AMSTERDAM - Denmark earns the biggest share of its national revenue from producing windmills and other clean technologies, the United States is rapidly expanding its clean-tech sector, but no country can match China's pace of growth, according to a new report.

Related readings: Clean energy: A goal for China, US  National lab for clean energy to open  Huge opportunity in China's clean energy market  China still leading clean energy investment

China's production of green technologies has grown by a remarkable 77 per cent a year, according to the report, which was commissioned by the World Wildlife Fund for Nature and which will be unveiled on Monday at an industry conference in Amsterdam.

"The Chinese have made a conscious decision to capture this market and to develop this market aggressively," said Donald Pols, an economist with the WWF.

Denmark, a longtime leader in wind energy, derives 3.1 percent of its gross domestic product from renewable energy technology and energy efficiency, or about euro 6.5 billion ($9.4 billion), the report said.

China is the largest producer in money terms, earning more than euro 44 billion ($64 billion), or 1.4 percent of its gross domestic product.

The US ranks 17 in the production of clean technologies with 0.3 percent of GDP, or euro31.5 billion ($45 billion), but those industries have been expanding at a rate of 28 percent per year since 2008.

"The US is growing substantially, so it seems the policy of (President Barack) Obama is working," Pols said. But the US cannot compare with China, he said.

"When you speak to the Chinese, climate change is not an ideological issue. It's just a fact of life. While we debate climate change and the transition to a low carbon economy, the debate is passed in China," Pols said. "For them it's implementation. It's a growth sector, and they want to capture this sector."

The report was prepared by Roland Berger Strategy Consultants, a global firm based in Germany. It gathered data on 38 countries from energy associations, bank and brokerage reports, investor presentations, the International Energy Agency and a score of other sources. It measured the earnings from producing renewables like biofuels, wind turbines and thermal equipment, and energy efficiency technology such as low-energy lighting and insulation.

"Clean technologies are really growing fast, but China is responsible for the majority of that growth," said Ward van den Berg, who compiled and analyzed the data for the consultancy firm.

Until recently, Chinese massive production of solar cells was aimed at the export market, but they are now making solar systems for the home market, as they have been doing for several years in wind energy, Van den Berg said.

Following Denmark and China, other countries in the top five clean-tech producers, in terms of percentage of GDP, are Germany, Brazil and Lithuania, the report said.