Traditional hydroponic gardening techniques have always been a bit ahead of their time, and generally only competitive with traditional farming for 'high value' crops. The vertical hydroponics movement is beginning to change that relationship by making it easier to grow traditional food crops at high densities in urban areas close to where the crops are sold and consumed. 'Vertical' refers to a class of hydroponic technologies that can be stacked - yielding much higher crop density than traditional greenhousing or hydroponic methods. I have recently been looking at hydroponic technologies suitable for vertical applications, and have found that cylindrical rotating methods appear to have some fairly significant advantages over traditional hydroponics.
Basically, rotational hydroponic methods consist of a cylinder containing rows of a suitable growth medium, a central lighting fixture, a water reservoir, and a chain drive system that rotates the cylinder at very low speed so each row of plants is dipped into the water reservoir a couple of times per day.
The advantages are simple - these rotational units can be stacked vertically, all plants are essentially equidistant from the light source, and rotational growing generates much larger and healthier plants than non-rotational methods. Combined with LED based lighting operating at only those frequencies at which plants absorb light energy, operating costs can be significantly reduced when compared with traditional hydroponic techniques.
One such system is sold by Omega Garden - although construction of something similar from readily available materials should not be a great challenge for anyone mechanically inclined. An international patent is pending on this technology.
The question is, why arent there more of these systems out there, what problems are associated with setting up small urban production facilities to generate various food crops or high value spice and oil crops, and what can be done to improve this technology even further?
After all, local food crops make a great deal of sense - especially when considering the continuing increases in transportation costs. Grow food near where it will be consumed, and I predict that developing technologies to make this feasible in urban areas will be an ongoing area of research over the next 20 years.