The main advantage of 316L stainless steel over SUS304 in a solar water heater is its superior corrosion resistance, especially in harsh environments.

316L stainless steel contains molybdenum, which enhances its corrosion resistance compared to SUS304. This makes it more suitable for applications where the water quality is poor or where the water contains chloride ions, which can accelerate corrosion. In solar water heaters, which are often exposed to varying weather conditions and water with different mineral content, 316L stainless steel provides better long-term durability and reliability.

Additionally, 316L stainless steel has higher creep, tensile, and yield strength compared to SUS304, which can make it more resistant to deformation and cracking under thermal and mechanical stresses, further improving its performance in solar water heater applications.