Row upon row of tilted boxlike containers holding black glass tubes top apartment complexes all over China. These solar water heaters can provide cheap, emissions-free hot water for cooking and bathing to China's rapidly growing urban population.
But for something that seems like an obvious solution to curbing emissions, solar heaters haven't caught on at similar scales around the world. And it's especially puzzling why solar thermal energy is the system of choice for consumers in a country that's the world's leading producer of photovoltaic panels.
The answers are a bit murky, weaving together global market forces, local regulations and an enigmatic inventor.
In China, there are different theories about the origin of the low-cost solar water heater design that has become so popular. Some experts said the technology came from a company called Beijing Tianpu in collaboration with Tsinghua University. However, rumors on the Internet swirl around Chinese entrepreneur Huang Ming, who commercialized the product into a sizable business in Shandong, a province near Beijing.
With fractured records and contentious claims, it's hard to figure out whether Huang really is the Henry Ford of solar water heaters in China. Despite the media attention, details about Huang and the origins of his invention are scarce. Ji Hongwei, a spokesman for Huang's firm, China Himin Solar Energy Group, would not comment for this story.
In past media interviews, Huang said he started tinkering with water heaters 20 years ago, selling around 1,000 units he designed to people in his neighborhood. Word spread, and his operations scaled up until he set up his self-financed company. Himin is now the largest solar water heater producer in the world.
Huang then went into politics, serving as a deputy to the National People's Congress, China's quasi-legislature. Since assuming the role seven years ago, he pushed for clean technology, including a renewable energy act in 2005 to reduce China's reliance on imported fuels.
A 'Wild West' solution in the East
Arthur Mol, a professor of environmental policy at Renmin University in Beijing, said the growth in solar thermal energy, unlike some other sectors in the Chinese economy, did not result from direct sophisticated government planning and subsidies.
"It was originally not completely a market model [either], for a long time [dealing] with some government involvement," Mol said. According to a paper by Mol authored jointly with scholars from Zhejiang Gongshang University and the Chinese Academy of Science, water heaters started gaining traction in the 1970s.
By the end of 2007, China accounted for more than 60 percent of solar collecting surfaces for water heaters installed in the world. Beijing's 11th five-year plan (2006-2010) for new and renewable energy has set a target to expand solar water heater installations by 9 percent by 2020.
So why aren't Americans as enthusiastic about emission-free hot water?
"This is really not at all a luxury good; this is something average homeowners have," said Matthew Carlson, CEO of Sunnovations, a solar thermal technology developer and distributor in the United States.
One big reason is that there are few, if any, building codes that regulate water heater installation in China. Carlson recounted visiting the country and seeing the results. "Whole roofs of these buildings are littered with heaters and pipes running along the outside into each individual apartment," he said. "The whole process is pretty much Wild West, it seems."
In the United States, by contrast, homeowners have to contend with byzantine local permitting requirements, which differ from city to city and can cost more than $2,000 in some instances. For a $30,000 PV system, this is a significant hurdle, but for an $8,000 solar thermal system, it's practically a wall.
Advantages lost in translation
The U.S. Department of Energy is tackling solar energy's hidden costs in its SunShot Initiative, which aims to make solar energy competitive with fossil fuels by 2020, but solar water heaters aren't included in this definition, Carlson said.
Another issue is the technology. "The most common technology in the U.S. is an indirect system which has a pump. In China, the system used is a thermosiphon, a passive system without a pump," said Tim Merrigan, a researcher at the National Renewable Energy Laboratory (NREL). "The thermosiphon system requires that you have a storage tank on the roof. The drawback in the U.S. is that typically people have water tanks in their basements or garages."
In a Chinese high-rise, this means people living near bottom floors have to wait longer for hot water from their faucets while people near the roof have less water pressure in their shower heads.
When the weather gets cold, the solar heaters often produce water that is lukewarm at best. Nonetheless, this is still a vast improvement for many people in the country migrating from rural areas without such amenities into cities.
In Zhejiang province, a relatively wealthy locale in the east of China, a solar water heater can retail for as little as $290, much cheaper than solar cells. Solar water heaters also convert more of the sun's energy into a usable form for a given area than photovoltaics, a distinct advantage on crowded rooftops. However, the Zhejiang devices usually last less than seven years, far short of their expected 10- to 15-year operating life.
A further complication in the U.S. is that a thermosiphon system is usually routed into a home's existing water lines. It usually requires some form of backup, such as a gas or electric heater. The alternative is an active solar water heating system that uses a pump to pressurize and circulate water.
These systems also have to tolerate a wider temperature span in many parts of the United States, from freezing winter to balmy summers, while delivering a consistent water flow at a fixed temperature for decades. This can drive costs further, so most homeowners are content with a simple tank with an electric coil or a gas burner in it, heating water in their basement.
Economics of two different worlds
A report from NREL showed that the typical solar water heater installation costs between $5,000 and $10,000 in the United States, while Chinese consumers pay between $300 and $1,000. Annually, China installs 6 million solar water units.
"The U.S. market is relatively small, with 8 million water heaters sold every year and only about 30,000 being solar water heaters," explained Merrigan of NREL. "There has been some increase in recent years from before, when only 6,000 or 7,000 were sold. The rise is partly due to the 30 percent federal tax credit and partly due to the state incentives like those in California and Massachusetts."
These incentives, however, have to offset relatively cheap energy in most parts of the country. About half the water heaters in the United States run on natural gas, which is scraping record-low prices. The remainder use propane, heating oil or electricity -- more expensive, but not enough to drive people to look for alternatives.
Contrast this to China, where the average consumer has less purchasing power. This means electricity bills take a relatively bigger bite out of paychecks, so urbanites are more inclined to bet on solar thermal energy to save cash.
Sunnovations' Carlson said now there are other countries, like South Africa and Uruguay, where the variables -- government incentives, cheap technology and high energy prices -- are similar to China's. They will likely emerge as the next hot spots for solar water heaters. "Water heating takes up 22 percent of [South Africa's] national energy budget," he said. "South Africa is definitely one of those places where there can and should be a massive deployment."
Meanwhile, according to Xi Wenhua, a Chinese representative for solar energy technology promotion and transfer at the United Nations, U.S. and Chinese experts continue to exchange information on solar water heaters.