I am a practitioner of solar water heaters. The 18 tubes you mentioned should be 58*1800. If it is this model, the merchant's selling price should not exceed 1,600 yuan including installation and material costs.
But I would like to inform you that 99% of manufacturers with registered trademarks similar to "Peking University" and "Tsinghua" are just through colleges and universities, that is to say the trademarks are not registered at all. . Whether the quality is good or not depends on your luck. Among them, I know that only the brand "Tsinghua Sunshine" is a registered trademark, but during this year's solar water heater industry summit, it is very likely that the brand "Tsinghua Sunshine" will no longer be used in the second half of the year.
Due to relatively low production and technical thresholds and weak supervision, our industry has experienced a serious mix of badns and bad. In recent years, the phenomenon of sidelining Beijing's brands and universities has actually occurred. mainly related to universities, it doesn't matter at all. In recent years, there has been a trend of marginalizing electrical appliance brands, such as "Haier Sunshine", "Gree Sunshine" and "Midea Sunshine". In fact, they have nothing to do with other big companies. your own backyard. Here the couple along with the seventh and eighth aunts gave birth. Those also used under the banners of "Hong Kong Four Seasons Muge" and "International Emperor Ming" are all fake.
As for the website, there is no authoritative site. You can only check brands one by one.
The key components of the solar water heater are the insulation of the water tank, the material and thickness of the liner steel, and the quality of the vacuum tube. However, evene those in our industry cannot use them. Things without damaging the product or using precision. The instrument cannot be identified, but once it is damaged due to substandard quality, it cannot be repaired. For example, if the water tank liner is leaking, you need to find the leak point, completely destroy the end cap on one end of the water tank, dig out the insulation layer, weld it with hot welding. the arc under argon, refoam it with polyurethane, then find a new tip to attach it. After all that trouble, the cost is about the same as buying a new water tank, and the solder joint won't last long.
So, I advise you to spend a little more money and buy a branded one.
I would like to recommend a few to you. The quality ranges from good to slightly worse, but they are all suitable for everyday use. Tsinghua Sunshine, Huangming, Temple, Linorite, Yicanon, Four Seasons Muge, Taiyangyu, Sangle, Sangxia, Meiling, Royalstar, etc., of course there are some I can't remember. Depending on the model you want, the prices of these brands are expected to be above 2,800 yuan.
Let me clarify that I am not an employee of any of the above companies. The company I work for doesn't have as many outlets as they do and there may not be any outlets where you would want to put it.
If you have any questions, you can ask me and I can be your free consultant.