High-rise farms?

Some people think that the future of farming will contain high-rise farms; farms in multi-story urban buildings, either custom built or added to existing skyscrapers as a retrofit. I personally think they are too inefficient to be part of the future of farming and simply represent a subsidy dumpster, but I'd be glad to hear other's thoughts on that.

Let's confine this discussion to structures over three stories, and exclude rooftop gardening, which is a different matter.

The main reason I think they are inefficient has to do with lighting. As any gardener knows, even a few feet from a sunny window, plants tend to droop. They need a lot more light then indoor areas allow for. So such a structure would have to be quite thin, or would have to depend on florescent lights. To make these light sustainable, they would have to be run by solar panels; these panels would however take up space somewhere, while losing some energy to transmission and conversion. Thus they would have a larger foot print then the area of plants they would sustain. Such a building would shade other areas, which could have been used for growing; they could not be next to one another, or they would shade one another.

There seem, however, to be other inefficiencies. The taller these buildings get, the harder they are to heat and cool, and the more energy is spend pumping water up into them.

Even as a retrofit, I think the yields are likely to be low without florescent lighting.

They would probably be too expensive for producing staple crops, but would instead probably produce fruits and vegetables. But most cities have enough open land and rooftops to grow all their fruits and veggies; this being so, what purpose would the high rise farm fulfill?

Some say that they could recycle wastes from their own building or other buildings nearby, which is true. But I think this could also be done at ground level, with less expense.

Some also say that they would be great demonstration projects. But if the demonstration project is fundamentally unsound, what does it justify? In that case it would be greenwashing.

Purpose built structures have a huge energy footprint for construction.

Here is an article discussing some of these problems, with hard figures.

https://www.alternet.org/story/146686/why_planting_farms_in_skyscrapers_won%27t_solve_our_food_problems

Can anyone justify these high-rise farms?

To clarify, I'm not skeptical of the value of cities, or of urban agriculture, just of this particular form of urban agriculture.

Personally, I think that if it's too energy intensive, it's been designed wrong, especially if we're discussing retrofits.

If we're discussing a more permacultural idea like mixed-use high rise buildings that focus on food production and addressing other community needs, like organic waste disposal, community housing, and energy production, I think the arcology model is right up our alley. I have gone into it in detail in a post in Gilbert's thread on the place of skyscrapers in a permacultural city. The link is below.

https://permies.com/t/72275/Skyscrapers-place-permaculture-city

If we're just talking about single-purpose structures, I don't know if high-rise farms make sense. As you point out in several places, they create shade. Why tall structures instead of, say, geodesic ones?

For me, I used to just assume that high-rise farms would be part of the picture. We live in tall buildings to maximize the number of people per area of land mass for efficient delivery of services. Wouldn't it work for urban farming too? And it might, but it might not be the best idea. Thank you, Gilbert, for this opportunity to discuss these issues in detail.

-CK

Maybe thinking about the towers as having multiple zones migt help.
Not enough sun? What grows in the shade? What grows in the dark?
Can we build the tower as a hollow cylinder?
As a curvy wall?
Can it be a shade structure for other buildings?
Can it use greywater?
Blackwater?
Climate control im such a tower shoud be passive,or at least aimed the needs of plants and animals, not people.
Animals fed from city dwellers waste is perhaps a better use of this space.
Not the waste of individual households as much as that of resturaunts, hospitals,grocery stores, brewerys, food distributers, etc.
Cardboard and pallets into mycilium, leftovers into eggs,blackwater into methane, greywater into evaporative cooling, etc.
The more i think about, it, cities are like  human being factory farms.
The sunlight and other resources that a plant needs are already in use, raising humans.
Rats, roaches and other humans already make a living off of the waste of human cities.
We are better off trying to turn the waste from that enterprise into gains than  grow plants inside a factory.
Unless we can grow an desirable edible plant off of humanure,in the dark.
That would be awesome.

Maybe thinking about the towers as having multiple zones migt help.
Not enough sun? What grows in the shade? What grows in the dark?
Can we build the tower as a hollow cylinder?
As a curvy wall?
Can it be a shade structure for other buildings?
Can it use greywater?
Blackwater?
Climate control im such a tower shoud be passive,or at least aimed the needs of plants and animals, not people.
Animals fed from city dwellers waste is perhaps a better use of this space.
Not the waste of individual households as much as that of resturaunts, hospitals,grocery stores, brewerys, food distributers, etc.
Cardboard and pallets into mycilium, leftovers into eggs,blackwater into methane, greywater into evaporative cooling, etc.
The more i think about, it, cities are like  human being factory farms.
The sunlight and other resources that a plant needs are already in use, raising humans.
Rats, roaches and other humans already make a living off of the waste of human cities.
We are better off trying to turn the waste from that enterprise into gains than  grow plants inside a factory.
Unless we can grow an desirable edible plant off of humanure,in the dark.
That would be awesome.

Hi William,

I agree that a vertical farm could be built in many shapes, some much more efficient then others. But I doubt any would get over the fundamental constraints solar access, and in any case this requires purpose built structures, not retrofits; as I pointed out above, I don't see these as particularly sensible.

And I agree that animals and decomposers would be a better usage of the space; they'd require a much less intensive remodel. That is a very interesting list of potential uses.

Hi Chris,

I agree that we could stack lots of functions into existing buildings, and should do so; William provides lots of such ideas above.

As a young gardener, I struggled to start tomato plants a foot away from a fairly sunny window; my failures there make me quite skeptical of productive plant growing being one of these stacked functions. Once I built a heated frame in my yard with a clear, plastic cover and a heat mat, I had much more success; it is easier to provide heat then light.  In any case, the sun access could be used for so many other things; water heating, natural lighting of office or bedroom space, electricity generation, etc.

Also, if plants are wanted, there are many beautiful plants that would purify the air and water, while not needing as much light as grains or vegetables; they are mostly sub-canopy tropicals. But I'm not sure what kind of yields could be got from them, and any yield would be low due to their low energy capture. They do still need some light, of course.

Of course, rooftop gardens are a great idea, especially with a greenhouse over them; they'd capture waste heat and provide a beautiful place to sit.

So I guess if farm means the raising of non-photosythic creatures to recycle wastes, I'm all for it, with the caveat that I'm still not convinced of the utility of buildings over ten stories or so, as posted in my companion thread. https://permies.com/t/72275/Skyscrapers-place-permaculture-city

Here are two articles on vertical farming:

https://medium.com/bright-agrotech/9-reasons-why-vertical-farms-fail-244deaecd770

https://www.fastcompany.com/40420610/has-this-silicon-valley-startup-finally-nailed-the-indoor-farming-model

It is hard to say anything about the future of vertical farming. There have been a number of failures with vertical farms
going bankrupt...but the new companies springing up to take their place claim that they have learned from the failures.

As far as retrofitting existing skyscrapers, I think that that might be a real can of worms that should probably not be opened.  Skyscrapers are feats of engineering, and to try to put soil and water on the sunny side is going to completely unbalance the situation, besides the fact that they floors are not necessarily meant to take all that extra weight.  I'm no engineer, but that's my thoughts on the retrofit idea.

Now for purpose built structures, I would think that the way to go for high rise farms is to build a building that is long on the North/South axis, rather than (and perhaps counter-intuitively) the East/West axis of say a greenhouse.  The design would require that the building steps up from the bottom layer, with each floor being slightly smaller than the next.

Lets say it was a university building.  The first few floors could be classrooms, and as the system of floors gets smaller, they could be dormitories.  Every step on the Sunward side has an outdoor rooftop garden and small courtyard, and a indoor greenhouse space, and lounge areas.  The inner wall of this could contain some windows for passive lighting beyond to the poleward side, where living quarters exist.  These living quarters could also be naturally lit partially from the sides, as the building is narrow on that axis.

The inner wall could be built with a passive water wall, or other aquaculture set up.  worm bins, black soldier fly, and meal worms et cetera which do not need sun could be on the poleward side.    

Interesting articles.

The two questions that I have they didn't cover are: do these farms still save energy when compared to conventional farms when lifecycle costs are factored in? In a few decades at most, all those LEDs or florescent tubes will have to be replaced; and I imagine the other equipment is similar. And, if the city has enough open space and rooftops to grow all the vegetables the city eats (most if not all of them do) why invest in all the LEDs and solar panels? Its really just shifting light around, and losing some on the way, unless they are breaking the laws of thermodynamics.

If electricity consumption keeps going up, our goal of 100% renewable electricity will keep getting farther away. There are already plans to electrify all our transportation and space heating; if we electrify all our vegetable growing as well, we will never get there.

Another interesting point was that even with low wages, labor costs were a problem; they have to try to minimize the number of people they employ.

Hi Roberto; I think that is probably about right; basically rooftop and balcony gardens on a larger scale.

I hadn't even thought about the weight issue in a retrofit; it would probably be considerable. We don't want the leaning towers of Manhattan.

Retro-fitting buildings sounds like an iffy idea--the weight factor alone will cause problems.

Lots of flat-roofed buildings already built that could be converted into city gardens.

Maybe future buildings could be designed like the Waldspirale, located in  Darmstadt, Germany

I completely agree with Gilbert's analysis, it's the same thing I said when I first heard the idea ten years or so ago, and so far nobody's been able to convince me otherwise. Rooftop growing is great, so are pots in windows. A tall building will get more solar radiation overall than its footprint would as flat land (provided there's no other tall buildings around), but that's offset by the light that's not hitting the ground in the shadow of the building. As someone who personally sees a future ahead where energy isn't nearly as cheap as it is now, I can't see agriculture dependent on artificial lighting going very far.

Hi Roberto; I think that is probably about right; basically rooftop and balcony gardens on a larger scale.

 Well, not exactly balcony gardens.  I think of a balcony as being an open structure--basically a platform, usually with a railing or fence surrounding it on three sides, that is roofed by the balcony on the floor above.  What I was thinking was more like a greenhouse on the sunward side of each floor with a rooftop garden in front of the greenhouse on it's sunward side.  Each floor would be stepping up to the poleward side and being smaller than the previous floor below it.  An outdoor water system could possibly cascade as shallow overflow ponds off each floor onto the next one down at one given spot from off of each roof.    

A tall building will get more solar radiation overall than its footprint would as flat land (provided there's no other tall buildings around), but that's offset by the light that's not hitting the ground in the shadow of the building.

 This (directly to the poleward) side is a great place to conserve water in ponds, and have a green space/park for relaxation/ native plants and trees, as well as domesticated plants which can provide food without much sun.  This could also be a place of gray water or black-water processing.  All the water that is not being utilized by the plants in the building itself, and any overflow from larger rain events, can be directed to this water feature and forest area.  This shaded area, particularly right against or very near the building could be a wood waste generated hot water system (urban areas produce a massive amount of woody waste from tree pruning, and dead tree and branch removals.  This might also be a good place for fish and poultry, black soldier fly, mealworms, and worms.    

I personally think they are too inefficient to be part of the future of farming

  this is probably true.
I personally believe in a decentralized strategy for our population.  Rather than urbanization, I think that rural pastoralism, and smaller town restructuring is the answer.  If we are to have any hope of ecological cities, most of the private vehicles would have to be banned, leaving most of the street space (a huge area) for food production.  Train tracks and train tops could be solar panels, giving plenty of charging potential in many sunnier locations, and the trains would take the place of cars and trucks for commuters and for transporting goods.  Everything else can and should be done by chinese wheelbarrow, cart, or bicycle.  As much as I do not like the idea of continuing to build in cities as I do not think that they have a place in long term permaculture, I think that the trend of continued urban growth might be pretty hard to reverse until we build resilient rural and small town models that are enticing enough to be an attractive alternative.   And, since new buildings will be built, it might be a good idea to have some design strategies that might work with as many permacultural ideas as possible, so that urban high-rise architects can benefit from our thoughts.

As someone who personally sees a future ahead where energy isn't nearly as cheap as it is now, I can't see agriculture dependent on artificial lighting going very far.

I agree, but I don't think that artificial lighting is necessary.  Also, as the future progresses, the idea of creating a building solely to grow food, seems like it would likely not be cost effective when made of energy intensive concrete and steel.  How can it be?  That is the biggest argument that I can think of to think that the idea/strategy will eventually peak and crash with no hope of recovery.

Whatever you think currently, it is part of the future. Like it or not. Already we grow perfect veg over vats in warehouses. SOld at a perfect price and called organic. YEa, it is like that. If a useless wall of glass and concrete can be used as green spaces or production of food or just oxygen, we are saving the world in one more step. Most of you do not comprehend cities of 50 million,...100 million. I do as I have inhabited them. So yes, if it can produce something for humans I am all for it.

Our space habitats will prove the point. This argument goes the way of sliding doors.

Remember Star Trek? The sliding doors. Oh all these scientists told us it would never happen here on earth. Too much energy, foolish science fiction stories. Yea, just stupid.

I walk past many many automatic sliding doors all day long.

Our megastructures can and will be the greenhouses of the future. The same BTU's can and are being used double purposed. Spaces in normal weather condition in and outside of the megastructures. Can and MUST be utilized to grow and produce products. If not for the air itself and enjoyment, then for food and creation of jobs. Better mental space and to bring the masses back to the reality.

I drive past and do stuff in such structures. If not in them, then on the grounds. Face it kids. 8 billion hungry people will very very soon be 10 billion. The changes in the weather and our dynamic universe,.....well can be our doom or a pleasant future. Embrace it. Permiculture is the cornerstone of this. THINK! It is part of our future. Like it or not.

Gilbert Fritz wrote:Some people think that the future of farming will contain high-rise farms; farms in multi-story urban buildings, either custom built or added to existing skyscrapers as a retrofit. I personally think they are too inefficient to be part of the future of farming and simply represent a subsidy dumpster, but I'd be glad to hear other's thoughts on that.

Let's confine this discussion to structures over three stories, and exclude rooftop gardening, which is a different matter.

The main reason I think they are inefficient has to do with lighting. As any gardener knows, even a few feet from a sunny window, plants tend to droop. They need a lot more light then indoor areas allow for. So such a structure would have to be quite thin, or would have to depend on florescent lights. To make these light sustainable, they would have to be run by solar panels; these panels would however take up space somewhere, while losing some energy to transmission and conversion. Thus they would have a larger foot print then the area of plants they would sustain. Such a building would shade other areas, which could have been used for growing; they could not be next to one another, or they would shade one another.

There seem, however, to be other inefficiencies. The taller these buildings get, the harder they are to heat and cool, and the more energy is spend pumping water up into them.

Even as a retrofit, I think the yields are likely to be low without florescent lighting.

They would probably be too expensive for producing staple crops, but would instead probably produce fruits and vegetables. But most cities have enough open land and rooftops to grow all their fruits and veggies; this being so, what purpose would the high rise farm fulfill?

Some say that they could recycle wastes from their own building or other buildings nearby, which is true. But I think this could also be done at ground level, with less expense.

Some also say that they would be great demonstration projects. But if the demonstration project is fundamentally unsound, what does it justify? In that case it would be greenwashing.

Purpose built structures have a huge energy footprint for construction.

Here is an article discussing some of these problems, with hard figures.

https://www.alternet.org/story/146686/why_planting_farms_in_skyscrapers_won%27t_solve_our_food_problems

Can anyone justify these high-rise farms?

To clarify, I'm not skeptical of the value of cities, or of urban agriculture, just of this particular form of urban agriculture.

Once you exclude rooftop gardens from the discussion, you have really put  your heavy thumb on the scale of that argument since you remove the best source of light. Retrofits would be a waste of time, effort and $$$, for sure. I do see a lot of potential recycling for humanure and grey water, though because of the large number of humans living in a town, that is also where sources of grey water and humanure could be harvested: we can be resources to our source of food too, and our trash could be burned for heat, either in human buildings or farms. It will be better to have park-like structures in towns, that would have their own footprint, instead of attempting to cobble together a high rise and a farm.

Glad to see this topic getting some discussion.

Firstly, I have to say that by retrofit, I mean a thorough redesign of buildings and their systems to within the structural tolerances of said buildings. I mean, is it a disaster to renovate homes or apartment blocks? If the retrofit is disastrous, it's because there was a failure in either conception, design, or execution. I am not suggesting people start running garden hoses and building planters will ye, nil ye, until buildings start tipping over. Yes, if you fail to plan, and if you don't know what you're doing, it's a can of worms better not opened. If, however, you're looking to employ a whole new field of urban permies, that's another can of worms entirely.

To be frank, I prefer the idea of designing new structures to this end, but again, I think the idea of eliminating living and working space from these designs is contrary to permaculture.

I like the idea of a large triangular building, with the equator-oriented point obviously being designed to maximise sun exposure. I like the idea of the equator side stepping back every level, to offer a terraced effect and outside space or potentially convertible space, with perhaps glazings that slide aside seasonally, or huge windows that open to the exterior and allow exchange between outdoor and greenhouse life, especially pollinators. The side facing opposite this could easily be covered in a grade of less-expensive solar panelling designed to make use of indirect light, and from what I'm seeing in technology today, it's likely to be transparent by the time we're hypothetically building these structures.

Also, I don't understand the idea some people have about an expensive energy future. Solar panels are becoming more efficient, cheaper to produce, and longer-lasting. Battery energy density is only growing, and renewables are comprising larger and larger portions of the energy pie. We are likely to pay more for everything in the future, I fear, but I don't think the cost of energy will outpace costs for anything else.

The other shape that I like, of course, is a large suntrap with terraced balcony spaces that also step back to offer more sunlight to lower levels. The shape ultimately would have to be dictated by the climate and prevailing conditions, and such a sun trap obviously would have to remain shallow to keep the ends from shading the interior structure at sunrise and sunset, unless the structure morphed subtly, or turned on a turntable (you laugh, but I have seen some disturbingly immense freestanding structures with this feature, probably the largest being the observation deck at the CN Tower in Toronto, but also multi-story concrete dwellings and private houses; I used to watch HGTV).

Either way, I see these as stepping stones to Arcologies, which I honestly feel are the ultimate iteration of permacultural city building. We don't need to build them, don't get me wrong. But I like the ideals, the idea that you can have a huge system in operation, a system of interconnected and independent systems, fully self-contained,  and designed so that there is no waste, and ultimately if there is anything exiting the larger system, it leaves cleaner than it entered.

I was never a fan of cities, and living in one hasn't improved my opinion. But they aren't going anywhere. It would take something truly cataclysmic to make people deurbanize en masse, and it would be an unmitigated disaster. Roberto, ask yourself where 7 billion people would decentralise to. The answer is farmland, and then wilderness. We would have no global zone 5 left unless it was naturally uninhabitable. And that's if people left willingly and over a longer timeframe. We do that, and all the little interdependent cycles that keep this planet habitable will probably break down, and we all die.

Decentralisation would require the population of the Earth to shrink. I don't think that's likely to happen until we have destinations off-world where we can live. So I think that purpose-built permacultural architecture involving the integration of living, working, food production and food waste recycling space is the best way to have lots of people under one roof in an urban context that can still be designed to promote community. I reject the idea of buildings nobody lives in, but for the sake of argument, what would a high-rise permacultural endeavour (minus living space) do for a community but offer outreach, education, and assistance programs, as well as grassroots food waste recycling? Wouldn't this just make it a village hub within a larger community?

I think we need to keep a firm handle on sprawl. Also, we can't change the minds of those people who feel at home in cities of over two million or whatever. We can offer what we see as better options, but some will never leave the city. They like the urban environment, and would only acknowledge the veracity of our arguments if shown, but in their urban contexts. And that's fine. That's great, in fact. That means that those of us who want to practice broad-acre permaculture will be able to do so. We can keep wilderness wild, and we can have farms, preferably permaculture farms, and we can afford to provide necessary services to everyone because lots of people will still be crowded together in easy-to-service locations as opposed to spread all over everywhere.

So quite simply, they need a permacultural redesign, but I think cities are critical to our current and future survival. Wishing it were otherwise is counterproductive. I love small rural permacultural farms. I think everyone who wants to work one should have one. I love larger permacultural properties, too, and I think that that should be an option, too. And I think that people in urban settings, for whatever reason, whether personal preference or financial inability to choose otherwise, should have as many opportunities to practice permaculture as everyone else, within the realm of possibility. To me, this includes urban farming space, urban livestock, and a diversity of growing spaces. We don't need a mass exodus out of the cities; we need to redesign our cities to be permacultural systems. Whether the purpose-built structures we use to help with this are called high-rise farms, or even resemble what we know as city buildings today, is another matter.

-CK

Gilbert Fritz wrote:they would have to be run by solar panels; these panels would however take up space somewhere, while losing some energy to transmission and conversion. Thus they would have a larger foot print then the area of plants they would sustain.

Totally agree. I had an online discussion/argument with someone who was saying you could rotate plants on a turntable as not every plant wants 100% sunlight or you could stack them and use LEDs etc. For me it's simple maths, there's only so much incident sunlight per square metre of planet, however you slant or rotate the leaf surface doesn't change this. Sure some plants want part shade but then simply plant them on the ground under the shade of something that wants full sun.

In the end to evaluate urban farming inside buildings I look at it like this.

Build up 100% of the space with concrete and steel then try to farm 25% of the internal space

OR

Build up 75% of the space with concrete and steel and reserve 25% of the space for outdoor growing

Which of these two choices makes most since?

Photovoltaic efficiency stands at around 20%.
Plant photosynthesis efficiency stands at around 5% max.
Rough figures but they'll do for some speculation...

Thinking maybe a decade or more out. Let's say 100 photons hit a patch of land over a period of time.
If the photons hit a leaf, 5 maximum of them get used to grow the plant, the rest are the wrong frequency eg green light and get reflected or get turned to heat on the leaf surface
If the photons hit a solar panel with 30% efficiency (this is future speculation, remember) and we can then send light from a grow-LED that ONLY gives out photons that will be used by the leaf at a rate that the leaf can use them all, maybe after transformers and resistances and losses etc maybe we can send 20 tuned photons and maybe the plant will successfully use 10 of them.

So, speculation, but reasonable future scenario? We could have a closed structure with PV panels on top and LED inside, getting more growth per square metre than natural daylight?

Hi everyone,

Thanks for the discussion.

The topic of the role of cities in permaculture is interesting, but we should all be careful not to end up in the cider press; population, peak oil, and other dangerous topics are lurking around the corner!

My biggest unanswered questions right now is: if there is an abundant energy future, why not build huge greenhouses on the edge of town, and fly or shuttle the produce in with electric planes or trains? If there is a low energy future, where will all the grow light electricty come from?

For those arguing that growing areas could be integrated with living areas while still using natural light, I'm all in agreement; but every proposed vertical farm I've seen so far uses electric lights; without them, more then one level of growing is impossible. Steve's reply discusses this a bit . . .

Photovoltaic efficiency stands at around 20%.
Plant photosynthesis efficiency stands at around 5% max.
Rough figures but they'll do for some speculation...

Thinking maybe a decade or more out. Let's say 100 photons hit a patch of land over a period of time.
If the photons hit a leaf, 5 maximum of them get used to grow the plant, the rest are the wrong frequency eg green light and get reflected or get turned to heat on the leaf surface
If the photons hit a solar panel with 30% efficiency (this is future speculation, remember) and we can then send light from a grow-LED that ONLY gives out photons that will be used by the leaf at a rate that the leaf can use them all, maybe after transformers and resistances and losses etc maybe we can send 20 tuned photons and maybe the plant will successfully use 10 of them.

So, speculation, but reasonable future scenario? We could have a closed structure with PV panels on top and LED inside, getting more growth per square metre than natural daylight?

Steve, interesting idea. I'd still guess that even in this really optimistic scenario, the embodied energy of panels, lights, and structure would eat up any energetic advantage, and further, even this scenario means a doubling of the space, or two floors of plants for one floor of panels; it couldn't be made to do three floors of plants without more space for panels. And there would need to be a battery bank and some redundant panels or outside energy to cover cloudy days.

Whatever you think currently, it is part of the future. Like it or not. Already we grow perfect veg over vats in warehouses. SOld at a perfect price and called organic. YEa, it is like that. If a useless wall of glass and concrete can be used as green spaces or production of food or just oxygen, we are saving the world in one more step. Most of you do not comprehend cities of 50 million,...100 million. I do as I have inhabited them. So yes, if it can produce something for humans I am all for it.

Our space habitats will prove the point. This argument goes the way of sliding doors.

Remember Star Trek? The sliding doors. Oh all these scientists told us it would never happen here on earth. Too much energy, foolish science fiction stories. Yea, just stupid.

I walk past many many automatic sliding doors all day long.

Our megastructures can and will be the greenhouses of the future. The same BTU's can and are being used double purposed. Spaces in normal weather condition in and outside of the megastructures. Can and MUST be utilized to grow and produce products. If not for the air itself and enjoyment, then for food and creation of jobs. Better mental space and to bring the masses back to the reality.

I drive past and do stuff in such structures. If not in them, then on the grounds. Face it kids. 8 billion hungry people will very very soon be 10 billion. The changes in the weather and our dynamic universe,.....well can be our doom or a pleasant future. Embrace it. Permiculture is the cornerstone of this. THINK! It is part of our future. Like it or not.

Daniel, why exactly are these structures necessary? To feed the world? But where will the panels to power all this be parked? On farmland? With all that energy, why not grow food on the panel land, and ship it into the city? The wild critters would be happier with permaculture farms then with panel fields.

Gilbert Fritz wrote:I'd still guess that even in this really optimistic scenario, the embodied energy of panels, lights, and structure would eat up any energetic advantage

You're probably right, but it might be a close call in the not too distant future.

Photovoltaic vs photosynthesis. There are enough losses in both that, with tweaking, either could be made to win.

If photosynthesis is currently winning, then why are we (in the loose term of the word "we", I personally am not) building PV "farms" instead of planting trees?

Pigs root. Chickens scratch. Humans build.
Our ability to direct the behavior of humans is the most limited,so we should avoid efforts that rely on that.
By working with the behavior of the dominate species, we save our selves wasted efforts, and learn from nature.
Humans are like elephants, they dominate the landscape and transform it. No Permie is likely to advocate training elephants to poop only in certian places,and digg incertian ways. That would be counterproductive.
Why make plans that require we retrain humans?
How about we plan to use the existing structures when they become available/affordable?
They will still be there after they are no longer viable as office space.
Growing plants isnt the only thing Permies do,so shoehorning that activity into a tower is like using hugle culture for everything.
On the other hand, marginal results from minimum inputs are still worthwhile,so even if its not feeding the world  as long as a tower can profitably produce something other than people housing, we are stacking functions succesfully.
We will be able to influence what gets built when we have an profitable alternative, because that is what motivates the human hive.
Even then, you need to convince the herd its a safe thing to do.

When Permies start getting rich renting office space and growing food in it, we will change how towers are used and built.
Meanwhile humans will build towers, bees will build hives.
Build the trap hive for humans, that's how you harvest their efforts.

Energy cost for lighting is one issue.

But there is a bigger issue. The pump costs to raise water vertically is enormous.  

REading through this thread, I wish to add my 2 cents, and that is about how much they are actually worth.  Maybe.

I agree with other posters that some degree of urban tower farming is inevitable, but not for the same reasons.  Our world is growing in human population, and is already rather dense in certain regions.  The greatest energy input for modern farming isn't the non-organic fertilizers made from fossil fuels, nor even the amount of sunlight energy that the plants actually consume in order to grow; it's the energy required to transport them from the farm to the food processing plant, and from the food processing plant to the grocery store.

So if you take those two growing trends together, then consider a future-present, near term energy crunch (due to climate change, peak oil or something else) then urban farming becomes a necessity for humanity to avoid one of the dystopian predictions from a 1970's movie.  I can't imagine that entire buildings would be retrofit for this purpose, but access to natural sunlight isn't the limiting factor, as grow light LEDs have become incredibly efficient & effective.  Also keep in mind, all the energy spent on artificial lighting for growing plants also contributes to the heat demand for the building during wintertime, so perhaps the most productive (and profitable) times for an urban farming operation is during the heating seasons, when normal farming is at it's least productive anyway.

As another poster has already pointed out, a greater energy input than artifical lighting would be water pumping, yet this is something that we already do for towers.  This effect would likely result in multi use towers locating the grow operations in the lower floors anyway.

Also, as another poster already noted, for purpose built structures (but why would we ever do this?) a long building oriented north to south would actually result in greater overall natural lighting, much in the same way that an east-west solar array results in net-overall more useful electric power; by spreading out the energy received over the course of a full day, resulting in more of it being able to be used (without storage).  So while most plants will do better with some natural sunlight exposure, very few require natural sunlight to do well.  If such an urban structure were ever built, it would very likely be shaped like an equilateral triangle, with the grow operations located close to the windows on either side, and business offices and other human need spaces located towards the center of the triangle.

Where that energy required for the balance of lighting, or for the water pumping, might come from is not really a concern for predicting that such a thing will happen eventually, somewhere; simply because the net energy consumed will still be less than the current system that has resulted in the 1000 mile garden salad.  Human needs will demand that such an operation exist, whether they are operations integrated into existing multi-use structures or they are purpose designed and built environments.  

I would also predict that, should a purpose built structure for growing water intensive crops were ever to be built, they will be built in the arid Middle East before Europe or the US.  Salt-free water is, itself, an expensive resource in many areas of the Middle East, for which a closed loop environment would be ideal for retaining water.  Think of such a building as a huge greenhouse, for which too much heat & humidity are common problems.  Humidity, being water in the air, would be a recoverable resource for an arid region; and there is plenty of otherwise useless, sandy space to mount solar panels to make up the difference.  Furthermore, the Middle East also has the fastest growing populations in the world today; with most of the modern/Western world barely above replacement birthrates.

Hi Creighton,

I agree with you that transportation is currently a huge cost. And maybe LED grown produce would use a bit less the 1000 mile produce. And I also agree that retrofits would be more feasible in some ways then new construction for this purpose. However, wouldn't small farms right outside of town have a lower energy use then either 1000 mile produce OR LED grown produce? In other words, if we're doing this because of an energy crunch, investing in lots of LEDs and hydroponics might not be as doable. If we don't have an energy crunch, why do it?

Also, this does not take into account that most current florescent light or LED growing systems are producing tomatoes, lettuce, etc. They wouldn't work very well for staple crops. In an energy crunch, that is what people need; people can survive (though maybe not thrive) without vegetables.

If an energy crunch occurs, wouldn't a more rational response be standard urban farming, with greenhouses and rooftop gardens, while shipping in grains and other staples from nearby farms? My city, Denver, has plenty of room to grow all the vegetables we would need, without a single LED. The staple crops won't be grown in Denver even with LEDs.

I think this is one of the big confusions about this topic; how many calories are going in, and how many calories are going out? Lettuce is mostly water; vitamin water perhaps, but still water. To feed people, we need calories.

A quick bit of looking around the web shows that transporting a head of Romaine lettuce from California to Maine takes around 3000 BTUs of energy. An LED grow light assembly draws 40 watts of power to grow 5 lettuce plants and they take 60 days to produce, during which the lights are on 12 hours a day. The lights are drawing 130 BTUs an hour; this equals 1560 BTUs a day, 93,600 over the 60 days; 18,720 BTUs per plant. And that does not account for the embodied energy of the lights, panels, and wiring, nor the pumping and hydroponics system.

That's pretty convincing to me. The grow lights could become 6 times more efficient without negating this point.

And a farm right outside of town will need a lot less energy for transportation.

Transportation equation here: https://books.google.com/books?id=QMHdDgkRjDkC&pg=PA217&lpg=PA217&dq=energy+used+to+transport+a+head+of+lettuce+100o+miles&source=bl&ots=zzaRIm8pgB&sig=WO0MkCbjueNlNTzgWEkRFj-3XoU&hl=en&sa=X&ved=0ahUKEwjNqcmzmLDXAhUCxGMKHeYIBxwQ6AEIKDAA#v=onepage&q=energy%20used%20to%20transport%20a%20head%20of%20lettuce%20100o%20miles&f=false


And Light equation here: https://www.linkedin.com/pulse/how-many-led-watts-required-per-square-foot-grow-space-jay-lee

Technology.....translucent greenhouse panels that both admit light--and generate electricity:

http://www.ecosnippets.com/alternative-energy/solar-greenhouses-generate-electricity/

A brief explanation:

Electricity-generating solar greenhouses utilize Wavelength-Selective Photovoltaic Systems (WSPVs),
a novel technology that generates electricity more efficiently and at less cost than traditional photovoltaic
systems. These greenhouses are outfitted with transparent roof panels embedded with a bright magenta
luminescent dye that absorbs light and transfers energy to narrow photovoltaic strips, where electricity is produced.

Gilbert Fritz wrote:A quick bit of looking around the web shows that transporting a head of Romaine lettuce from California to Maine takes around 3000 BTUs of energy. An LED grow light assembly draws 40 watts of power to grow 5 lettuce plants and they take 60 days to produce, during which the lights are on 12 hours a day. The lights are drawing 130 BTUs an hour; this equals 1560 BTUs a day, 93,600 over the 60 days; 18,720 BTUs per plant. And that does not account for the embodied energy of the lights, panels, and wiring, nor the pumping and hydroponics system.

Most likely 3000 BTUs of fossil energy though, right?  How many renewable electric refrigerated veggie trucks are cross-crossing the country now?  And does the 3000 BTUs figure account for the embodied energy of the trucks, the fuel distribution system, the interstate highway system, etc?  What's the bigger investment, some artificial lighting equipment or 46,876 miles of concrete and asphalt?

Gilbert Fritz wrote:That's pretty convincing to me. The grow lights could become 6 times more efficient without negating this point.

And a farm right outside of town will need a lot less energy for transportation.

Transportation equation here: https://books.google.com/books?id=QMHdDgkRjDkC&pg=PA217&lpg=PA217&dq=energy+used+to+transport+a+head+of+lettuce+100o+miles&source=bl&ots=zzaRIm8pgB&sig=WO0MkCbjueNlNTzgWEkRFj-3XoU&hl=en&sa=X&ved=0ahUKEwjNqcmzmLDXAhUCxGMKHeYIBxwQ6AEIKDAA#v=onepage&q=energy%20used%20to%20transport%20a%20head%20of%20lettuce%20100o%20miles&f=false


And Light equation here: https://www.linkedin.com/pulse/how-many-led-watts-required-per-square-foot-grow-space-jay-lee

I'm not necessarily disagreeing with your conclusion but I am challenging the idea that all BTUs are equivalent.  Perhaps spending 6x the energy on something is worthwhile if the energy comes from a less polluting, renewable source.  (Also, not to shatter anyone's conceptions, but I can assure you that even in Winter in Maine the sun does shine a _few_ hours a day ;).

If photosynthesis is currently winning, then why are we (in the loose term of the word "we", I personally am not) building PV "farms" instead of planting trees?

I'd guess because electricity is much more convenient and versatile?

I'm not necessarily disagreeing with your conclusion but I am challenging the idea that all BTUs are equivalent.  Perhaps spending 6x the energy on something is worthwhile if the energy comes from a less polluting, renewable source.  (Also, not to shatter anyone's conceptions, but I can assure you that even in Winter in Maine the sun does shine a _few_ hours a day

Of course it does :) But in a farm set up for maximum production under LEDs, this would probably be irrelevant.

I'm sure they are not equivalent. Then again, most electricity is still fossil fuel powered too, so the electricity use would require even more BTUs of fossil fuel use. I'm sure that will change; but so will transportation technology.

In any case, we don't have to ship produce across the country! There is open land within an easy drive in every city, even New York! Just think what the comparison would be between LED produce and produce grown only a few miles away! There are also lots of flat roofs available.

Most likely 3000 BTUs of fossil energy though, right?  How many renewable electric refrigerated veggie trucks are cross-crossing the country now?  And does the 3000 BTUs figure account for the embodied energy of the trucks, the fuel distribution system, the interstate highway system, etc?  What's the bigger investment, some artificial lighting equipment or 46,876 miles of concrete and asphalt

Yes, but lots of other things besides that lettuce travel over those miles of concrete. Nothing else is grown with those lights.

Technology.....translucent greenhouse panels that both admit light--and generate electricity:

http://www.ecosnippets.com/alternative-energy/solar-greenhouses-generate-electricity/

A brief explanation:

Electricity-generating solar greenhouses utilize Wavelength-Selective Photovoltaic Systems (WSPVs),
a novel technology that generates electricity more efficiently and at less cost than traditional photovoltaic
systems. These greenhouses are outfitted with transparent roof panels embedded with a bright magenta
luminescent dye that absorbs light and transfers energy to narrow photovoltaic strips, where electricity is produced.

Interesting technology.

I'd still guess that the embodied energy of such panels would be much higher the typical glass or plastic greenhouses.

And I'd also guess that at very most these panels would be able to provide light for one extra layer of plants, so we now have two layer of plants (one directly from the sun, one fed by the lights) before we need to find more space for panel elsewhere.

In fact, due to winter and cloudy days, we would probably still need extra space for backup panels, or, in other words, the "first floor" plants would have to cover a smaller surface area then the "second floor" panels.

Gilbert Fritz wrote:Hi Creighton,

I agree with you that transportation is currently a huge cost. And maybe LED grown produce would use a bit less the 1000 mile produce. And I also agree that retrofits would be more feasible in some ways then new construction for this purpose. However, wouldn't small farms right outside of town have a lower energy use then either 1000 mile produce OR LED grown produce? In other words, if we're doing this because of an energy crunch, investing in lots of LEDs and hydroponics might not be as doable. If we don't have an energy crunch, why do it?

We might do it in small bits, such as edible potted plants tucked into rarely used corners of a high-rise condo, for the emotional & psychological benefits of greenery, as well as the contribution to the winter heat load of the building.  I can grow quite the garden salad for a family in 16 square feet, no matter how it's orientated.

Also, this does not take into account that most current florescent light or LED growing systems are producing tomatoes, lettuce, etc. They wouldn't work very well for staple crops. In an energy crunch, that is what people need; people can survive (though maybe not thrive) without vegetables.

Yes & no. Staple crops are not likely to do well in such a contrived environment, I agree; but vegetables for a well rounded, nutritious diet are still necessary.  If we didn't truck in vegetables to urban areas, we'd likely start seeing cases of scurvy within a year.  Disease from malnutrition will kill you just as dead as actual starvation from calorie deficit.

If an energy crunch occurs, wouldn't a more rational response be standard urban farming, with greenhouses and rooftop gardens, while shipping in grains and other staples from nearby farms? My city, Denver, has plenty of room to grow all the vegetables we would need, without a single LED. The staple crops won't be grown in Denver even with LEDs.

Perhaps more rational for Denver, but some cities can't exist without fossil fuel energy anyway, at least not at their current populations, and Denver is likely one of them.  Denver Water uses an incredible amount of energy to pump water, both up towards the mile high city, and around it.  Los Vegas can't support it's population without pumping water horizontally across many miles, & half the people would be hard pressed to survive a single summer without air conditioning.  Half of Toronto would freeze without fossil fuel energy, but only after about 5 years of cutting down all the combustible forests within a few days walk.  There simply isn't enough wood growth to heat the buildings that northern cities have now in any sustainable manner.  If there is such a short-term energy crunch, a lot of these existing towers won't be "livable" anything similar to how they are currently used anyway.  And if you read my post about the ideal building, the grow LED's would only be used half of the time anyway.

I think this is one of the big confusions about this topic; how many calories are going in, and how many calories are going out? Lettuce is mostly water; vitamin water perhaps, but still water. To feed people, we need calories.

I don't disagree, but most staple crops can be shipped in much more energy efficient ways, such as in bulk packaging across water on a sailing ship.  Vegetables tend to be more energy intensive because they don't keep well, and their freshness is directly related to their nutritional value.  So long distance shipping on a slow boat doesn't work for these, still important, crops.  These are the very crops that are ideally grown within walking distance of consumption, and also would do best partially grown under LEDs.  Growing beans, rice and wheat on large farms near a small water port, and then shipping them to a large port, is very energy efficient and likely to be how the vast majority of staple crops are grown forever.  But mankind cannot live on bread & water alone, and herbs, spices and vegetables are where the energy savings can be found.  Granted, if you personally live in a major port city, a large volume of fresh vegetables could be grown at the edge of the city and shipped into town on a daily basis from not very far by water also; but there is a limit to how far away fresh vegetables could be grown and still be fresh at the point of sale; so if urban farming is going to be a logical economic endeavor then those high value, short viability type crops are going to be what is grown.

Gilbert Fritz wrote:

Yes, but lots of other things besides that lettuce travel over those miles of concrete. Nothing else is grown with those lights.

Nothing else is grown, but that doesn't mean that those lights aren't useful beyond growing cilantro in a strange location.  As I have already mentioned, northern cities have long heating seasons, and any energy use inside the building's envelope contributes to the building's total heat demand.  Also, those grow LED's are still visible by human eyes, and would work fine as night lights for human safety.  For that matter, the LEDs don't have to be the full blown purple grow LED's, they could be wider spectrum lights for human benefits.  And grow lights aren't the only way to do this, a sunpipe would work well too.

"As another poster has already pointed out, a greater energy input than artifical lighting would be water pumping, yet this is something that we already do for towers.  This effect would likely result in multi use towers locating the grow operations in the lower floors anyway. "

I think you underestimate the power that a 3 phase 5 or 10hp pump consumes and that is generally the minimum size motor used.

One should understand another aspect. Just because it is technically feasible to DO something does not make it economically feasible. There are hundred things in life doable, but far fewer that are economically so.

But I have an alternate proposal -- move the consumption, aka the people. With the tech we have today a large percentage of the population can work from anywhere. There are small towns across this country that would welcome the population boost. Re-enable the Homestead Act for small towns. Run the numbers and it is probable its a better impact statement; millions of permaculture homesteads across the fruited plain.

And access to fresh vegetables might not even be the main reason humanity decides to build such an urban structure.  Pollution or climate change might force particular populations in various regions to proactively create healthy air for humans to breath, and integration of enclosed gardens might be part of such a strategy, wherein the very fresh garden salads would be a side benefit.

As mentioned, arid regions in the Middle East have growing populations, and such a dedicated or integrated use building might serve as part of a desalination process, or even an urban greywater recovery process.  Astronauts on the International Space Station recycle their own urine, but don't get the additional benefit of nitrogen hungry vegetable crops; and the desalination of seawater is a very energy intensive process.  Perhaps, with a large enough population and a high enough value for salt-free water, some new or future city would build a parallel sewage network to segregate human urine simply because it's less energy intensive to recycle urine alone than desalinate seawater for it's large population.  Or instead change building codes that forces new construction to segregate urine and recycle it within it's own building structure.  In either case, the edible produce would simply be a convenient byproduct of a state-sanctioned waste stream processing method.  Dehumidifiers and condensation tend to produce some rather clean water, if they are done right, and the leaves of plants will 'breathe' out water into the air quite a bit faster than the same surface area of an otherwise dead evaporation pool.  A purpose built machine might be able to do it better, but it's hard to beat the maintenance & support requirements of a living thing that does the same thing just living; and the plants would have a net-negative carbon footprint.  Probably even if some grow lights were required.  There is an indoor snowskiing resort in Dubai, with 22,500 square meters of well lit and heavily air conditioned floor space.  I can imagine such a space being retrofitted towards such an endeavor.

john mcginnis wrote:"As another poster has already pointed out, a greater energy input than artifical lighting would be water pumping, yet this is something that we already do for towers.  This effect would likely result in multi use towers locating the grow operations in the lower floors anyway. "

I think you underestimate the power that a 3 phase 5 or 10hp pump consumes and that is generally the minimum size motor used.

I am an electrician by trade, I assure you that I'm not underestimating that.  In any case, a 3 phase motor will consume about 5% more energy than is theoretically required to move the water, not more.  It is not like a combustion engine that requires an idle power just to be available when water needs to move; I can turn a 20 hp motor by hand, and they only run when necessary.  And most towers don't require a pressure booster pump for the first several floors anyway, which is one reason that I mentioned that possibility.  Many urban environments still have (mostly) gravity fed municipal water capable of pushing a useful volume of water up to about the 5th floor.  There are exceptions, of course, such as Denver.

One should understand another aspect. Just because it is technically feasible to DO something does not make it economically feasible. There are hundred things in life doable, but far fewer that are economically so.

But I have an alternate proposal -- move the consumption, aka the people. With the tech we have today a large percentage of the population can work from anywhere. There are small towns across this country that would welcome the population boost. Re-enable the Homestead Act for small towns. Run the numbers and it is probable its a better impact statement; millions of permaculture homesteads across the fruited plain.

That might be a viable alternative in many cases. I'm not advocating that such urban gardening structures or retrofits should be constructed, I'm saying that they will be constructed.  Somewhere, and perhaps in very niche urban environments; but they will be built.  

Gilbert Fritz wrote:A quick bit of looking around the web shows that transporting a head of Romaine lettuce from California to Maine takes around 3000 BTUs of energy. An LED grow light assembly draws 40 watts of power to grow 5 lettuce plants and they take 60 days to produce, during which the lights are on 12 hours a day. The lights are drawing 130 BTUs an hour; this equals 1560 BTUs a day, 93,600 over the 60 days; 18,720 BTUs per plant. And that does not account for the embodied energy of the lights, panels, and wiring, nor the pumping and hydroponics system.

That's pretty convincing to me. The grow lights could become 6 times more efficient without negating this point.

And a farm right outside of town will need a lot less energy for transportation.

All true, of course, but that same building in Maine can use every BTU of waste heat that those grow lights produce between about October and March.  Even if our theoretical building has a heat pump, they don't do better than electric restive heat below about freezing, which would cover your 60 day requirement quite nicely.  And no matter how we might feel about nuclear power, it can produce electricity without either carbon emissions or a fossil fuel supply; but it can't push a lorry/trailer truck down the interstate.  The same could be said for hydroelectric power.  I live in one of the cities that has direct, local access to a hydroelectric power plant (McAlpine-Locks-and-Dam) that can produce about 10 megawatts right downtown.  That isn't remotely as much electricity as the city uses today, but might be enough to keep the downtown district lit and water pumping.

While I am leary of technology that needs to be vetted in terms of its overall cradle-to-grave (or cradle?) footprint, I love the idea of augmenting off-season indoor growing with tuned LEDs. You can get lots of light here in the winter (Toronto), but as the angle of the sun decreases, it filters through a greater distance of atmosphere. I think it's that or the angle of incidence that makes growing using sunlight in the off-season (read: six to eight months of the year) a little anemic. Even in situations where the access to the sun, through advantageously placed glazing walls or solar tubes, is maximised, these lights would make up for the seasonal drop-off in solar availability.

I also love the idea of transparent photovoltaic glazings. I know Paul has always been skeptical about the value of sunlight after it has passed through a glazing of any sort, and what the glazing itself might filter out, in the same way that windows with coatings to reduce solar gain in hot climates do, and what effect that might have on the health of the plant and healthiness of the food it produces. But I like the idea of supplementing with the aforementioned LEDs because, as mentioned in other posts, they would be most needed during the time of year when additional heat is required, so their waste heat, still barely anything compared to High Intensity Dispersion or Metal Halide bulbs, is hardly wasted. I would like to see comparisons at this point, though. I would prefer to heat with something efficient, and bulbs that produce heat as a byproduct of their intended function might only do that as well as an old electric baseboard heater, which are notoriously expensive when used exclusively.

One thing I haven't seen mentioned is ground-source heat pumps for climate control. All that heat from solar gain needs to go somewhere. There is an excellent video in Geoff Lawton's series about an air-based heat battery system implemented in an Albertan greenhouse that consists of an air intake at the highest point where hot air gathers in the greenhouse and a ducted fan pumping that air through a duct, down through the insulated concrete slab to a horizontally-laid weeping tile running its length. The heat in the air is transferred to the soil beneath the structure all summer, and then is released when the temperature drops. In a much larger structure, a heat-exchanger and heat-storage medium could be used to increase heat capacity and could also couple to in-floor radiant heating, pumping said storage medium through piping set in concrete slabs.

If one is of the opinion that high-rise urban farming is a bad idea, nobody's good ideas will convince that one. But I, for one, think it's illogical to form such unreasoned biases against what are essentially tools in the permaculture toolbox. I wouldn't use a hammer for tilling or electronics, and I wouldn't expect a combine to do a good job harvesting my intensively managed garden. We need those people critical of these ideas to list and quantify what they feel are the weaknesses of these ideas, and in some respect that is being done. But I don't find it particularly useful when specific issues are being discussed, and then out of the blue, someone who sounds like they haven't bothered reading the whole thread posts something dismissive and advocates a solution that, while it may have merits in its own context, does nothing to further a discussion about the best way to grow things where and when they don't want to for climatic or seasonal reasons. It's like trying to discuss permaculture with Paul Wheaton, not having listened to any of his podcasts.

-CK

Wow, lots of discussion here. I'm trying to understand this; and I hope I'm not being snarky. I still can't understand it.

A couple of quick points; human urine is half as salty as seawater.

I agree that if this would be useful anywhere, it would be useful in the Middle East. Then again, they might have more serious problems.

I think Denver has a largely gravity fed water supply; it comes down from higher elevations in the mountains as snowmelt.

If LEDs are producing significant amounts of waste heat, they'd be significantly less efficient then they might be. Turning sun into electricity and then turning that back into heat is a huge waste.

Pollution or climate change might force particular populations in various regions to proactively create healthy air for humans to breath, and integration of enclosed gardens might be part of such a strategy, wherein the very fresh garden salads would be a side benefit.

One person needs ten thousand leaves to provide themselves enough oxygen; similarly for any cleaning functions they might provide. Poor slum dwellers in the third world, where pollution is the biggest problem, will not be able to afford this.

There is an indoor snowskiing resort in Dubai, with 22,500 square meters of well lit and heavily air conditioned floor space.  I can imagine such a space being retrofitted towards such an endeavor.

Yes, and the same crowd that currently benefits from the snowskiing will eat the salads. I'm not worried about them!

Ground heat tubes are an excellent idea, I think.

But I have an alternate proposal -- move the consumption, aka the people. With the tech we have today a large percentage of the population can work from anywhere. There are small towns across this country that would welcome the population boost. Re-enable the Homestead Act for small towns. Run the numbers and it is probable its a better impact statement; millions of permaculture homesteads across the fruited plain.

Good point.

We might do it in small bits, such as edible potted plants tucked into rarely used corners of a high-rise condo, for the emotional & psychological benefits of greenery, as well as the contribution to the winter heat load of the building.  I can grow quite the garden salad for a family in 16 square feet, no matter how it's orientated.

But that is rather different then a high rise farm.

Perhaps more rational for Denver, but some cities can't exist without fossil fuel energy anyway, at least not at their current populations, and Denver is likely one of them.  Denver Water uses an incredible amount of energy to pump water, both up towards the mile high city, and around it.  Los Vegas can't support it's population without pumping water horizontally across many miles, & half the people would be hard pressed to survive a single summer without air conditioning.  Half of Toronto would freeze without fossil fuel energy, but only after about 5 years of cutting down all the combustible forests within a few days walk.  There simply isn't enough wood growth to heat the buildings that northern cities have now in any sustainable manner.  If there is such a short-term energy crunch, a lot of these existing towers won't be "livable" anything similar to how they are currently used anyway.  And if you read my post about the ideal building, the grow LED's would only be used half of the time anyway.

So, because these cities already use lots of energy they should use more? I'm not sure what your point is here.

I think that using artificial lights to boost the season a little bit is also a great idea; I've started hundreds of tomato plants under lights, which allows my field to use solar input more efficiently during the season.

Anyway, all these details are beside the point. I can understand growing some plants in sunny windows; I've done it myself, though one shouldn't overestimate the yields. I also think that stepped greenhouse type buildings are a wonderful idea.

But I still don't understand the draw for growing under LED lights. It is really just shuffling sunlight around. Land is not really necessary to grow crops in one sense; what is necessary is solar access. Every area of ground on earth gets a certain amount of sunlight per year, no more and no less. Stacking up the plants on one area under banks of LED lights and spreading the solar panels to grow them out on other pieces of land seems like an unnecessary energetic cost.

In short, so long as I see unused lawns, rooftops, balconies, parks, greenbelts, and parking lots all around me, I think vertical farms are a technology looking for a problem.

Gilbert, the whole light shuffling description ceases to be accurate if you look at the idea of tuning the LEDs to provide more of the plant-useful light spectrum and capturing whole sunlight with photovoltaics. It is more akin to distilling the parts of sunlight useful to the plant and delivering it to plants either on its own or to fortify anemic levels of natural daylight in seasonally inhospitable conditions. Or like aquaponics, where root zone exposure to nutrients, water, and dissolved oxygen are maximised.

As we all know, too much sunlight can burn sensitive crops or cause them to bolt beforetime. What if tuning the spectrum of their light allows you to input more energy to the system in a controlled fashion, excluding harmful or damaging light and replacing that with the appropriate parts of the spectrum for that stage of growth?

This kind of thing could be extremely advantageous in the north, as you pointed out, and where light levels and not temperature are the obstacles to season extension.

-CK

Chris,

Put that way, it does make more sense.

But I wonder; does the efficiency gained overcome the inefficiency of the panels, transmission, storage, and conversion back into light? As somebody pointed out, LEDs produce at least some heat, which is a loss; panels are only 10 percent efficient. Plants are only 5 percent efficient, but now we have combined both those relatively inefficient processes, photosynthesis and photovoltaics. Add in the lifecycle energy costs for both LEDs and panels, and they'd have to be even more efficient to break even.

I don't have enough of a scientific background to be able to answer these questions; I really don't know. My gut feeling is that it does not work out, but then I'll admit to being prejudiced.

And I also agree that filtering out the damaging part of the spectrum is useful, but shade cloth does a pretty good job for a lower price.

Starting plants early under lights is a great idea (I do it) because the small energy investment there translates to a much greater energy capture in the field. But even there, I wonder what the numbers would look like; maybe it is not such a great idea after all. I don't know.