When discussing underground farming, one of the topics people have consistently shown interest in is energy.
"Won't growing food underground require too much energy?"
It's a fair question to which we want to bring clarity with this article.
According to the 2021 Global CEA Census Report, vertical farms have a significantly higher average energy use at 38.8 kWh per kg of produce as opposed to traditional greenhouses, which average 5.4 kWh per kg.
According to the same report, the biggest sources of energy consumption in vertical farming are:
- Lighting - 55%
- Cooling/vents - 30%
- Heating - 11%
As you can see from the chart, the biggest factor behind vertical farming's energy disadvantage versus greenhouses is lighting.
Most of the energy that goes into crops in modern agriculture comes from sunlight, but also from the fossil fuels used to create fertilizers. So, when growing indoors without sunlight, the challenge can seem insurmountable.
- You need to replace both sunlight and fossil fuels as energy sources.
- Not all of the light produced through LEDs converts into useful biomass. In fact, only about 2% of the total energy from LED's turns into chemical energy in the plant. Outside, where the light is free abundant and cooling is not an issue, that's fine. When you're in a confined space and have to pay for the light and get rid of the heat, that complicates things.
From a horticultural point of view, our underground farming systems are very similar to surface-level vertical farming you may be more familiar with. Crops are grown using hydroponics, with LED lights providing plants with the light wavelengths and durations they need in order to grow at their best. An HVAC system keeps the environment at a desired temperature and humidity level.
The bulk of energy consumption comes from LED lights and the HVAC system.
Here's a couple reasons why the underground farming systems we have designed have an advantage in regards to LED, HVAC and more.
1. LED Efficiency
LED lights are expected to be more efficient due to the radial beam pattern. Since light intensity for any light source drops off quickly with distance (inverse square law), on a flat canopy the PPFD reduces in intensity not only due to beam angle, but also since it is getting farther away from the LED. Think of a right triangle where the hypotenuse is the distance the light has to travel; one side is the distance from LED to canopy, and the last side is the flat canopy. This is why the light is brightest directly underneath. LED manufactures try to counteract this with optics and spacing lights closer together. With a circular plane for the canopy, we can reduce the effect of the canopy "moving away from the light" by wrapping the canopy around the light.
This image should help with the visualization where b would represent a flat canopy, the circle represents our canopy and c would be the distance from led to canopy. Our system wont be exactly like that as our lights aren't quite exactly in the center but the same concept applies.
We also expect to have better efficiency since we don't need to have gaps in our circular canopy for isles/walkways where the light can escape, we only need to light the areas needed for plants.
2. Underground stable climate
Underground temperatures are stable, almost indifferent to surface shifts, so less energy is required to keep an adequate climate inside of the systems. While the lights are on, the cool soil helps to dissipate some of the heat produced by the lights, thus reducing the cooling load on the HVAC system. Conversely, when the lights are off, some of the heat absorbed by the soil will be released back into the growing area reducing the amount of artificial heating required.
We use drilling equipment to create the environments, and can drill extra passive geothermal capacity on site so as to further reduce energy consumption of HVAC systems.
Since we are building in vertical shafts, we leverage gravity in our designs to save on energy. For example, we a save lot of the energy used for pumping nutrient solutions compared to many vertical farms by letting gravity do most of the work.
The future is probably bright
This being said, there are further reasons to be optimistic about energy consumption:
- See Haitz law for LED and semi-conductors rate of improvements — any breakthrough in lighting tech could change everything, just like the invention of blue light in 1989... which changed everything in this space.
- Certain crops like mushrooms take nearly no energy if grown underground. That's because they don't need a lot of light to grow and they prefer a cool environment.
- Our software and product teams are focused on energy consumption per weight of crop. Through the process of testing, continuous design improvements, AI and industry insight we will reduce our energy consumption.
- The percentage of energy produced using renewable is increasing year over year:
- Battery technologies are seeing massive investments and will most likely broaden significantly in capacity, price and range of applications.
- Nuclear energy is progressing in a direction that would allow for higher modularity, safety and without the supply chain issues that usually plague it.
- Geothermal power has developed only a fraction of its potential. US DOE’s GeoVision study points out that improved technologies could help increase domestic geothermal power generation nearly 26-fold by 2050.
- Certain countries have big potential in hydropower (ex. Canada and Brazil) and can take advantage of it with little downside.
- Investments in research on passive systems (mirrors, Fresnel lenses), along with material science improving light reflection inside the Forges, have the potential to save a lot of energy.
- Energy efficiency can be increased by integrating the farming of other crops or organisms which can grow in underground environments by taking advantage of the "waste light" that the plants do not use. This would increase the percentage of energy converted into useful biomass.
- Humanity so far has shown little sign of slowing down its total energy production/consumption — or lacking the ability to innovate to meet that. It has more to do with economics than the actual capacity. When it comes to food and survival there is a high likelihood that the market and economics will get distorted by more and more government involvements not just to address on-going issues but to intensify the development of solutions.
To conclude — yes, energy is a challenge in underground farming just as in all other forms of sunless indoor agriculture. There are plenty of arguments on both sides of the spectrum on the subject, and there would be a lot to say about the plant science side as well.
Nevertheless, an approach that deals with the energy challenge from multiple angles is key, and we are aware and confident in that regard. We are looking forward to letting growers and communities take advantage of this new technology.