Solar Water Heating System Panels

European Solar Engineering

Hot Solar Water panels are manufactured with a  mechanical connection between the absorber plate and heat transfer pipework in the panel (No welding, soldering, brazing, etc…). The absorber is folded around the panel pipework. This is the key to longevity & performance making this technology the choice of Mechanical Engineers around the World.  

patented folded solar heater absorber on copper pipe

Welding is generally considered a strong joining method, but it can have weaknesses depending on various factors. Here are some reasons why a weld is be considered a weak joint in a solar water heater panel:

  1. Lack of Fusion: If the welding process doesn’t achieve proper fusion between the base metals and the filler material, it can result in weak spots within the weld. Lack of fusion can occur due to insufficient heat, improper welding technique, or contamination of the base metals.

  2. Porosity: Porosity refers to the presence of tiny gas pockets within the weld metal. These pores weaken the integrity of the weld and can lead to failure under stress. Porosity can occur due to inadequate shielding gas, improper welding technique, or contamination of the weld area.

  3. Inclusions: Inclusions are foreign materials, such as slag or oxides, that get trapped in the weld metal during the welding process. These inclusions create discontinuities within the weld, reducing its strength and integrity.

  4. Weld Defects: Various defects can occur during the welding process, such as cracks, undercutting, or incomplete penetration. These defects weaken the weld and compromise its structural integrity.

  5. Heat Affected Zone (HAZ): The HAZ is the area surrounding the weld where the base metal has been heated but not melted. Depending on the welding process and the base metal properties, the HAZ may experience changes in microstructure and mechanical properties, potentially leading to weakness.

  6. Stress Concentration: Welds often create stress concentration points, where stress is localized, leading to potential failure under load. Sharp corners, abrupt changes in thickness, or abrupt changes in geometry can exacerbate stress concentrations in weld joints.

  7. Environmental Factors: Exposure to corrosive environments, high temperatures, or other external factors can degrade the weld over time, leading to weakness and eventual failure.

Overall, while welding can produce strong joints when done correctly, the potential for weak welds exists due to various factors such as lack of fusion, porosity, inclusions, defects, heat affected zone, stress concentration, and environmental factors. Proper welding techniques, materials selection, and inspection are essential to minimize the risk of weak weld joints.

While it’s true that welding is generally avoided in aircraft construction, the reason isn’t solely due to the weakness of weld joints. There are several other factors that contribute to the preference for other joining methods in aircraft and solar water heater panel manufacturing:

  1. Weight Considerations: Welded joints can add unnecessary weight, which is a critical factor in design. Designers strive to minimize weight to improve ease of handling, especially when roof mounting. Welded joints often require additional material for reinforcement, whereas alternative joining methods, such as folding, riveting or bonding, can achieve comparable strength with less weight.

  2. Fatigue Resistance: Welded joints are more susceptible to fatigue cracking compared to other joining methods. folding, for example, distributes the load over a larger area, reducing stress concentrations and improving fatigue resistance.

  3. Inspection and Repair: Welded joints can be challenging to inspect for defects, particularly internal flaws such as lack of fusion or porosity. Non-destructive testing methods may be required to detect these defects, adding complexity and cost to the manufacturing process. Additionally, repairs to welded joints may be more difficult and time-consuming compared to other joining methods.

  4. Material Compatibility: Solar water heating panels are made from lightweight materials such as aluminium and copper. These materials may not be well-suited for welding due to concerns about heat distortion, metallurgical changes, or material compatibility. Alternative joining methods, such as folding, offer better compatibility with these materials.

  5. Design Flexibility: Welding imposes certain constraints on design flexibility, particularly in complex or curved structures. Folding offers greater flexibility in shaping and forming the absorber around the copper pipe, thereby increasing the heat transfer efficiency.

Overall, while welding can be a strong and effective joining method in many applications, its limitations in terms of weight, fatigue resistance, inspection, material compatibility, and most importantly heat transfer capability make it less desirable for solar water heating panels. 

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