Some of the world's most polluted cities are in China, so it's no surprise that clean energy sources are one of the country's ­research-and-development priorities.

The Solar Energy Institute at Shanghai Jiaotong University, for instance, has built a one-story, 245-square-meter prototype house that relies on multiple forms of ­renewable energy, supplemented with ­energy from conventional sources. The house's power system includes an array of photovoltaic cells that generates 1,700 watts of electricity under peak sunlight conditions, and three sets of 300-watt wind turbines. The system can generate about 3,000 kilowatt-hours of electrical power each year, mainly for lighting, household electrical appliances, and water pumps.