To make sure everyone eats well in our crowded world, we need to innovate. Vertical farming systems, which grow plants intensively in an indoor setting, could be part of the answer – but to use them on a large scale we need to overcome key problems, especially the management of the energy-intensive, expensive light the plants need to grow. Now scientists show how manipulating light according to the needs of specific crops could make them grow stronger and healthier while minimizing energy use.
"The biggest benefit of vertical farming systems is that healthy food can be grown much more closely to consumers in places where this is impossible otherwise: in mega-cities, in deserts, and in places that are cold and dark during large parts of the year," said Dr Elias Kaiser, first author of the article in Frontiers in Science. "The biggest challenge is the costs associated with electricity use."
Shedding light on the problem
Many vertical farming systems are run using constant environmental conditions, which require lots of expensive electricity for maintenance. The scientists' analysis shows that these demanding conditions are unnecessary: using dynamic environmental control, they suggest, we can achieve vertical farming which is more cost-effective and which raises healthier plants.
"We were motivated by the rhythms that plants show on diurnal as well as on developmental timescales, which require their growing environment to be adjusted regularly in order to steer their growth perfectly," said Prof Leo Marcelis of Wageningen University, senior author. "We outline a strategy that makes use of plant physiology knowledge, novel sensing and modelling techniques, and novel varieties specifically bred for vertical farming systems."
Because plants' biological functions are heavily influenced by environmental conditions like temperature changes, light wavelengths, and the amount of CO₂ in the atmosphere, manipulating the environment allows a vertical farming system to manipulate plant development. Lighting is a critical variable; all plants need it to photosynthesize, and different light wavelengths have different effects on different plants. This variable is also particularly sensitive to electricity pricing, so offers opportunities to make efficiency gains.
"Fluctuations in electricity prices can be used to the advantage of vertical farming systems, by using more electricity when it is cheaper," explained Marcelis.
The authors created a model for testing smart lighting that aims to keep plants' ability to photosynthesize steady over the course of a day, while still lowering electricity costs. They found that an optimization algorithm could cut electricity costs by 12% without compromising plants' carbon fixation, just by varying the intensity of the light.
They then tested whether varying light intensity affected the growth of leafy plants like spinach which are often grown in vertical farms, and found that there was no negative effect. This remained true even when the plants were subject to irregularly changing light intensity, rather than a predictable, regular pattern.
The seeds of the future
Other critical issues remain to be resolved before vertical farming can help feed the world.
"Many of the proposed solutions have not been tested at the larger scales that vertical farms represent—they may have been shown at the single-plant level, but not yet at the whole crop stand level," cautioned Kaiser.
Dynamically adjusting air flow rates, temperature, and CO₂ according to plants' needs could potentially offer opportunities to minimize electricity costs. Farmers will need suitable sensors and models to help them monitor and adjust the environment, as well as new cultivars bred for vertical farming. These cultivars could take advantage of the potential for local production in sheltered conditions to focus on better nutrition and sensory qualities, rather than robustness or shelf-life. More research is required to calibrate all these variables and strike the right balance between high-quality and high-yield crops.
"In a vertical farm all growth conditions can be exactly controlled, which is very important to optimize yield, quality, and resource use efficiency," said Marcelis. "However, the technical possibility of keeping them constant does not mean that keeping them constant is the best solution. Once dynamic environmental control has become established, both the energy use and costs of the used energy can be substantially reduced, increasing the profitability and sustainability of vertical farms."
