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Diving into using renewable energy, automation, and emissions:

Part 2: Improving the productivity of vertical farms

“As renewable energy seems to be a great solution for vertical farms, can solar energy be used to power them?” says Francesco Orsini, Professor at the Department of Agricultural and Food Sciences at the University of Bologna.

As we continue Francesco’s research on how to improve the productivity of vertical farms, solar energy is the next ‘grand opportunity.’ He points out the following question: ‘Can solar panels feed vertical farm’s energy needs?’

Click here to zoom in on the photo (Source: van Delden et al., 2021, NATURE Food)

Powering vertical farms with solar energy
Exploring the topic, Francesco shares that 480MJ (megaJoule) per m2 can be derived from PV panels yearly. The energy required for LED lighting in a one-layered production facility consumes 1.502 MJ per m2 per year. At the same time, a 9-layer LED production facility consumes about 13.518 MJ per m2 per year. Thus, when taking the 9-layer facility 13.518/480 MJ solar energy generated yearly, about 28.2m2 can be run on solar power.

Click here to zoom in on the photo (Source: van Delden et al., 2021, NATURE Food)

Meaning that there is still a lot of work for renewable energy providers to increase the overall energy generation of solar. Van Delden et al., 2021 from Nature Food note that values calculated on a specific location (52°N) may vary in other places. They only considered lighting, and may be doubled when including climate and operations.

Greenhouse gas emissions

A visual by Sandison et al., Food En Sec 2022; Kikuchi et al., J Clean Prod, 2018; Martin et al., Sustainability, 2019; Pennisi et al., Sustainability, 2019; Wildeman, Thesis, 2020; Song et al., 2021; Martin et al., Front Sust Food Syst 2022; Rufi-Salis et al., FAO, 2022; Sandison et al., 2022; Beaumont de Oliveira et al., Acta Hort, 2023; Martin et al., Sust Prod Consumption, 2023; Martin, C755 report, 2023.

As seen in the graph above, the Greenhouse Gas (GHG) emissions of vertical farms over the years are displayed. In 2018, an average vertical farm emitted 19kg of CO per kg of fresh leafy greens. Yet in 2019, that number decreased by 68%, dropping to 6kg of CO per kg of leafy greens. In 2020, the industry saw an even lower drop as it reached 2,5kg of CO per kg, which might have to do with Covid-19 at the time.

These digits are quite significant, yet, from 2018 onwards, the number of studies in Life Cycle Assessment (LCA) has increased too. Coming from 1 LCA research to 13 is quite a difference, meaning that not all numbers might be accurate…

Credits: Dall E 3

Automation or job creation?
Are vertical farms creating job opportunities, or should they adopt automation? Francesco wonders. Quoting research by Kozai, 2020, and Stanghellini and Raaphorst et al. 2019, 15-tier Japanese vertical farms operated manually require 50 to 300 employees per ha of land.

However, a highly automated Dutch greenhouse, which is split up into five different product categories, uses a significantly lower number of employees. A tomato grower uses 4 employees per hectare; a Cherry tomato grower uses 6-7 employees per hectare; a cucumber grower uses 4-5 employees per hectare; and a rose grower uses 10 employees per hectare. That means that automation is not always economically feasible in small facilities such as vertical farms. On the other hand, they provide a lot of job opportunities in tech and such.

Recovery of transpired water
Having discussed the opportunities in renewable energy, now Francesco highlights the recovery of transpired water.

When it comes to inputs for a vertical farming system, 100% irrigated and humidified water is put into a system. 17% of that total number is used by plants and the substrate. Another 7% goes ‘lost’ to ventilated air. Then, about 76% of the inputs are recycled by dehumidifying the air and recirculating it in the system. Yet, as Niu et al. (2005) discovered, risks that are associated with materials, such as panels for the walls and floor, glue for piping, and coolant for air conditioners, might emit volatile organic compounds that are potentially toxic to plants. Thus, there is always a risk of contaminating your plants when dehumidifying air and converting it into a resource.

Credits: VerticalFarmDaily, photo taken at VAXA Iceland

In conclusion, Francesco ends by dividing his observations into three. According to him, technology and optimized design have a great role in enhancing the resource use efficiency and the environmental performances of vegetable crop production systems.

While it can improve food system sustainability, the technological level needs to be seized to the local social, economic, and environmental conditions.

Engagement of stakeholders and civil society in understanding and recognizing food system sustainability is key to driving and supporting innovation.

The University of Bologna is organizing its 3rd International Workshop on vertical farming, VertiFarm 2024, on January 16-19 at the University itself. Click here to obtain more information.

For more information:
Francesco Orsini, Professor
University of Bologna
[email protected]