Except for regular cleaning of panels, it requires almost no maintenance.

Despite its advantages, its high initial cost is the biggest obstacle to wide use. Though the price of system components has decreased greatly in recent years, it still costs about 1.1-2 yuan per kwh for a large solar power plant in remote areas and 4 yuan per kwh for a solar power station combined with architecture.

By 2015, it is estimated the cost can be reduced to less than 1 yuan per kwh.

It is true, however, that air pollution and dust in Shanghai in other cities reduce the intensity of sunshine and slightly shorten the life of solar panels, possibly leading to less efficiency than in rural areas, says Shi.

"Nonetheless, solar power is still a good, sustainable choice that can be achieved in Shanghai," he says.

Big Green Walls

The Expo 2010 Theme Pavilion sets records not only for the world's biggest non-column-supported space and largest solar energy system on the roof, but also (it is said) for the world's largest living green outer walls to demonstrate ecology in design and construction.

The pavilion's east and west walls are covered in greenery. Plants are placed in small pots in metal shelves. Designers use small, hardy, easy-to-grow evergreen shrubs, some of them flowering. The green walls help block the outside heat in summer and keep heat from escaping in winter.

Research shows that in summer indoor temperature in structures with green walls is usually 5 degrees Celsius lower than that in those with glass walls in summer. This helps save on air-conditioning by as much as 40 percent.

In winter, the green walls keep indoor heat from radiating to the outside. They also prolong the life of the walls and reduce damage from wind.

In addition, the green walls are expected to absorb about four tons of carbon dioxide while releasing oxygen through photosynthesis.

(Shanghai Daily October 27, 2009)