375px-Vertical_farm2.jpgI see Boing Boing has vertical farms back in the conversation spotlight. Much like any SF/F geek, I have to say, the idea intrigues me. Now that we know cities provide efficiencies, thus making them more green than non-urban areas, the idea of making cities even more self sufficient is powerful and intriguing.

The little scientist type in me also wonders whether there might not be efficiencies further found by large scale hydroponics in managed areas (as well as less runoff, more recycling, and so on). As David Pescovitz at Boing Boing points out, this is similar to the idea of creating a self sustaining area.

While I’ve seen a lot of blog posts batting the idea of skyscraper farms around, I’ve seen very little number crunching.

I’m no economist or urban planner, but let’s crunch some quick numbers.

One of the more famous advocates of the Vertical Farm concept, Dickson Despommier, estimates a 30 story farm would feed about 10,000-50,000 people (depending on which article he’s speaking in). Let’s be charitable and assume 30,000 per 30 story skyscraper.

A 30 story skyscraper can cost as much as half a billion dollars. So we’re looking at a unit cost of at least that to build these, and that’s not considering the hydroponic and recycling technology costs!

New York has 10 million people. To feed New York, you’d need roughly 334 of these buildings, with the building cost being at least $150 billion.

That’s affordable on a country scale (10 years of NASA-like budget).

But the fact is, the existing land sprawling out around New York and the US and gasoline to transport the goods from the heartland to NYC is still far cheaper when an accountant crunches the figures.

As much as I love the concept, I don’t see it happening on the scale imagined or the cities imagined. If it does happen, it will be via the reclamation of unused city spaces that are converted on medium sized projects slowly, maybe at the heart of a decaying city like Detroit (in fact I’ve posited a scenario in my piece for Metatropolis about this, as I do believe failed cities provide an avenue for possible urban farming).

Dickson Despommier and a number of others has a more detailed look at the land use/acres per person scenario in EcoEng that acknowledges some of these challenges and puts out answers to them, but most articles taking on the concept seem to be much more of the ‘wow big idea’ sort.

Until the movement cost of fuel to get cucumbers from Ohio to NYC or bananas from the Caribbean to NYC is too high and more economic pressures are brought to bear on the displacement of where food is grown to where food is consumed, I doubt vertical farms will happen.

Far more likely farming continues where it has, but slower alternate delivery methods happen. Like large blimps or sail powered refrigerated trains or sail powered cargo ships moving produce at a slower speed from the point they’re grown to a city.