In the spirit of R Ranson's post about spending money wisely to save money (which I just started reading... a great read by the way)... I was thinking of a big project as part of my future farm plans.

It was somewhat random that in my surfing through Permie land I came across a podcast yesterday with Paul and a couple of folks about hot water.  I listened to it, despite the agonizingly long thing about legionella disease (which is a good thing to know about), and I got to some other juicy stuff that probably wont kill you.  So Here's the Podcast  Skip to halfway if your are interested in Jean Pain, and the other ideas in my thread today... but they aren't detailed in the podcast... it was more of a seminal concept.  Caleb also mentions Milkwood Permaculture's Rocket Stove Hot Water Heater.  So I visited this site too.

I've been interested in Jean Pain for a long time. And that's what I waded through the Legioneer's disease to get to.  But I was disappointed.  There was really not much new or exiting info in the podcast in regards to getting systems like Pain's happening.

The thing that really got me jumping though, was when Caleb got onto the subject of creating a large hot water boiler/gasifier/electricity generator.  I really like the idea.

I have been toying with the idea of getting into Jean Pain's stuff.  But the investment to get the thing rolling is... more than a bit of a jump. 

Why I think this idea of Caleb's is a jump worth taking for me:

  1.) A guy who owes me a favor said he'd sell me a chipper really cheap.  I figure if I chipped wood and dried it, it would be great for gasification.  I have a lot of wood in my woodlot, and plan to devote a good chunk of my meadow to produce more... lots more.
 
  2.) I purchased a tank off a water truck.  It's stainless steel and 800 gallons.  It was used to water an orchard in Canada's Okanogan Valley in the past.  I was originally intending to put my water line through it, so that every time I turn on the tap it would flow cold creek water through the pipes thus keeping the water in the tank cool itself cool.  The tank would be in a celler, but part of it would be through a wall into the pantry.  The plan was to turn this part through the wall (the pump cabinet made of plate steel) into a fridge, and have access to it off the kitchen in the pantry... blah blah.  A cool idea, but... now I'm thinking that that idea might not work out as good as I thought since the water in the creek is warmer in the summer and the water tank will be constantly trying to gain temperature homeostasis with the celler space.  Might be possible to have that work.  Still toying with the idea of doing that or something similar, but I think this tank might serve a similar purpose, except hot.  Really hot.   Hot enough to heat my yet to be built 60X16 foot greenhouse for a week.

  3.)I have a strong interest in biochar, but my retort is quite small, and so not very productive for a 40 acre permie farm.

  4.)I have a small creek and have toyed with hydro-electric, but, although I do have the head, I have yet to calculate the volume (probably, to be honest, because I'm afraid it wont be enough), but it is also because to get the head to really make it worth it, I would have to dig a three thousand-ish foot trench, and buy that much pipe, plus build the generating system and get the heavy wire to bury from the generator back from the bottom of the property (to get maximum head) to the structures where I want to build them.  I don't have a machine, and the cost of the trench alone (to go below frost) would be quite high, let alone the rest, and so when I stumbled upon the work of Ben Peterson on Youtube, and as a result his ad for his book, I'm very much considering getting: Wood Gasifier Builder's Bible: Advanced Gasifier Plans to Build Your Own Wood Gas Generator. Make Free Biofuel at Home.  Since I just received word that my bid for a welding position at work was successful (holy crap, nobody with higher seniority bid this job... I can hardly believe it!), and I will be trained for free to learn it... I might be able to construct a Ben Peterson style gasifier for under $2000 Canadian, if I do the welding and source the parts myself.  I still need to dig a water line, but if it's just for my house and garden I have more than enough head to do that with a much shorter line.

  5.)I have a plumber friend and a gas fitter friend who would probably help with negating the boom squish of hot water and the boom death of flammable gasses.  Even though I think I could figure it out.  I might get them to do the finicky bits.

  6.)I have a pretty new diesel generator that has hardly any hours that I could probably sell or trade for one that might run efficiently off wood gas.

  7.)I have a virtually limitless quantity of used 5 gallon buckets at my disposal (I think... they do get 'recycled' <-whatever that means... but I think the Railway I work for gets charged to recycle them so I might be able to get them to let me have them for free).  The buckets had hydraulic oil in them... for track maintenance machines.  So I was thinking of filling the pails with rocks and sand, and stacking them near the water tank, making a wall with them on three sides of the tank, and filling the gap between them and the water tank with cob and stones.  Thus massively boosting the thermal battery capability of the water tank.  Part or all of the North wall of the greenhouse could also be built of these.

  8.)I purchased a defunct refrigerator semi truck trailer 53 feet long for $3000 Canadian.  It is the cheapest largest insulated shed that money can buy as far as I know.  I plan to drop the thing on the ground (remove the wheel chassis system), and use it as the back of the North wall of the greenhouse (the front of it will be thermal mass of some sort... possibly stacked buckets full of sand and stones, covered with stucco).  North of the truck I plan to build a wood storage shed.
 
  9.)I have an enormous quantity of dead pine on my land, falling down that I would like to get into a shed so that I can either burn it efficiently or build with it.

  10.)I know several people who have hot water boilers with pex water lines in their floors, so I know that I can get this knowledge fairly easily to go from the gasifier unit to the tank.  I'm not sure the best way to create the heat exchanger... so I could sure use ideas there.

Sorry, this is such a massive post to start a thread, I hope that people make it far enough to get my request for help.  

Am I missing anything?  Tell me how to hook the bits together in the most efficient way.

Maybe I missed it but what is your goal?  Hot water for potable use?  Hot water to heat the house or greenhouse?  Electricity to go off grid?  Maybe all of the above?  Do you have any wind or solar resources? 

Thanks for your response Mike

Maybe I missed it but what is your goal?  Hot water for potable use?  Hot water to heat the house or greenhouse?  Electricity to go off grid?  Maybe all of the above?  Do you have any wind or solar resources? 

 

Hot water to heat the greenhouse for sure, and hot water for the house... maybe (I would like that).  In the later case, a line would have to be dug below frost, and insulated and be about 300 feet with the present house location plan (which I could move closer).  It would be a separate line that is gravity fed, enters the tank full of hot water and gains exchanged heat and carries on to the house. 

Nothing is built yet.  No house.  No greenhouse. Just an outhouse up the hill and some garden space!  The pad for the greenhouse area has been leveled.  The semi trailer is sitting on it, but at the wrong location, and has to be moved into position.  Electricity to go off grid, Yes. I have no grid connection yet, and have no want to hook up to it... unless I somehow develop a system with excess to sell... and even then I think I could sell to my neighbors. 

Wind is sporadic and when it really comes it REALLY comes, but then it's not reliable so should be part of the equation.  Solar...  Well, right now, Dec 8th, the day starts to brighten around 7:15 am, and right now, as I write, it's dimming dusk at 4:11, but the direct sunlight on the land (house site) is considerably less.  I work away from the land, but from what I seem to remember from the weekend, I'd reckon that the Sun didn't get past the mountain and trees to hit the house site until around 11 and ducked behind the mountain around 1:45.  That is if the sun is not obscured by clouds... which is pretty often here on the wet/west side of the Rockies, although today was a gloriously sunny -20 C day minus the wind chill (not that temp has anything to do with Solar gain), but I don't think there is much potential there. I should note that although there are people with solar projects here, most have backup systems with diesel generators, or have such small energy needs that they can suffer through the low light situations... So it is possible.   I could also build a smaller hydro set up with less head, because at least that is constant, and combine it with the gasifier generated electric... which is definitely worth considering, since I do have to dig a shorter trench for my waterline and buy pipe anyway.    

So I should say that the main goal is to create electric power for the property, but getting hot water heat for the greenhouse/ hot water, and biochar out of it... them's the fancy icing on the cake.

Thanks Roberto, that helps.  I don't have much knowledge in the electricity generation department so unfortunately I can't be of much service.  In my area I spend as much to be tied to the grid as I do for the electricity I consume

I did look at that link for the rocket water heater and it looks neat.  If you're trying to heat a greenhouse it seems to me that it would be simpler to heat it directly with a rocket mass heater than to heat water and transport that to the greenhouse and get the heat to go into the greenhouse.  Unless getting heat piped into grow beds is you goal and then maybe hot water is the way to go...

I'm interested in the Jean Pain method myself.  My thoughts are to put the compost inside the greenhouse so the heat is right where you need it.  I'm still working on my greenhouse design but I'm leaning towards an A frame shape with straw bale insulation on the North, East and West.  I'm also thinking about a solar pool cover for the glazing.  It's like really beefy bubble wrap.

Hi Jay.  Thanks for you interest and time in responding and talking about your own plans for your place.  I must not have been very clear with something I wrote.

So in this following quote from your last post, I need to clarify and expand your knowledge of my ideas, so that we may come to further ideas together, and maybe someone else will join in too

If you're trying to heat a greenhouse it seems to me that it would be simpler to heat it directly with a rocket mass heater than to heat water and transport that to the greenhouse and get the heat to go into the greenhouse.  Unless getting heat piped into grow beds is you goal and then maybe hot water is the way to go... 

  The plan as written so far in this thread (not written in stone... this is presently in brainstorm space/time continuum!) was to have the gasifier heater in the greenhouse, directly beside the main storage unit, which is the 800 gallon hot water tank surrounded by solid thermal mass (cob, rock, buckets with sand and rocks).  The piped hot water would be to the house, and that would not be used for heating, but for hot water use in the taps.  I'm considering having the house close, or right up to the greenhouse in order to eliminate the problem of long distance piping, and of trenching and insulation of the pipes. The house will be heated by passive solar design, combined with RMH, an old fashion cook stove, a cob bread oven... etc.

I inserted some numbers in your quote so I respond directly to that part

1.)My thoughts are to put the compost inside the greenhouse so the heat is right where you need it.  2.) I'm still working on my greenhouse design but I'm leaning towards an A frame shape with straw bale insulation on the North, East and West.  3) I'm also thinking about a solar pool cover for the glazing.  It's like really beefy bubble wrap.

 
1.) Instead of Jean Pain system inside the greenhouse itself I'm thinking of a massive deep cottonwood/poplar hugulkultur/buried wood bed that encompasses most of the greenhouse area, with keyhole beds built above grade with large stones embedded in the keyholes to absorb and radiate heat.  I think that on the south I will have an insulated wall below grade and above grade and then berm against the above grade portion to create a wallipini out of it.  I'm also considering putting a double layer of plastic outwards from that wall (with six inches of dirt and sod on top of the plastic, and insulate under that plastic with 6 inches of dry duff as Paul suggested in his Wofati build ideas.  I might go with the Jean Pain system but not in the greenhouse... in a separate contained building against the house (with truck or machine access for easy of construction of the heaps), just for the hot water in the house, skipping trying to generated it via heat exchanging in the 800 gallon tank. 
2.) How are you planning to protect your straw bales from moisture?
3.)I'm not familiar with the solar pool cover.  I did look at them on google just now.  Do you think that it would be effective to grow behind?  Seems to me that it would provide the heat, but the quality of light might be altered significantly.  Do you know of anybody by example using this as glazing?  I'm very curious.  At this point I don't have glazing and like the idea of insulated glazing like this.  How is it for UV decay over time/lifespan?

To further clarify my plans:  The hot water to heat the greenhouse will just be radiated from the massive water tank/thermal battery of cob/rock/stone/sand, just as an RMH bench radiates to provide heat for within a structure or the area immediately around the outdoor RMH butt warmer.  The hugulkultur/microbial activity will do it's warming magic, as will the stones in the keyholes of the beds, and the greenhouse will be as insulated as I can make it from the outside air... so I will not be piping any hot water in the beds.  The beds will be built once, and directly on the Earth, with no protection below them and no piping at all within them.  I want uninterrupted connection to the Earth in the beds, and the soil structure, once built, will be disturbed as little as possible.  I have an idea to have the soil surface to be possibly mulched with biochar (inoculated with compost and fungi) as the char will be developed in the gasifier system.  The dark surface created by the biochar will further enhance solar heat gain.  Or the biochar could be mixed in to darken a shredded wood mulch.

Thanks for the clarifications Roberto!

I don't know enough about gasifiers, but keeping the big tank in the greenhouse with cob/mass around it sounds like a wonderful heat source for your greenhouse.

Keeping with the numbers... 
1) I read this book on compost heat by Gaelan Brown which helped me figure some stuff out.  Somewhere (not necessarily in that book) I heard that you need to have a compost pile at least 4' to a side in order to generate good heat.  Bigger is better.  They also give off CO which plants like.  I don't know if biodegrading hugulkultur beds generate heat or not.  Aeration is part of the bacterial process as I understand it so you need to get air into a Jean Pain system.
1.2) I'm also planning on insulating outside the foundation.  I debated enclosing some of the dirt outside the foundation wofati style so that it becomes thermal mass for the greenhouse.  But I'm not sure how likely that is to work properly.  And if you do that as you proposed, would the insulation against the below grade foundation negate the effect of the thermal mass just outside it (block heat from getting to/from that mass)? 
1.3) If you have the materials and a structure to do compost heat next to the house, you can do a whole lot of heating with it (not just potable water).  In some book or website I've seen there's a farmer that used a shipping container shaped structure and filled it with manure/compost.  He hung water pipes from the ceiling and circulated water through them.  He was heating a large building with the water.
2)  I haven't figured straw bale moisture protection out and it's next on my list of things to research.  For the roof my initial thought is to start with a wooden structure.  Then put old roofing tin across the wood poles. Then a layer of plastic.  Then the straw bales.  Then some housewrap.  Then some 2x4 sleepers.  Then a cheap (metal, ondura, fiberglass, etc) roof attached to the 2x4s.  At the edges it would have ridge caps and protection.  I'm assuming I'd need some air flow through/above the bales which would require some vented soffits or something.  For the walls I'm assuming I'll just have a stack of straw bales with 2x4's as furring strips on the inside and outside.  Then have plastic on the inside and housewrap on the outside.  Then attach finish materials to both sides.  Like I said though, these are just my initial thoughts and I need to do much more research on them.
3)  I've found some references to pool covers being used on greenhouses.  Here's the best bit of info I've found so far (Greenhouse Forum).  They handled golf ball size hail and the sun of Texas for 10 years for one lady so I think they're definitely durable.  It sounds like they give decent light.  I haven't seen a R value for them yet, probably because they aren't designed for insulating air.  I was going to call a pool place but haven't gotten around to it yet.  I am quite interested in this material.  They put it bumpy side down so the snow will slide off of it.  I'm wondering if you put it bumpy side up and then covered it with a layer of greenhouse plastic if you would get even better insulation (more air pockets between the air pockets).

I'm also planning on insulating outside the foundation.  I debated enclosing some of the dirt outside the foundation wofati style so that it becomes thermal mass for the greenhouse.  But I'm not sure how likely that is to work properly.  And if you do that as you proposed, would the insulation against the below grade foundation negate the effect of the thermal mass just outside it (block heat from getting to/from that mass)?  

  Mainly, in my present plan, the thermal mass is designed to be within the greenhouse glazed catchment only.  This would be in the extremely deep damp warm microbe and fungi rich soils, in the stones in the keyholes, in the water tank/aggregate storage zone, in the back wall of stone/buckets filled with aggregate, cob... etc.  The foundation will be insulated downwards four feet from the bottom of windows on the South wall , and the outer area insulated outwards, maybe 10 feet.  In this case, the area outside does not act as thermal mass, and is not expected to contribute to thermal mass, but instead it adds a huge amount of additional insulation to the foundation, thus it creates isolation from the outside environment in winter, enveloping a large area of external Earth.  This increases the thermal inertia.  I could just go with insulation outwards, just below the sod, and not have the insulated wall.  It would be cheaper (pretty much free, because the duff just takes some time to gather and haul), so there is that, and then the area under this insulation on the outside becomes part of the thermal mass, which seems to be what you are saying.  But I'm not sure if that is the best way to do it yet.  I'd rather keep more of the main heat stored in the living greenhouse soil area and not outside.  But this way with thermal mass extending outside (without an insulated wall) is possibly the way to go, and I'm open to trying to figure out what is the best way to do it to maximize solar gain, while minimizing heat loss, while doing all of it with as few resources/time/money/ etc as possible.  I'd like to be convinced that that is the way to go.  But, like with how I started this thread, I'm willing to spend some to save more in the future, and so if I have to pay to insulated downwards at the wall because that is the best way to do it, then that's what I will do.   Right now I have a steady good paying job, but I plan to quit it within three years, as I find it to be an ethical compromise.  It's paying the mortgage and getting the infrastructure together... after that... I want to do permaculture/market farming here.   

I will respond to the rest of your post in the morning.

Roberto...you really impress me and remind me a lot of myself. You have no idea how much your hydro project sounds like mine in problems, right down to distances and height and everything, and for that reason mine has never progressed far either. Like you, I also enjoy Jean Pain's experiences with compost heat.

My biggest cost, home wise and as a commercial sheep farm, is in heating water/electricity. If I could reduce those costs, I would be much farther ahead, which sounds like you. So I think about how to get rid of those costs and be more competitive...a lot!

I know nothing about gasification units, but have wondered (way too much) about the potential of using compost heat for electrical generation, not via gasification...though I am not denouncing it, just thinking on a diverging path (an ex-railroader, Machinist/MOW myself), but of the possibility of using geothermal/compost heat via a Sterling Engine?

My concept is simple; since a Sterling Engine is powered by the difference of hot and cold, would it be possible to create the "heat" via composting sheep manure and wood chips on one side of the engine, and then for the "cool" side having pex tubing buried in the ground drawing the 57 degree water via geothermal cooling. Now I am not sure the difference would be enough to power an engine, but if that was an issue I could easily operate an ice house and cool my Sterling Engine via that. In the meantime, the compost pile would give me long term heating.

Is it possible? I am not sure, it sounds plausible, because I am not reinventing the wheel or messing with thermal dynamics, physics or mechanical engineering. My real concern is finding a working Sterling Engine. I know they exist, but I have only seen tiny explain-the-concept engines like soda cans and the like...nothing that truly performs work like powering a jenny. But I share the concept with you as I deeply respect you, and would love to get your take on my crazy idea?

My only other idea...and it had progressed some...is biogas from my sheep farm manure, but it seems problematic at this time.

A secondary idea, and one I share because you may be able to benefit from this too, is to build an off-grid cabin close to the turbine site and have it powered via the microhydro. By renting it to potential Permie people who would like to dip their toes in the Permie lifestyle for a week or two without commitment, the income from that could be earmarked for my grid-tied house and farm.

Hi Travis.  Thanks for the compliments and your thoughts on such projects.  I feel a kindred spirit coming from the Straw discussion and beyond.  I sent you a Purple Moosage about your Sterling engine idea. I have only a passing glance of knowledge of these devices. While I understand that the temperature difference between hot and cold drives the engine, I'm wondering if the difference between your New England creek and the ice is going to be worth the effort for the icehouse.   Since you have gravity water from a creek (Which is relatively cold) and need the hot water to move through your in-floor heating (<-which I'm assuming was a jean pain ish plan to heat your greenhouse), you could take the water from the creek and run to the cool side of your engine in the same cycle of water that eventually gets heated by the compost to be brought to the hot side of the sterling.  But perhaps the creek not being cold enough in relation to the hot?.  You could have an ice area and run the cold water underneath it?  I like the idea of the sterling engine but I have trouble wrapping my brain around it.  How does the cold side stay cold.... by constantly cooling it?  It seems that that alone would be the inefficiency.   The hot side and cold side need to be very insulated from each other.  We should definitely move this to another thread!  

Hi Mike:

Somewhere (not necessarily in that book) I heard that you need to have a compost pile at least 4' to a side in order to generate good heat. 

  The thermophilic community seems to respond well to these dimensions or greater in my experience.  Clearly if a person wants a long term project (heating for the winter) it will have to be much bigger, or that person will be building piles all the time. 

I don't know if biodegrading hugulkultur beds generate heat or not. 

Yes. True. Not when compared to hot compost.

Aeration is part of the bacterial process as I understand it so you need to get air into a Jean Pain system.

I'm not sure if Pain did that.  It seems that the structure of the shredded wood being piled up had enough aeration.  All I have found on the subject is piling it up and moistening it in layers.

references to pool covers being used on greenhouses.

  I'm hoping for tempered glass, but this does sound intriguing.

They put it bumpy side down so the snow will slide off of it.  I'm wondering if you put it bumpy side up and then covered it with a layer of greenhouse plastic if you would get even better insulation (more air pockets between the air pockets).

This makes sense.  The only thing that might throw it off is that condensation might happen between those layers.

Hi Travis

My only other idea...and it had progressed some...is biogas from my sheep farm manure, but it seems problematic at this time. 

  This might not be as complicated as you think.  You might want to try creating a different permies thread for this, or try posting something on a different forum altogether.  You are definitely not reinventing the wheel on this one, or the Sterling Engine, though, like I said, I know little about the potential of your Sterling proposal.  Keep at it.

I think I can give you some advice with my vast experience building compost piles. We never called them that, we simply were trying to feed our sheep and cows with silage and doing everything possible to stop heat build up, but it happens anyway. Even with new technology with amazing silage compactors, we are getting a lot of heat, so hot you cannot stick your hand into the feed very long. It has to cool off a bit before the cows/sheep will eat it. So honestly I don't think you would need aeration.

Another thought I had regarding heating water is to use the wind. I always thought using wind energy converted to mechanical energy and to electrical energy was a lot of conversion and waste. What if there was a way to make a windmill that produced hot water instead? I know from my work on locomotives that "from the heat of compression, combustion takes place", the proven theory behind diesel engines. I also know from my tractor that if you put the hydraulics through the relief valve, the oil gets hot pretty quick. So what if you created a simple windmill that moved a swash plate up and down pumping water (or oil) through a relief valve? By constantly doing so the water (or oil) would get hot. If that swash plate and oil was a tank inside a tank (boiler mate), it would heat the surrounding water up and could be used to heat a greenhouse (or anything else). In theory it is easy to scale up or down because the more captured wind, the more volume or pressure could be gleaned. At the same time, as the wind sped or slowed up, the amount of displacement that took place would be proportional. In an ideal world, a digital wind gauge would tell a plc (computer) to open or close an adjustable aperture on the relief valve so you would get some heat at low wind speeds (less of a load on the windmill) and higher amounts of heat during wind gusts.

The same could be said of an air compressor, since it gets mighty hot from pumping up that air. Rather then dissipate it to atmosphere, you could surround the compressor with a water jacket and use the heated water for various uses.

Or you simply could have a windmill churn a water cooled engine. It would not fire on diesel or propane, but rather just crank the one or two cylinders up and down causing the engine to heat up. Water flowing through the water jacket would then heat up and be available for use. Control of the compression to match the wind speed could be what amounts to a jake brake coupled to the valves. On all of these, a centrifugal clutch would allow the wind mill to spin fast enough before the appliance kicked in.

I agree that I'll need a much bigger pile than 4' by 4' by 4'.  I was leaning towards 4' by 5' by 40' but now I may do more of a cylinder 6-8' diameter about 6' high to conserve floor space.

Yes, Jean Pain used wood chips for his pile but from what I've read, the size of the wood chips allowed for air to permeate the pile and the mass of the pile and its own heat caused air to rise through the pile and self-aerate.  In my system I would hope for some self-aeration but have forced aeration just in case.

I'll keep researching the pool cover but I definitely have high hopes for it.  I know many people use two layers of plastic with air inflated between them.  If that doesn't have condensation issues, I don't know why it wouldn't work with a pool cover as one (or two) of the layers.  Of course two layers may block too much light.  When I get farther on my design I'll start a thread on it so we can all put some thoughts together on it.

As for the stirling engine, here's a low temp, large scale one I found a few months ago.Link

we are getting a lot of heat, so hot you cannot stick your hand into the feed very long. It has to cool off a bit before the cows/sheep will eat it. So honestly I don't think you would need aeration. 

  I agree.  I've made fairly dense compost piles that were quite wet and they generated so much heat that I could not put my hand in it.

That said, if you check out the subject system in this permies discussion thread link  (watch the under three minute video) you can see that they build their piles without aeration.  However, in this case they constantly flow the liquid in the pile, thus adding a consistent aerobic element in the heap along with consistent moisture. 

This obviously requires a powered pump.  I don't know how important or necessary that pumped liquid is if the material is shredded instead of just chipped, or if the material has the right particle size in the first place. 

So here's my take on it based on my experience and what I observe in this video and what I read of Jean Pain's project.  In Pain's heaps there was no aerobic element beyond the construction of heaping up the material.  I just re-read it-meaning the Mother Earth News articles.  The material in the one in this video is fairly course in comparison with Pain's, I think.  Pain's system shredded the material into pieces that were the size/shape of matchsticks (except bent and twisted as it was ran through a home made methane powered chipper/shredder machine.  This increased the ratio of surface area to the particle volume, allowing that much more exposure to water, thus to microbes. 

In comparison, a large wood chip has way more mass/volume in the ratio to the surface area that is available to moisture and microbes, thus more liquid and more aeration are needed to support the microbial activity to break down the volume in the large chip size and produce the heat. 

In the case of silage, there is a very high potential for the microbial activity for this same ratio reason.

In the permies thread I linked to, here's the youtube embed of that project:

Hi Travis.  If you are considering the windmill idea to generate electricity, I think that a simpler idea that might work might be to have the windmill run a small fan directly.  Every time the windmill runs, no matter what volume of wind is hitting the mill, the fan runs.  The fan pumps air into a line and compresses it into two tanks, alternately.  These tanks are your batteries.  Number one is charging while number two is being used as forced air to run a turbine, or directly to run air driven tools.

Hi Mike.  Thanks for the Sterling Engine link.  I'm embedding the video here: 

Some real interesting work done by these folks. 

Travis: just after minute 7 (total 9:57) the narrator mentions the temperature needed for this design (which he says is low for a typical Sterling Engine design).  100-200 C.   This is higher than I thought. 

I know many people use two layers of plastic with air inflated between them.

  I've heard of this, and read of this, including some having a heater blower (instead of just a fan) blowing warm air in the gap between glazing layers (usually plastic) so that it isolates/buffers the outside to inside temperatures creating a high thermal inertia for internal temperatures to be lost to the outside.  Of course using heat/fan energy is resource intensive, so this is not optimum. 

Simply inflating the space might be enough to do the trick, particularly in places that don't get as cold out.

If that doesn't have condensation issues, I don't know why it wouldn't work with a pool cover as one (or two) of the layers.

I might be imagining your idea wrong, but here's what I'm thinking with the condensation idea:

I think that with the inflated layers, the two layers are not touching... the air is forced to push the layers apart.  The surface area of the individual sheets of plastic in the inflated system is what it is by square footage, and they are flat so air flow is pretty equal everywhere.  When you lay the pool cover bubble side up and lay another piece of plastic on top, there is no continuous gap.  The surface area of the bubble side of the pool cover is much greater than that of the flat plastic sheet over it. The way I see it, this gives thousands of places for condensation to collect, and no forced air to keep the system dryer.  I might be dead wrong.  That's just how I see it. 

You are right to think that your pool cover/extra layer of greenhouse plastic would increase the insulation as the upper layer of plastic (if laid on top/outside of the bubbles of the pool cover) would trap all that much more air (in the gaps between the individual bubbles and the tangents created by the relatively flat plastic laying across the top of the bubbles).  

Very interesting. I did some searching and could not find a price on the Sterling Engine. Still a wee bit small at 1.5 KW, but if teamed up with compost heat where it was producing power 24 hours a day, it would be producing over 1000 KW's per month. This is the same greatest asset of micro-hydro; slow and steady is what adds the KW's up. But do not be discouraged by the higher than anticipated heat side of the engine Roberto. They actually said something at 7.35 minutes in, and that is the overall way a Sterling Engine works. It is not based on low temperatures, but rather the difference in temperature between the warm and cool sides. In there case it is 100-200 C's, BUT if you get the cool side lower in temperature, then the hot side can be lower in temperature proportionately, and still work. That is why I mentioned the ice block house and running the chilled water through there...greater temperature difference.

I am convinced more than ever now that compost heat powering a Sterling Engine that could power a small jenny could work. Thanks guys!!

As for compost, yes I suppose you are right I was contradictory in overstating my situation in being ideal for compost heat. Thanks for pointing that out, sometimes I need to be reminded I am one confusing guy.

For those that read my unedited post, please not from this point on...with further thought, I have realized that maybe compost heat is viable for me. That is because I have some interesting things kicking around, and my position on this hill may actually be to my advantage.

After reading the above and lengthy posts slower, and gleaning more information, I am wondering if I would be able to utilize a 53 foot insulated 18 wheeler trailer I have kicking around and not using? What if I made a deep excavation in my hillside, placed the trailer into the cut, fortified the roof so it would hold weight, then cover the top with at least 4 feet of fill. Only the back doors would be exposed. Through them I could fill the box full of wood chips and other compost materials like hay, sheep manure and the likes Then if I ran pex along the top and spaced closely together, theoretically it would warm the water and could be pumped to my house's for residential heating.

This may be doable. It is an all mechanical operation; loading and unloading the compost. There would be no moving of pex within the pile of compost. It would be a permanant set up. Heat would be slow to escape if encapsulated underground. Being positioned on a hillside, I can make the deep cut required and still have the trailer doors open "to daylight" as the term is known. This is obviously an adaption of what another guy is doing, but may actually work. It is 127 cubic yards of compost after all.

I found the youtube video where I saw the farmer with the compost to heat his sheds.  There is a TON of great info on this webinar.  The farmer is at the 26 minute mark.

With the semi trailer you would likely need an aeration system so air is either naturally drawn under the pile and rises up through it, or you force air in from above and let it escape out the bottom.  Either has its advantages/disadvantages. 

Enjoy: