Feature: Thermal management
Solar inverters and BESS will need materials that can meet many requirements
Thermally-conductive silicones for renewable energy technologies
By Jayden Cho, Global Segment Leader, Display, Industrial Electronics and Microelectronics, and Julien Renaud, Technical Service and Development engineer, both at Dow Consumer Solutions
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enewable energy technologies such as photovoltaic (PV) inverters and battery energy storage systems (BESS) must withstand the high levels
of heat generated by power electronics. Tey also need to resist the spread of fire, a crucial safety concern despite a low rate of thermal runaway incidents in solar panels and lithium-ion batteries. For the designers of renewable energy
technologies, it is also important to find material solutions for outdoor environments. Termally-conductive silicones
withstand high temperatures, removing heat from sensitive components. Designers can choose materials that are fire-resistant and with specific flame ratings, such as UL 94 V0. Among their many advantages, thermally-conductive silicones can withstand a wide range of temperatures whilst retaining their properties over time. Tey resist dust, moisture and humidity and are flexible and stress-relieving, making them perfect for outdoor environments and applications where there are vibrations.
Protecting PV inverters Solar inverters, or PV inverters, change the solar panel’s direct current into alternating current for homes, buildings and appliances. Direct current is channeled through a transformer, then lower the voltage and run the current through insulated gate bipolar transistors (IGBTs) that support high voltage switching. PV inverters contain many components that can generate significant heat, and these systems are expected to last between five and 25 years. An inverter changes the current from
DC to AC. Te most common type of solar inverter is the string type, typically used with a group of adjacent solar panels. By contrast, a micro-inverter is connected to a single solar panel for maximum control, efficiency and flexibility. For both, string inverters and micro-inverters, designers can select silicone thermal encapsulants, thermal interface materials (TIMs) and thermal gels to protect their components. Silicone conformal coatings, adhesives and sealants are also used for environmental protection, electrical insulation, UL 94 flame resistance and, ultimately, reliability. Silicone thermal encapsulants fill the
gaps between the electronic components and the enclosure in the inverter’s inductance module. Tese materials have low viscosity, or resistance to flow, for filling and dispensing with equipment such as static mixers. For inverter modules with complex geometries that may resist flow, there are silicone-based materials with various flows. Primer-less adhesion helps to increase protection and, ultimately, long-term reliability. Once cured, silicone thermal encapsulants remain in place. Although curing can be achieved at room temperature, an optional oven cure can accelerate processing. Most silicone thermal encapsulants have
a thermal conductivity (TC) of 0.3-3.2W/ mK. By contrast, air has a much lower TC of 0.024W/mK at 0°C. Although thermal conductivity varies with temperature, the TC of air does not improve significantly as the temperature rises. Terefore, because a higher TC indicates a faster rate of heat transfer, silicone thermal encapsulants dissipate heat more quickly than air that would otherwise fill the gaps between components. Tey also protect components against dust, moisture and humidity.
www.electronicsworld.co.uk November 2023 37
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