1. Introduction
With the increasing global energy demand and the growing concern about environmental protection, solar energy has emerged as a clean and renewable energy source. Solar panels, also known as photovoltaic (PV) panels, are widely used to convert sunlight into electricity. However, the efficiency of solar panels is affected by various factors, among which temperature is a crucial one. As the temperature of solar panels rises, their conversion efficiency decreases. Therefore, it is of great significance to develop effective cooling technologies for solar panels to improve their performance and extend their service life. This article reviews the research progress of solar panel cooling technologies at home and abroad in recent years, analyzes the advantages and disadvantages of various cooling technologies, and looks forward to the future development direction.
2. Air Cooling Technology
2.1 Natural Convection Cooling
Natural convection cooling uses air as the heat transfer medium and relies on the natural flow of air to dissipate heat from the solar panel. This method is simple and cost-effective but has limited cooling capacity. The following are some common natural convection cooling methods and their research results presented in a table:
| Researcher | Cooling Method | Cooling Effect | Impact on Conversion Efficiency |
|---|---|---|---|
| 李思琢 (Li Sizhuo) et al. | Ribbed structure on the back of the panel | When the air temperature drops by 5 °C, the conversion efficiency of the ribbed panel is increased by 0.418% on average compared to the non-ribbed panel | – |
| Gotmare et al. | Perforated fin structure on the back of the panel | The temperature of the panel with perforated fins drops by about 4.2% compared to the non-finned panel | – |
| 蔡康 (Cai Kang) et al. | Fin cooler | When the fin height is 10 – 20 mm and the spacing is 20 – 40 mm, the panel temperature can be reduced by a maximum of 15 °C, and the power generation efficiency is increased by about 12% on average | – |
| Moshfegh et al. | Air channel on the back of the panel | – | – |
| Brinkworth | Air channel on the back of the panel | The panel temperature can be reduced by 15 °C | – |
| Mittelman et al. | Air channel on the back of the panel with convection – radiation combined heat transfer | When the heat dissipation per unit area on the back of the panel is greater than 200 W/m², about 30% of the heat is dissipated in the form of radiation | – |
| 杨洪兴 (Yang Hongxing) et al., 赵春江 (Zhao Chunjiang) et al. | Air channel on the back of the panel with natural ventilation | The panel temperature can be reduced by 15 °C, and the power output can be increased by about 8.3% | – |
| 黄护林 (Huang Hulin) et al. | Air channel on the back of the panel | The surface temperature of the panel with an air channel is nearly 20 °C lower than that of the panel without an air channel | – |
| 苗佳雨 (Miao Jiayu) | Natural ventilation cooling system with horizontal and inclined air channels on the back of the panel | The photoelectric conversion efficiency can be increased by a maximum of 8.4% compared to the non-cooling system | – |
2.2 Forced Convection Cooling
Forced convection cooling uses external force, such as a fan, to accelerate the air flow and enhance the heat dissipation of the solar panel. This method has a better cooling effect than natural convection cooling. The research results of some forced convection cooling methods are shown in the following table:
| Researcher | Cooling Method | Cooling Effect | Impact on Conversion Efficiency |
|---|---|---|---|
| Teo et al. | Forced convection circulation cooling system | The power generation efficiency of the panel is increased from 8% – 9% to 12% – 14% | – |
| Mazon – Hernandez et al. | Comparison of natural and forced convection cooling | The power generation power of the panel with forced convection cooling is increased by 15%, and the temperature is reduced by about 15 °C compared to natural convection cooling | – |
| Irwan et al. | Comparison of forced air cooling and forced water cooling | The output power of the panel with forced air cooling is increased by 32.23%, and the panel temperature is reduced by 6.1 °C compared to the panel without a cooling device | – |
| 张晓霞 (Zhang Xiaoxia) et al. | Simulation of the cooling effect of the finned air channel on the back of the panel under forced and natural convection | The surface temperature of the panel under forced convection is 50 – 60 °C lower than that under natural convection, and the power output is increased by 40% | – |
| 申长军 (Shen Changjun) et al. | Ventilation cooling with cold air generated by an evaporative cooler | The surface temperature of the panel is reduced by 10.5 °C compared to the panel without cold air cooling | – |
| 邓鹏杰 (Deng Pengjie) et al. | Optimization of the fin height and spacing in the air channel on the back of the panel under forced convection cooling | When the fin height is 70 mm and the fin spacing is 5 mm, the cooling effect is the best | – |
2.3 Advantages and Disadvantages of Air Cooling
The advantages of natural convection cooling are simple installation and low cost, but the cooling effect is limited. Forced convection cooling has a better cooling effect but requires additional energy consumption for the fan. In general, air cooling is suitable for applications with relatively low power requirements and less strict temperature control requirements.
3. Water Cooling Technology
3.1 Surface Water Cooling
Surface water cooling sprays water on the surface of the solar panel to form a water film for cooling through convection heat transfer and evaporation heat absorption. The research results of surface water cooling are as follows:
| Researcher | Cooling Method | Cooling Effect | Impact on Conversion Efficiency |
|---|---|---|---|
| Krauter | Surface water cooling | The maximum temperature drop of the panel can reach 22 °C, and the power generation power can be increased by about 10.3% | – |
| Tomar et al. | Comparison of the cooling effects of five materials of panels under surface water cooling | Among the five types of panels, the single-crystal silicon panel has the best cooling effect, with an average daily power generation efficiency increase of about 0.89% | – |
| 陈剑波 (Chen Jianbo) et al. | Study on the cooling effect of surface water cooling at different spray amounts | When the spray flow rate is 0.9 m³/h, the corresponding water film thickness is 1.1 mm, and the cooling and water film light transmittance effects are the best | – |
| 梁宁文 (Liang Ningwen) et al. | Numerical simulation of the relationship between the performance of surface water-cooled panels and various factors | When the water mass flow rate is controlled around 0.2 kg/s, the comprehensive performance of the surface water-cooled panel is the best | – |
3.2 Channel Water Cooling
Channel water cooling uses circulating cooling water in the channel to directly or indirectly contact the back of the solar panel to transfer heat to the external environment. The research results of channel water cooling are shown in the following table:
| Researcher | Cooling Method | Cooling Effect | Impact on Conversion Efficiency |
|---|---|---|---|
| Salem et al. | Channel water cooling system | The average temperatures on the front and back of the panel are reduced by 9.7 °C and 14.5 °C, respectively | – |
| Nahar et al. | Simulation of the influence of different water channel heights on the cooling effect of channel water-cooled panels | When the water channel height is increased from 10 mm to 20 mm, the maximum temperature drop of the panel can reach 10.2 °C | – |
| Bashir et al. | Comparison of the channel water cooling effects of single-crystal and polycrystalline silicon panels | The single-crystal silicon panel has a better water cooling effect, with an average temperature drop of 13.6% and an average power generation efficiency increase of 13% | – |
3.3 Advantages and Disadvantages of Water Cooling
The cooling effect of water cooling is better than that of air cooling. Surface water cooling can also reduce the reflection loss of solar radiation and clean the dust on the panel surface. However, water cooling has higher costs, more complex equipment, and more difficult maintenance. In addition, the application of water cooling is limited in areas with water shortages.
4. New Cooling Technologies
4.1 Phase Change Material Cooling
Phase change material cooling uses the latent heat absorption of phase change materials to cool the solar panel. The research results of phase change material cooling are as follows:
| Researcher | Cooling Method | Cooling Effect | Impact on Conversion Efficiency |
|---|---|---|---|
| Indartono et al. | Using palm oil and coconut oil as phase change materials | The palm oil phase change material has better cooling performance. When the thickness of the palm oil phase change material is 102 mm, the maximum temperature drop of the panel is 9.6 °C, and the power generation power is increased by 23.8% | – |
| 李凌瞳 (Li Lingtong) | Using paraffin as a phase change material with a water cooling system | The application of phase change materials in the cooling system can slow down the temperature rise rate of the panel, and the average power generation efficiency and maximum thermal efficiency of the system are increased to 16.8% and 59.8%, respectively | – |
| Chandel et al. | Combining heat sinks and conductive agents with phase change materials | Can improve the overall efficiency of the panel | – |
4.2 Heat Pipe Cooling
Heat pipe cooling uses the evaporation and condensation of the working fluid in the heat pipe to transfer heat and cool the solar panel. The research results of heat pipe cooling are shown in the following table:
| Researcher | Cooling Method | Cooling Effect | Impact on Conversion Efficiency |
|---|---|---|---|
| 吴双应 (Wu Shuangying) et al. | Heat pipe cooling in a flat-panel solar photovoltaic-thermal conversion device | The power generation efficiency of the device with heat pipe cooling can be increased by a maximum of 2.29% compared to the device without heat pipe cooling | – |
| Li et al. | Simulation of the cooling effect of heat pipes | The maximum temperature drop of the panel is 39 °C | – |
| 胡国豪 (Hu Guohao) | Design of a separated gravity heat pipe with non-condensable gas for panel cooling | The average surface temperature of the panel can be reduced by 15.05 – 30.72 °C, and the greater the solar irradiance, the greater the cooling range | – |
4.3 Jet Impingement Cooling
Jet impingement cooling sprays high-speed water jets onto the back of the solar panel through nozzles for cooling. The research results of jet impingement cooling are as follows:
| Researcher | Cooling Method | Cooling Effect | Impact on Conversion Efficiency |
|---|---|---|---|
| Abo – Zahhad et al. | Jet impingement cooling system with a coolant mass flow rate of 50 g/min | The maximum temperature drop of the panel can reach about 65 °C, and the greater the coolant mass flow rate, the greater the cooling range of the panel | – |
4.4 Microchannel Cooling
Microchannel cooling uses microchannel heat exchangers to cool the solar panel. The research results of microchannel cooling are as follows:
| Researcher | Cooling Method | Cooling Effect | Impact on Conversion Efficiency |
|---|---|---|---|
| Yang et al. | Microchannel cooling system for panel cooling | When the water mass flow rate is increased from 5.35 g/s to 37.7 g/s, the average temperature of the panel can be reduced by about 25 °C | – |
4.5 Advantages and Disadvantages of New Cooling Technologies
New cooling technologies such as phase change material cooling, heat pipe cooling, jet impingement cooling, and microchannel cooling have good cooling effects but also have some problems. Phase change materials have low thermal conductivity, which limits the improvement of panel conversion efficiency. Heat pipe cooling, jet impingement cooling, and microchannel cooling have high costs and difficult maintenance.
5. Conclusion and Outlook
5.1 Summary of Cooling Technologies
In summary, different cooling technologies for solar panels have their own characteristics. Air cooling is simple and low-cost, but the cooling effect is limited. Water cooling has a better cooling effect but has higher costs and more complex equipment. New cooling technologies have good cooling effects but also have some problems that need to be overcome. The following table summarizes the characteristics of different cooling technologies:
| Cooling Technology | Cooling Effect | Cost | Complexity | Maintenance Difficulty | Impact on Conversion Efficiency |
|---|---|---|---|---|---|
| Natural Convection Air Cooling | Limited | Low | Low | Low | Slight improvement |
| Forced Convection Air Cooling | Better than natural convection | Medium (due to the need for fans) | Medium | Medium | Significant improvement |
| Surface Water Cooling | Good, can reduce radiation reflection and clean dust | Medium (including water supply and spraying equipment) | Medium | Medium | Significant improvement |
| Channel Water Cooling | Good | High (including water channels and circulating systems) | High | High | Significant improvement |
| Phase Change Material Cooling | Good | Medium (depending on the price of phase change materials) | Medium | Medium (phase change materials may need to be replaced) | Limited by low thermal conductivity |
| Heat Pipe Cooling | Excellent | High (heat pipes and related accessories) | High | High | Good improvement |
| Jet Impingement Cooling | Excellent | High (nozzle and high-pressure water supply system) | High | High | Good improvement |
| Microchannel Cooling | Excellent | High (microchannel heat exchanger) | High | High | Good improvement |
5.2 Future Research Directions
Future research on solar panel cooling technologies can focus on the following aspects:
- Optimization of surface water cooling: Reduce the water film coverage area of surface water cooling to improve water utilization efficiency and reduce water consumption.
- Enhancement of phase change material performance: Develop new phase change materials with higher thermal conductivity to improve heat transfer efficiency and enhance the cooling effect and conversion efficiency of solar panels.
- Cost reduction of new cooling technologies: Research and develop low-cost manufacturing and maintenance technologies for heat pipe cooling, jet impingement cooling, and microchannel cooling to improve their economic feasibility and application range.
- Hybrid cooling technology: Combine different cooling technologies to utilize their respective strengths and overcome their disadvantages. For example, combine air cooling and water cooling, or use phase change materials in combination with other active cooling methods to achieve better cooling effects and energy utilization efficiency.
- Intelligent control of cooling systems: Develop intelligent control systems that can adjust the cooling strategy according to the actual operating conditions of solar panels, such as temperature, irradiance, and power generation efficiency, to realization optimal cooling and maximum energy output.
In conclusion, the development of efficient and reliable cooling technologies is crucial for improving the performance and stability of solar panels. Through continuous research and innovation, it is expected that more advanced and practical cooling solutions will be available in the future, promoting the wider application and development of solar energy.