Ask any six-year-old in a Chinese street, 'What's a solar water heater and what's it for?' Without hesitation they will tell you: 'A solar water heater is on the roof of a building to make hot water for the shower'. This story is told by Hongzhi Cheng, vice secretary-general of the Beijing-based Chinese Solar Thermal Industry Federation (CSTIF) and head of The Sun's Vision, a company based in the city of Dezhou in Shandong province.

Dezhou, one hour by car south of Beijing, has become one of China’s solar towns due to the presence of Himin Solar, one of the country’s largest solar water heater manufacturers. For a German visitor with an interest in solar thermal technology, driving in the city provides an exciting tour past scores of roof and facade installations.

From Retrofits to Central Systems

Dezhou is also a great city to see how the solar thermal industry is developing from retrofitted systems for individual households towards large-scale rooftop solar fields serving entire buildings.

The residential retrofit market, where flat owners install their own solar thermal systems on the roofs of existing buildings, now accounts for some 60% of the market and its share is still edging down, says Yunbin Le, deputy general manager at the Sino-German solar water heater manufacturer Linuo Paradigma and its sales director for the Chinese market.

In a simple version of the technology, the system owner opens the water tap in the morning and waits until the tank on the roof is full. When they come back from work, they can use the heated water until the tank is empty. The systems consist of unpressurised water-filled vacuum tubes and the shower water flows directly through the tube and the tanks.

The next generation of solar water heaters are found on large apartment buildings, which represent a rapidly growing market segment. The new clients are housing companies that design roofs to host enough thermosiphon systems for each flat to be sold with solar hot water. These housing companies must meet solar obligations imposed by several cities and municipalities since the Renewable Energy Law of 2006. Most local governments now require solar water heaters to be installed in new civil buildings of up to 12 storeys.

‘As a builder you do not receive building permission from the municipality unless you have demonstrated the plan for integrating solar hot water into the building,’ says Fude Li, a project engineer for Linuo Paradigma.

In a new apartment building with Linuo Paradigma solar water heaters in Jinan in Shandong province (see overleaf), the solar systems are attached to cement blocks that are integrated into the roof during construction. They are also equipped with temperature and water level sensors so they can fill up automatically.

Building-integrated Systems Take Off

The third generation of solar thermal technology in China consists of building-integrated systems. Himin Solar is blazing a trail with several demonstration projects in Dezhou’s ‘Solar Valley’.

Utopia Garden Project is one of the Solar Valley’s most recent multi-family buildings, where flats of 300-600 m2 nestle amid verdant gardens and combine energy-efficiency standards with renewable energy supplies. Marketing the flats, along with the construction and design of their ecological housing technology, is in the hands of Himin Solar Energy Real Estate, a subsidiary of Himin Solar Group.

The ‘demonstration of future modern living’ is what makes people buy the flats, says Chen Ping of Himin Solar’s brand management department. ‘The price of the flats is around RMB12,000 (US$1900) per square metre, around 50% higher than comparable apartments because of the advanced renewable energy technology and the intelligent home technologies,’ she says. But she claims their owners will pay as little as a quarter of normal energy costs.

In a new apartment building solar systems are attached to cement blocks integrated into the roof (Source: Barbel Epp)

Four blocks with a total of 298 flats have already been sold and occupied. Two additional blocks are under construction. These buildings’ rooftop solar installations are visible from some distance, with 504 vacuum tube collectors arranged horizontally in massive wave-shaped metal stands extending for several metres above the buildings. With a gross collector area of about 756 m2, the pressurised heat-pipe vacuum tubes supply central heating and cooling systems for entire building complexes. Surplus heat is stored underground in seasonal borehole storage.

Yet central solar heating and cooling systems still provide only a minor share of the solar thermal market. ‘Larger commercial installations provided up to 15% of the total market volume in 2011, whereas 85% is still residential,’ says Jiuwei Wang, Himin’s deputy general manager and chief marketing director.

Pressurised Balcony Systems

Each flat at these new developments also includes a vacuum tube collector installed in the facade and a 300-litre tank on the balcony to supply hot water. These solar systems represent a totally new generation of residential solar water usage in China. They are pressurised, indirect systems with u-pipe collectors, and a closed-loop solar circuit filled with glycol. If the facade collector fails to reach 60°C, the electric element in the tank compensates. Solar domestic hot water is therefore separate from the buildings’ central heating and cooling system.

Despite being far more expensive than retrofitted, open-loop solar water heaters, these balcony systems still enjoy high demand, says Yunbin Le from Linuo. ‘Today 180-litre systems are more common than 100-litre systems.’

In Linuo Paradigma’s solar shop in Jinan a 100-litre balcony system with 13 tubes is sold, including installation, at RMB6880 - almost twice as much as a pressureless system with 18 tubes.

Shop prices for systems from Sangle Solar Energy, another of China’s five biggest solar water heater manufacturers, are generally 10%-15% lower than for Linuo Paradigma, yet display a similarly large gap between the two technologies. Customers pay RMB5860 for a closed-loop balcony system with a flat plate collector and a double wall tank, or no more than RMB2690 for a pressureless solar water heater with 20 water filled tubes and a 180-litre tank.

Aesthetic tastes seem to decide whether companies pick vacuum tubes or flat-plate collectors, says Chen Liang, marketing planner for international business development at Sunrain Group, China’s largest manufacturer of solar water heaters in 2011. ‘Flat-plate collectors in the facade are more beautiful than vacuum tubes, according to building designers,’ he says.

Sales Double for Balcony Systems

Balcony systems are popular for multi-family buildings that lack roof space for a solar unit for each apartment. ‘We produced 60,000 tanks for balcony systems last year and we expect a doubling this year,’ says Jie Xu, Linuo Paradigma’s production manager.

Linuo Paradigma’s solar tank manufacturing and system assembling factory in Jinan produced one million sets in 2011. Its 300 full-time workers produce 784 different tank models, sold both as OEM units and under the Linuo Paradigma brand.

The company also recently opened an automated ‘tank-in-tank’ production line for balcony systems. Pressurised enameled cylinders for domestic hot water are purchased externally. All manufacturing steps are performed in a single, highly automated U-shaped line: screen printing, punching and bending of the tank jacket, inner tank pressure testing, preassembling, foaming with polyurethane insulation as well as packaging. ‘We can run the whole line with a maximum capacity of 500 tanks a day with around 30 workers,’ says Jie Xu.

At the Utopia Garden project, solar hot water tanks rest on balconies behind a facade of horizontal vacuum tubes (Source: Barbel Epp)

Linuo Paradigma’s balcony systems feature vacuum tube collectors. To improve the thermosiphon flow in the solar circuit of balcony systems, the company has developed a special type of u-pipe vacuum tube. The copper piping in the horizontal tubes form more the shape of a V than a U. Continuously rising pipe supports the natural flow of the hot water to the tank above the collector. ‘We do not see technical problems with vacuum tubes in the facade up to 36 floors,’ says Yunbin Le.

China’s tall buildings seem to have no upper limit for solar thermal installations. The industry aims high and still has huge growth potential, says Hongzhi Cheng. ‘Only 30% of the market demand is fulfilled yet in the rural area. We expect the rural segment to grow [from around RMB100 billion ($15 billion) today] to RMB600 million.’ But he predicts even stronger growth of thousands of billions of renminbi for the large-scale solar thermal sector. European visitors will then be astonished by even more solar thermal installations on Chinese skylines.