This floating greenhouse could make densely-populated port cities much more self-sufficient and sustainable. Using only energy from the sun, these hydroponic farms can purify all the water they need from bodies of water that are either to salty or polluted for human consumption. Given the high labor intensity of hydroponics, this innovation may not be cost-effective in the U.S., but it may work out in developing countries where labor costs are relatively low. Having experienced the pollution, crowding, and low prices in Bangkok, Guangzhou, and Jakarta, I would think these places would be good for pilot projects.