Today we caught up with Dr. Dickson Despommier, a professor of environmental health at Columbia University, who is arguably the world’s leading proponent of “vertical farming” or, if you will, industrial scale hydroponic and aeroponic crop production within high-rise buildings. If you go to his website www.verticalfarm.com, you will find a very in-depth body of work exploring the feasibility of this idea.
|A cross-sectional depiction of the vertical farm.|
It makes a lot of sense. In a way, it totally inverts the conventional wisdom of many of today’s agriculturalists. Instead of using the biosphere to power the technosphere, we are using the technosphere to power the biosphere.
That is to say – and this is a loose, but useful, interpretation of these terms – if the technosphere corresponds to the global industrial economy, we currently need about 550 quadrillion BTUs per year to power our machines, and biofuel coming from our biosphere will be hard pressed to supply this amount of energy.
Notwithstanding the rising use of biosphere for biofuel, for the most part our biosphere still only has to be used to grow food, and we can feed all of humanity for only about 17 quadrillion BTUs per year. This is based on 2,000 calories per day per human, which equates to 2,326 watt-hours per day per human, times 6.0 billion humans, times 365 days per year, which equates to 582 gigawatt-years to fuel all of humanity. At 33.4 gigawatt years per 1.0 quadrillion BTUs, that is a paltry 17.4 quadrillion BTUS.
So it makes more sense to use the technosphere – factory farming, high-rise agriculture – to provide biological energy to people, then to use the earth’s biosphere to provide biofuel energy to the machines of civilization. Because on this earth, machines use 30 times as much energy as humans, and that ratio is probably set to increase.
On Despommier’s website there is a wealth of rigorous analysis regarding just how much caloric energy you can extract from a high-rise building; more than can be summarized here. Go there. Read it.
But a few very salient points emerge. If only a portion of a high-rise was dedicated to hydroponic and aeroponic agriculture, the building would be able to process its waste water – as well as waste water from elsewhere on the utility grid – using it to water the plants AND to reuse as drinking water. Here’s how: The grey water extracted from sewage would be subjected to biological and mechanical filtration, then it would be used to water the plants. The plants, in turn, would transpirate heavily in the indoor environment, and dehumidifiers would harvest this water – this transpirated water would be pristine drinking water, able to be pumped back upstairs or into the utility grid for reuse. This concept of using transpiration from plants in a commercial high-rise agricultural operation to provide the last mile of grey water purification in the urban environment is revolutionary. Along with the surprisingly low, and dropping, cost of desalination, and advances being made in primary sewage treatment, this innovation could SOLVE the issues of potential water scarcity in the urban environment.
The quantity of food that a high-rise farm might produce is also surprising. Because the plants are grown in optimal conditions – abundant light and water, and no pests – they can yield 3-4 crops per year instead of one, and each crop may require no more than five vertical feet of space. This means each story of high-rise space occupying an area of one acre, for example, can literally produce twelve times as much food per year as an acre of ordinary farmland. This multiple order-of-magnitude increase in potential productivity per unit of land, combined with the proximity to market, combined with the water and energy positive nature of the undertaking, means high-rise farming is merely waiting for economic and political conditions to align in its favor. The technology for high-rise farming is for the most part already here, and it will be available when we need it to feed the burgeoning megacities of this world.