Solar updraft towers are an oft-overlooked source of alternative energy, although they do require a great expanse of space and copious amounts of sunlight. Fortunately Namibia’s arid desert region provides plenty of space for such a generator, and the country sees around 300 days of sunshine per year.

Solar updraft towers generate energy by using sunlight to heat the air within a vast transparent greenhouse situated at the base of the chimney. As the hot air rises, it is funnelled into the reinforced concrete chimney, driving a series of wind turbines which in turn generate energy.

The structure’s greenhouse base provides the perfect environment for growing crops, which actually allow the plant to produce energy after the sun has set. The water used for crops is heated during the day and transfers this energy to the tower at night.

Original article: Mike Chino. Inhabitat. 10 September 2008. Read more…

Prof. Dickson Despommier at Columbia University in New York, tasked his students to come up with innovative solutions to this problem. They started studying the idea of rooftop gardening for cities but quickly discarded that approach – too small scale – in favour of something more ambitious: a 30-story urban farm with a greenhouse on every floor.

These high-rises will utilise hydroponic farming and require 4 – 6 times less acreage (depending on crop) than traditional farming, be entirely organic, utilise grey-water and recycle black-water, produce energy via methane generation from composting non-edible parts of the plants and greatly reduce the transport requirements of food.

Valcent, a tech company based in El Paso, Texas, is trying out the process. At their lab, potted crops grow in rows on clear vertical panels that rotate on a conveyor belt. Moving them gives the plants the precise amount of light and nutrients needed, an optimization that lets him grow 15 times as much lettuce per acre as on a normal farm, using 5% of the water that conventional agriculture does. The company aims to finish a commercial-scale facility by early 2009.

Despommier’s plans are even grander. He has drawn up models for a 30-story, city-block-size vertical farm that would have transparent walls to maximize sunlight and would produce enough food for 50,000 people. “With about 160 of these buildings, you could feed all of New York,” he says. His idea has intrigued architects, but Despommier concedes that it would cost hundreds of millions to build a full-scale skyscraper farm. That’s the main drawback: construction and energy costs would probably make vertically raised food more costly than traditional crops. At least for now.

Original article: Bryan Walsh. TIME. 11 December 2008. Read it… or read more here…