China's energy needs are expected to double by 2030, but a study in the journal Science says the country could produce 30% less carbon dioxide if it uses wind power to meet them. It is estimated China will need to increase its capacity by 800 gigawatts by 2030 to meet demand � roughly double its current capacity. The study, in the journal Science, proposed a way for wind power to make up most of that increase and, if it did, said China's emissions of carbon dioxide could be 30% lower. Using meteorological data to assess the potential for wind power in China � the world's largest emitter of carbon dioxide � the researchers also say wind could theoretically supply all of the country's energy, though it only laid out the figures for meeting half its needs. "The world is struggling with the question of how do you make the switch from carbon-rich fuels to something carbon-free," lead author Michael McElroy, a professor of environmental studies at Harvard's School of Engineering and Applied Sciences, said. "The real question for the globe is: what alternatives does China have?" Coal currently supplies 80% of China's electricity, and hundreds of coal-fired power plants are built every year to keep pace with demand, but Beijing is also investing heavily in renewable energy. It plans to build seven large wind-power bases over the next decade, and already ranks fourth in the world in terms of installed capacity, at 12.2 gigawatts � about equal to the energy produced by two dozen average-sized coal-fired plants. It trails only the US, Germany and Spain in installed capacity, but not all of those turbines are hooked up to the electricity grid. In fact, just 0.4% of China's electricity is supplied by wind � or around 3 gigawatts. The researchers behind the Science study proposed that the country could produce 640 gigawatts from wind farms, assuming they ran at 30% average capacity � a measure of how much output can reasonably be expected from a wind turbine. Average capacity takes into account that wind is fickle, and calculates more or less how much of the time you can expect a turbine to be working at full capacity.