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(Created page with "thumb Vertical farming is the idea that food could be grown in tall towers with multiple floors, which is supposed to save space and use less land (thus saving more of the environment), but on close examination we see that it doesn't. ==Not a solution to feed the world== ===Powering the grow lights=== Natural sunlight is proportional to land{{x|Sure, technically you could argue that a tall building captures more sun than the land...")
 
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[[File:vertical-farm-1.jpg|thumb]]
[[File:vertical-farm-1.jpg|thumb]]
Vertical farming is the idea that [[food]] could be grown in tall towers with multiple floors, which is supposed to save space and use less [[land]] (thus saving more of the environment), but on close examination we see that it doesn't.
Vertical farming is the idea that [[food]] could be grown in tall towers with multiple floors, which is supposed to save space and use less [[land]] - thus saving more of the environment - but on close examination we see that it doesn't.


==Not a solution to feed the world==
==Not a solution to feed the world==
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{{dp
{{dp
|photosynthesis.spectrum_of_sun
|sunlight.visible_fraction
|
|43%
|How much of the sun's energy spectrum can plants use for photosynthesis
|How much of the sun's energy is in the visible part of the frequency spectrum
|By factoring this in, we're being very charitable to vertical farming, by assuming the LED lights (unlike sunlight) are entirely frequencies of light that plants use.
|[https://sos.noaa.gov/catalog/datasets/climatebits-solar-radiation/ ClimateBits: Solar Radiation - Science On a Sphere - NOAA]
}}
{{dp
|sunlight.photosynthesis_fraction
|sunlight.visible_fraction
|How much of the sun's energy is in the "photosynthesis-friendly" part of the frequency spectrum
|We factor this into the equation because we assume that grow-lights are targeted at the frequencies that plants can use most efficiently for photosynthesis.<br />
<br />Due to lack of data, we have to assume this is roughly equal to the 'visible light' fraction of sunlight.
<br />Plants may somewhat make use of infrared as well, but this is offset by their lower utilization of green light (which isn't ''that much'' lower (according to [http://www.esalq.usp.br/lepse/imgs/conteudo_thumb/Which-regions-of-the-electromagnetic-spectrum-do-plants-use-to-drive-photosynthesis.pdf this source]) - as long as the plant has enough leaves, it will still ultimately absorb most of the green light it receives).
}}
{{dp
|<nowiki>crop_land</nowiki>
|<nowiki>15000000 km^2</nowiki>
|<nowiki>Agricultural land used for growing crops - global total</nowiki>
|<nowiki>https://ourworldindata.org/land-use</nowiki>
}}
{{dp
|<nowiki>sunlight_average</nowiki>
|<nowiki>200 watts per m^2</nowiki>
|<nowiki>Solar irradiance, averaged over a whole year INCLUDING nights, cloudy days, etc.</nowiki>
|<nowiki>Note: This varies by region.</nowiki><br /><nowiki>
https://www.newport.com/t/introduction-to-solar-radiation</nowiki><br /><nowiki>
http://www.ftexploring.com/solar-energy/insolation.htm</nowiki>
}}
{{dp
|<nowiki>solar_panel.efficiency</nowiki>
|<nowiki>17%</nowiki>
|<nowiki>Efficiency of an average solar panel</nowiki>
|<nowiki>Some solar panels are more efficient than this, but they tend to be expensive and contain more rare metals.</nowiki>
}}
{{dp
|<nowiki>led.efficiency</nowiki>
|<nowiki>58%</nowiki>
|<nowiki>Energy-efficiency of a typical LED light</nowiki>
|<nowiki>Kusuma, P., Pattison, P.M. & Bugbee, B. From physics to fixtures to food: current and potential LED efficacy. Hortic Res 7, 56 (2020). https://doi.org/10.1038/s41438-020-0283-7</nowiki><br /><nowiki>
https://www.nature.com/articles/s41438-020-0283-7</nowiki><br /><nowiki>
</nowiki><br /><nowiki>
"Blue LEDs are now 93% efficient, phosphor-converted “whites” are 76% efficient, and reds are 81% efficient when run at the near-optimal conditions of 100 mA mm−2 and a junction temperature of 25 °C."</nowiki><br /><nowiki>
...but then...</nowiki><br /><nowiki>
"Typical fixture efficacy</nowiki><br /><nowiki>
Using more typical parameters:</nowiki><br /><nowiki>
1. Drive current achieves 90% of the reported LED efficacy.</nowiki><br /><nowiki>
2. Temperature management achieves 90% of the reported LED efficacy (at 25 °C).</nowiki><br /><nowiki>
3. The LED driver is 90% efficient.</nowiki><br /><nowiki>
4. Protected LEDs in the fixture achieve 92% optical efficiency.</nowiki><br /><nowiki>
The resulting fixture efficacy would be 0.90 × 0.90 × 0.90 × 0.90 = 67% of the reported efficacy of the LEDs."</nowiki><br /><nowiki>
</nowiki><br /><nowiki>
I decided to average 'ideal' red & blue efficiencies, and then multiply by the 'real world' stuff. Result: 58%</nowiki>
}}
{{dp
|<nowiki>energy.tfc</nowiki>
|<nowiki>9937.70 Mtoe/year</nowiki>
|<nowiki>Global energy usage - total final consumption (TFC)</nowiki>
|<nowiki>Includes: fuel (80.7%) + electricity (19.3%) AFTER it is generated.</nowiki><br /><nowiki>
</nowiki><br /><nowiki>
Does not include the fuel used in generating electricity. See [energy.tes] for that.</nowiki><br /><nowiki>
</nowiki><br /><nowiki>
Citation: "Key World Energy Statistics 2020" IEA</nowiki><br /><nowiki>
- Page 47 - Simplified energy balance table - World energy balance, 2018</nowiki>
}}
}}
{{calc
{{calc
|crop_land * sunlight_average * solar_panel.efficiency * led.efficiency / photosynthesis.spectrum_of_sun
|crop_land * sunlight_average * sunlight.photosynthesis_fraction / led.efficiency
|energy.tfc
|energy.tfc
}}
}}


In other words, we would need _ times more energy than the world currently consumes!
In other words, we would need '''168 times''' more energy than the world currently consumes!


Since most energy currently comes from fossil fuels, this would be disastrous for the environment.
Since most energy currently comes from fossil fuels, this would be disastrous for the environment.


=====But what if the energy came from renewables?=====
=====But what if the energy came from renewables?=====
We already have a [[energy#Limits to other energy sources|hard enough time scaling up renewables]] - but let's imagine it was easy. Still, vertical farms would defeat their entire purpose: They wouldn't save land.
We already have a [[energy#Limits to other energy sources|hard enough time scaling up renewables]] - but let's imagine it was easy. Still, vertical farms would defeat their entire purpose: They '''wouldn't save land.'''


<!-- The amount of land needed for [[solar]] panels would vastly outweigh the amount of crop land saved. -->
<!-- The amount of land needed for [[solar]] panels would vastly outweigh the amount of crop land saved. -->
{{calc
{{calc
|photosynthesis.spectrum_of_sun / led.efficiency / solar_panel.efficiency
|sunlight.photosynthesis_fraction / led.efficiency / solar_panel.efficiency
|
|
}}
}}
In other words, to grow an acre worth of plants{{x|and I'm not talking about the footprint of the building. By "grow an acre worth of plants", I mean for example having a 1/8 acre building with 8 storeys}}, you would need over _ acres of solar panels!
In other words, to grow an acre worth of plants{{x|and I'm not talking about the footprint of the building. By "grow an acre worth of plants", I mean for example having a 1/8 acre building with 8 storeys}}, you would need over '''4''' acres of solar panels!


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