1887

Vertical farms

Feeding the world's increasingly urban population could entail building multistory farms in cities.

Artist Mariano Las Heras grows all he needs for his own subsistence in a small patch of land in the tiny village of Arenillas in northern Spain. Because he does not use pesticides, deer sometimes help themselves to his plethora of potatoes, peapods, squash, and tomatoes, but Las Heras sees this as a form of recycling and a fair price for a sustainable lifestyle.

By the middle of this century, the world's population will reach 9 billion, 80% of whom will live in urban centers. Not all 9 billion of us will have carved out as harmonious an existence as Las Heras. Still, we all need to eat. Feeding an increasingly urban population means that we must produce food closer to cities with a fraction of the resources consumed by large-scale farms.

Traditional industrial agriculture not only taxes the world's limited arable land, but also requires high costs in energy and transportation to reach the hungry public. One proposed solution is to grow food inside tall urban buildings.

Growing fruits and vegetables in controlled environments is not new, but developing large-scale indoor farms in urban environments to accommodate another 3 billion people has led to new technologies and lofty goals.

Indoor farms take root

Dickson Despommier, professor in Columbia University's Department of Environmental Health Sciences, published the latest version of a vertical farm concept in 2010. Motivated by rooftop farming—that is, cultivating plants on flat rooftops in cities—Despommier and his students brought the decades-old idea indoors.

The vision is a 30-story farm on one city block that could feed 50 000 people. The upper floors would comprise hydroponic crops—that is, crops grown using nutrient-rich water instead of soil; lower floors would house chickens and fish that consume plant waste. Heat and light would be provided by renewable energy sources, and nitrogen and other nutrients would be sieved from animal waste and city sewage. Farms would be built in abandoned warehouses with minimal refurbishment requirements and would create dozens of local jobs.

The potential advantages of vertical farming include restoring degraded land; reducing agricultural runoff and recycling solid waste; and ensuring year-round crop production that is move resistant to hail storms, drought, and other natural events. Furthermore, locating vertical farms in cities would reduce the carbon cost of transporting from food from field to city.

Trays of lettuce in SPREAD's Nuvege vertical farming environment. CREDIT: SPREAD

Trays of lettuce in SPREAD's Nuvege vertical farming environment. CREDIT: SPREAD

Asia currently holds “best in show” status in the vertical farming world. The Tohoku tsunami of March 2011 inundated and polluted farmland in Japan's Sendai region. The stress on agriculture was exacerbated when, following the Fukushima disaster, elevated radioactivity was found in local produce. In response, the Japanese government prompted those involved in the then-boutique vertical farm industry to expand and innovate. “There are around 140 plant factories in Japan, and this number is growing,” says Naoki Matsumoto of SPREAD farms, headquartered in Kyoto.

SPREAD farms, branded as Nuvege, use soilless technology and a lighting network that balances LED light emissions and advances photosynthesis through exposing the plants to increased levels of carbon dioxide. This controlled-environment technology increases the yield rate of vegetable growth without threat from weather, climate, or contaminants. A SPREAD farm uses 30 000 horizontal square feet in a four-story building to provide 57 000 square feet of growth environment. “We produce only lettuce, but the variety of produce grown in plant factories is. . . increasing,” adds Matsumoto.

Following lectures by Despommier and World Health Organization representatives in 2009, South Korea leaped into action and in 2011 had built indoor farms in which to experiment with lighting, feeding mechanisms, and seed viability. The country's Rural Development Authority's farm in Suwon occupies a three-story building crammed between high-rise apartments. The farm's goal is to develop optimal cultivation methods that can compete on the open market while gradually going off-grid in terms of energy consumption.

As suggested by these examples, a critical element of vertical farms is their independence from outdoor light and climatic conditions. Challenges of indoor farming include lighting mechanisms, water circulation, and energy efficiency. But those challenges can be met. Advances in controlled environment agriculture and hydroponics make vertical farming feasible and profitable, as evidenced by examples proliferating around the world.

Let there be light

Green Spirit Farms in New Buffalo, Michigan, grows plants in Rotary Vertical Growing Stations (RVGS), modified to grow 540 flowering plants in 36 square feet, along with Vertical Growing Stations (VGS), a modified tray system that grows 1013 leafy plants in 36 square feet. The RVGS unit comprises an Omega Garden, a rotating cylinder that houses plants arranged around a central light source. The plants are grown in rock wool cubes, nourished by a mineral solution that uses less water than a typical hydroponic system.

Experimenting with different light sources led Green Spirit father and son founders Milan and Dan Kluko to choose a 200-W induction lamp for the centerpiece of its rotating cylinders, which uses an electromagnet to excite argon gas as its light source. “We look at how little power we can use,” says Milan Kluko. A four-level VGS uses 800 W per level (3200 per station); a six-unit VGS uses 600 W per unit (1200 W per station). The induction lamp provides full spectrum light, as similar to sunlight as possible, and operates at 130 °F maximum temperature, which does not require a cool tube and is thus immune to the associated problems of refraction. With no filaments to wear out, one induction lamp can last for eight years.

Green Spirit's Omega Garden system consists of a rotating cylinder that houses plants arranged around a central light source. CREDIT: Green Spirit

Green Spirit's Omega Garden system consists of a rotating cylinder that houses plants arranged around a central light source. CREDIT: Green Spirit

“We don't run plants 24/7,” explains Kluko. “They do better when rested six to eight hours a day. Plants outdoors [photosynthesize during the day and] grow in the dark. When plants shut down from photosynthesis to nighttime, it takes two hours to transition. That's nonproductive biology.” By using a row of red or green LED lights to emulate morning and take the plant out of sleep mode and into active mode, Green Spirit has increased production by 20%. The farm is entirely independent of daylight, and operates at off-peak hours when electricity is cheaper.

Anecdotal evidence from Despommier suggests that mimicking daylight patterns is going to be a hot topic for revolutionizing the growing industry. One proposal, from a researcher in Germany, is to use a three-filament light bulb to simulate sunrise, midday, and sunset, and to save energy by gradually adjusting lights instead of flicking them on and off. “Photosynthesis is a complicated cycle that hasn't been measured in great detail,” says Despommier. “But here's a guy who said let the plants figure it out, and I'll give them the light they see outdoors.”

While Kluko advocates the induction lamp and full spectrum light, many other farms use LEDs to feed their hungry plants. From a physics perspective, LED light has the potential for near 100% efficiency, but achievable efficiency is far less due to energy lost as heat. In early 2013, Philips Lighting announced an LED prototype that has improved performance from 50–70 lumens per watt to 200 lumens per watt.

If LEDs continue to become cheaper and better, indoor plant productivity could be even more promising. Dutch company PlantLab has developed a formula for maximizing efficiency of indoor plant production based on a matrix analysis of salt solutions, nitrates, oxygen, lighting, and other variables. The analysis included lighting schemes with LED wavelength combinations from red to blue. “Imagine this as a set of lab experiments for students in a beginning horticulture class,” explains Despommier. “You've got alfalfa. How many ways are there to grow alfalfa?” Varying all parameters to optimize for growth and yield leads to a formula for how to grow each type of plant (available to companies wanting grow crops).

As another illustration of LED technology, the Controlled Environment Agricultural Center (CEAC) at the University of Arizona uses certain wavelengths to optimize several aspects of plant productivity, including grafting. Grafting entails taking one plant that has, say, a resistant rootstock and combining it with another that has, say, a good flavor of fruit. The two sets of tissue are joined together in order to propagate the desired gene. Far-red spectrum (700–800 nm) light makes plants stretch and can be used to create a very elongated plant stem, perfect for grafting. Red light (600–700 nm) leads to a shorter plant, which can be useful for finishing a grafted plant. Finding the best composition of LED wavelengths—the specific ratio of blue and red—to maximize photosynthesis or growth rate or flower development creates new opportunities in plant cultivation.

Water, waste, and efficiency

Of course, in addition to light, plants need water to grow. One major advantage of hydroponic farming is that it requires less water than a traditional farm and thus is not subject to contamination, availability, or water-related natural events.

“We don't need water to prepare the soil,” explains Kluko. He cites an outdoor farm at the University of California, Davis, as requiring 6.5 gallons to produce one head of Romaine lettuce and the University of Arizona as using 25 gallons per head. By contrast, Green Spirit Farms uses 0.33 gallons. “We charge one vertical growing station with 150 gallons [of water] per growing cycle.” Plants finish growing before all that water is consumed, and the nutrient-rich water is reclaimed into the system.

The system uses rock wool soaked in pH-adjusted water, into which seeds are placed. After 7–10 days in the nursery, plants grow in the vertical stations. The nutrient tank recirculates the entire time, with just one commercially available pump per station. The fully automated system keeps a constant record of how much water cycles, as well as the water’s pH and dissolved-oxygen content. SPREAD in Japan also uses a pump to circulate water. In neither case does pumping represent a significant electricity cost.

Trays of leafy greens at Chicago-based Farmed Here. CREDIT: Farmed Here

Trays of leafy greens at Chicago-based Farmed Here. CREDIT: Farmed Here

Chicago-based Farmed Here, owned and operated by Jolanda Hardej and sited in a three-story post-industrial warehouse, uses symbiotic cultivation of plants and fish (tilapia) in water to create a system in which nutrients are entirely recirculated. Farmed Here grows plants in six-high stacked beds with a series of mechanical pumps that circulate water between fish tanks and plant trays. Aeroponics further decreases freshwater consumption by keeping plant roots in a nutrient-rich mist, and reduces weight on upper tiers by eliminating water flows. They grow twelve times the yield of traditional farming using 97% of the fresh water consumed per outdoor acre. A new 90 000 square foot facility opened in March 2013.

At Green Spirit farms, arugula grows 28 plants per square foot of growing space, while outdoors it would be 0.72 plants. The leaves are cut over five to six harvests and grow back in seven days. Kale is kept alive for seven to eight harvests and comes back in six to ten days. Most leafy greens spend around 20 days in a tray until harvest. And Green Spirit, like most vertical farming facilities, is careful not to compete with traditional farmers during a crop's outdoor season.

The verdict on the vertical?

At present there is no way to compare all the parameters of indoor and traditional farms including cost of land, yields, fertilizers, water, and energy. “It's like comparing the special theory of relativity to general relativity!” says Despommier. “[Traditional] farming is not a good business model: You can have a 50% margin of failure and still be in business.” Environmental failures such as droughts and floods happen, and climate change is leading to more variability and unexpected events.

Indoor farmers, however, are proving to be successful. Gotham Greens, in New York City, operates a 2000 square foot hydroponic indoor farm. During Hurricane Sandy, they remained fully operational. However, neighboring outdoor rooftop farm Brooklyn Grange lost everything. Many vertical farms in operation today have solved problems of energy and yield and have found markets for their products. “The hope is to become so successful, that in ten years we could contemplate intervening in a place like the Philippines that just got creamed [by a typhoon],” says Despommier.

Like any other radical concept that has technology as its base, prices associated with vertical farming will drop over time. The transition to urban farming has only existed for a few years. There will be some success and some failure, but the timing is perfect in terms of climate change and natural events that impact whether a crop will yield.

The vertical farm looks nothing like Mariano Las Heras' all-natural farm in Arenillas. But the end goal—producing what is needed where it is needed, minimizing waste, and remaining carbon neutral—is the same.

Comments

http://aip.metastore.ingenta.com/content/aip/magazine/physicstoday/news/10.1063/PT.5.4002
Loading
Submit comment
Close
Comment moderation successfully completed
This is a required field
Please enter a valid email address
This feature is disabled while Scitation upgrades its access control system.
This feature is disabled while Scitation upgrades its access control system.
ec53185b92e297f26a707ada48e7a20c ptol.magazine_postzxybnytfddd
Scitation: Vertical farms
http://aip.metastore.ingenta.com/content/aip/magazine/physicstoday/news/10.1063/PT.5.4002
10.1063/PT.5.4002