Introduction
Among the different renewable energy sources, wind power and solar power are the most popular green energy alternatives for fossil fuels. They play a significant role in reducing our dependence on fossil fuels. Solar panels and wind turbines are used to harness solar and wind power, respectively. The photovoltaic cells inside solar panels transform the sun’s radiation into electricity, whereas the generator connected to the wind turbine blade converts the energy of the rotating blade into mechanical power.
Thermal Management for Solar Power Conversion Systems
Solar energy is a clean, sustainable, abundant, accessible, and affordable energy resource. Photovoltaic (PV) energy generation, which allows the direct energy conversion of the solar energy to electricity, has attracted a lot of interest from both scientific and practical points of view. Research and development activities have been taking place in both traditional and advanced PV solar cell technologies, including silicon, multi-junction, dye-sensitized, and perovskite solar cells.
Photovoltaic Cells
Photovoltaic cells convert sunlight into electricity, making them a cornerstone of solar power systems. However, these cells are subject to heating during operation, which can significantly affect their efficiency and lifespan. For most commercial solar cells, only ~15% of the incident solar energy is converted into useful power, while the rest is converted into heat inside the solar cell. Since heat has such substantial negative effects on solar cells, several research attempts has been made to manage it.
A popular cooling method for PV cells is the use of heat spreaders or heatsinks. However, the microscopic imperfections between the two surfaces of the solar panel and heatsink gives air pockets, which raises the thermal resistance between the two surfaces. In order to fill in these micro gaps, thermal interface materials (TIMs) and thermal phase change materials (PCMs) were used to enhance the thermal flow from solar cell to heat sink. These thermal interface materials have excellent wetting and minimal, void free bondlines that help minimize the thermal impedance and in exchange maximize the reliability and performance of those devices.
Concentrated Solar Power (CSP) Systems
Photo from the US Department of Energy Office of Energy Efficiency and Renewable Energy
In CSP systems, mirrors are used to concentrate incident solar irradiation. The focused or concentrated sunlight is converted into high-temperature heat, which is then channeled through a conventional generator. The plants consist of two parts: one that collects solar energy and converts it to heat, and another that converts the heat energy to electricity.
in CSP Systems Units
To enhance the overall thermal efficiency of CSP systems, thermal management is applied on different units, such as solar receivers, thermal storage units, and heat exchangers. This is to ensure efficient energy capture and conversion.
Thermal Management for Wind Power Conversion Systems
Image from Vensys Energy AG
Wind turbines with indirect grid connections typically use power converters, which convert alternating current (AC) to direct current (DC) with a rectifier. DC signals are then converted back to usable AC using an inverter. In this process, the current passes through a series of Insulated Gate Bipolar Transistor switches (IGBTs). The more frequently the switch is turned on and off, the closer the current flow becomes to a true sine wave. The more sine-like the flow, the purer the power. The resulting AC is matched to the frequency and phase of the grid.
Even with efficiency improvements, a wind turbine’s power generation systems and subsystems must manage ever increasing heat within its limited nacelle space. In addition, even if incurred power losses are as little as 3–5%, thermal management systems would have to dissipate 200–300 kW and more of heat.
Air cooling has been used effectively in small-scale wind turbines but it is not practical for removing the heat produced in MW-scale units. Its thermal capacity is so low that it is difficult to blow enough air across a motor or through the converter to maintain reliable operating temperatures. That is why water cooling is used more often than air for larger wind turbines.
Thermal interface materials are found in the gearbox and generator of wind turbines to manage heat generated during operation. Effective thermal management helps in increasing the efficiency and lifespan of these components.
Thermal Interface Materials for Renewable Energy Systems
When selecting thermal interface materials for renewable energy systems, key properties to consider include excellent thermal performance, low thermal resistance down to 0.04 ˚C·cm²/W, and high thermal conductivity up to 8 W/m·K. Optimal surface wetting and low contact resistance are crucial, along with great conformability to fill microscopic voids and cavities. High reliability and long life are essential, ensuring no bleed-out, pump-out, or flow-out issues, as well as no aging effects such as dry-out over time and degraded thermal performance. Stable thermal impedance across accelerated aging tests is also important.
Phase Change Materials
| Product | Thermal Impedance [℃⋅cm2/W] ASTM D5470 | Thermal Conductivity [W/m⋅℃] ASTM D5470 | Reliability High Temperature Soak at 150 ℃ [h] ASTM E1461 | Pad Thickness [mm] | Remark |
| PTM7000 & PTM7950 | 0.04 – 0.06 | 6.0–8.0 | >1500 | 0.20–1.00 | High Thermal Performance |
| PTM6000 | 0.06 – 0.08 | 3.5–4.5 | >3000 | 0.20–1.00 | Advanced Reliability |
| PTM6000HV | 0.10 – 0.12 | 2.5–4.0 | >3000 | NA | For IGBT Application |
All the 7XXX series (PTM7000, PTM7900, and PTM7950) meet the reliability requirements for solar and wind energy applications. Honeywell’s testing protocols include up to 1000 thermal cycles, 92 hours of Highly Accelerated Stress Test (HAST), and 1000 hours of High-Temperature Storage (HTS). In commercial applications, some renewable energy customers have pushed PTM7900 beyond these limits. They have reported successful performance even under more severe conditions, including extended temperature cycling, prolonged temperature and humidity exposure, and increased shock and vibration tests. For more information, see the Reliability Report of PTM7950.
One- and Two-Part Hybrid Gels
Innovations in the TIMs technology, such as hybrid gels, can be a game changer thermal management of renewable energy systems. Hybrid gels provide effective thermal properties and high conformability along with its high compressibility. These materials are formulated to deliver high dispense rates for improved productivity, long-term reliability, and easy reworkability.
| Product | Thermal Conductivity (W/m⋅K) |
| HT5010 | 5.0 |
| HT7000 and HLT 7000 | 7.0 |
| HT9000 | 9.0 |
| HT10000 & HLT 10000 | 10.0 |
Conclusion
As the renewable energy sector continues to grow, the importance of high-quality TIMs will only increase, ensuring optimal thermal management and long-term operational stability. By investing in cutting-edge TIMs, we can support the development of more efficient, durable, and sustainable energy solutions for the future. Contact us and our application engineers and in-house thermal experts will help you out with product selection for your application requirements.
