In the context of global energy demand growth and the depletion of traditional fossil fuels, solar energy has emerged as a key solution due to its wide distribution, abundant reserves, and clean nature. As a core component for converting sunlight into electricity, solar panels face the challenge of efficiency degradation caused by elevated operating temperatures. For every 1°C rise in cell temperature, the photoelectric conversion efficiency drops by 0.4%–0.5%, and prolonged high temperature can cause permanent damage to the solar panel structure. Among various cooling technologies, the photovoltaic-phase change material (PV-PCM) system has shown promising results. However, the poor thermal conductivity of PCM limits internal heat transfer and cooling speed. Adding metal fins to the PCM layer has been demonstrated to effectively improve the thermal performance of the PV-PCM system. In this work, I focus on a novel design that integrates internal and external fins with PCM to enhance the thermal management of solar panels. Through comparative experiments and numerical simulations, I systematically investigate the effects of irradiance, PCM thickness, fin geometry, and fin dimensions on the cooling performance and electrical output of solar panels.
The solar panel temperature is a critical factor affecting its power generation efficiency. The photoelectric conversion efficiency η of a solar panel under standard test conditions (STC: 25°C, 1000 W/m²) is given by:
$$ \eta = \eta_{\text{STC}} [1 – \beta (T_{\text{PV}} – 25)] $$
where TPV is the solar panel temperature (°C), β is the temperature coefficient (typically 0.0045 for crystalline silicon solar panels), and ηSTC is the efficiency at STC. This negative correlation drives the need for effective cooling strategies for solar panels.
Research Methodology
I designed an experimental system consisting of a solar simulator, a comparative solar panel setup, and a data acquisition system. The PV-PCM system includes a conventional solar panel with a back-mounted aluminum container filled with PCM (paraffin-based, melting point ~45°C). The structural layers of the solar panel and the PCM container are listed in Table 1.
| Layer | Thickness (mm) | Density (kg/m³) | Specific heat (J/(kg·K)) | Thermal conductivity (W/(m·K)) |
|---|---|---|---|---|
| Glass | 3.0 | 3000 | 500 | 1.80 |
| EVA (front) | 0.5 | 960 | 2090 | 0.35 |
| Silicon cell | 0.3 | 2330 | 677 | 148.00 |
| EVA (back) | 0.5 | 960 | 2090 | 0.35 |
| TPT backsheet | 0.1 | 1200 | 1250 | 0.20 |
| PCM (paraffin) | 40.0 | 850 (solid) / 780 (liquid) | 2000 (solid) / 2300 (liquid) | 0.20 |
The heat transfer model considers the thermal energy absorbed by the solar panel, which is calculated as:
$$ E = (1 – \rho_{\text{PV}}) G_T – \eta G_T $$
where ρPV is the reflectivity of the solar panel surface, GT is the solar irradiance (W/m²), and η is the instantaneous efficiency. The heat dissipated from the front glass surface and the back aluminum surface is given by:
$$ Q_T = h (T_{\text{gl}} – T_{\text{amb}}) + \sigma \varepsilon_{\text{gl}} F_{ts} (T_{\text{gl}}^4 – T_s^4) $$
$$ Q_B = h (T_{\text{al}} – T_{\text{amb}}) + \sigma \varepsilon_{\text{al}} F_{tg} (T_{\text{al}}^4 – T_g^4) $$
where h is the convective heat transfer coefficient, σ = 5.67×10⁻⁸ W/(m²·K⁴) is the Stefan-Boltzmann constant, εgl = 0.95 and εal = 0.02 are the emissivities of glass and aluminum, Fts and Ftg are view factors to sky and ground, and Ts, Tg are sky and ground temperatures.
For the PCM phase change, I adopt the apparent heat capacity model proposed by Biwole et al. The effective specific heat CP(T) is:
$$ C_P(T) = \begin{cases} C_{Ps}, & T < T_m – \Delta T/2 \\ C_{Ps} + (C_{Pl} – C_{Ps}) B + L h_D, & T_m – \Delta T/2 \le T \le T_m + \Delta T/2 \\ C_{Pl}, & T > T_m + \Delta T/2 \end{cases} $$
where Tm is the melting temperature, ΔT is the phase change temperature interval, CPs and CPl are specific heats of solid and liquid PCM, L is latent heat, and B is the liquid fraction defined as:
$$ B = \begin{cases} 0, & T < T_m – \Delta T/2 \\ \frac{T – T_m}{\Delta T} + 0.5, & T_m – \Delta T/2 \le T \le T_m + \Delta T/2 \\ 1, & T > T_m + \Delta T/2 \end{cases} $$
To improve convergence, a Dirac delta function D(T) is used:
$$ D(T) = \frac{e^{-(T – T_m)^2 / [(T_{P,l} – T_{P,s})/4]^2}}{\sqrt{\pi} \, [(T_{P,l} – T_{P,s})/4]^2} $$
The density and thermal conductivity of PCM are similarly expressed using the liquid fraction:
$$ \rho = \begin{cases} \rho_s, & T < T_m – \Delta T/2 \\ \rho_s + B (\rho_l – \rho_s), & T_m – \Delta T/2 \le T \le T_m + \Delta T/2 \\ \rho_l, & T > T_m + \Delta T/2 \end{cases} $$
$$ k = \begin{cases} k_s, & T < T_m – \Delta T/2 \\ k_s + B (k_l – k_s), & T_m – \Delta T/2 \le T \le T_m + \Delta T/2 \\ k_l, & T > T_m + \Delta T/2 \end{cases} $$
Experimental Investigation
I conducted experiments at a tilt angle of 30° under three irradiance levels: 600, 800, and 1000 W/m². The ambient temperature was maintained at 25°C. A conventional solar panel without PCM (denoted as PV) and a PV-PCM system were tested simultaneously. The solar panel surface temperature was measured using thermocouples attached to the backsheet.
Figure 1 (inserted image) shows the experimental setup.
As shown in the experimental results, the solar panel surface temperature of the PV-PCM system was always lower than that of the bare PV system under all irradiance levels. At 1000 W/m², the bare solar panel temperature stabilized around 115°C, while the PV-PCM system reached approximately 95°C, a reduction of 20°C. At 800 W/m², the temperatures were 98°C (PV) and 80°C (PV-PCM), a reduction of 18°C. At 600 W/m², the temperatures were 85°C (PV) and 68°C (PV-PCM), a reduction of 17°C. The cooling effect became more pronounced at higher irradiance, indicating that PCM effectively absorbs excess heat from the solar panel.
The open-circuit voltage (Voc) of the solar panel also benefited from the temperature reduction. At 1000 W/m², Voc of the bare solar panel stabilized at 16.2 V, while that of the PV-PCM system was 17.5 V – an increase of 1.3 V. At 800 W/m², the values were 16.8 V and 18.2 V, respectively, a gain of 1.4 V. At 600 W/m², they were 17.8 V and 18.8 V, a gain of 1.0 V.
The maximum power output (Pmax) followed a similar trend. At 1000 W/m², the bare solar panel produced 8.2 W, while the PV-PCM system delivered 9.0 W – an improvement of 0.8 W (9.8% increase). At 800 W/m², the power increased from 7.5 W to 8.0 W (6.7% increase). At 600 W/m², the power rose from 5.5 W to 6.0 W (9.1% increase). These results confirm that PCM cooling of solar panels enhances both voltage and power output, particularly under strong solar radiation.
Numerical Simulation Study
Mesh Independence Verification
To ensure accurate simulation results, I performed mesh independence tests using COMSOL Multiphysics. Five mesh schemes with element counts of 12,917; 28,666; 67,174; 94,085; and 130,905 were evaluated. The average surface temperature of the solar panel in the PV-PCM system was monitored. The temperature changed from 67.50°C (12,917 elements) to 67.12°C (67,174 elements), and further to 67.10°C (94,085 elements) and 67.05°C (130,905 elements). Since the variation beyond 67,174 elements was less than 0.05°C, I selected 67,174 elements for subsequent simulations to balance accuracy and computational cost.
Validation of Simulation Accuracy
I validated the simulation model against experimental data for the PV-PCM system at 1000 W/m² and 30° tilt. The maximum difference between predicted and measured solar panel surface temperature was less than 0.6°C, confirming the reliability of the numerical model. Additionally, the phase change behavior was verified by comparing with Biwole’s benchmark study; the temperature contours at various time steps matched closely, ensuring that the PCM melting process was correctly captured.
Effect of PCM Thickness on Solar Panel Cooling
Using the validated model, I investigated the impact of PCM thickness (10, 20, 30, 40, and 50 mm) on the solar panel surface temperature under 1000 W/m² and 30° tilt. The results are summarized in Figure 2 (described here) and Table 2.
| PCM thickness (mm) | Final solar panel temperature (°C) |
|---|---|
| 10 | 85 |
| 20 | 62 |
| 30 | 48 |
| 40 | 40 |
| 50 | 39 |
Thinner PCM layers (10 mm) led to rapid temperature rise because the limited heat storage capacity was quickly saturated. As thickness increased, the thermal inertia grew, resulting in lower and more stable solar panel temperatures. The solar panel temperature decreased from 85°C at 10 mm to 40°C at 40 mm, but further increase to 50 mm only reduced it by 1°C. Therefore, a 40 mm PCM thickness offers the best balance between cooling performance and material cost for the solar panel cooling system.
Influence of Internal and External Fin Geometry
To enhance the poor thermal conductivity of PCM, I designed four types of internal and external fin configurations: (a) triangular fins (left-oriented), (b) triangular fins (right-oriented), (c) trapezoidal fins, and (d) rectangular fins. The fins were made of aluminum (thermal conductivity 237 W/(m·K)) and attached to the inside and outside of the PCM container backplate. Figure 3 (described) illustrates the fin shapes.
The solar panel surface temperature and PCM liquid fraction were monitored over 120 minutes under 1000 W/m². The results are given in Table 3.
| Fin geometry | Solar panel temperature (°C) | PCM liquid fraction |
|---|---|---|
| Triangular (left) | 42 | 0.85 |
| Triangular (right) | 47 | 0.92 |
| Trapezoidal | 45 | 0.78 |
| Rectangular | 48 | 1.00 |
The triangular (left) fin configuration performed best, achieving the lowest solar panel temperature (42°C) and a moderate PCM liquid fraction (0.85), indicating effective heat transfer and delayed complete melting. The rectangular fins caused the fastest complete melting (liquid fraction = 1.0) and a higher solar panel temperature (48°C), due to less efficient heat distribution. Trapezoidal fins offered intermediate performance. The superior performance of the triangular (left) fins can be attributed to their ability to create natural convection currents within the PCM and improve heat spreading, which is critical for solar panel thermal management.
Optimization of Fin Geometry Parameters
Based on the best fin shape (triangular, left-oriented), I optimized the base widths of the internal and external fins. Three sets of dimensions were tested, as summarized in Table 4.
| Fin position | Condition 1 | Condition 2 | Condition 3 |
|---|---|---|---|
| Internal fin 1 | 6 | 7 | 8 |
| Internal fin 2 | 5 | 6 | 7 |
| Internal fin 3 | 4 | 5 | 6 |
| Internal fin 4 | 3 | 4 | 5 |
| Internal fin 5 | 2 | 3 | 4 |
| External fin 1 | 2 | 3 | 4 |
| External fin 2 | 3 | 4 | 5 |
| External fin 3 | 4 | 5 | 6 |
| External fin 4 | 5 | 6 | 7 |
| External fin 5 | 6 | 7 | 8 |
| External fin 6 | 7 | 8 | 9 |
The time evolution of the solar panel surface temperature for the three conditions is shown in Figure 4 (described). In the early stage (0–30 min), all conditions exhibited similar temperature rise rates. Between 30 and 80 min, Condition 3 (larger base widths) maintained a lower temperature than Conditions 1 and 2. After 80 min, the solar panel temperature under Condition 3 stabilized at around 39°C, while Conditions 1 and 2 reached 42–44°C. The improvement is attributed to the larger fin base area, which provides better heat conduction paths into the PCM and enhances the effective thermal conductivity of the composite system. Therefore, Condition 3 emerged as the optimal fin geometry for solar panel cooling.
Discussion
The combination of PCM and fins effectively addresses the intrinsic low thermal conductivity of PCM, significantly improving the thermal management of solar panels. The experimental results demonstrate that the PV-PCM system can lower the operating temperature of a solar panel by up to 20°C under high irradiance, leading to a 9.8% increase in maximum power. This temperature reduction is critical because the efficiency of a typical silicon solar panel drops by 0.45% per degree Celsius rise; thus, a 20°C reduction translates to a 9% efficiency improvement, which aligns well with the measured power gain.
Simulation results further reveal that increasing PCM thickness from 10 mm to 40 mm progressively reduces the solar panel temperature. However, beyond 40 mm, the marginal benefit diminishes. This is because the PCM layer acts as a thermal buffer: once the thickness exceeds a certain value, the additional PCM does not receive enough heat to complete melting within the operating timeframe, and the temperature gradient across the layer becomes less effective. Hence, a 40 mm thickness is recommended for practical solar panel cooling systems.
The fin geometry plays a pivotal role in distributing heat within the PCM. Triangular fins, particularly with a left-oriented acute angle, create a more uniform temperature field and delay complete melting compared to rectangular or trapezoidal fins. The reason lies in the fact that triangular fins induce secondary flows in the liquid PCM due to buoyancy effects, enhancing convective heat transfer. Rectangular fins, although providing a larger surface area, tend to create stagnant zones where heat accumulates, leading to earlier saturation. The optimization of fin base widths shows that increasing the width (up to Condition 3) further improves heat transfer because thicker fins reduce thermal resistance along their length.
The combined effect of irradiance, tilt angle, PCM thickness, and fin design yields an optimal operating point: at 1000 W/m², 30° tilt, 40 mm PCM thickness, and triangular (left) fins with the geometry of Condition 3, the solar panel temperature can be maintained below 40°C even under peak sunlight. This condition maximizes the electrical output while ensuring the long-term durability of the solar panel components.
It is also noteworthy that the cooling performance of the solar panel depends on the ambient conditions. In this study, I fixed the ambient temperature at 25°C and the tilt angle at 30°. In real installations, higher ambient temperatures or lower tilt angles may reduce the cooling effect. Nevertheless, the relative benefits of PCM and fins are expected to remain significant because the underlying heat transfer mechanisms are governed by the same physical principles.
Conclusion
In this work, I have systematically investigated the enhancement of solar panel cooling performance using PCM combined with internal and external fins. The major findings are:
1. The PV-PCM system reduces the operating temperature of the solar panel by 17–20°C under irradiance of 600–1000 W/m² compared to a bare solar panel. The open-circuit voltage increases by 1.0–1.4 V, and the maximum power output improves by 6.7%–9.8%.
2. Increasing PCM thickness from 10 mm to 40 mm lowers the solar panel temperature from 85°C to 40°C. Further increase to 50 mm only reduces temperature by an additional 1°C, making 40 mm the optimal thickness for the solar panel cooling system.
3. Among different internal and external fin geometries, triangular fins oriented to the left yield the best thermal management performance, achieving a solar panel temperature of 42°C compared to 45–48°C for other geometries at the same PCM thickness.
4. Optimizing the fin base widths (Condition 3, larger width) further reduces the solar panel temperature to 39°C, providing an additional 3°C improvement over the baseline fin dimensions.
5. The optimal operating condition for the proposed PV-F-PCM system is at irradiance of 1000 W/m², tilt angle of 30°, PCM thickness of 40 mm, and triangular (left) fins with Condition 3 dimensions. This configuration effectively maintains the solar panel temperature within a safe and efficient range, enhancing both power output and lifespan.
This study offers a comprehensive understanding of the coupled thermal phenomena in solar panel cooling and provides a practical engineering guideline for designing next-generation photovoltaic systems. The integration of PCM and fins is a promising approach to mitigate the temperature-related efficiency losses of solar panels, contributing to more sustainable and efficient solar energy utilization.