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GANYAO, China -- A solar-power revolution is being staged on China's rooftops.

But instead of harnessing the sun to generate electricity, China has quickly emerged as the world leader in using solar power for a more mundane task -- providing hot water for showers and washing dishes in dwellings that often have no other source of heat the year round.

The low-frills, low-cost technology isn't suitable for heating rooms or houses but is fueling a boom in solar power in China's poor countryside as well as its modernizing urban centers. Already, China claims an estimated 30 million solar households, or nearly 60% of the solar capacity installed in the world, according to Worldwatch Institute, a Washington, D.C., environmental group.

In Ganyao, a village in eastern Zhejiang Province, bathing used to mean a dip in the local creek or a trip to a communal bathhouse, says 55-year-old Hu Xingying. But for $145 three years ago, Ms. Hu bolted a sleek contraption of glass tubes linked to a green water tank onto the tiled roof of her farmhouse and now enjoys hot showers inside. "We can afford to use it," she says.

Now, China's solar industry is turning its sights on the U.S., hoping that soaring energy costs and a new tax credit for solar-energy usage from the Bush administration will spur Americans to consider cheap solar power for their swimming pools, showers and dishwashers. As part of the 2005 Energy Policy Act, U.S. consumers can receive a 30% tax credit, up to $2,000, on the cost of qualifying solar systems installed before the end of 2007.

Michael Humphreys, co-owner of Apricus Solar Co., based in the Chinese city of Nanjing, sees an "extremely big change" in U.S. demand. He shipped nearly four times as many containers of equipment to the U.S. last year than in 2004, and business may triple this year, he says.

Increasingly, the average Chinese household views a solar water heater as a standard appliance, right after a washing machine on the list of priorities. The units are relatively affordable because of cheap materials, low labor costs and intense competition among an array of Chinese solar companies.

Of course, solar can be a fickle heating source. A day of sunshine is needed to warm a day's water need, so clouds rule out the next day's hot shower. Thick air pollution in China's urban areas can lengthen the time it takes to warm water.

And there is nothing pretty about the way cheap solar collectors are fixed onto Chinese roofs. Big apartment complexes are topped with a mishmash of A-shaped devices, since each household has its own. Water lines dangle unceremoniously down the building's side and into apartments.

Heating water by sunshine -- a process known as solar thermal -- is a low-tech sister to the related method of using the sun to make electricity, called photovoltaic power generation. "It's a lot more sexy to produce electricity than hot water," says Keith Winston, owner of Earth Sun Energy Systems, Hyattsville, Md., which has imported thermal equipment from China for the past year. "But the reality is, solar thermal is far more cost-effective right now."

China's government has encouraged adoption of solar technology. Cities like Shanghai have written stricter energy-efficiency requirements into building codes, for example. At this month's National People's Congress, Premier Wen Jiabao cited solar as an alternative to fossil fuels as he pledged that the country would cut energy use by 20% as a percentage of gross domestic product over the next five years.

As it is, household heat is denied to many Chinese. In winter, the government provides heat only half the year and only in the northern half of China. It provides none in the south. And everywhere, arranging for hot water is the individual's responsibility.

The country's embrace of thermal solar technology stands in stark contrast to the country's poor environmental record overall. The country's own sudden appetite for fuel has driven global energy costs to records, making alternative power sources more palatable.

China is home to hundreds of companies that increasingly dominate the manufacturing of the heart of the solar hot-water system: sunlight-absorbing evacuated thermal tubes. Resembling fat, black florescent lightbulbs, the tubes cost as little as $110-$125 a square meter (10.764 square feet) to make and install in China, a fraction of going prices elsewhere of $800 to $1,000, says Eric Martinot, a visiting Tsinghua University professor who prepared the Worldwatch report.

In the more technically complex photovoltaic solar-panel business, Chinese companies have also made inroads. Among the world's top 10 solar-cell producers is Suntech Power Holdings Co. of Wuxi, China, which is listed on the New York Stock Exchange. The global giants in the photovoltaic business, like General Electric Co. and BP PLC, aren't active in solar-thermal equipment.

Apricus, a closely held Sino-Australian joint venture, is one of only two China-based companies that produce solar-thermal equipment eligible for the U.S. tax credits, according to the Florida-based Solar Rating & Certification Corp.

Li Wei, vice general manager of Beijing Sunda Solar Energy Technology Co., the other certified company, says the tax credit has helped U.S. sales, although sales to Europe remain higher.

Yet, the solar thermal industry's growth remains strongest in China. In the rugged east coast province of Zhejiang, the penetration of solar is hard to miss. Colorful lean-tos, the size of compact cars, sit atop most apartment buildings and farmhouses.

The trend reflects how a relatively poor country has found an economical route to higher living standards, such as daily showers. "Around Qiandao Lake about 95% of homes have one," says Hong Yongping, owner of Chunan Meidadianqi Co., an appliance retailer in the area.

In fact, free solar power may be worsening water wastage and pollution, already big environmental problems in China. As Ms. Hu notes, "We don't care much about how much water we use now."

At Ms. Hu's farmhouse in Zhejiang province, the glass-and-steel solar device set on her black tiled roof is fed by an orange tube that runs from the ground-level water main, through a duck corral and up the length of her front wall. But environmental benefits and aesthetic value aren't her chief concern. "There's no relationship," says Ms. Hu. "It's cheap and convenient."