Synergetically integrated vertical farms: Reducing energy and resource use through synergies between vertical farms and cities

Reducing energy and resource use through synergies between vertical farms and cities

Abstract

At present, agriculture is confronted with the significant challenge of increasing production to meet escalating global food demands, while simultaneously dealing with reduced land and resource availability. Moreover, there is an imperative need to lower greenhouse gas emissions for climate change mitigation. In response to these agricultural challenges, vertical farming has emerged as an evolving agricultural method designed to enhance productivity while minimising resource usage and environmental impact. Vertical farms achieve this by cultivating crops in vertically stacked hydroponic systems within an uniformly controlled indoor environment using active climate control systems and artificial light. Through this approach vertical farms operate independent of external climate factors and produce stable year-round yields.

Vertical farming is often advocated as a sustainable food system, as they offer several benefits over conventional farming systems, including efficient land use, high yields, minimal water and nutrient usage, the redundancy of pesticides and herbicides, and the ability to be located within or adjacent to cities where food demands are high. However, a major challenge for vertical farming is the substantial electricity use for artificial lighting and climate control. Despite this drawback, literature recognises vertical farming as a potential strategy to enhance energy and resource use efficiency in both agriculture and cities by creating synergies between both entities.

This study, centred in the Netherlands, addressed the research question:

How can the synergetic integration of vertical farms within cities reduce energy and resource usage as well as carbon emissions of both entities collectively?

The primary focus of the study was the exchange of residual heat produced by VFs with the cold generated when heating buildings in the city, i.e., energetic synergy.

To evaluate the potential of vertical farms to grow food in a sustainable way, this study extended beyond efficient land use and high yields, considering the entire life cycle of the crops cultivated in vertical farms. A carbon footprint assessment compared lettuce produced in an operational vertical farm to open-field farming and greenhouse cultivation in the Netherlands. The findings revealed that the substantial electricity use for artificial light and climate systems outweighed the aforementioned benefits of vertical farming from a carbon footprint perspective.

The high electricity use for artificial light results in the production of substantial quantities of waste heat. Starting at the building scale, we explored how this heat can be captured and reused for building heating. Furthermore, the potential to exchange flows of water and nutrients between the building and the vertical farm (to reduce the need for external inputs) were studied. On the larger urban scale, the possibility to create thermal energetic equilibrium within the local district heat networks using the excess heat from vertical farms was analysed. Moreover, we explored alternative lighting strategies for vertical farms to respond to electricity price fluctuations, addressing imbalances between electricity generation and consumption in the electricity grid, while ensuring the continuous production of fresh vegetables for the city.

Finally, we evaluated the potential benefits of integrating vertical farms with urban energy systems in terms of an overall carbon footprint. To this end, a carbon footprint assessment was performed for four different scenarios for the city of Amsterdam, ranging from a reference city relying on conventional farming methods and existing energy systems, to a city using residual heat from vertical farms that simultaneously attune their electricity use with the availability of renewable energy in the grid. The findings revealed that this attuned and synergetic integration of vertical farms with urban energy systems effectively reduced the collective energy use of both the vertical farm and the city, lowering the carbon footprint of vertical farms in cities. However, despite these carbon savings, the overall carbon footprint of such a synergetic city still surpassed that of cities relying on fossil-based heating and conventional farming for vegetable and fruit consumption. Although the energy used for heating was reduced by the integration of vertical farms, the overall increase was still attributed to the substantial energy use for artificial light to cultivate crops in vertical farms.

Furthermore, the study highlighted the need for careful consideration of location, crop selection, light use efficiency, and the use of residual heat to minimise the additional carbon emissions by the integration of vertical farms into cities. The observed increase in greenhouse gas emissions should be weighed against the potential benefits vertical farms bring to cities, including enhanced food security, self-sufficiency, replacement of fossil-based heating systems, efficient land use, and the flexibility offered to the electricity grid by attuning the LED lighting according to the availability of energy, reflected in the electricity prices.

Finally, the study revealed a trade-off between carbon footprint reduction and the essential need for flexible electricity operations in cities. Attuning LEDs to enhance grid stability, while crucial for cities, increases the carbon emissions of vertical farms. In summary, the synergetic integration of vertical farms presents substantial benefits for cities in terms of crop production, land use, flexible electricity utilisation, and heat supply. However, when focussing on the carbon footprint, vertical farms, even those in synergy with the city, face a significant challenge in competing with conventional farming systems due to the substantial use of electricity for lighting. Further development of effective lighting systems, perhaps hybrid with use of daylight, might leverage this backlash.