MICAH said: "@TEAPOT7: I'm guessing the solar water heaters rate a "(?!)" because they are likely of limited use in a country where due to air pollution the sun rarely shines. But that's just a guess. Maybe there's still enough energy getting through that smog to heat up the water?"

According to this article, 30 million Chinese households had them in 2006. The systems are much cheaper than in the West (starting at$190 USD), and popularity is also due to the efficient evacuated tubes that allow the heaters to function even under gray skies and at temperatures well below freezing.