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Engineering | Center for Negative Carbon Emissions (CNCE)

Recently, the Washington Post had an captivating article on indoor farming.1  Improvements in lighting efficiency make controlled environment agriculture economic.  LED lights not only deliver photons, they deliver the right color at the right time, shaping and optimizing ag-products in ways that were impossible before. The opportunities for higher productivity and better quality seem limitless.  This advance connects to our work, as air capture technology could pump ambient carbon dioxide into controlled environments and integrate seamlessly with temperature and moisture control. Modulating carbon dioxide concentrations also affects productivity and quality of the harvest. 

So how does the old curmudgeon Jevons get into this upbeat story?  Jevons, a nineteenth century British economist, is famous for noting that improving efficiency in resource use can precipitate higher use.  He applied this concept to coal, but it also applies to electricity.  LED lights represent a vast increase in efficiency. As is often the case, this advance was driven by necessity.  After the Fukushima disaster, Japanese firms faced a severe shortage of electricity.  To keep the light on in Tokyo’s famous Ginza Shopping District, the industry needed to move from neon lights to LEDs. 

Meanwhile, controlled environment agriculture was not going anywhere. The cost of electricity was just too high to pay for artificial light.  LEDs changed all of that.  The investment is becoming even more valuable as we begin to understand how to best take advantage of artificial light and help feed a world with ten billion people. However, the energy cost is vast. 

Photosynthesis can convert about 1% of the light energy into biomass calories.  LED light tailored to the plant’s needs maybe a little better, but it is highly unlikely that more than 1% of the primary energy going into the production of electricity will show up as caloric value in the produced biomass.  Because not all plant material ends up directly on the table, some stays in field, some produces dairy products, or meat before it ends up on the table, it takes many calories of biomass production for one food calorie.  Therefore, in controlled environment agriculture it will likely take several hundred calories of primary energy to produce 1 food calorie.  One person’s metabolic energy intake of 2000 kcal/day translates into 100 Watt. This is 1% of our per capita primary energy consumption.  Feeding one person with plants grown under artificial light, would require a multiple of the energy this person is consuming today.   

Could it be done? Is it worth it?  Perhaps. Harvesting more and more food from closed environments, eliminating the uncertainties of weather and reducing the vast footprint of food production, could be very worthwhile.  But it cannot be done in a world that aims to mitigate other problems, including climate change, by drastically reducing energy consumption.  Energy is useful and valuable. Rather than discouraging its use, we should make it sustainable. 

1 Growing the future, High-tech farmers are using LED lights in ways that seem to border on science fiction By Adrian Higgins in Cincinnati, Washington Post, Nov. 6, 2018