4 ms·

Anything under an existing farm + 95% the energy it takes to treat/move the water is a win I would have thought.

Symmetry 10y ago
It would be but they'll be lucky to only use 100 times as much electrical/mechanical energy as a traditional far. If you include sunlight they'll use less energy than a traditional farm but that comes for free at no environmental cost.
DennisP 10y ago
You're forgetting the vast energy provided free to a regular farm by sunlight. Average daily solar energy falling on each square meter of the Earth is 6 kWh [1]. You're right that irrigation is a significant energy cost: for example [2], irrigating 135 acres in Nebraska will use 50,000 kWh over the course of one season. But an acre has 4046 square meters. Based on the global average, that same 135 acres will collect 3,277,260 kWh of solar energy over the course of a single day. That's the energy an indoor farm has to consume from power stations, just for lighting. Optimizing spectrum can cut the lighting energy in half, and other measures like packing plants more tightly can help, but even if you reduce it by 90% it still dwarfs the energy expense of regular farms. It may be a reasonable expense for particular crops that don't want full sun anyway, but energy usage isn't likely to ever be an advantage for indoor farms. An acceptable disadvantage in certain cases, maybe. [1] https://en.wikipedia.org/wiki/Solar_irradiance#Earth https://en.wikipedia.org/wiki/Solar_irradiance#Earth [2] http://www.loup.com/docs/energysvc/energywise/EW-Tip-Irrigation.pdf http://www.loup.com/docs/energysvc/energywise/EW-Tip-Irrigat...
- mistermann 10y ago
  > That's the energy an indoor farm has to consume from power stations, just for lighting. To reproduce natural sunlight, but is that level actually needed for adequate plant growth?
  - DennisP 10y ago
    No, which is why I included the sentences after that. It's a lot of energy even if it reduced the lighting requirement by 99%. It might be feasible for certain crops, but it's still going to be much more energy than an outdoor farm uses. Seems to me greenhouses are a better way to go: free lighting, while still using less water and chemicals.
    - tomp 10y ago
      But if you reduce the energy by 99%, you can reduce the size of the farm by 97%, cover it with solar cells (at 30% efficiency), that's still a big win!
- EGreg 10y ago
  Why can't a farm capture natural sunlight and redistribute it? Even a low-tech method like mirrors ought to do it. As long as all the wavelengths that the plants need are reflected by the mirror. Why not?
  - DennisP 10y ago
    To collect as much sunlight as the regular farm, you'll have to spread mirrors over the same area. So why not save all that money and plant the crops directly on the ground? If you want them indoors, to save water and chemicals, use greenhouses; you can use cheap plastic sheeting instead of expensive mirrors.
    - EGreg 10y ago
      The sunlight of a regular farm is largely wasted. The plants are spread apart because of their moisture and soil needs and most of ths sunlight hits dirt. Now, there may be bacteria in the regolith which we don't know about, and we'll find out why they are neededin certain proportions... but even so, we can be collecting dirt from all over the place for the next crop... It seems that sunlight hitting plants that are "closer together" and stacked vertically will be far more efficient. Besides, some plants don't even need the full sunlight to grow!
      - deleted 10y ago
        [deleted]
      - fencepost 10y ago
        Actually on most farms there's probably not a bit of dirt to be seen under the crop being raised, at least not for bulk crops like corn and soybeans and once the growing season is well under way. Any dirt not covered in the desired crop isn't bare and absorbing sunlight, it's space that's probably growing weeds or other undesirable plants (e.g. soybeans during a corn year for places that rotate their crops).
- Animats 10y ago
  "same 135 acres will collect 3,277,260 kWh of solar energy over the course of a single day." 3 terawatt-hours? No, something is wrong there. Peak solar energy at the earth's surface is about 1 KW per square meter.[1] Over 24 hours, you average maybe a third of peak. 135 acres is 54.5 hectares, or 545,000 square meters; about half a square kilometer. So we get about 4360 kWh over a day. That's raw sunlight; solar cells are maybe 15-20% efficient in conversion. (Corn plants are about 1.5% efficient in conversion) [1] https://livingonsolarpower.wordpress.com/2013/03/23/basic-solar-energy-math/ https://livingonsolarpower.wordpress.com/2013/03/23/basic-so...

It would be but they'll be lucky to only use 100 times as much electrical/mechanical energy as a traditional far. If you include sunlight they'll use less energy than a traditional farm but that comes for free at no environmental cost.

DennisP 10y ago

You're forgetting the vast energy provided free to a regular farm by sunlight. Average daily solar energy falling on each square meter of the Earth is 6 kWh [1]. You're right that irrigation is a significant energy cost: for example [2], irrigating 135 acres in Nebraska will use 50,000 kWh over the course of one season. But an acre has 4046 square meters. Based on the global average, that same 135 acres will collect 3,277,260 kWh of solar energy over the course of a single day. That's the energy an indoor farm has to consume from power stations, just for lighting. Optimizing spectrum can cut the lighting energy in half, and other measures like packing plants more tightly can help, but even if you reduce it by 90% it still dwarfs the energy expense of regular farms. It may be a reasonable expense for particular crops that don't want full sun anyway, but energy usage isn't likely to ever be an advantage for indoor farms. An acceptable disadvantage in certain cases, maybe. [1] https://en.wikipedia.org/wiki/Solar_irradiance#Earth https://en.wikipedia.org/wiki/Solar_irradiance#Earth [2] http://www.loup.com/docs/energysvc/energywise/EW-Tip-Irrigation.pdf http://www.loup.com/docs/energysvc/energywise/EW-Tip-Irrigat...

mistermann 10y ago
> That's the energy an indoor farm has to consume from power stations, just for lighting. To reproduce natural sunlight, but is that level actually needed for adequate plant growth?
- DennisP 10y ago
  No, which is why I included the sentences after that. It's a lot of energy even if it reduced the lighting requirement by 99%. It might be feasible for certain crops, but it's still going to be much more energy than an outdoor farm uses. Seems to me greenhouses are a better way to go: free lighting, while still using less water and chemicals.
  - tomp 10y ago
    But if you reduce the energy by 99%, you can reduce the size of the farm by 97%, cover it with solar cells (at 30% efficiency), that's still a big win!
EGreg 10y ago
Why can't a farm capture natural sunlight and redistribute it? Even a low-tech method like mirrors ought to do it. As long as all the wavelengths that the plants need are reflected by the mirror. Why not?
- DennisP 10y ago
  To collect as much sunlight as the regular farm, you'll have to spread mirrors over the same area. So why not save all that money and plant the crops directly on the ground? If you want them indoors, to save water and chemicals, use greenhouses; you can use cheap plastic sheeting instead of expensive mirrors.
  - EGreg 10y ago
    The sunlight of a regular farm is largely wasted. The plants are spread apart because of their moisture and soil needs and most of ths sunlight hits dirt. Now, there may be bacteria in the regolith which we don't know about, and we'll find out why they are neededin certain proportions... but even so, we can be collecting dirt from all over the place for the next crop... It seems that sunlight hitting plants that are "closer together" and stacked vertically will be far more efficient. Besides, some plants don't even need the full sunlight to grow!
    - deleted 10y ago
      [deleted]
    - fencepost 10y ago
      Actually on most farms there's probably not a bit of dirt to be seen under the crop being raised, at least not for bulk crops like corn and soybeans and once the growing season is well under way. Any dirt not covered in the desired crop isn't bare and absorbing sunlight, it's space that's probably growing weeds or other undesirable plants (e.g. soybeans during a corn year for places that rotate their crops).
Animats 10y ago
"same 135 acres will collect 3,277,260 kWh of solar energy over the course of a single day." 3 terawatt-hours? No, something is wrong there. Peak solar energy at the earth's surface is about 1 KW per square meter.[1] Over 24 hours, you average maybe a third of peak. 135 acres is 54.5 hectares, or 545,000 square meters; about half a square kilometer. So we get about 4360 kWh over a day. That's raw sunlight; solar cells are maybe 15-20% efficient in conversion. (Corn plants are about 1.5% efficient in conversion) [1] https://livingonsolarpower.wordpress.com/2013/03/23/basic-solar-energy-math/ https://livingonsolarpower.wordpress.com/2013/03/23/basic-so...