Denmark earns the biggest share of its national revenue from producing windmills and other clean technologies. As a longtime leader in wind energy, Dwnmark derives 3.1% of its gross domestic product (GDP) from renewable energy technology and energy efficiency.
The United States is rapidly expanding its clean-tech sector but China is 'on another level'.
China is the largest producer in money terms, earning more than €44 billion - 1.4% of its GDP.