Reuters: U.S. Commerce Secretary Gary Locke heads to China this weekend, leading a delegation of 24 American companies hoping to break through barriers to China’s vast and fast-growing clean energy market. China, the world’s largest emitter of carbon dioxide and other greenhouse gases blamed for global warming, is plowing tens of billions of dollars — if not more — into wind, solar, nuclear and other non-fossil energy projects, a market U.S. companies are eager to tap. Predictions …