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Solar water heater technical defects
Solar water heaters are often marketed as a long-term investment that doesn’t cost money, but in reality, this is not entirely true. The truth is that solar water heaters rely heavily on electricity or gas for heating, especially in regions with frequent cloud cover, rain, snow, or limited sunlight. In places like Shanghai, where over 67% of the days are rainy, up to 70% of the heat used by solar water heaters comes from electric or gas sources. This means that, in practice, their energy consumption can be even higher than that of heat pump water heaters.
In addition, many solar water heaters in northern areas are equipped with an "electrical antifreeze belt" to prevent freezing, which also consumes a significant amount of electricity. Beyond that, there are several technical issues inherent in the design of solar water heaters that make them less efficient and more problematic.
First, the hot water pipes in solar systems can be up to ten meters long, leading to significant water waste each time the system is used. For example, a standard 12mm diameter pipe holds about 0.113 kg of water per meter. If the average length is 15 meters, that’s about 1.7 kg of water wasted per use. With six uses per day, that's 10.2 kg of water wasted daily, 360 kg monthly, and 4,320 kg annually — a staggering 43,200 kg over ten years. Wasting so much water just to save some electricity is not sustainable, especially when many cities in China already face severe water shortages.
Second, solar water heaters require full-day sunshine to heat water, and even then, they typically only provide hot water at night. During the day, the supply is often insufficient, making it hard to guarantee a 24-hour hot water supply. This leads to poor user comfort and convenience.
Third, the solar panels need to be installed on rooftops, which makes them bulky, heavy, and potentially damaging to the roof’s waterproofing. They also affect the aesthetics of buildings, particularly in high-end residential areas.
Fourth, the so-called “opto-electric complementarity†technology — where electric heating is added to supplement solar power — is not fully effective. Most solar water heaters on the market struggle during winter when sunlight is weak. Many companies now add electric heaters or oil boilers to compensate, increasing costs and energy use. The problem lies in controlling when the electric heater should turn on — temperature or time-based controls often fail due to unpredictable weather conditions.
Lastly, the majority of solar water heaters currently on the market are non-pressurized models, commonly known as “falling water†systems. These are inconvenient to use, with only one pipe for both filling and draining, making them uncomfortable and outdated compared to modern pressurized systems.
Overall, while solar water heaters may seem environmentally friendly, their real-world performance and efficiency fall short of expectations, raising questions about their practicality and sustainability.