Vertical agriculture can strengthen the independence of cities from the global food network, but whether this is useful or not differs from region to region. The energy and raw material consumption will not always outweigh the benefits, concludes Luuk Graamans in his research, for which he obtained his doctorate cum laude on 11 March. 

Growing food locally in closed production systems, so-called vertical farms or plant factories, can yield large, clean harvests. Light and nutrition are precisely attuned to the crop, pesticides are hardly needed and the weather is of no influence. So consistent quality and reliability of supplies are guaranteed. And a crop of lettuce doesn't need to be transported thousands of kilometres before it reaches your dinner table. The Amsterdam-based vertical farm GROWx, for example, guarantees that freshly harvested vegetables will arrive in your kitchen the very same day - delivered by bicycle. In theory, local food production can enable cities to become independent of the international food network. "This is crucial, because if this network is disrupted, a large city will quickly run out of food supplies," says Graamans. "My research investigated whether you can increase the resilience of cities with vertical farming. And whether the ultimate climate control it provides is necessary and efficient?"

Energy consumption is climate-dependent

His research focused mainly on the energy balance and on resource consumption. Growing crops in buildings almost always requires more energy than growing them in the open air because of the use of LED lighting and climate control, but it requires far less water; the water is easy to recycle. For a desert country like Abu Dhabi, this is an attractive option. Vertical farms also minimise land use, because several layers of cultivation fit into a single building floor. This might therefore be a valuable solution for an extremely densely urbanised city like Hong Kong, for example, which imports 98 per cent of its fruit and vegetables. 

The energy consumption turns out to be strongly dependent on the climate zone in which the 'plant factory' is situated. A lot of electricity is needed for heating in the cold, dark north of Sweden, while in Abu Dhabi, it is needed for cooling. Yet vertical farms only beat greenhouses in terms of energy efficiency in cold Sweden. In the Netherlands, with its mild climate, it’s different - in terms of energy, vertical farming offers more potential in an extreme climate than in a mild climate. Can adjustments to the building structure be helpful? To a limited extent, Graamans concludes. "But a transparent façade can yield savings of up to 12 per cent. So intermediate forms of vertical farms and greenhouses might also be considered.

Finally, he explored the possibility of using surplus heat from vertical farms in the urban energy network. This could even be a stabilising factor in a network that runs primarily on wind and solar energy. Graamans: "Then you would have a food production system that supplies heat as a residual product. Or a heat pump that delivers food as a residual product.

72 Teslas or 174,000 meals

Graaman’s calculations show that vertical agriculture can make a significant contribution to supplying a city. Converting Hong Kong's Central Plaza skyscraper (222,000 m² of cultivation area) into a vertical farm would provide some 16 million kilos of crop, he calculated. "That is enough to provide more than 174,000 people with a daily portion of 250 grams of vegetables." In fact, the cost in terms of electricity would be the same as the average annual cost of running 72 Tesla cars. 
Plenty of interesting possibilities, one could conclude. Is his research a plea for more, or even only, vertical agriculture? "No, my plea is for the possibilities for each location to be investigated, and what the ideal building design would be." 
Specifically for this purpose, he devised the STACKED method. This maps out the energy and 'raw material consumption' efficiency of plant factories and shows where this can be improved. 
Unoccupied office buildings may be suitable for vertical farming, but perhaps the technology will only really take off when humankind starts colonising other planets, Graamans philosophises. "Space, unfortunately, is not a climate that is conducive to food production. Growing crops in closed systems such as plant factories might prove to be crucial for the survival of the human species there." 

Image: Unsplash; Markus Spiske

Published: May 2021
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