Sealing Technologies
Solar: A “hot” topic

Direct use of the sun’s energy via smart energy conversion systems such as solar thermal collectors and photovoltaic modules is in principle the solution to all our energy problems and an all-round hot project with special sealing components. We look at two solar sealing applications from Simrit.

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Application 1: Designed to “electrify“ the rays of the sun

Simrit has developed a Liquid Silicone Seal for high thermal and UV stability. The multi-lip part is designed as a two-component (2C) part with the seal injection-molded to the thermoplastic box lid.

In these times of exploding raw materials prices, where crude oil prices have reached historic highs, use of “free” energy from the sun is becoming increasingly attractive. Dismissed a short while ago as a mere ecological trend, it has developed into a major industry over the last few years.

As the importance of the solar — and in particular the photovoltaic — industry for energy recovery grows, so do demands on quality and service life of the components used. After all, most of the components in a solar cell are found on the rooftop and are exposed for decades to the ravages of the weather. This situation also defines the demands on the sealing materials used in a solar module. Thermal stability at temperatures ranging from -30°C to 130°C, high UV stability, and an optimized seal profile ensuring that the seal is as impermeable as possible are just some examples.

A multi-lip seal is required

Improvements in the quality of the components create new possibilities for utilizing the sun’s energy more efficiently. For this reason, Simrit is working closely with a global technology group on optimizing the so-called terminal boxes beneath the solar panels. These boxes usually consist of a lower enclosure housing the connections as well as a lid with a seal. The seal must prevent ingress of moisture, dust, and other undesirable media on the one hand and compensate for the lid and enclosure production tolerances on the other hand. Compensation of the minimum and maximum tolerances in O-rings would lead to high insertion forces, but optimization of the installation spaces available has led to a reduction in seal dimensions. That’s why it was hardly possible to avoid using a multi-lip seal.

Liquid silicone is particularly suitable

Simrit developed such a multi-lip radial seal for terminal boxes on solar modules. Liquid silicone rubber was used to make this component, as it is very resistant to environmental influences — which makes it particularly suitable for this sealing function. Liquid silicone rubber is thermally stable, resistant to aging, and largely resistant to water, ozone, and UV radiation.

The liquid silicone seal shape has been adapted precisely to the installation space for photovoltaic terminal boxes, and the seal lip contour has been optimized for this sealing function via FEM calculations. The terminal box lid is clipped to the enclosure for easier installation. The seal must reliably compensate for any tolerances in the enclosure and the lid to provide an optimized permanent seal. The multi-lip sealing edge structure in particular contributes to this.

2C part version

The enclosure lid and the optimized seal can optionally be designed as a single 2C part. Here, the silicone seal is injection-molded onto the thermoplastic material of the lid in a single production step. In this way, the two parts can be joined permanently. This simplifies assembly, guarantees secure fitting of the seal, and reduces logistics requirements. The advantages provided by this 2C solution to customers are manifold. Only one part must be purchased, production of this part is more cost effective, and assembly is greatly simplified. Besides that, the seal cannot be lost or installed incorrectly. It goes without saying that only approved and certified materials are used.

The 2C solution for the terminal box on a solar module offers customers maximum safety in operation as well as outstanding sealing materials.

Application 2: The bar is high

Simrit has developed a customized sealing component made from the elastomer material 70 EPDM 291 for the innovative solar collectors from Kingspan Solar. A patent application has been submitted for the new component.

Simrit has been supplying O-rings to Kingspan Solar, part of the global Kingspan group from Ireland, for approximately five years. When Kingspan Solar began their search for sealing concepts suitable for their innovative evacuated tube collectors, Simrit, whose quality products have long been known to Kingspan Solar, was their first choice.

The requirement was an overall quality sealing concept that, in addition to having a long service life, must be resistant to both excessive heat and pressure from the solar panels. Temperatures of over 200°C and pressure of 8 bar can easily occur in the collector and at pipe junctions. As such, the collector manufacturers demand long-term stability of the seal to ensure efficiency under these conditions.

Technically advanced and easy to install

Meeting the demands on the seals for the new evacuated tube collectors according to the heat pipe principle was technically challenging. A direct thermal contact between the condenser and the heat transfer medium had to be sealed effectively. When the heat transfer medium and steam from the pipes come into contact with each other, they create a hot and wet environment demanding absolute performance of the seal in terms of sealing, as well as pressure and heat resistance.

A waterproof seal was required that could withstand temperatures of more than 200°C, pressures of up to 8 bar, and could be installed easily without requiring tools by the heating installer. The sealing component had to provide a circumferential seal to provide protection externally from air and internally from the heat transfer medium.

“Without development of a completely new sealing design, it would never have been possible to insert a very hot and wet evacuated tube into the manifold without use of an additional tool,“ explains Richard Pelan, Senior Product Design Engineer at Kingspan Solar. “Simrit was involved in the development right from the start; otherwise a sealing component that met the tough demands we had to place on scope of functionality and flexibility for use in our evacuated tube collectors would never have come into being.“

Patent pending

The patent-pending sealing component, developed in less than two years by the materials and seal specialists together with engineers from Kingspan Solar, is based on the elastomer 70 EPDM 291. This elastomer exhibits very low relaxation — even after thousands of hours in water at 200°C. The likewise very low compression set of 70 EPDM 291 guarantees a long service life. This material also scores high on thermal stability and pressure resistance.

The EPDM elastomer developed by Simrit passed all tests defined internally by Kingspan Solar as a prerequisite for use in their in-house Thermomax solar collector series. The component not only meets EN12975 requirements and the European SolarKeymark requirements for solar collectors, but also fulfills the considerably more stringent requirements of Kingspan Solar. The European Solar Keymark requires that the sealing component be able to withstand 1.5 times the maximum operating pressure of 8 bar, hence 12 bar; Kingspan Solar raises the maximum to 40 bar. The sealing component was able to meet these extreme demands and thereby lives up to Kingspan Solar’s maxim of always being a little bit better than what the most demanding customers ask for. “This can only be achieved through cooperation with the world’s best suppliers,“ says Kingspan Solar’s Senior Quality Manager, Dr. Tommy Williamson.

You can download a .pdf of Simrit’s Solar Technology brochure by clicking on the brochure icon at left.

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