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Comment by jdietrich | Hacker News Reader

Farmland isn't just a place to put some plants while they grow. A farm is a giant solar power facility, one that converts solar energy, carbon dioxide and water into carbohydrate. Monbiot doesn't stress the point enough - it's all about light.

When we say that we have a shortage of farmland, what we mean in practical terms is that we have a shortage of flat areas with good drainage to function as solar collectors. Going vertical doesn't increase the amount of light you can gather, so it doesn't increase the amount of food you can produce.

Vertical farming is only remotely feasible if we see the cost of energy fall ten-thousand fold. That's only likely if we crack nuclear fusion. Of course, such an abundance of energy would render any worries about food production moot.

Unfortunately, we appear to live in a world where supposedly educated adults are unfamiliar with such advanced scientific concepts as photosynthesis.

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When we say that we have a shortage of farmland, what we mean in practical terms is that we have a shortage of flat areas with good drainage to function as solar collectors.

Well, it is a bit more complicated than that. A huge problem in agriculture is the depletion of soil. For example, over time intensively irrigated soil tends to become contaminated with excess salts which destroys its fertility, yet still leaves it as flat, well-drained, and sunny as ever.

I completely agree, however, that the first-order consideration in growing plants is the availability of light.

Of course it's a bit more complicated, but we again come back to energy - soil improvement is essentially an energy input, be it oil-derived fertilisers, organic matter or fallow.

Aquaponics actually gets you pretty close to a closed-cycle ecosystem.

I read the other day about a family of four which grows all its food from an old in-ground swimming pool in their back yard. They put a greenhouse covering over it, filled a couple little ponds inside with tilapia, added vegetables and chickens. After one year they're extracting all the veggies, fish, and eggs they can eat.

Potatoes give about 6 million food calories per acre. (Wheat and most other plants yield less.) Assuming 8,000 calories per day, the family would need at least 1/2 an acre to survive. An Olympic-sized pool is 0.3 acres, so it's a bit beyond the edge of possible. I doubt their pool was that large, and since most other vegetables, to say nothing of fish and chickens, are less efficient food sources, I suspect they get a good fraction of their calories from elsewhere.

To check myself, this seems like a good thread: http://urbanevolution.org/thinktank/viewtopic.php?f=6&t=... . The strongest advocates for intensive and efficient agriculture say "less than half an acre (~ 0.2 hectares) can support a family of four" and "a vegan diet can meet calorie and protein needs from just 300 square metres using mainly potatoes. A more varied diet with plenty of fruit and vegetables, grains and legumes would take about 700 square metres." Say it's 2500 square meters for a family of 4 = 0.6 acres.

So, no, I don't think they get most of their food from the area of their backyard pool.

Your arguments are compelling but I'm not yet convinced it's impossible. One of their main crops is duckweed, an aquatic plant that grows very rapidly, though I haven't found specific numbers. Duckweed feeds their tilapia, which also breed and grow quickly. They say they extract eight tilapia every day, along with eggs and vegetables. Their chickens eat a lot of insects, a reserve of calories neglected by your potato field.

Their website is at http://gardenpool.org. It doesn't yet have as much detail as I'd like but hopefully more is forthcoming.

Here's someone else who harvests 6000 pounds of food per year from a tenth of an acre, with 350 different crops: http://urbanhomestead.org/urban-homestead

It seems to me that exploiting a lot of ecological niches might be more productive than monoculture. You can't extract more calories than sunlight provides (not counting insects from surrounding areas), but maybe sunlight is not the most limiting factor.

Vegetables have about 100 calories per pound. (See http://www.beyondveg.com/billings-t/cal-par/calorie-paradox1... ). You can get higher by picking the right plants so let's say 300 calories per pound. At 6,000 pounds per year that's 1.8 million calories. At 2500 calories per person per day that's enough for two people for a year.

For a family of 4 that's at least twice the area, or 0.2 acres needed, and likely more as the web page says their max was 6,000 pounds. It also doesn't say which plant those were, nor what the moisture content was. After all, if a watermelon is 15 pounds then that's 400 watermelons, and each one gets 11 sq. ft, but most of that is water weight.

And as for the gardenpool, as best as I could tell, duckweed is 6 times more productive than corn, and tilapia at best consume 1.5 lbs to produce 1 lb of weight. Not all that weight will be edible, and corn isn't as productive as potatoes, but the numbers work out that it might be 2-3 times more productive than my potato number for the same area.

However, I think the numbers for duckweed yield are in pig waste water or something else with a lot of nutrients in it, and everything is here is under best conditions, which also means a lot of care taking. Which potatoes don't need.

BTW, the web site says 8 eggs per day, not 8 fish. It looks like it takes 5 months for tilapia to mature to eating weight, and 8 fish a day would mean stocking 1,200 fish at a time. What they don't say is, is duckweed the only food source for the fish or are they adding other feed?

They also mentioned that they need a swamp cooler to keep the temperature in check. Assuming that's 200W average over 24 hours, that another 4,000 kcal ("food calories"), or almost enough for two people. They get that off the grid, but if they needed to provide their own fuel source for heating and cooling (tilapia can't handle cold water) then that's another factor in the energy equation. Potatoes are hardy in northern, cool climates.

Oops, yep, 8 eggs. They say "unlimited" tilapia but I imagine the limit there is how much of it they're willing to eat!

The aquaculture idea is that wastes from the fish, and in this case the chickens, puts lots of plant nutrients in the water. Maybe not as much as pig waste water, I don't know.

200W doesn't sound like that much power...solar panels on the roof, where you can't grow crops anyway, and/or wind turbines could provide that. Those are local resources you can't otherwise use to produce food, sort of like exploiting another ecological niche.

Potatoes are certainly convenient and productive, though I wouldn't want to subsist on them alone. Some people are growing them in tall boxes for easy extraction, and I was startled to see how much they claimed to produce.

Re: 6000 lbs/year, that must be why they sell their stuff instead of eating it.

This has been very interesting.

Which leads me to ask - what do the chickens eat?

I see that gardenpool gives a timeline on the side. They didn't stock the pool with tilapia until May 2010. Their page at http://gardenpool.org/?page_id=242 says "A tilapia matures from egg to harvest size (1.5 lbs) in only 6-9 months."

It hasn't been long enough for the new spawn to reach edible size. How can they say "unlimited" when they don't have the experience to know if it's stable? I suspect they are being overly optimistic.

Regarding 200W - I don't know what their swamp cooler needs, and they say they installed solar power. I picked 200W because that looks like a common size for portable home devices.

Looking now, I think solar cells are about 20 sq ft for 200 W. Since they need to work during the night as well (though not as much), call it 40 sq. ft of otherwise unused space. I was thinking that that would go into the area calculation, but as that's about 0.1% of an acre, it's not a big contribution.

And yes, I've found it interesting as well.

In part they eat bugs but I wouldn't think that would be sufficient in such a contained area. It's not like they're set up in a swamp.

Polyface Farms seems to feed their egg layers entirely on bugs, cattle droppings, and maybe a bit of greenery:

"The Eggmobile is a 12 ft. X 20 ft. portable henhouse and the laying hens free range from it, eating bugs and scratching through cattle droppings to sanitize the pasture just like birds in nature that always follow herbivores as biological cleansers." http://www.polyfacefarms.com/products.aspx

Of course that's a much larger operation. They keep moving, so cleaned areas can recover. They've got forested areas nearby which play a part in the ecosystem. They claim higher overall productivity than conventional farms producing the same stuff, but nothing extreme.

The peril of aquaculture is sometimes everything suddenly goes haywire and dies. Eventually the kinks get worked out and it's pretty stable, but the pool people may well have surprises in store.

I do love the idea of a little self-contained ecosystem, almost like a space colony. I hope people do a lot more experiments along these lines.

One idea from Marshall Savage's Millennial Project is edible algae, like spirulina. According to him it's absurdly productive in a small space, and the numbers from the "algae for fuel" people seem to bear that out. A turnkey system for producing it safely would be pretty neat, but I haven't been able to find much information. Everybody's talking biofuel. I wouldn't exactly want to subsist on algae but it could be great as a supplement in flour or stews, as fish feed, etc. How healthy it would be to eat large quantities seems to be a little uncertain, but supposedly it has a long history as a food.

If power isn't a concern (which it would be for the original topic of this thread) then the space programs have done research into small self-contained ecosystems, as you mentioned. I haven't looked them up before, but I see now that BIOS 3 (early 1970s Russia) had a 3-man crew for 180 days, with only some import of external food and air. It did need 400 kW of power, which if my 10W/sq.ft solar power is right means about 1 acre of solar panels. More if there's darkness.

Some other links: http://en.wikipedia.org/wiki/Controlled_Ecological_Life_Supp... and http://settlement.arc.nasa.gov/designer/regen.html . The latter says "The present crop growth chamber ... is about 12 m^2. The energy requirement of the system is about 15 kw of which 13 kw ... The present system provides complete nutritional needs of 1 person (a vegeterian)."

That power, at retail levels of about $0.10/kW hr, costs $36 per day. $18 if you can be diurnal. Sunlight puts out about 1kw/sq.m so that power is mostly going into replacing sunlight.

Which means, if that link is correct, that 12 sq.m is enough for a single person. But I'm at the end of my stamina for researching this topic.

Cheers!

I'll cap off my contribution with this guy who's eating nothing for the next two months but potatoes. Twenty every day. He's the Executive Director of the Washington State Potato Commission. http://20potatoesaday.com/

It's been fun!

"Going vertical doesn't increase the amount of light you can gather"

I am not sure that is true everywhere on the planet. If you get closer to the poles, the sun will, on average, stand lower above the horizon. That is why, in winter in Moscow, people sun while standing up.

Also, in summers close to the equator, getting less light per square meter may be a good thing, depending on what you are trying to produce.

I don't buy his argument that the cost of artificial lighting alone would be ~100x the current market value of the produce, especially when you use the solar collector analogy for farmland. Some quick googleing puts wheat in the 1% efficient range or less when converting light into carbohyrates. I have no idea where to find the exact number but it's not efficient at all. In a controlled environment the remaining 99% of the energy could be recycled. On top of that his calculation was based on the average sunlight for a day in England but that's probably more than wheat needs to grow optimally. I would love to see a more realistic calculation of this number.

That said I don't think vertical farms will ever be practical.

"In a controlled environment the remaining 99% of the energy could be recycled."

Thus violating the second law of thermodynamics. Do tell how we can recycle that energy, turning waste heat back into light, since that would also make solar cells more efficient, increase farming capabilities in cloudy/cold regions, and reduce our dependency on petroleum by making biofuels easier to grow.

For a starting point of the calculations, see http://en.wikipedia.org/wiki/Photosynthetic_efficiency .

Obviously you just put buckets under the plants to catch all of the light that falls through, and you have a machine that picks up the buckets and dumps them out over the top of the plants again. I think it'll help to paint the inside of the buckets white... or maybe black; not sure. Oh, and the bucket-dumping machine should be solar powered.

</sarcasm>

Oh, of course - Maxwell buckets will do the trick! Just need little robots with mirrors on each one to let light in and not let it out.

Put mirrors on the walls and ceiling and put reflective particles over the soil. That should let more light eventually end up on the plants.

You'll need mirrors which don't block the light. One-way mirrors are only half-silvered, which means they'll block more light than they'll recover. What you'll have to do is figure on something on the other side of the plants than the light source.

Take a look at the link to "Photosynthetic efficiency". Only about 13% of the light ("incomplete absorption") could be reused this way. Most of the rest of the energy is turned into heat.

Now, it is possible to be more efficient through layers. Take a jungle, where most of the energy is absorbed by the top level while lower-level plants make use of what energy comes through, eg, more efficient in dim light or better use of other parts of the spectrum.

You will be able to get some more efficiency by doing this, but it's going to be expensive, and nothing like "99%".

I think you're imagining something else. Here's what I mean:

   _________   Mirrored ceiling
   L  L  L     lights
  |        |   Mirrored walls
  |        |   
  | P P P     Plants
  | M M M     Mirrored surface with holes for plants
  | S S S     Soil

So any light that misses a leaf, reflects off a leaf or goes through a leaf will simply bounce around the room until it hits a plant.

I'm sure mirrors still convert some light to heat, but it seems like it would be a big improvement.

I see - you are talking about artificial lighting of the plants, while I was thinking of sunlight. With sunlight the ceilings will block the light going to the neighboring plants.

What you are saying seems to make sense for some circumstances, though I earlier pointed out there's isn't that much light which is going to waste which could be used for photosynthesis. I looked around for "mirror garden", on the thought that home gardens would be the most likely candidate for using mirrors, but the only mentions there were for decorative purposes.

I suspect there's a strong economic reason which makes it not practicable. Perhaps it's that a greenhouse with glass is more efficient because it makes better use of free natural light.

Maybe when my kid is older we will do this as ascience experiment. See if a "mirror garden" plant can grow with less light and how much less. Expect a blog post in ten years..

Hogs and chickens don't run on sunshine.

They stack pretty well.

And in urban areas the pipes are already in place.

Agriculture is messier than we all like to pretend.

I don't know if Despommier suggests this, but mightn't his idea make more sense if the towers were used for growing things like mushrooms?

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