A Glimpse Into Solar Thermal in China

Last week, I had the fortune to tour a production site of Beijing Tsinghua Solar Co., Ltd., one of China’s biggest manufacturers of solar hot water systems. While the facility itself lies in the brownish, dusty outskirts of Beijing, where the grass grows sparsely and the sky remains a stubborn gray from sunup until sundown, its products are anything but dirty—and I don’t just mean grubby.

Right now, China is one of the world’s most exciting solar markets. Here in Beijing, solar hot water systems crown the shingled rooftops of apartment and administrative buildings alike, a heartwarming sight given the PRC’s abysmal environmental record. Although China still has no nationwide solar subsidies for end users, it financially supports research and development of renewable technologies, and government decrees and subsidies apply to a few projects. In 2007, the Chinese market for solar water heaters grew at a rate of 30 percent, and the country’s total sales of solar water heaters came in at a hefty 32 billion RMB (around $4.6 billion US). $65 million US of this came from exports, and China’s newly installed solar hot water systems soared by approximately 75 percent, catapulting it to the forefront of countries in terms of newly installed capacity. China’s solar thermal capacity is projected to reach 2.3 billion square meters by 2015, with 20 to 30 percent of the population using solar thermal! One of the aforementioned big exporters, in addition to being a major force at home, is Beijing Tsinghua Solar Co., Ltd.

Tsinghua Solar is a venture of Beijing’s prestigious Tsinghua (Qinghua) University—basically the Chinese MIT. Incidentally, Tsinghua University also happens to be the original developer of evacuated tube technology, which is found in most Chinese solar thermal systems today, as opposed to flat plate collectors, which are predominant in Europe. An evacuated tube consists of two or three glass tubes, typically coated on the inside with aluminum or copper (or any other material with high conductivity) and enveloping one another like a cylindrical Russian doll. A robust, well-functioning Chinese-made solar thermal system typically lasts about a decade, sometimes more. As the evacuated tube technology was developed in the eighties, it has had plenty of time to mature.

The facility that I visited last week focused primarily on the production of the evacuated solar collector tubes. As soon as we—my Chinese host family and I—stepped inside the first room of the factory, I felt a blast of fiery heat from all around. Our tour guides, a blue-collared worker and a manager, warned us to watch out for the glass shards on the ground. Workers to my left and right unloaded stacks of individually wrapped glass tubes—the outer tubes—and placed each long, thin cylinder on a serrated conveyer belt. The heat came from the flames that erupted from a small machine halfway down the conveyer belt, and they heated up one of the open ends of the tube to melting point as another machine pulled said tube forward. This forced the open end, now melted, to collapse on itself and close up. At this point, the machine dumped the remnants of the tube’s “end” into a large metal bucket filled with other “ends,” their molten glass tendrils quickly solidifying. Further down the production line, three workers attached straw-like, reedy glass tubes to the newly formed closed ends by heating them up with a powerful flame and then fusing them together. It was fairly brutal work. The workers had to stick their faces right near the flames in order to attach the tubes accurately; at several points I actually feared that their hair would catch on fire. Several fans spun furiously in the cavernous room, although I’m not sure how much help they were.

Next, all of the tubes—both the outer and thinner inner tubes—underwent sterilization in several steaming chambers.

Then, in the following two rooms, the workers used giant, oven-like machines to plate the inside of the outer tubes—the ones that we just saw the workers heating up and fusing with other glass parts—with a coating made from various metals, presumably those with high conductivity. They did this by inserting the tubes into oblong chambers resembling refrigerators, which coated the inside of the tube with a mixture of chemicals that had to be baked to a certain temperature, at which point the coating would turn black. Numerous tests, tubes baked to a Prussian blue or navy, rested on nearby carts. Joining them were other rejected tubes, apparently faultless but full of defects to the workers’ practiced eyes.

After that, we entered a room dedicated solely to the fusion of the inner and outer tubes. Once the inner tube had been properly inserted into the larger outer tube, workers laid the assembled tube on a conveyer belt, which brought it to workers who would heat the open end—the one without the small thin tube sticking out—with a concentrated flame and then use a paddle-like tool to push the pliable ends together as the tubes spun quickly, thus ensuring uniform smoothness.

Afterward, workers transported these tubes to a room, where they were inserted into a box-like apparatus that created a vacuum in the tubes. Here, temperatures were extremely high and our guides warned us not to get too close.

Eventually, the now-“evacuated” tubes were transferred to a room where they were placed upright on an assembly line, with the thin tube that a few workers attached at the beginning of the production chain sticking out like a glass proboscis. As the tubes gradually migrated down the line, a worker heated up the protruding tube with a tightly controlled flame and then swiftly pulled the evacuated tube out, effectively closing up that end of the tube and leaving a curled tip where the narrow tube used to be.

Finally, the workers wheeled the solar collector tubes into a room where more oven-like machines awaited, preparing to layer the inside of the inner tube with a membrane of barium. Workers discarded those tubes that they deemed even slightly defective. Tight quality control ensured that there were stacks and stacks of rejected tubes, seemingly without defect.

Although we did not get to see how the solar collector tubes were attached to their accompanying water collectors, I walked away nonetheless impressed by the diligence and the quality control from the staff, and the passion and pride of the managers for their solar technology. Here’s to hoping for the increased success of solar in China, and more government incentives for solar—we’ll keep our eyes peeled for any further developments.