Solaculture: A novel approach for low cost energy?

[recursive prophet]

This seems to me like a very interesting approach to harnessing solar energy. I would greatly appreciate any input, critical or supportive, from the many knowledgeable posters who frequent this forum. You can click on the link and watch a short video, or just read the description of how it works.

The inventor, John Popovich, has a long history in solar innovation. Back in 1975 he was developing unique solar collectors, and was the keynote speaker at an ERDA funded ISES conference in San Diego on testing solar collectors/systems. It was attended by then Governor Jerry Brown (start recursion loop) and then Mayor Pete Wilson, with a cast of experts in radiation physics and fluid thermodynamics. Many procedures in testing solar were altered as a result of his feedback at round table workshops. Now, after being diverted forming several companies and designing LED's, he returns to earlier ideas on passive solar systems. What problems do you see in implementing Soaculture, and are there any flaws in the concept itself? Looks good to me, but my knowledge of other alternatives is now quite limited. Thanks.

Solaculture - A New Solar Economy http://solaculture.com/

Solaculture uses “Fluidynamic Solar Concentrator “ (Patent Pending) technology to organize and control local thermal, aerologic, hydrologic, and biologic flows for the production of food, water, fuel, heat, and electricity. The technology provides a means to remove CO2 from the atmosphere for plant growth and for the sequestration of carbon as humus in the local earth and a means to collect and store atmospheric water, evapotranspiration water, and precipitation water in the local earth for plant growth and other uses. Biogas can be produced from methanogenesis within the Fluidynamic Solar Concentrator array via animals and/or via thermally accelerated decomposition of organic matter within the soil or from sources such as sewage, garbage, and agricultural waste and the biogas can be used to provide heat and electricity.

Solaculture arrays can provide very high solar concentration at low cost. They are composed of regions of land or water covered with porous canopies and a means to provide a slow downward airflow thru the porous canopies to reverse and control the typical buoyancy induced upward air flow resulting from solar heating and water evaporation. Plants in some instances can act as canopies and present the minimal cost Solaculture array. Solaculture can provide enhanced environments for people, plant and animal communities by varying the canopy and earth properties, and the airflow rate and direction.http://solaculture.com/

 

[Furcifer]

Interesting, it reminds me of the subdivision in Okotoks Alberta but it collects the methane from rotting plant matter to increase efficiency in a turbine.

It's similar to the Energy center I created for a capstone project last year. Something like this Solarculture with perhaps another 40-80 acres of greenhouses and a few wind turbines would have extremely high efficiency. The biomatter from the greenhouses feeds the methane farm while the CO2 from the methane burned in the turbine feeds the biomatter in the greenhouses. Not only are these centers extremely efficient it's possible they could act as carbon sinks.

Unfortunately these centers require a sizable capital investment. I estimated something like this would cost about $100M to get going and not see an ROI for 15 years depending on the cost of electricity.

 

[Andrew Wiggin]

I'll believe this one when I see it work.

I don't see how the solar heating induces a downward flow through the membrane, for starters. I would expect an upward movement, as the hot air rises. Certainly this is an arrangement similar to a solar chimney, and those capture the upward movement of air for energy.

If he's inducing an inward flow of air by means of a blower, the power has to come from somewhere. If it's coming from the turbine that moves the methane and air into the burner, then basically he'd be describing a jet engine, but the power neccesary to pull air through square miles of porous membrane would be immense and there goes your effeciency.

He's talking about extracting methane from decompositon, and running the methane, plus the air that percolates through the membrane through a burner to power a turbine. Methane and air are flammable in mixtures from 5 to 17 percent at atmospheric pressure and reasonable temperatures, according to some brief googling. That's an awful lot of methane in a breathable atmosphere, and at the same time an awful lot of breathable atmosphere in a process that works best in anaerobic conditions. Trees may use carbon dioxide, but they also are aerobes and use oxygen. Keeping them in a condition where the leaves are in a mixture depleted in oxygen, and the roots are in a condition suitable for rot sounds rather implausible.

He talks about carbon sequestration, but this process is carbon neutral; he'd be using sunlight to make biomass, rotting the biomass to make methane and then burning the mixture and releasing it back into the atmosphere. he shows a condenser for the water, but water isn't the issue, or is a tangential issue. He's still releasing the carbon back into the atmosphere.

This could plausibly be done (and is done) as separate cycles. It's an old hippie commune thing from the 'Other homes and garbage' days. Sun on grass or grain, plants in cows or chickens, critter waste in an anaerobic digestor, digestor gas to a turbojet. (more likely an old light plant engine, or even a lawnmower belted to a car alternator, but a turbojet would work. You can make a decent turbojet from a turbocharger.) The point is that all the steps in this process require their own individual conditions to work efficiently, or work at all. Putting all the bits in one container, and trying to find an optimum condition that'll let the whole thing work well is problematic. Finding a condition that'll let the whole thing work at ALL might be problematic.

 

[macdoc]

Like using a bunch of feathers to drive a nail

THIS is efficient.

Small Nuclear Reactors Are Becoming Big Business
The race is on to develop refrigerator-size reactors that could power small towns or plants

http://www.businessweek.com/magazine/content/10_22/b4180020375312.htm

the sooner the world wakes up to it the better......instead of rube goldberg schemes.

Bottom line is small, compact source of continuous reliable power without C02 - all else falls into line after that in terms of sustainable practice.

This snip sums it up - nukes are stuck in mainframe era when it's iphone time now

John Deal, chief executive officer of Hyperion Power Generation, intends to apply for a license "within a year" for units that would power a small factory or towns too remote to be connected to traditional electricity grids. The Santa Fe-based company, as well as Japan's Toshiba, are vying for a head start over traditional reactor makers General Electric (GE) and Areva in downsizing nuclear technology.

"We're building iPhones when the nuclear industry has traditionally built mainframe computers," says Deal. Hyperion says it has more than 150 purchase commitments from customers, including mining and telecom companies, provided its technology gets licensed for operation by the U.S. government.

most of that is NIMBY crap.

 

[Furcifer]

If he's inducing an inward flow of air by means of a blower, the power has to come from somewhere. If it's coming from the turbine that moves the methane and air into the burner, then basically he'd be describing a jet engine, but the power neccesary to pull air through square miles of porous membrane would be immense and there goes your effeciency.

Turbines as small as he's describing are usually areo-derivatives. The heat from the outside air is gathered in the array. Assuming it's reused (+efficiency) and combustion air is cooled (+efficiency) it's a net increase in efficiency. (in theory at least)

he shows a condenser for the water, but water isn't the issue, or is a tangential issue. He's still releasing the carbon back into the atmosphere.

I think he means heat exchanger.

Finding a condition that'll let the whole thing work at ALL might be problematic.

Indeed. I'm not sure how you would go about collecting the methane. Hot water is useless unless you're using it in winter like the project in Alberta, and that's only in the winter. I think in order to see any efficiency you need to add a steam turbine. The hot water could then go into making steam.

The hardest part of these projects is figuring out what your limiting factors are. I found that you need to import biomass because even with 40 acres of greenhouse you can't keep a constant supply of plant material for the digester. If you add CO2 sequestering to the turbine you're left with a surplus of CO2 even with 200 acres of greehouse.

Instead of batteries in the system I designed I had a 40 acre Concentrated Solar Plant. Excess energy from the gas and wind turbines could be stored in molten salt, then used later in the steam turbine.

 

[Cuddles]

Sounds like an unnecessarily complex variation on the well established idea of farming algae for fuel. Since even that hasn't been demonstrated as a practical energy source yet, I doubt we'll be seeing this becoming popular any time soon.

 

[macdoc]

You got it Cuddles......Rube G would be proud.

There are SOME synergies to be had for sustainable agriculture but there is still the need for a reliable base load for industrial civilization without adding fossil carbon.

Simple in concept - damn hard to get to.

The tree hugger all solar/wind is just a pipe dream that gets in the way. Like the stuff above.

 

[recursive prophet]

First thanks to those who took the time to look at and comment on Solaculture. I hope most looked at the written description of this idea, as it covers many things not addressed in the video.

I will let John know about these comments, and hopefully he'll have time to let me record than write up his response and post it here. Later I will also give some details about his background, which I confess may influence my own POV on this concept. Seeing it from other perspectives is much appreciated.

There are SOME synergies to be had for sustainable agriculture but there is still the need for a reliable base load for industrial civilization without adding fossil carbon.

Simple in concept - damn hard to get to.

The tree hugger all solar/wind is just a pipe dream that gets in the way. Like the stuff above.

I don't think he is suggesting this as part of an all solar/wind nirvana Mac. Also I question your pipe dream conclusion wrt solar being mostly a tech speed bump. Perhaps the days of single solutions are gone? As in finance, might not diversification be the soundest strategy? This said, obviously not all innovations will be pragmatic.

Indeed. I'm not sure how you would go about collecting the methane. Hot water is useless unless you're using it in winter like the project in Alberta, and that's only in the winter. I think in order to see any efficiency you need to add a steam turbine. The hot water could then go into making steam.

I will definitely ask JP for details about this 3bod, but did you read the all the text? Apparently you have quite a background in this area. I had no idea.

Many thanks for your input. I worked in the solar energy field back in the seventies, but was focussed mainly on passive water and space heating systems for homes. I haven't really kept up, so it's great to get feedback from someone who has looked at all this relative to current economics.

 

[Furcifer]

I will definitely ask JP for details about this 3bod, but did you read the all the text? Apparently you have quite a background in this area. I had no idea.

Many thanks for your input. I worked in the solar energy field back in the seventies, but was focussed mainly on passive water and space heating systems for homes. I haven't really kept up, so it's great to get feedback from someone who has looked at all this relative to current economics.

Please do. I have access to a mountain of biomass that can be seen from space. If he's got a way to collect the methane I can make us all very rich. Very.

 

[ben m]

Hi Recursive, a few comments.

I don't think that either the "convection suppression" has been thought through correctly. A layer of warm air under a layer of cold air can't be kept inverted by a little suction on the bottom. It's unstable--- the Rayleigh-Taylor instability. The "equilibrium" state will be a random collection of chimneys or fingers of rising air, alternating with fingers of downgoing cold air. The only thing that the "convection-suppressing fan" can do is make the cold fingers slightly bigger than the warm fingers; it can't prevent the warm fingers from punching through. In any case, having a fan down there, and adding in all this downgoing airflow, means that you're cooling the thing that you wanted to allow to get hot.

The fiberglass radiation barrier is a nice idea, I'd be interested in seeing it in practice.

The "gas turbine" is rather strange. Is this supposed to be just running off the "hot air" supply under the canopy? There is very little energy available in mere hot air; it's tremendously inefficient to generate power from. In the configuration shown, the "turbine" is not an energy source, it's just a large (power-consuming) fan. Is the turbine supposed to be burning the air-methane mix? If there's enough methane in the air to burn in a turbine, your whole canopy is going to explode. Please try to convince me otherwise, with numbers, but without numbers all I have is an instinct (based on confined space and mine safety training) saying this doesn't work.

Anyway, the whole thing is working in the wrong direction entirely. If you have a lot of biomass and you want methane, keeping the pile at 50C is the easy part. Make sure the pile is a few feet thick; and it'll stay at 50C all on its own, as millions of larger-scale backyard compost piles are doing all over the world. All of this effort going into solar radiation control is ... well, a complete waste of effort. It's like building a water-conserving drip irrigation system for your kelp farm.

If you want to turn biomass into methane, put it in a pile and cover it with a few layers of plastic.

 

[recursive prophet]

Thanks for sharing Ben. Hope the quote from John below answers some of the questions presented here. If not, let me know.

"Very little energy is needed to cause a reversal of the typical solar and evaporation induced upward airflow and that energy can be provided by rising exhaust gas resulting from combustion of biogas and/or from an engine intake and/or from a blower/fan.

Furnaces, boilers, and cooling towers use both free and forced draft systems and the parasitic cost of forced draft is a tiny percentage of the system energy. A fireplace for example typically induces several times the air needed for combustion without a fan/blower despite the fact that the house is closed; the reason is that the stack gas is less dense than the local atmosphere and continuity demands that if the fireplace stack is causing air to rise, it is by extension causing the neighboring air to fall. See Wikipedia for stack effect or chimney effect thermodynamic relationships.

Greenhouses are increasingly being rationalized for reasons including increased crop yield, increased crop quality, increased growing season, reduced water needs, reduced insect problems, and reduced insecticide use. If greenhouses had perforated film covers, the intake of an engine driven generator could be connected to the greenhouses and used to create a slightly sub-atmospheric pressure within the greenhouses and by this means collect and recycle the water of evaporation from the earth and the water of transpiration from the plants within the greenhouses. Methane produced by anaerobic decomposition of organic media within the greenhouse could provide all or part of the engine driven generator fuel needs.

A perforated film covered greenhouse need not be costlier than an unperforated film covered greenhouse and a web search will reveal hoop house type film covered greenhouse costs as low as $.30/ft2, much lower than any other solar collector cost and these collector costs are already rationalized economically for food production, a process that can operate in conjunction with Solaculture and in fact be enhanced by reduced heat losses, water collection, water recycling, and CO2 addition.

Methane is being produced and released into the atmosphere in large quantities. Areas with existing high methane production rates include peat bogs, swamps, wetlands, coal mines, oil fields, rice paddies, landfills, cattle and swine operations, and sewage treatment facilities. Solaculture technology can also provide increased insitu production of methane by leaving crop waste in place for decomposition into humus. Since methane has more than 20X the global warming potential of CO2, some climate scientists are calling for a methane first approach to reducing greenhouse gases. If methane can be captured and converted to CO2 and H2O by combustion, work and heat can be derived, and the environment improved.

The small amount of energy used to cause a reversal in the typical solar driven upward air flow can be used to yield enormous benefits by creating more optimal environments for habitation and for the production of food and fuel, while reducing greenhouse gases by increasing net plant matter, by storing carbon as humus, and by converting methane to CO2 and H2O.

Civilization evolved in conjunction with excess created by the organization and manipulation of resources; first plants, and later animals, and water. Solaculture provides a means for the organization and manipulation of air in a manner beneficial to the environment and the economy. "Solaculture uses an aerologic organization system to enhance* hydrologic and biologic systems".

 

[ben m]

Thanks for sharing Ben. Hope the quote from John below answers some of the questions presented here. If not, let me know.

That doesn't answer any of my questions. The reason you can pull a downdraft through a chimney is that a chimney is long and narrow. It is totally unrelated to the question of pulling a downdraft from underneath a broad flat area; I repeat, this is the setup for an Raleigh-Taylor instability, which you're not going to address or understand by thinking about general chimney energetics.

Please remind me---what's the point of the perforations in the sheet, again? If you want to control the airflow in a greenhouse ... well, that's a regular old greenhouse. If you want to let air, in you open or close the door at the end. If you don't, you close it. If you want to reduce the pressure a little, you keep the door shut while the exhaust fan is drawing.

On the energetics: can you show your calculation for the energy requirements of a fan that gives the behavior you think you want?

And I don't understand your methanogenesis issues at all. Again, with sources you can move around---agricultural waste, feedlot waste, urban garbage---putting a sheet of plastic over the source is easy, and it's already being done. Depending on the geometry, the underlayment, etc., the fuel does a fine job of keeping warm just from bacterial metabolism. I have no idea what "solaculture" claims to be contributing to this problem.

If you're worried about peat bogs---well, at the moment peat bogs are huge fossil carbon stores that release some methane. You're proposing to heat them up, make them release oodles of methane, but capture it and turn it into CO2. While it's true that methane is 20x worse than CO2, your scheme would release more than 20x as much carbon, as CO2, than the bogs would have emitted on their own. It's like trying to stop a radioactive waste leak by blowing up the nuclear power plant.

Similarly for soil carbon. Turning agricultural soil into a hot methane-producing biodigester does not sequester carbon as humus. Turning soil into a biodigester encourages the conversion of humus to CO2 and CH4.

And, I repeat: I am skeptical that you can use your ultradilute methane-air for anything other than blowing up greenhouses. Do you have calculations which would convince me you can burn it in a turbine? Heck, my local sewage plant has real biodigester tanks, and even they can't do any economically-useful work with the biogas (too much H2S and CO2, I think) so they just flare it off.

 

[Furcifer]

And, I repeat: I am skeptical that you can use your ultradilute methane-air for anything other than blowing up greenhouses.

It's called premixing, you mix fuel into the combustion air. It tends to lower the burn temperature and therefore the NOX. It's pretty well known in the industry.

Without a constant concentration of methane it would be almost impossible to maintain turbine efficiency. It might not be as hard on a 3MW unit but I don't think anyone makes a system to handle a methane premix. You'd have to design it yourself, which would no doubt void any service warranty. I could see you melting a few rows of blades the first time the methane stopped flowing and the mixture went lean.

It would probably be safer to try and run a premix system in an ICE converted to natural gas.

 

[Andrew Wiggin]

I think this is an excellent idea to be subjected to the 'put your money where your mouth is' test. I can see how it's supposed to work, and perhaps the inventor just is that much more intelligent than I am, and has figured out how to optimize all the variables, solve all the little 'but what about' elements, and make a working product.

The raw materials for this are cheap; land, plants, tent poles, string, plastic sheet, and an engine. It wouldn't even have to be a turbine; biogas burns fine in a lawnmower engine. The modification is as simple as running a tube to the air intake and emptying the fuel tank. Just getting the engine to run using the greenhouse exhaust would be a victory, and give data for the full scale plant. I can see a one-acre pilot plant, assuming that the inventor owns some land, costing in the low thousands. If the engine is the sticking point, even a flare to burn the gas would demonstrate that the project made a burnable fuel, and give some data about efficiency and function.

I still think that this would work better as separate cycles, and as separate cycles all the problems with this plan are solvable and in fact have been solved in the past, although not to the extent of being world changing. I don't see what's special about trying to combine the cycles, or even what advantages are claimed for combining the cycles.

random aside; Bartertown in the sci-fi drama 'Mad Max Beyond Thunderdome' ran on biogas, with IIRC an interesting speech about the smell of energy.

http://www.imdb.com/title/tt0089530/quotes?qt0357252

 

[Myriad]

My reaction is similar to ben m's. The biochemistry seems like it might work but the fluid mechanics is suspiciously sketchy. I was quite surprised to read that a relatively small extraction fan would be sufficient to reverse the convection through the membrane over a large area. My main reason for reading on was curiosity about that claim, so I expected a clear rationale, if not some calculations, for it. None were offered.

The old joke about drilling more holes in an already leaky boat, "to let the water out," comes to mind. Sure, adding a pump does help -- but you're still better off without the holes.

It appears that an exhaust fan preventing air escaping by rising out of the membrane would only work if the extraction rate were sufficient to eliminate the temperature difference across the membrane almost entirely. Which pretty much nullifies the intended benefits of having the covering there in the first place.

Regarding the other main question on extraction and burning of the methane -- is there a way to extract methane from air; that is, concentrate a subcombustible mixture of methane and air, into a combustible one? If so, what range of input concentrations would allow the extractor to run on less energy than would be produced from burning the methane extracted?

Respectfully,
Myriad

 

[ben m]

Regarding the other main question on extraction and burning of the methane -- is there a way to extract methane from air; that is, concentrate a subcombustible mixture of methane and air, into a combustible one? If so, what range of input concentrations would allow the extractor to run on less energy than would be produced from burning the methane extracted?

I looked into this once---could you put a semipermeable membrane extractor in (say) a cattle feedlot, and turn the ppm methane into concentrated methane? The answer is basically No---the best membranes for the job have only a factor of 3 or 4 discrimination between CH4 and N2, which means you're doing a lot of work pumping on a lot of membranes. There are natural-gas wells that are uneconomical because the CH4/N2 mixture they put out is too expensive to separate. The main practical separation technique is cryogenic---you chill the whole gas stream (huge energy cost in the cooling, which you try to recover later in heat exchangers) and condense out the components you want.

 

[Furcifer]

Regarding the other main question on extraction and burning of the methane -- is there a way to extract methane from air; that is, concentrate a subcombustible mixture of methane and air, into a combustible one? If so, what range of input concentrations would allow the extractor to run on less energy than would be produced from burning the methane extracted?

This stuff: http://pubs.rsc.org/en/Content/ArticleLanding/2005/CC/b416752j

or fractional distillation. Fractional distillation is energy intensive. Finding a less energy intensive way of exacting methane would go a long way to solving global warming.

 

[recursive prophet]

This is the start of John Popovich's attempt to respond to each individual issue raised in this forum. I have increased the print size of his explanations to clearly distinguish his words from my own and Martin's. John asked me to express his gratitude to all who have taken the time to read about Solaculture and post their questions and critiques on this concept.

I'll believe this one when I see it work.

I don't see how the solar heating induces a downward flow through the membrane, for starters. I would expect an upward movement, as the hot air rises. Certainly this is an arrangement similar to a solar chimney, and those capture the upward movement of air for energy.

Solar heating and evaporation do lead to upward airflow. It is possible to reverse the typical upward flow of air resulting from solar heating and evaporation by the use of an engine or a fan and/or via stack effect. Membrane may be a poor choice of words as it often refers to separation at the molecular level, not a subject of interest in this case.

If he's inducing an inward flow of air by means of a blower, the power has to come from somewhere. If it's coming from the turbine that moves the methane and air into the burner, then basically he'd be describing a jet engine, but the power neccesary to pull air through square miles of porous membrane would be immense and there goes your effeciency.

The force required to reverse the typical solar induced upward flow is very small and is determined by the planform area and the difference in density over the height of the column of air where the flow reversal is desired (deltaPA). The work required is equal to the force times the vertical distance traversed (FxD). The slightly subatmospheric pressure within the canopy causes air to flow thru the holes in the canopy in proportion to the number of holes and the inverse fourth power of their equivalent hydraulic radius (Darcy’s law for laminar flow). More holes mean lower resistance and more flow. The equivalent hydraulic radius of a hoop house or other manifolding means can be several thousand times the equivalent hydraulic radius of the holes in the canopy film and the overall hydraulic resistance is as a consequence almost wholly determined by the hole resistance with very little dependence on the distance between the hole and the fluid mover.

The fan power required in watts is equal to the pressure difference in Pascals times the flow rate in cubic meters per second. A temperature difference of 200C and a height of 1 meter imply a pressure difference of ~100 Pascals which would require a minimum of ~10kw fan power for the 100 m3/s flow rate proposed for the 100 hectare array outlined in the Solaculture website. Assuming other resistances and real world fan efficiencies, a 500% increase in fan power would result in a 50kw requirement, a small amount for a 100 hectare array with a 1000 Megawatt peak solar input (50watts fan power required per peak Megawatt solar input). A large portion of the populated latitudes receives 2000kwh/m2/yr and a peak solar input of ~1kw/m2. Averaging the solar input over the 8800 hours in a year yields ~225w/m2 or a 24hr annual average of 225Megawatts input for a 100hectare array.

He's talking about extracting methane from decompositon, and running the methane, plus the air that percolates through the membrane through a burner to power a turbine. Methane and air are flammable in mixtures from 5 to 17 percent at atmospheric pressure and reasonable temperatures, according to some brief googling. That's an awful lot of methane in a breathable atmosphere, and at the same time an awful lot of breathable atmosphere in a process that works best in anaerobic conditions. Trees may use carbon dioxide, but they also are aerobes and use oxygen. Keeping them in a condition where the leaves are in a mixture depleted in oxygen, and the roots are in a condition suitable for rot sounds rather implausible.

A large volume of gas in explosive concentration is certainly not proposed and control means to prevent such concentrations are important. One of the ways methane from landfills is utilized is called cofiring, where an engine driven generator is fueled by natural gas supplemented by methane. Methane produced from decomposition of organic constituents within a landfill may be able to provide a portion of the load but not required to provide stoichiometric proportion. It is also possible to provide a portion of the methane in the airstream and a portion of much higher concentration from a plumbing manifold within the local earth. Catalysts can be used to burn very lean methane/air mixtures and gas turbines (Brayton cycle) typically operate with 5X the air required for stoichiometric combustion, so there are several means to operate engines or furnaces without creating an atmosphere with explosive potential. Methane is produced by microbial processes in the earth rather than by plants and some of it is transported thru the plants to the atmosphere but the bulk of the methane is transported thru the earth to the atmosphere. Methane is not apt to react with plants as it is a very stable molecule (CH4), which accounts for its high Global Warming Potential (GWP). The atmosphere in the canopy may include increased CO2 from exhaust gas recirculation (EGR) to accelerate plant growth.

He talks about carbon sequestration, but this process is carbon neutral; he'd be using sunlight to make biomass, rotting the biomass to make methane and then burning the mixture and releasing it back into the atmosphere. he shows a condenser for the water, but water isn't the issue, or is a tangential issue. He's still releasing the carbon back into the atmosphere.

If the net plant matter is increased, the greenhouse gases CO2 and H2O are removed from the atmosphere, and if a particular Solaculture array that represents a net increase in plant matter is operated in a carbon neutral scheme, atmospheric CO2 and H2O are still lessened by the net increase in plant matter and the sequestration of water within the local earth. Additional CO2 can be converted to carbon and stored as humus, which also greatly increases the quality of the soil.

Water is a big issue for a number of reasons: it is an important greenhouse gas and groundwater is being rapidly depleted and introduced into the atmosphere, increasing the greenhouse effect. Groundwater stores are part of a hydrologic cycle with timescales of thousands of years and anthropogenic depletion of groundwater stores may have an importance similar to the depletion of hydrocarbon stores. The American breadbasket is rapidly depleting the Oglala Aquifer that supports it and the consequences may be troubling. Many regions cannot support agriculture due to lack of water so the ability to capture and recycle water is an important part of Solaculture technology. There is evidence that droughts have caused the demise of civilizations, including the Mayan civilization in the Americas, so a means to create drought tolerant agriculture would be attractive. It’s easy for us to forget that our own civilization is very dependent on agriculture since so few of us are required in that effort at present, but we may be cruelly reminded as others have been and all the computers and all the kings’ men may be for naught. The vast majority of solar radiation impinging on a Solaculture array serves to convert liquid water to gaseous water. Solaculture is primarily a mechanism for the organized evaporation, transpiration, transportation and condensation of water. Plants may absorb as much as 3/4 of the sunlight striking them but the vast majority of this energy is used to evaporate water. Plants used evaporation to pump liquid water and other constituents from the earth and for cooling. The combined evaporation from the earth and transpiration from plants is collectively called evotranspiration and it is the primary vehicle for energy transport in Solaculture.

This could plausibly be done (and is done) as separate cycles. It's an old hippie commune thing from the 'Other homes and garbage' days. Sun on grass or grain, plants in cows or chickens, critter waste in an anaerobic digestor, digestor gas to a turbojet. (more likely an old light plant engine, or even a lawnmower belted to a car alternator, but a turbojet would work. You can make a decent turbojet from a turbocharger.) The point is that all the steps in this process require their own individual conditions to work efficiently, or work at all. Putting all the bits in one container, and trying to find an optimum condition that'll let the whole thing work well is problematic. Finding a condition that'll let the whole thing work at ALL might be problematic.

Reductionism manifests itself in product design in the separation of function mantra, but clearly biota are examples of integration of function and this must be an indication of economy of means and worthy of our pursuit. Plants use their vasculature as structure and mechanism. It might be an interesting design exercise to try to design them with separation of function.

Consider a closely spaced hoop house array with perforated film enclosures and the interior volumes connected to the air intake of an engine driven generator. As the load on the generator increases, the flow of fuel is increased to maintain a constant generator rotation rate. If the air entering the engine contains some methane, it simply means that the control system will have to add less fuel to maintain a constant rotational rate. The conditions within the array may change with time and the amount of methane may increase in a mature Solaculture array or via the addition of organic media such as manure, sewage, or agriculture waste and less supplemental fuel may be required. It doesn’t seem like a wildly complicated scheme.

 

[recursive prophet]

Whoops! A mistake I didn't catch. In the text John sent it reads 20 degrees C. Vb didn't recognize the symbol, and turned it into 200 degrees C. Sorry. Can anyone tell me if Latex is supported here??

 

[ben m]

So the plan is that your 100m3/s exhaust contains so much methane that you can burn it in a gas turbine? At 5% methane, that's 5m3/s of methane, or something like 200MW of thermal power. Given that methanogenesis is pretty inefficient (correct me if i am wrong) that would have to represent something like tens of gigawatts of non-methane-generating metabolic power.

A) Do you think you actually get 5m3/s of methane from the conditions in your greenhouse?

B) What's the point of all this solar-energy capture? If you're getting as much methane as you claim, the solar input is a tiny correction to the (huge) metabolic heat source in your greenhouse.

C) Your greenhouse needs to produce more methane-energy than it receives from the Sun. It's not a closed cycle sun-to-plant-to-humus-to-methane plant. Either it's a dump site with shipments of biomass getting trucked in ... or it's going to have a lot, lot, lot less than 5% methane in that 100m3 extractor fan stream.