Roof Top Tomatoes Can it Work?

German engineer Volkmar Keuter believes it can. "What could be fresher?" In his mind he sees an IT guy signing off for the day, taking the lift (or stairs) to the roof where he has the pick of the week's growth in the roof-top 'designer' green house.

What's more, Keuter wants the produce grown from the building's purified waste water and waste heat.

Keuter says waste heat from buildings and additional solar modules would be enough to supply the greenhouses with the energy they need. Semi-transparent solar cells are ideally suited for the purpose because they do not rob the plants of the light they need to grow.

Water consumption is minimal in a self-contained system, water used for the plants is circulated back, cleaned and reused. Multifunctional microsieves and photocatalytic and thus self-cleaning coatings keep the water quality high. Nutrients for the plants can be filtered out of rainwater and waste water.

"Our concept relies on hydroponic systems or hydrocultures.

A thin, controlled film of water is all it takes for plants to absorb needed nutrients. The advantage: the yield is ten times higher, and soil is too heavy for many building roofs.

That is why we are working on systems to supply plants with nutrients, "the researcher reports.

Actually, there are many varieties of plants suitable for growing on city farms. "Along with vegetables and fruit, we also want to look into growing plants that produce active ingredients for medications."

In Germany there are around 1,200 million square meters' worth of flat-roofed, non-residential buildings. Roughly a quarter of this area could provide herbs and vegetables with a place to thrive.

The plants would then absorb some 28 million metric tons of 28 CO2 in Germany's cities each year. This is the equivalent of 80 percent of CO2 emissions produced by industrial operations in Germany.

"Our cooperation partner, BrightFarm, a US firm, has already completed several projects in New York.

The company started out in 2005 with a small research institution on a raft before going on to build greenhouses atop a school for teaching purposes.

This year, 1500 square meters' worth of roof space were developed in both the South Bronx and Brooklyn."

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