Whether the ongoing World Expo is "green" enough, as organizers have promised, actually depends on whether the grid at the Expo site is "smart" enough.

The smart grid used by the Expo was the country's first pilot project that boasted the most advanced technology in the field, said Zheng Long, director of the Electricity Office under the Shanghai Municipal Committee of Economy and Information Technology.

He said the pilot project included solar energy used at various pavilions, an energy storing system, intelligent substations, trouble call management, intelligent buildings, a charging/discharging system for electric cars, as well as other systems.

"The smart grid has introduced clean energy, such as wind and solar power, to the Expo, which helps to fulfill the promise of a green Expo," he said.

Wind and solar energy are usually subject to weather changes and can not produce uninterrupted supplies, so it is difficult to smoothly transmit the power via a traditional grid that carries only a stable thermal power supply.

China is now taking the lead in solar and hydropower generation and its wind power installed capacity ranks fourth in the world. However, nearly one-third of the wind power generated in the country has been rendered redundant due to transmission bottlenecks, experts said.

But the "smart grid," an upgrade of traditional ones that simply send power from generators to users, aims to solve the problem.

Smart grids are an intelligent system capable of seamlessly integrating alternative sources such as solar and wind from power suppliers into the electricity network. It is also capable of routing power in more optimal ways to respond to a very wide range of conditions, and to charge a premium to those using energy during peak hours.

At the Expo, more than 200 pavilions are users of the smart grid, with the central command lying in the basement of the State Grid Pavilion.

This high-tech substation, known as the "Heart of Energy" at the Shanghai World Expo, is a key part of the smart grid at the Expo, which guarantees a smooth power supply to various pavilions, said Zhang Zheng, director of the smart grid research and promotion office of the Shanghai Municipal Electric Power Company.

The smart grid has contributed greatly to hosting a green Expo, said Zheng, the electricity office director.