Plant factories as the most viable version of the vertical farm. However, energy remains a challenge for plant factories, both in terms of cost and carbon footprint, spoiling it’s otherwise very positive environmental profile.
We also identified that vertical farms would need to grow a broader range of crops to have a beneficial global impact.
So why aren’t we doing that? To be economically viable in the foreseeable future, (gentle music) plants grown in vertical farms ideally need the following characteristics: high edible mass percentage,low plant height, fast growing cycles, suited to hydroponic growing short shelf life. While these factors area good rule of thumb for determining the current profitability of a crop.
There is one fundamental barrier to being able to grow every crop type. That is electricity. Leafy greens don’t require much light to grow as they are made of around 95% water and their edible mass makes up most of the crop. Compare that to rice crop which provides the most calories worldwide, supplying 19% of global human calories. It is just 15% water and has a much lower edible mass percentage.
Unfortunately growing rice using artificial lighting would require about 30 times more energy than lettuce. Rice grown in a vertical farm using current technology would produce extremely expensive rice and have a significant energy demand. Energy is the major constraint for plant factories and the overwhelming factor that dictates what plants can be grown. For this reason, this blog series will mostly focus on the energy constraints of vertical farms.
I’ve broken crop types into three broad categories based on their approximate energy requirements. Phase 1: Leafy greens and Herbs,this is the current phase. Phase 2: Vegetables, Roots,Pulses and ground fruits, which will require 2.5 times more energy per kilo. Phase 3: Staple crops,nuts and Tree Fruits with 30 times more energy per kilo. Energy constraints aside, what impact could introducing each phase of crops have on the global problems.
(electrical sizzling) If vertical farms were to become the sole production method for the phase 2 crops, we could expect to reclaim 2.1% of global habitable land from agriculture. Water is another story. This category of food is highly water intensive, pulses in particular have a relatively high demand for water. Growing this category in vertical farms would save a significant 23% of global freshwater consumption.
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This change alone could have a profound impact on global water security. Though it’s not a significantly greater saving than what could be achieved using hydroponic greenhouses. If we add phase 3 crops, we can expect to reclaim 15.5% of global habitable land. Most of which could be returned to wildlife. Once again with water, the change would be dramatic.
Introducing Phase 3 to vertical farming would reduce global freshwater consumption by an astonishing 91%. This would completely transform global water security. (electrical sizzling) Given the huge potential of introducing Phase 2 and 3 crops to plant factories, it’s essential to investigate ways to reduce the energy constraint. Without a dramatic reduction in energy consumption, Phase 2 and Phase 3 in particular cannot be realized.
So how can we reduce the energy cost of vertical farms? To do this, we need to understand more about yield and how it relates to energy efficiency. Yield is an indicator of a farms operational efficiency. (upbeat music) While it’s relatively simple for traditional agriculture, there are numerous ways to measure yield in vertical farms. For the purposes of this blo .we will define absolute yield as: edible kilo per meter squared surface area per year.
We will define footprint yield as: edible kilo per meter squared land area per year. An outdoor field only has one level, so the land and surface area are the same. This means absolute and footprint yield mean the same thing for traditional agriculture. For a vertical farm, things are different. Doubling a five layerfarm to a 10 layer farm, doubles the footprint yield, because it produces twice the amount for the same building footprint.
Absolute yield remains the same however, because doubling the layers doubles the surface area. So which yield should we measure for vertical farms? A 70 times greater foot print yield sounds impressive but is it a fair comparison? Some critics argue not, claiming it makes their efficiency seem greater than it really is. When talking about land savings, footprint yield is a fair comparison. As doubling the layers of your vertical farm doubles the land you save from displacing field production.
However, it’s important to remember that doing so would double the energy requirement. If you are using solar to provide that energy, then doubling the energy would double the solar footprint. This should be factored in when comparing footprint yields. In reality, for most crop types, the area of additional solar panels is very small when compared with the vast land savings of adding more layers to a farm. While the 70 times greater footprint yield seems high, it’s only going to get higher in the future.
Plant factories can have an arbitrarily high footprint yield, because they can grow as with as many levels as are economically viable. Future vertical farms will likely have a footprint yield hundreds of times greater than the best outdoor farms, this will allow them to leverage a significant economy of scale. While footprint yield is valuable measure of farmland saved, it’s not necessarily the best indicator of the operational efficiency for a vertical farm.
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After all, Skyscraper farms would boast very impressive footprint yields, yet would not be profitable. As stated before, the biggest challenge for plant factories, is energy. If doubling the surface area,doubles the energy requirement then it makes more sense to use a measure that is independent of then umber of levels in a farm. (gentle music) For this reason, all future references to yield in this blog series will mean absolute yield unless stated otherwise.
With this in mind, how do plant factories increase the yield of a given level? Plant factories that grow produce faster get more harvests per year and increase yield as a result. They can also grow plants closer together in the horizontal dimension, this greater density increases absolute yield. Increasing the edible mass per plant also increases the yield. That is achieved by growing a higher percent edible mass plant or by growing larger plants.
Increases in absolute yield for a given energy input, leads to a higher energy efficiency. As such, improvements in absolute yield are vital for plant factories. Energy efficiency can be thought of as the most critical metric in vertical farms. The higher the kilos of edibles mass per watt, the higher the energy efficiency. This metric can be considered the fundamental determinant of what crops can be grown in a plant factory.
Not only is it essential for the profitability of current farms, improving this number has a direct result on how much they can positively affect the global challenges. For the purpose of this blog series, when you hear yield improvement,it means energy saving. (electrical sizzling) Technology in this area is improving quickly, but what can plant factories do to reduce the energy overhead? The key is to maximize the kilos of edible mass per watt of light and also reduce the dollar per watt of electricity.
So what changes can be made to improve it? Vertical farms can increase the yield of any given plant beyond what is seen in hydroponic greenhouses. And it’s not just because of their additional growing layers. They have much greater temperature, atmospheric and light control than greenhouses. This allows for superior growing conditions and waste elimination.
Plants only absorb certain wavelengths of light. Using LED grow lights allows plant factories to use specific light recipestailored to each plant, enhancing the energy efficiency. While a vertical farms, atmosphere, nutrient and light control already far surpass current growing methods. There are many opportunities to increase it further. Plant growth is complex and affected by many parameters. There is still a considerable amount of work to be undertaken to understand the optimal conditions for plants.
Outdoor plants use changes in sunlight (gentle music) to determine when to grow and flower. Normally this is dictated by the environment but LED’s can emit different recipes of light at different growth phases of the plant. These light recipes can alter many of their characteristics. They can be tailored to increase the flowering portion, reduce the root growing phase and even control how the plant tastes.
This allows plant factories to increase the edible mass percentage significantly. Energy a plant uses building one-edible structure is waste energy. This is inconsequential for sun grown plants but is critical to vertical farms. Field grown lettuce has about 40% edible mass when considering root system sand inedible outer leaves, while vertical farms have managed to achieve 92% edible mass.
But that’s not the only advantage of light recipes. Since they can be used to trigger growing cycles, they can accelerate plant growth considerably. While field grown lettuce can be harvested twice per year, vertical farms can harvest up to 12 times per year. Even rice can be harvested about four times more often than when grown in a paddy field. While the edible mass percentage for lettuce is approaching its limit, that’s not necessarily true for other plants.
Despite being a new industry, yield improvements are happening quickly. This is partly due to new possibilities with data analysis. Vertical farms have a multitude of sensors measuring many parameters. From, temperature, to nutrient levels. The plants are analyzed with cameras and sensors which monitor plant health in real time. Because plant factories control the environment so effectively, it’s considerably easier to actively run experiments and interpret the data.
Maximizing yield by the fine tuning of variables such as CO2 and humidity levels. Not only that, but due to having considerably more harvests per year, they have a lot more opportunities to experiment, collect data and learn. This allows for a learning rate that is a number of magnitudes higher than other growing methods. As a result, vertical farms are hiring data engineers and sensor specialists as a significant percentage of their workforce.
Artificial Intelligence already plays a key role in many vertical farm operations. Despite this, it’s still at an early stage. As sensors continue to get cheaper and more capable, the opportunities for vertical farms increases considerably. A number of plants are poorly suited to vertical farms, due to low edible mass percentage, being ill suited to hydroponics,or being a tall crop.
Since, current commercial outdoor crops have no need to consider these parameters they breed plant varieties that thrive outdoors and are often in compatible with vertical farms. Plant Factories have different priorities and require different seed types as a result. There are many dwarf varieties of existing crops, that could be utilized. If they can match existing crop quality with a seed optimized for short height, hydroponics and high edible mass percentage, then the energy requirement for replacing existing crops could shrink significantly.
Additionally, seeds can be bred for faster harvest cycles, not a requirement for most current crops. Many current crops sacrifice breeding for peak yield so as to breed for vital resistances. This isn’t necessary in vertical farms because of their sealed conditions. Unlike greenhouses,they don’t need to vent and are run like a clean room environment. These yield improvements alone can significantly reduce the energy gap for future crop types, but it’s not the only improvement available.
This area has a huge potential for improvement, especially for plant factories that utilize genetically engineered seeds. Gene editing techniques are getting much cheaper and easier to implement. This has a lot of potential for both indoor and outdoor farming in the future. In the last few years LED light shave improved considerably. Special units are being developed specifically for indoor growing and their efficiency is anticipated to improve by 50% in the next decade.
Efficient LED’s run colder, not only does this save electricity but allows them to be placed closer to the plant without risking heat damage. This allows plant factories to fit more levels into a fixed building height,increasing footprint yield. Closer positioning increases light penetration into the canopy allowing plants to be grown closer together and increasing absolute yield.
It also reduces light bleed and increases light absorption efficiency, reducing energy requirements. Greater use of reflective bay materials, deeper penetrating green wavelength light and mid level bay lighting can further reduce the total energy requirements. It’s not just efficiency though. LED’s are increasingly capable of delivering a broader spectrum of light, allowing for greater control and yields.
The cost of the units are also falling quickly, while the unit lifespan continues to improve. This will reduce the depreciation costs for future vertical farms, and is essential for improving their cost competitiveness. If there is one technology that could transform the potential of vertical farming, it’s renewable energy. It has the potential to solve the environmental and economic outlook simultaneously.
Solar for instance is projected to half in cost over the next decade. This will bring its cost below traditional production methods in many areas of the world. Reducing the cost of electricity will be the final step, enabling vertical farms to grow a broader range of products.