The concept, definition and economics of Vertical Farming

A stacked-shelf, sealed shed is the common, present-day concept of VF but this is not as defined by Dickson Despommier, the originator of the term. For him, indeed, VF means growing on many levels in a vertical stack so as to economise on land usage and have crops produced close to where they will be consumed. He uses a longer phrase, namely 'controlled environment vertical farming' (CEVF), when referring to the more limited, highly technical kind. In this article likewise, the term VF is not necessarily confined to the use of artificial light and a fully-controlled environment. We are primarily concerned with the economics, the real costs of growing food by VF, and will first say a little about how much food humans need to survive.

How much food do people need?

Simply put, a human adult requires about 2,000 kcal per day, more if doing heavy work or sport. Carbohydrate and protein contain some 4 kcal/g whilst fats are somewhat more energy-dense at around 9 kcal per gram. For reasons of the peculiarities and limitations of our metabolism we need a little of each and also a range of minerals and other micro-nutrients and vitamins in tiny amounts. It is true that in a prosperous society it is easy to eat too much so that foods of rather low calorie but high vitamin content may fetch premium prices: nevertheless, if you don't get enough calories, and in digestible form, you will starve. Wheat flour contains little water and some 5-10% of protein, so given a little supplementation with other foods, 500g suffices for an adult for one day. Lettuce and tomatoes contain 95% or more water and the carbohydrate is nearly all indigestible fibre.

Lettuce and tomatoes cannot support human life, but wheat can with very little else added. Wheat is a staple foodstuff, the others are not. If we wish to provide sufficient food for the rapidly increasing population of the world, we must consider staples first and although there may be objections to discussion in terms of wheat  -  because some folk react badly to it  -  the same arguments apply to all staples and wheat is a fair example to use; as in an article, "Vertical Farms could grow all the wheat we need", which appeared in Hortibiz last week, based upon a scientific paper that had appeared a few days earlier (www.pnas.org/cgi/doi/10.1073/pnas.2002655117).

Could they really? It is a very important question that deserves to be fully and critically examined.

How much wheat can be produced under artificial light, at what cost?

In an experiment over twenty years ago, Monje and Bugbee grew wheat to maturity in just 70 days in a controlled environment using light totalling 50 megajoules (MJ) per square metre per day for 70 days. That's a total of 3500MJ. One unit of electricity (1 kWh) is 3.6MJ, so the electrical energy used was 972 kWh/m2, and the yield of grain was 1.4 kg per square meter   -   694 kWh per kg of grain, and mature grain contains some 10-11% water. Allowing for water content, this means that about 0.55% of the energy supplied was converted into protein and carbohydrate; which may seem low but is in line with expectations. The paper now being discussed then considers, theoretically,  how much more grain could be produced if changes are made to the conditions used by Monje and Bugbee  -  even more intense light, for 24 hours per day instead of 20 hours, and increased atmospheric carbon dioxide concentration. There is also a question of the proportion of grain produced versus straw and roots. Perfectly reasonably they introduce  a somewhat better proportion of grain and project that five harvests per year could be produced if each takes only 70 days.

So the yield per harvest is higher and there are five per year; it should surprise no-one that a yield of 20kg per square metre per year seems attainable. That's 200 tons per hectare as compared with the current world record of 17 tons in the open field; 2,000 tons per hectare of ground area for a 10-storey CEVF.

In terms of quantity, the world could be fed that way, no doubt about it, but at what cost? The lengthy discussion may be hard to follow, but the eventual conclusion is not and is summarised here using actual figures from their Appendix. To produce 2,026,647 kg of grain is predicted to require 799,364,000 kWh of electricity at a cost of US$15,987,286. That works out at 394 kWh per kg; so distinctly better than that old experiment, no real reason to doubt that it can be achieved, though still an awful lot of electricity. It is when we come to the money that serious questions arise. The cost of electricity is US$7.99 per kg product, but assumes supply at US$ 0.02 (2 cents) per kWh. If instead we assume 10 cents per kWh the cost would be US$40 rather than US$8/kg and even the lower figure is many times more than the price of wheat produced in the ordinary way   -   in 2017, US$ 210/ton FOB Gulf of Mexico; 21 cents per kg.

No businessman would invest in an enterprise which is guaranteed to lose money. I am certainly not alone in emphasising the huge discrepancy between dreams and reality: there is no present business case for growing wheat in a CEVF, nor is that what the authors argue for. They do suggest that by 2050 the margin of loss will be less, though still large because other costs are estimated at little less than electricity. They do make the case for governments to prepare for the use of CEVF, so as to be ready in all respects for a predictable food-supply crisis just like we should be ready to deal with future pandemic viruses; and in the same way, those preparations cannot be left to private business and private investors.

In the meantime, better use of sunlight can be obtained using a developing technology, without having to rebuild existing greenhouses. Temperature- and CO₂-controlled environments already deliver higher yields in good old single-layer horticulture and there is nothing to prevent a VF having glass walls. Whatever price electricity may be, sunlight is free, and free to download. "Anything that exploits 'free' is at my kind of price", as a well-known Dutch grower told us at GreenTech last summer.

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Source: Goedemorgen