A Holistic Look At Vertical Farming’s Carbon Footprint And Land Use

Editor's Note: This post was written by Till Weidner, a Postdoctoral Researcher at ETH Zürich with an interest in urban farming and energy. Weidner’s publications include: Energy optimisation of plant factories and greenhouses for different climatic conditions (2021) in Energy Conversion and Management, Regional conditions shape the food–energy–land nexus of low-carbon indoor farming (2022) in Nature Food, and Estimating the potential of building integration and regional synergies to improve the environmental performance of urban vertical farming (2022) in Frontiers in Sustainable Food Systems.

It’s no secret that a host of simultaneous crises have been pressuring the current food system. With a worsening climate, biodiversity loss, a global pandemic, and war, we’re being challenged both from a supply resilience and an environmental sustainability perspective.

Vertical farming has slowly become one of the more eye-popping solutions to these growing challenges, attracting billions in private funding.

With all the hype in the industry, many proponents claim that vertical farming is more sustainable than the current food supply, citing reductions in land, water, and pesticide use alongside reduced food miles.

However, environmental sustainability is not a single-issue concept. And, as a result, vertical farms face a lot of criticism about how “sustainable” they truly are. According to respondents of the 2021 Global CEA Census, 70% of CEA operators believe that the industry is susceptible to excessive greenwashing.

We need to consider the holistic sustainability of bringing farming indoors. 

Even though there is evidence behind vertical farms significantly reducing freshwater withdrawal and the loss of biosphere integrity from pesticides, the main area of concern is greenhouse gas (GHG) emissions and land use.

Alongside researchers from Michigan State University and the Stockholm Environment Institute, I recently dove into why this is a problem. 

When looking at carbon footprint, we often see claims around the reduction of food miles. In truth, data shows that food miles contribute very little to the total carbon footprint when compared to “on-farm” emissions (this includes energy inputs).

As part of this research, we modeled dynamic CEA systems in 10 different locations (Chart 1), optimizing lighting and climate control to obtain the lowest specific energy consumption (energy spent per unit mass of food produced, in this case a mix of vegetables). This included electrifying air conditioning using heat pumps and refrigeration cycles for dehumidification. Results in Chart 1 indicate that vertical farms require at least 16-20 kWh per kg (depending on the location, main contribution lighting), while open ventilated greenhouses can have much lower specific energy requirements. 

Similarly, according to respondents of the 2021 Global CEA Census, indoor vertical farms, on average, use 38.8kWh per kg of harvested crop. Given that the global average carbon intensity of electricity is 475g CO2 per kWh, we can assume that, on average, vertical farms have a carbon footprint of 18.43kg CO2 per kg of harvested crop. 

Comparing this to Our World In Data’s calculations on GHG emissions per kilogram of food product - where beef, the highest emitter, emits 99.48 kg CO2, rice emits 4.45 kg CO2, and tomatoes emit 2.09 kg CO2 - vertically farmed produce clearly doesn't live up to its image of sustainability from the perspective of carbon footprint when fossil fuel-sourced energy is used. 

While there is potential here for renewable electricity being generated and used in vertical farms, it has also been found that most renewable energy infrastructure (solar photovoltaic and wind turbines) require vast amounts of land, while also having their own unique set of ecological challenges (e.g. the accidental killing of large birds of prey).

Here are the top takeaways on the impacts of renewable energy generation on the total land use of vertical farms.

The direct (growing facility) and indirect (renewable energy generation) land footprint was calculated and compared with open field vegetable farming (Chart 2).

In 8 of 10 locations analyzed, it was found that the indirect land use of vertical farms leads to similar or higher total land footprint than open field farming. Greenhouses were much more favorable in this regard, with greatly reduced total land footprints. 

Here, it’s important to note that the picture strongly depends on local conditions; the favorability of one growing method over another can differ from what the combined land footprint indicates. 

For example, although combined land use is lower for CEA in Boston, there is limited availability of land for renewable energy generation (cluster 1 on Chart 3). The most favorable locations have vast amounts of land for energy generation and very little suitable farmland (e.g., Reykjavik and the UAE).

It’s clear that while switching to renewable energy greatly reduced the carbon footprint, other impacts such as land use might worsen. 

Based on our modeling work, we suggest that to consume energy more efficiently, vertical farms should:

1. Use energy-efficient LEDs - increased efficiency from 52% to 75% reduces energy requirements by up to 21%.

2. Moderate the Daily Light Integral (DLI) levels at long photoperiods (the period of daily illumination received by an organism) - up to 20% less energy required when compared to higher DLI levels or shorter photoperiods.

3. Use water cooling for LEDs - up to 23% reduced energy consumption

4. Have a climate control system that can simultaneously optimizes for yield and energy - up to 60% reduced energy consumption

5. Spend more time developing energy efficiency strategies, especially in regards to cooling systems - here, the savings depends on current energy strategies

Note: Indicated energy savings refer to specific energy (kWh per unit mass of produce) of an optimally run facility. 

Sourcing energy from renewable sources is also an imperative for sustainability. However, as shown by these publications, it’s important to note that general claims about land savings of indoor farming are often incorrect. The picture strongly depends on the location and the metrics considered (absolute or relative land use).

We have identified a host of further carbon footprint reduction potentials for CEA, including re-using waste heat from air conditioning systems of vertical farms to substitute space heating inputs of nearby buildings, replacing single-use plastic in the supply chain, and sourcing growing medium from waste material. However, they are a drop in the ocean if fossil fuels are used to power a farm. As a result, oftentimes, open-field produce still has a lower carbon footprint.

Practitioners should always consider sustainability holistically and avoid greenwashing in their communications. We can only hope to grow this industry sustainably if we can be transparent about the performance of individual vertical farms.

FURTHER READING

An Entrepreneur’s 9-Step Guide To CEA Facility Design

Glasshouse Lighting: Is It Time To Turn Off Traditional Options?

Agritecture & TensoAI Partner To Build Crop Models For More Predictability On Farms