Would an American building owner tolerate a roof line such as that seen here? Could an American architect stomach such an appearance? Doubtful. These are evacuated tube solar water heaters as seen on rooftops throughout the cities we visited in China. China is encouraging the use of this technology and the results are visually apparent. But are the energy savings (and consequent emissions reductions) significant?
A report by the National Renewable Energy Laboratory (NREL) concludes that solar thermal water heating has the technical potential to save about one "quad" (quadrillion, or 10^15, btu) of primary energy per year, or right at 1% of our primary energy consumption. This would result in the avoidance of the emission of between 50 and 75 million metric tons of carbon dioxide and potentially save on the order of $8 billion per year in energy expenditures. The report is dated April of 2007, so the financial considerations are likely more compelling now, with rising primary energy costs. It would seem as if China were on the right track.
The evacuated tube technology is capable of delivering hot water even when skies are cloudy and temperatures are cool. In fact, they can operate in ambient temperatures below freezing. So, are there downsides? Not many, the primary negative is the payback period. For reasons I can't clearly explain, the Chinese systems typically cost on the order of 4,500 yuan, or about $660. In the U.S. similar systems cost more like $5,000 installed. This is a major disincentive, though beneficial tax treatment may reduce the cost in some areas. And although some think they're ugly (and my %&*^%^#@^ homeowners' association would scream bloody murder), I think they're lovely.