As a researcher in the field of renewable energy, I have devoted considerable attention to the thermal management of photovoltaic systems. Solar photovoltaic technology has been deployed worldwide, yet one of its primary limitations remains the negative temperature coefficient of power output. The efficiency of crystalline silicon solar panels typically decreases by 0.4% to 0.65% for every 1 °C rise above the standard test condition of 25 °C. In many practical installations, the operating temperature of an uncooled photovoltaic module can easily exceed 60 °C, which drastically reduces the electrical yield and accelerates the degradation of the module. To address this issue, passive cooling using phase change materials (PCMs) has emerged as a promising solution. The PV-PCM system integrates a layer of phase change material behind the photovoltaic panel, absorbing excess heat during the melting process and releasing it during solidification, thereby controlling the panel temperature within a desirable range. In this study, I systematically investigated the cooling performance of a PV-PCM system through experiments and numerical simulations, with a focus on the thermal and electrical behavior of the solar panel, the influence of environmental parameters such as irradiance and ambient temperature, and the actual performance under realistic weather conditions.
1. Literature Review and Research Objectives
The concept of using PCMs for thermal regulation of photovoltaic modules dates back to the late 1970s. Since then, numerous researchers have explored both experimentally and numerically the benefits of integrating PCMs with solar panels. For instance, biwole et al. demonstrated that a PCM layer could keep a solar panel below 40 °C for 80 minutes under constant irradiation of 1000 W/m². Huang et al. developed a two-dimensional numerical model to predict the thermal behavior of building-integrated photovoltaics with PCMs and reported that a 30 mm thick paraffin layer maintained the panel surface below 35 °C under typical UK weather. More recent studies have focused on the selection of suitable PCMs, the optimization of PCM thickness, the incorporation of metallic foams or fins to enhance thermal conductivity, and the addition of nanoparticles to improve heat transfer.
Despite the abundance of research, several gaps remain. Many previous studies concentrated on the thermal performance during the melting phase, while the reverse process of solidification and its impact on the panel temperature during the night or after the irradiance diminishes was less frequently analyzed. Moreover, the applicability of PV-PCM systems under different climate conditions, specifically the combined effects of irradiance intensity and ambient temperature, has not been fully quantified. In this work, I aimed to address these issues through a carefully controlled experimental campaign and a subsequent numerical study. The specific objectives are as per the following:
- To experimentally evaluate the cooling performance of a PCM layer attached to the back of a 12 W rated solar panel, including the temperature reduction of the panel surfaces and the resulting improvement in electrical output parameters.
- To investigate the influence of irradiance level (600, 800, and 1000 W/m²) and ambient temperature (7.3 °C, 14.1 °C, and 20.7 °C) on the overall cooling effectiveness of the PV-PCM system.
- To observe the temperature behavior during the solidification phase of the PCM after the light source is turned off, providing insight into the complete melting–solidification cycle.
- To develop a numerical model based on the actual weather data of a representative city in Northeast China, considering wind speed, soil temperature, and sky temperature, and to simulate the cooling performance of the PV-PCM system on a day with maximum solar irradiation.
2. Experimental Setup and Methodology
The entire experimental campaign was conducted in a controlled indoor environment to eliminate unpredictable external disturbances. The test rig comprised four major subsystems: (i) a solar simulator emitting light in a spectral range very close to that of the sun, (ii) two identical photovoltaic panels, one bare and one equipped with a PCM layer, (iii) a data acquisition system for temperature and electrical parameter measurement, and (iv) a radiometer to calibrate the irradiance level.
The solar simulator was a matrix of 15 independent xenon lamp linear light sources. It provided a uniform irradiation area of 2 m × 2 m with non-uniformity and instability both below 5%. The spectrum of the xenon lamps is closely matched to that of natural sunlight, especially within the spectral response range of crystalline silicon solar cells. The photovoltaic panels used in this study were commercially available modules with a maximum power rating of 12 W, an open-circuit voltage of 19.2 V, and a short-circuit current of 0.825 A. The overall dimensions of the panels were 350 mm × 235 mm × 17 mm. To ensure accurate comparison, the two panels were selected from the same production batch and exhibited identical initial electrical characteristics.
The phase change material selected for this investigation was paraffin wax. The choice was based on a comprehensive analysis of the available literature and the local climate condition. According to previous studies, the melting point of PCMs used in PV cooling applications generally ranges from 25 °C to 45 °C, with the average value around 38 °C. For the northeast temperate continental monsoon climate, the ambient temperature in summer often exceeds 30 °C, so a PCM with a melting range of 37.5 °C to 42.5 °C was selected. The latent heat of fusion was 170 kJ/kg, and the material exhibited high chemical stability, non-corrosiveness, and negligible supercooling. The PCM was melted in a water bath and subsequently poured into the back cavity of the solar panel to form a uniform layer of 30 mm thickness. A 2 mm thick aluminium container was used to hold the PCM in place and to provide sufficient mechanical rigidity.
Temperature monitoring was performed using K-type thermocouples with an accuracy of ±0.1 °C. Two thermocouples were attached to the center of the upper surface of each panel (one on the bare PV panel and one on the PV-PCM system), and two other thermocouples were attached to the center of the lower surface. The electrical outputs of the solar panels were measured by a PROVA 210 solar cell analyzer, which can measure the I-V characteristic curve, open-circuit voltage, short-circuit current, maximum power, and fill factor with an accuracy of ±1%. The analyzer was connected to a computer for continuous data logging. The experimental procedure was as follows: first, the radiometer was placed at the same height as the panels, and the solar simulator was adjusted until the target irradiance was reached. Then, the irradiance was maintained constant for a period of 300 minutes (the “light on” period), followed by a “light off” period of 480 minutes to observe the cooling behavior of the panels and the PCM solidification process. Data was recorded every 20 minutes.
During the experiments, the inclination angle of the solar panels was fixed at 36°, consistent with the latitude of the local site. Since the indoor experiment did not involve wind, the convective heat transfer coefficient was solely due to natural convection. However, for the later numerical simulation, the effect of wind speed was incorporated using an empirical correlation.
3. Theoretical Fundamentals
The temperature of a photovoltaic module under sunlight is determined by the balance between the absorbed solar energy and the heat losses through convection, radiation, and the electrical power extracted. The effective heat absorbed by the solar panel can be expressed as:
$$
G_{\text{eff}} = G \cdot \tau_g \cdot \alpha_{PV} \cdot (1 – \eta_{el})
$$
where \(G\) is the incident solar irradiance, \(\tau_g\) is the transmittance of the glass cover with a typical value of 0.95, \(\alpha_{PV}\) is the absorptance of the silicon layer with a typical value of 0.9, and \(\eta_{el}\) is the electrical efficiency of the solar panel at the operating temperature. The electrical efficiency decreases linearly with temperature:
$$
\eta_{el} = \eta_{STC} \left[ 1 – \beta \left( T_{PV} – 25 \right) \right]
$$
where \(\eta_{STC}\) is the efficiency under standard test conditions (taken as 13% for the employed panel), \(\beta\) is the temperature coefficient (taken as 0.0045 K⁻¹), and \(T_{PV}\) is the current panel temperature in °C.
The heat loss from the front surface of the solar panel to the surroundings consists of both convective and radiative components:
$$
Q_{\text{front}} = h_{\text{conv}} \left( T_{\text{glass}} – T_{\text{amb}} \right) + \varepsilon_{\text{glass}} \sigma F_{T,s} \left( T_{\text{glass}}^4 – T_{\text{sky}}^4 \right)
$$
Similarly, the heat loss from the back surface of the PV-PCM system or the bare panel can be written as:
$$
Q_{\text{back}} = h_{\text{conv}} \left( T_{\text{back}} – T_{\text{amb}} \right) + \varepsilon_{\text{back}} \sigma F_{Tb,g} \left( T_{\text{back}}^4 – T_{\text{ground}}^4 \right)
$$
Here, \(h_{\text{conv}}\) is the convective heat transfer coefficient, \(\varepsilon\) is the emissivity, \(\sigma\) is the Stefan–Boltzmann constant, \(F_{T,s}\) and \(F_{Tb,g}\) are the view factors from the top and bottom surfaces to the sky and ground, respectively. The sky temperature is estimated from the ambient temperature:
$$
T_{\text{sky}} = 0.0552 \cdot T_{\text{amb}}^{1.5}
$$
Since the panels are tilted at an angle \(\alpha\), the view factors are:
$$
F_{T,s} = \frac{1+\cos\alpha}{2}, \quad F_{Tb,g} = \frac{1-\cos(\pi-\alpha)}{2}
$$
For the convective heat transfer coefficient, when wind speed \(u\) (m/s) is considered, a common empirical expression is:
$$
h_{\text{conv}} = 5.70 + 3.80 \cdot u
$$
In the PCM layer, heat transfer involves both conduction and natural convection in the liquid phase. The governing equations for the PCM domain are the continuity, momentum, and energy equations, together with the enthalpy-porosity method for phase change:
$$
\frac{\partial \rho}{\partial t} + \nabla \cdot (\rho \vec{v}) = 0
$$
$$
\frac{\partial (\rho \vec{v})}{\partial t} + \nabla \cdot (\rho \vec{v} \vec{v}) = -\nabla p + \nabla \cdot (\mu \nabla \vec{v}) + \rho \vec{g} \beta_T (T – T_0) + S
$$
$$
\frac{\partial (\rho H)}{\partial t} + \nabla \cdot (\rho \vec{v} H) = \nabla \cdot (\lambda \nabla T)
$$
where \(H\) is the total enthalpy, which is the sum of sensible enthalpy \(h\) and latent enthalpy \(\Delta H\):
$$
H = h + \Delta H, \quad \Delta H = \beta L
$$
Here, \(\beta\) is the liquid fraction given by:
$$
\beta =
\begin{cases}
0, & T < T_s \\
\dfrac{T – T_s}{T_l – T_s}, & T_s \le T \le T_l \\
1, & T > T_l
\end{cases}
$$
The thermophysical properties of the selected paraffin wax used in the simulation are listed in Table 1.
| Property | Value |
|---|---|
| Melting temperature range | 37.5 °C – 42.5 °C |
| Latent heat | 170 kJ/kg |
| Density | 800 kg/m³ (Boussinesq approximation) |
| Specific heat (solid) | 2600 J/(kg·K) |
| Specific heat (liquid) | 3600 J/(kg·K) |
| Thermal conductivity (solid) | 0.21 W/(m·K) |
| Thermal conductivity (liquid) | 0.19 W/(m·K) |
4. Experimental Results and Discussion
I conducted five different experimental cases to evaluate the cooling effect of the PCM. The cases were selected to represent varying irradiance levels and ambient temperatures. Table 2 summarizes the conditions for each case.
| Case | Irradiance (W/m²) | Ambient temperature (°C) |
|---|---|---|
| 1 | 600 | 20.7 |
| 2 | 800 | 20.7 |
| 3 | 1000 | 20.7 |
| 4 | 1000 | 7.3 |
| 5 | 1000 | 14.1 |
4.1 Temperature Reduction of the Solar Panel
For each test, the upper surface center temperature and the lower surface center temperature of both the bare solar panel (denoted as \(T_A\) and \(T_B\)) and the PV-PCM system (denoted as \(T_{A’}\) and \(T_{B’}\)) were recorded. The results clearly show that the PCM layer significantly reduces both the steady-state temperature and the rate of temperature rise. In case 1 (600 W/m², 20.7 °C), the bare PV panel reached an average upper surface temperature of 78.44 °C, whereas the PV-PCM system had an average upper surface temperature of 58.83 °C. This corresponds to a reduction of 19.61 °C. The lower surface temperature was reduced by 20.71 °C, from 76.07 °C to 55.36 °C.
In case 3 (1000 W/m², 20.7 °C), the bare panel reached an average upper surface temperature of 111.44 °C, while the PV-PCM system remained at 84.67 °C, yielding a 26.77 °C reduction. The lower surface temperature was reduced by 28.15 °C. It is noteworthy that in the case of the lowest ambient temperature (case 4, 7.3 °C), the temperature reduction was the largest: the upper surface temperature was lowered by 33.94 °C, and the lower surface temperature was lowered by 36.51 °C. Table 3 lists the detailed temperature reductions for all cases.
| Case | \(\Delta T_A\) (upper surface, °C) | \(\Delta T_B\) (lower surface, °C) |
|---|---|---|
| 1 (600 W/m², 20.7 °C) | 19.61 | 20.71 |
| 2 (800 W/m², 20.7 °C) | 22.39 | 24.16 |
| 3 (1000 W/m², 20.7 °C) | 26.77 | 28.15 |
| 4 (1000 W/m², 7.3 °C) | 33.94 | 36.51 |
| 5 (1000 W/m², 14.1 °C) | 30.34 | 32.46 |
Another important observation concerns the cooling process after the irradiance was terminated. The bare PV panel cooled down from its maximum temperature to room temperature in approximately 80 minutes, whereas the PV-PCM system required about 480 minutes to cool to the same condition. This prolonged cooling time is a direct consequence of the latent heat released during the solidification of the PCM. During the solidification process, the PV-PCM system’s temperature remained above the bare panel temperature for a significant period, which could be advantageous in certain applications that require heat recovery or frost protection. The delayed cooling also reduces thermal stress on the solar panel materials, potentially extending the lifespan of the module.
4.2 Electrical Performance: Open-Circuit Voltage and Short-Circuit Current
I measured the open-circuit voltage and short-circuit current for both the bare PV panel and the PV-PCM system during the light-on period. The open-circuit voltage of a silicon solar cell decreases with temperature due to the increase in the reverse saturation current. The measurements confirmed that the PCM layer mitigated this voltage drop. For instance, in case 1, the average open-circuit voltage of the bare PV panel was 18.43 V, while the PV-PCM system had an average of 19.51 V, corresponding to a 1.08 V enhancement. In case 4, where the ambient temperature was lowest, the voltage enhancement reached 1.96 V (from 17.70 V to 19.66 V). The short-circuit current, on the other hand, is only slightly temperature-dependent; it tends to increase with temperature. Therefore, the cooling effect of the PCM slightly reduced the short-circuit current, but the magnitude of this reduction was negligible compared to the voltage gain. The maximum reduction of short-circuit current was 13.08 mA observed in case 4. Table 4 summarizes the electrical parameter differences.
| Case | \(\Delta V_{OC}\) (V) | \(\Delta I_{SC}\) (mA) |
|---|---|---|
| 1 | 1.08 | 2.25 |
| 2 | 1.28 | 2.31 |
| 3 | 1.47 | 3.38 |
| 4 | 1.96 | 13.08 |
| 5 | 1.53 | 8.31 |
4.3 Fill Factor
The fill factor of a solar panel is defined as the ratio of the maximum power to the product of open-circuit voltage and short-circuit current:
$$
FF = \frac{P_{Max}}{V_{OC} \cdot I_{SC}}
$$
The fill factor is sensitive to series and shunt resistances, and typically decreases with increasing temperature. In all experiments, the PV-PCM system exhibited a higher average fill factor than the bare PV panel. The enhancement ranged from 0.02 to 0.04. The largest enhancement of 0.04 was observed in case 3 and case 5. In case 4, an enhancement of 0.03 was recorded. These improvements confirm that the lower operating temperature improves the overall I-V characteristics of the solar panel.
4.4 Maximum Power and Maximum Efficiency
The maximum output power of the solar panel was directly measured by the solar analyzer. Since the panel had a rated maximum power of 12 W under standard test conditions, the actual output during the experiments depended on the irradiance and the operating temperature. The PV-PCM system consistently outperformed the bare PV panel in terms of average maximum power and average maximum efficiency. The maximum efficiency was calculated as:
$$
EFF_{Max} = \frac{P_{Max}}{G \cdot A}
$$
where \(A\) is the area of the solar panel (0.08225 m²). Table 5 lists the average maximum power and the average maximum efficiency for both systems in each case, as well as the corresponding improvements.
| Case | \(P_{Max}\) (bare, W) | \(P’_{Max}\) (PV-PCM, W) | \(\Delta P_{Max}\) (W) | \(EFF_{Max}\) (bare, %) | \(EFF’_{Max}\) (PV-PCM, %) | \(\Delta EFF_{Max}\) (%) |
|---|---|---|---|---|---|---|
| 1 | 6.62 | 7.17 | 0.55 | 13.41 | 14.52 | 1.11 |
| 2 | 7.94 | 8.80 | 0.86 | 12.07 | 13.37 | 1.30 |
| 3 | 9.32 | 10.60 | 1.28 | 11.33 | 12.88 | 1.55 |
| 4 | 9.50 | 10.85 | 1.35 | 11.56 | 13.19 | 1.63 |
| 5 | 9.43 | 10.75 | 1.32 | 11.47 | 13.06 | 1.59 |
The results clearly demonstrate that the cooling effect of the PCM not only lowers the temperature of the solar panel but also translates into meaningful gains in the electrical output. The maximum power improvement ranged from 0.55 W to 1.35 W for the tested conditions. The highest improvement was observed in the low-ambient-temperature case, where the temperature reduction was also the largest.
5. Influence of Environmental Factors on PV-PCM System Cooling Performance
To understand the applicability of the PV-PCM system under different weather conditions, I systematically varied the irradiance and the ambient temperature while keeping other factors constant.
5.1 Effect of Irradiance Intensity
Keeping the ambient temperature at 20.7 °C, I conducted experiments at 600, 800, and 1000 W/m². The results show that the cooling effectiveness of the PV-PCM system increases with increasing irradiance. This is because higher irradiance produces a larger amount of heat that must be dissipated, and the PCM is capable of absorbing a greater portion of that heat before reaching its melting point. The average upper surface temperature reduction increased from 19.61 °C at 600 W/m² to 22.39 °C at 800 W/m² and 26.77 °C at 1000 W/m². Likewise, the maximum power improvement increased from 0.55 W to 0.86 W and then to 1.28 W. The maximum efficiency improvement increased from 1.11% to 1.30% and 1.55%. These trends are summarized in Table 6.
| Irradiance (W/m²) | \(\Delta T_A\) (°C) | \(\Delta T_B\) (°C) | \(\Delta P_{Max}\) (W) | \(\Delta EFF_{Max}\) (%) |
|---|---|---|---|---|
| 600 | 19.61 | 20.71 | 0.55 | 1.11 |
| 800 | 22.39 | 24.16 | 0.86 | 1.30 |
| 1000 | 26.77 | 28.15 | 1.28 | 1.55 |
The physical explanation is straightforward: the amount of heat generated by the solar panel is proportional to the incident irradiance. When the PCM is present, it acts as a thermal reservoir. During the melting period, it absorbs a large amount of latent heat, effectively suppressing the temperature rise of the solar panel. The higher the irradiance, the more latent heat is consumed, and the greater the temperature difference compared to the bare panel, which has no such thermal buffering capacity.
5.2 Effect of Ambient Temperature
To isolate the effect of ambient temperature, I maintained the irradiance at 1000 W/m² and conducted experiments at 7.3 °C, 14.1 °C, and 20.7 °C. The results show that the cooling performance of the PV-PCM system deteriorates as the ambient temperature increases. The upper surface temperature reduction decreased from 33.94 °C at 7.3 °C to 30.34 °C at 14.1 °C and 26.77 °C at 20.7 °C. The maximum power improvement decreased from 1.35 W to 1.32 W and 1.28 W, while the maximum efficiency improvement decreased from 1.63% to 1.59% and 1.55%. These findings are listed in Table 7.
| Ambient temperature (°C) | \(\Delta T_A\) (°C) | \(\Delta T_B\) (°C) | \(\Delta P_{Max}\) (W) | \(\Delta EFF_{Max}\) (%) |
|---|---|---|---|---|
| 7.3 | 33.94 | 36.51 | 1.35 | 1.63 |
| 14.1 | 30.34 | 32.46 | 1.32 | 1.59 |
| 20.7 | 26.77 | 28.15 | 1.28 | 1.55 |
At lower ambient temperatures, the temperature difference between the solar panel and the environment is larger, which enhances the natural convective heat loss from the back side of the PV-PCM system. Moreover, the PCM solidifies more quickly during the early stages, allowing it to absorb more sensible heat during the subsequent melting. Thus, the PV-PCM system is more effective in colder climates. In hot climates, the passive cooling provided by the PCM becomes less pronounced, although it still yields a beneficial effect.
6. Numerical Simulation of a PV-PCM System under Real Weather Conditions
To extend the applicability of the experimental results, I developed a transient three-dimensional numerical model using ANSYS Fluent. The model considered the actual structure of the solar panel, including the glass, EVA, silicon cell, EVA, and Tedlar layers, as well as the 30 mm thick PCM layer inside an aluminium container. The geometry was based on a single solar cell with dimensions of 40 mm × 50 mm, which adequately represents the thermal behavior of the larger panel without excessive computational cost. The model incorporated the enthalpy-porosity formulation to simulate the phase change process, and the Boussinesq approximation was used to account for natural convection in the liquid PCM.
Before performing the actual weather simulations, I validated the model against the experimental data from the indoor tests. The boundary conditions in the model were set to match the laboratory conditions (\(G=1000\) W/m², \(T_{\text{amb}}=20.7\) °C, no wind). The simulated temperature response was in good agreement with the measured data. The maximum deviation was 6.29 °C for the PV-PCM system, corresponding to a relative error of 10.95% at the initial stage, while the average deviation was 4.08 °C. This level of accuracy is considered acceptable for engineering predictions.
After validation, I used the model to simulate the cooling performance of the PV-PCM system under realistic weather data for the day with the highest irradiation of the year (June 2) in a representative city in Northeast China. The input data included the hourly solar irradiance, ambient temperature, wind speed, and soil temperature. Since the ambient temperature and wind speed varied significantly during the day, I implemented them as user-defined functions (UDFs) to capture the time-varying boundary conditions. The soil temperature was assumed to be constant at 9 °C, and the sky temperature was calculated from the ambient temperature using the empirical relationship mentioned earlier. The convective heat transfer coefficient was computed from the wind speed using the correlation \(h = 5.70 + 3.80u\).
The simulated results for the 24-hour period are presented in the following sections. The time step was set to 10 seconds, and the model was run for 8640 steps to cover a full day. The initial temperature of the entire system was assumed to be equal to the ambient temperature at midnight (13.84 °C).
6.1 Temperature Response on the Maximum Irradiation Day
The simulation showed that the bare PV panel temperature closely followed the solar irradiance profile. The panel started heating after sunrise (around 4 a.m.) and reached its peak value of 51.39 °C at 11 a.m. The temperature remained above 40 °C for about six hours, from 9 a.m. to 3 p.m. In contrast, the PV-PCM system exhibited a much slower temperature rise. It reached 37 °C at 9 a.m. and then remained almost constant at around 40 °C from 10 a.m. to 1 p.m. thanks to the latent heat absorption of the PCM. After 1 p.m., the temperature began to decrease gradually, and after 4 p.m. the cooling rate increased. By 8 p.m., the PV-PCM system approached the temperature of the bare panel. The maximum temperature difference between the two systems was 10.56 °C, occurring at 11 a.m. This demonstrates that the PCM can effectively cap the peak temperature of the solar panel on a clear sunny day.
Another interesting phenomenon was observed in the afternoon. Between 3 p.m. and 8 p.m., the PV-PCM system became slightly warmer than the bare PV panel. This is due to the solidification of the PCM, which releases the stored latent heat. The negative temperature difference reached a minimum of -6.27 °C at 4 p.m. Although this may seem disadvantageous, it actually provides a thermal buffering effect that prevents rapid cooling of the solar panel during the late afternoon and evening, potentially reducing thermal fatigue.
6.2 Efficiency and Power Improvement
Using the simulated temperature difference \(\Delta T = T_{PV} – T_{PV-PCM}\) and the temperature coefficient \(\beta = 0.0045\) K⁻¹, I calculated the instantaneous efficiency improvement \(\Delta \eta\) and power improvement \(\Delta P\) of the PV-PCM system relative to the bare PV panel:
$$
\Delta \eta = \beta \cdot \Delta T
$$
$$
\Delta P = \Delta \eta \cdot G \cdot A
$$
The results showed that the maximum efficiency improvement of 4.75% and the corresponding power improvement of 3.76 W for a 12 W rated module occurred at 11 a.m. During the hours when the PCM was in the solidification phase (after 3 p.m.), the efficiency improvement became negative, reaching a minimum of -2.82% at 4 p.m. Over the entire day, the PV-PCM system still provided a net positive gain. The cumulative net increase in the output power over the 15-hour irradiation period was estimated to be 12.50 Wh for the module with a peak rating of 12 W. This corresponds to a significant relative enhancement when considering the total daily energy yield of the module.
7. Concluding Remarks
In this comprehensive study, I have experimentally and numerically investigated the cooling performance of phase change materials integrated with solar photovoltaic panels. The key findings are as follows:
- The presence of a 30 mm thick paraffin-based PCM layer significantly reduces the operating temperature of the solar panel. Depending on the irradiance and ambient temperature, the average upper surface temperature of the solar panel was lowered by 19.61 °C to 33.94 °C, and the lower surface temperature was lowered by 20.71 °C to 36.51 °C.
- The electrical performance of the solar panel is substantially improved. The open-circuit voltage was increased by 1.08 V to 1.96 V, the fill factor was increased by 0.02 to 0.04, the maximum output power was increased by 0.55 W to 1.35 W, and the maximum efficiency was increased by 1.11% to 1.63% for the tested cases.
- The PV-PCM system prolongs the cooling time after the irradiation stops. The bare PV panel cooled to ambient in about 80 minutes, whereas the PV-PCM system required 480 minutes. This delayed thermal response is beneficial for reducing thermal stress and could be exploited for heat recovery applications.
- The cooling performance is enhanced by higher irradiance levels but reduced by higher ambient temperatures. Therefore, the PV-PCM system is particularly suitable for regions with high solar irradiation and relatively low ambient temperatures.
- The numerical simulation based on actual weather data of a maximum irradiation day showed that the PV-PCM system can keep the solar panel temperature below 40 °C for most of the day, with a peak temperature reduction of 10.56 °C. The estimated daily energy gain was 12.50 Wh for the 12 W module, which is equivalent to an efficiency improvement of about 4.2% at the peak time.
In conclusion, phase change materials offer a reliable, passive, and maintenance-free solution for improving the performance and lifetime of solar photovoltaic panels. The outcomes of this research provide valuable guidance for the design and application of PV-PCM systems in various climatic regions. Future work should explore the use of enhanced heat transfer techniques (e.g., metallic foams, fins, or nanoparticles) to further improve the thermal conductivity of the PCM and to optimize the melting temperature for different geographical locations.