gracing the Taj Hotel in central London and the exit wall of Edgware Road Tube Station, among other locations. Aesthetics aside, green walls are credited with reducing air pollution and improving air quality. 8 Algae-powered building To prove the dynamism of the “living wall” concept, look no further than Hamburg’s International Building Exhibition. Instead of sweet-smelling flowers, the south-facing facades of the zero-carbon apartment complex are laced with green-tinged algae. The walls’ external fabric includes a “bio-skin” of hollow grass panels on which the algae photosynthesizes and grows. Periodically, the algae is harvested from the walls and fermented in a biogas plant to produce electricity. 9 Smart rubbish bins Forget gas-guzzling dumper trucks and smelly skips. City authorities around the world are now turning to solar-powered “trash compactors” to keep litter off the streets. The 150-gallon-capacity rubbish bins are equipped with a motor that pushes down the rubbish when it nears the top. The motor is powered by solar panels embedded in the lid. The newest BigBelly bins include a wireless monitoring system that notifies rubbish collectors when the bins are full. 10 Spray paint Finally, desperate times may sometimes call for desperate measures. That’s clearly what was going through the minds of authorities in Chengdu, one of China’s fastest