3	78.6	9.35	10.45	53.3	37.9	32.5	10.45	11.68	8.57	7.56
515	82.2	89.1	9.62	10.42	56.3	38.8	33.6	10.42	11.68	8.6	7.56
589	95.4	101.5	9.76	10.38	58.4	39.5	33.8	10.38	11.65	8.63	7.59
688	103.2	112.2	9.04	9.82	64.5	40.2	34.4	9.82	11.04	9.18	8.06
625	101.5	110.6	9.78	10.66	63.6	41.5	34.2	10.66	11.83	8.38	7.45
758	112.8	119.8	8.96	9.52	68.6	44.5	34.6	9.52	10.33	9.5	8.68
785	117.2	123.8	8.99	9.5	70.2	46.3	34.8	9.5	10.14	9.53	8.87
825	121.8	131.8	8.89	9.62	71.3	47.5	35.1	9.62	10.2	9.4	8.8
874	126.2	133.5	8.7	9.2	73.2	49.8	35.4	9.2	9.37	9.87	9.67
903	127.6	137.8	8.51	9.19	73.5	50.5	35.6	9.19	9.45	9.88	9.58
916	129.4	139.2	8.51	9.15	74.5	51.8	35.7	9.15	9.44	9.93	9.6
892	125.8	130.6	8.5	8.82	70.4	51.2	35.3	8.82	8.86	10.34	10.29
812	118.5	128.2	8.79	9.51	69.4	50.2	35.1	9.51	9.51	9.52	9.52
788	113.8	125.5	8.7	9.59	68.4	49.2	34.9	9.59	9.7	9.43	9.31
742	107.2	119.4	8.7	9.69	66.1	48.7	34.7	9.69	9.94	9.32	9.07
725	103.6	120.1	8.61	9.98	64.6	48.1	34.3	9.98	10.44	9.02	8.57
678	95.8	112.5	8.51	10	61.4	47.2	34.2	10	10.51	9	8.51
632	92.7	106.9	8.84	10.19	59.6	46.8	33.8	10.19	10.48	8.81	8.54
584	90.6	99.2	9.35	10.23	58.8	46.3	33.6	10.23	10.6	8.78	8.43
505	78.2	86.2	9.33	10.28	57.2	45.6	33.5	10.28	10.6	8.73	8.44
452	70.6	78.3	9.41	10.44	53.8	45.2	33.2	10.44	10.65	8.58	8.39
398	62.2	70.4	9.41	10.66	50.6	44	33	10.66	11.04	8.38	8.05

.

3.1. Energy Analysis

Figure 4 depicts the hourly variation of PV, PV-PCM cells, and PCM temperatures. Throughout the study, the conventional PV panel’s average temperature was 50.3 °C. The standard PV panel’s PV cells heated up to a high of 74.5 °C, which is 38.8 °C higher than the surrounding temperature at 1:15 p.m. In addition, the PV-PCM panel’s temperature reached 51.8 °C, which is 16.1 °C greater than the surrounding air temperature. The average temperature of the PV-PCM panel was recorded as 43.34 °C. PV cells’ most significant temperature differential was 22.7 °C for a PV-PCM panel and a standard PV panel. The experiment’s average PV cell temperature difference was 16.98 °C. The PV-PCM panel’s temperature was maintained between 35 °C and 44 °C from 10.00 a.m. to 12.00 p.m. as a result of a good transfer of heat from the PCM to the PV cells, which caused the PCM to begin changing its state from solid to liquid. However, the temperature started to rise at 12.00 p.m. and reached 51.8 °C by 1.15 p.m. This happened during the transformation of the PCM from a solid to a liquid because more solar heat was absorbed than was necessary for the phase shift of the PCM. Around 1.15 p.m., the PCM’s temperature decreased as the solar heat gain was minimized.

Figure 5 shows the hourly variations of electrical power and electrical efficiency of standard PV cells and PV-PCM cells. Based on research and calculations due to PV cell temperature, the efficiency of energy and electric power production using typical PV panels is shown in Figure 5. The PV-PCM system produced a maximum of 139.2 W electrical power during a higher radiation fall of 916 W/m2 and was 7.57% higher than the PV standard system. The PV-PCM system’s average value of electrical power production was 100.32 W, while it was 91.64 W for the reference system. The PV-PCM system’s average power generation was 9.46% higher than that of the standard PCM system. The PV-PCM system’s average electrical efficiency was 9.96% higher than the standard PV system. The results suggest that PV-PCM electricity increased to its maximum under the specified conditions by 17.5% and electrical power increased, on average, by 9.46%. The PV-PCM panel’s most significant improvement in energy generation efficiency under the tested conditions was 1.84%, while the average increase throughout the experiment was 0.92%. The reason behind the increment in electrical power and efficiency is the integration of PCM, which leads to a decrease in the PV/PCM cell temperature. The decrease in cell temperature leads to an increase in current and voltage output, hence the PV-PCM system produces more power than the PV system.

3.2. Exergy Analysis

Exergy efficiency and the exergy destruction ratio throughout the day are displayed in Figure 6. The maximum exergy efficiency of 14.79% was recorded during low solar irradiation and 9.33% during higher radiation. The average increase in the PV-PCM system’s energy effectiveness is 7.57%. Similarly, the lowest EDR was recorded during the most intense radiation fall, and vice versa during the highest radiation fall. The average decrease in EDR is 7.06% for the PV-PCM system. The exergy efficiency values were lower than the PV system from 12.30 p.m. to 2.30 p.m. due to the PCM reaching its liquid state from its solid state and the opposite for EDR. This is because the PV-PCM system’s heat storage capacity is better than the PV system. Therefore, in the PV-PCM system, heat loss to the surrounding is higher than in the standard PV system. Thus, it causes the exergy efficiency to drop and the exergy destruction ratio to rise. The wind velocity could be another reason for this. When wind velocity is assumed to be constant, the system exergy efficiency of PV-PCM is always superior to the PV system. Hence, it can be concluded that the wind takes more heat from the PV-PCM system from 12.30 p.m. to 2.30 p.m. This trend varies from 2.30 p.m. onwards due to the initiation of the phase transition of PCM from liquid to solid.

It is observed from the research work that the electrical power increased by 13.45 W for every 100 W/m² rise in solar radiation. Similarly, it was 4.05 W at a 1 °C drop in PV cells. Additionally, electrical efficiency increases by 0.39% for every 100 W/m² decrease in solar radiation. Furthermore, electrical efficiency increased by 0.21% for every 1 °C drop in the PV cell temperature. When comparing this with a base PV system, an electrical power increment of 4.74% and 5.78% was produced for a 100 W/m² variation of solar radiation and a 1 °C change in cell temperature, respectively. Similarly, 1.03% and 1.15% of electrical efficiency vary for each 100 W/m² variation of solar radiation and 1 °C change in cell temperature. Hence, it is concluded that the performance of the PV-PCM system is higher than that of the base PV system. Therefore, the integration of PCM behind the PV panel performs well by decreasing the panel temperature and effectively increasing the electrical performance of the PV-PCM system.

3.3. Comparison of Present Work with Previous Research Articles

Table 5. Comparison of PV-PCM system with previous studies.

References	Average Electrical Efficiency (%)	Average Exergy Efficiency (%)
[38]	9.23	7.99
[39]	8.36	-
[40]	9.62	-
Current Work	9.9%	10.96%

shows a comparison between the performance parameters of PV and PV-PCM systems gained in the current analysis and those obtained in earlier research. However, the proposed PV-PCM systems perform much better than in the preceding studies.

4. Conclusions and Future Scope of Work

This work examined the improvement of the PV system’s energy and exergy conversion efficiency by introducing HS 36 PCM behind the PV panel. The following results were obtained:

➢

The PV-PCM system produced a maximum of 139.2 W, which is 7.57% higher than the reference PV system. The average electrical efficiency of the PV-PCM system is 9.9% higher than that of the reference PV system.

➢

The integration of PCM in the PV panel imparted an average decrease in PV cell temperature of 16.98 °C.

➢

Similarly, the average exergy efficiency rise is 7.55% higher than the reference PV system. In addition, the exergy destruction ratio decreased by 7.1% by introducing the HS36 PCM on the evaporator side.

In the future, the study can be extended with different kinds of PCMs for different climatic conditions. This study also recommends the integration of PCM with different encapsulation materials. In addition, blending the different volumes of suitable nanoparticles in PCM would possibly enhance its heat transfer capability through the augmentation of its thermo-physical characteristics.