Striking diamond and triangle shapes in dark and light blue sparkle on the roof of the huge World Expo 2010 Theme Pavilion. But the geometric shapes are more than decoration - they are solar panels that power the pavilion.

The theme of the Expo is "Better City, Better Life," and that means clean renewable energy.

The 143,000-square-meter pavilion was completed late last month. It is believed to be the world's biggest non-column-supported exhibition space and have the world's largest rooftop solar energy system.

The system is already up and running and soon will be connected with the national power grid.

The solar panels cover 30,000 square meters, half of the total roof area. Gross power output is 2.83 megawatts.

Unlike typical rectangular solar panels, these are deliberately cut and shaped into patterns of 18 rhomboids (diamond shapes), each 36 meters by 72 meters and 12 triangles.

The solar panels use 16,250 polycrystalline silicon pieces, according to Zhao Guojing, vice general manager of Shanghai Shenergy New Energy Investment Co, designer and manufacturer of the solar energy system for the pavilion.

The system can generate 2.8 million kwh each year, enough for the average annual energy use of 2,500 local families. The electricity is sent to the national power grid and made available together with other energy.

It can contribute to a reduction of carbon dioxide discharge by 2,800 tons per year, amounting to about 1,000 tons of coal, according to Joseph Shi, general manager of the Theme Pavilion Project Branch of Shanghai World Expo Co.

"As the Shanghai Expo theme is 'Better City, Better Life,' we must use sustainable energy in the venues, and of course the Theme Pavilion," says Shi. "Solar energy is the best choice."

Solar energy also powers the China Pavilion and Shanghai Expo Center, while some venues near the Huangpu River make energy out of water for air-conditioning.

China began developing solar energy as early as the 1950s, but it was mostly used in limited, high-tech fields, such as powering satellites.

It was not until the late 1990s that China developed a few solar power plants in remote areas that had not electricity for general civilian use. In recent years a few solar power systems were launched in Shanghai, Beijing and Shenzhen in Guangdong Province.

Most solar power plants in China today are in open rural areas where enormous panels can capture as much sunshine as possible.

Combining solar power systems with architecture like that of the Theme Pavilion isn't as easy as many people think, says Shi. Careful design and use of the right materials are crucial.

The heavy solar panels (think of the weight of sand crystals) add at least 20-30kg per square meter to the roof, requiring much stronger bearing capacity and support.

The panels must be slightly angled to get as much sunshine as possible and are only supported by pillars above the roof, thus they need to be able to withstand strong wind. Penetrating the roof with pillars also increases the possibility of water leaking on rainy days.

And the artistry of using the diamonds and triangles fitted together - instead of fewer rectangular panels - makes it more difficult to ensure that the power of each panel is uniform and the energy flows smoothly.

Solar energy requires plenty of sunny days, but it's steadier than wind power, not limited by geology like geothermal power and it's inexhaustible, unlike hydropower.