RIZHAO, CHINA — Before her family bought a solar water heater, Liu Yan would bathe the way many working-class Chinese have for generations: boil water, dampen a rag and wipe away the dirt.
Today, the 40-year-old mother and her family shower every day and wash their dishes with hot water. The stainless steel heater affixed to her red-tiled roof cost about $220.
The device has become a symbol of China's rising standard of living and its leap into the era of clean energy.
In the seaside city of 2.8 million where Liu lives in Shandong province, 99% of households use solar water heaters. The mattress-sized contraptions dominate Rizhao's skyline, resting haphazardly on almost every residential rooftop.
In the global race to develop green technology and stem climate change, China has quickly become a leading producer of solar panels and wind turbines. It also dominates the lesser-known technology of solar water heaters.
Using principles of solar heating more than a century old, the humble, low-cost devices consist of an angled row of cola-colored glass tubes that absorb heat from the sun. The most common models fill the tubes with cold water. As it heats, the water rises into an insulated tank where it can remain hot for days.
The devices have improved so much over the years that some don't need direct sunlight -- all the more valuable in China's often hazy and smoggy cities. Newer models have electrical heaters inside the water tanks that switch on if the water gets too cold on frigid days.
Popular in some parts of the United States around the turn of the 20th century before being made obsolete by cheap natural gas, solar heaters are now hailed as one of China's greatest environmental success stories. More than 30 million homes have the devices, accounting for two-thirds of the world's solar water heating energy.
Manufacturers are eyeing foreign markets, including customers in Southern California.
"China absolutely dominates the global market and they've done it relatively quietly and without a lot of fanfare," said Christopher Flavin, president of the Washington-based Worldwatch Institute. "It's an interesting example of their ability to take technology that was developed elsewhere and adapt it to their market on a scale no one had conceived of."
The widespread development of solar heaters in China can appear paradoxical in a country that leads the world in carbon dioxide emissions and where two-thirds of the rivers and lakes are contaminated.
