CLIMATE CHANGE SUMMIT: CLEAN AS A BREEZE

Over the past five years, a new crop has sprouted across the broad, fertile plains of northern Germany. Sprinkled among the barns and silos are thousands of 100-ft.-tall towers topped by sleek, fiber-glass blades that whirl slowly in the breeze. Functioning as clean, trim powerhouses, these modern windmills turn even gentle currents of air into strong currents of electricity, energizing the region's businesses and homes without hurting the environment.

Half a world away, on the Indonesian island of Java, hundreds of rural families have mounted small, silvery panels on poles near their homes. Made of silicon semiconductor chips similar to the...