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Offline roamer

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"Earth Works Energy"
« on: March 09, 2013, 07:46:55 PM »
Earthworks Label
Earthworks Label
Wanted to get a thread going for a an energy concept I'm going to be exploring more and hopefully developing at the foxstead.  I've attached some very rough conceptual sketches to aide in explaining the concept.  I've yet to really download the idea in full though so don't get too bent out of shape if all the pieces are not yet there, in fact feel free to brainstorm with me.

Design Intent:
The earthworks power system will be designed to deliver a steady 1kW of electrical power and approximately 20 KW of thermal power that can be extracted via hydronic heat.  The surplus of hydronic heat will support year long hydronic and aquaculture operations.  In addition to heat and power the earthworks plant also thermally assists in humanure and other composting.  This process is symbiotic as the released compost heat contributes to the overall cycle efficiency, while the high temp solar energy assures safe composting of dangerous crap bacteria. 

The system is able to provide steady state power by heating a large insulated thermal mass, which can carry the system for days without sunlight before running out of power.  In the event of long cold or cloudy streaks the system draws on dual biomass heat sources, which are an integrated biomass burning rocket stove and a large ongoing composting process.

All the components of the earthworks power system are designed to be of utmost simplicity, the unit can be built with earth, polyprolyene bags, ferrocement materials, pvc tubing, some mylar film, greenhouse film, off shelf windmill components an inverter and deep cycle auto batteries.  Of note is that the batteries are not used for storage per say, they function more less as system damping and therefore few batteries are needed for the system.

In summary the earthworks plant will act as a multi functional low tech resilient power system that is within easy reach for most DIYers.  It will serve as the core of any off grid power and food systems by providing system electricity, thermal heat, and composted soil ammendments.

Design Theory:
The theory of operation of the unit is really quite simple.  Air behaves roughly like an ideal gas where Pressure*Volume=N*R*Temperature, which means that for a fixed volume pressure increases linearly with temperature.  It is this pressure increase cause by temperature which will provide the motive force to turn the 1kW wind turbine mounted horizontally in the duct.
Efficiency of the electrical system is bounded by carnots law which states efficiency=1-Temperature Cold (in absolute units)/Temperature Hot (in absolute units).  Since the system will run on average at 160F and exhaust to the ground at 65deg F our upper limit electrical efficiency will be 15%.   A non optimized wind turbine though will be very sub optimal at capturing this expansion gas and so I am figuring we will operate at 1.5% overall electrical efficiency or 10% of the Carnot maximum.  For intial prototyping it does not pay to try to increase this, but should the design catch on I believe that that efficiency could easily be doubled.  I also have ommited the fact that I intend to spray the hot exhaust post turbine before it goes into the ground with cold water.  The heat of evaporation will subcool this exhaust and further reduce backpressure and increase power, I have not done the calc on this, but suspect that it may make performance much better than I am estimating here.

Efficiency of the thermal system is a bit more straightforward.  It is the efficiency of the collector minus losses in the heat storage building.  I placed this at 30% overall efficiency. 

Construction
Building:
The core of the system is nothing more than a well insulated high thermal mass crude building with a south facing black wall that has concentration and greenhouse film acting on it to help trap the heat.  This structure can be built easily out of either earth bags or compressed earth bricks.  It is best to build into the ground and then if possible use the evactuated earth for building the sidewalls.  The ground can be insulated in a number of ways, but plastic and straw may prove the cheapest.  Similar insulation strategies will work for the walls, A double walled structure with the void filled with straw will work well.  The front wall though is not to be insulated so that it can transfer the heat to the structure.

Chimney:
This can be built with bricks, bags but needs to be ducted to fit the 4' wind turbine well.  It may be easier to scrap for large corrogated tubing or something similar...

Below Ground Water Tank:

Earthworks Sketch Side
Earthworks Sketch Side
Earthworks Sketch
Earthworks Sketch
...........
« Last Edit: March 09, 2013, 07:59:37 PM by roamer »

Offline RE

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Re: "Earth Works Energy"
« Reply #1 on: March 09, 2013, 09:31:25 PM »
How goes work on the Prospectus?

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Re: "Earth Works Energy"
« Reply #2 on: March 10, 2013, 10:46:19 AM »
I stewed a bit on this device this morning, and it seems to me you could Model it in small scale to see how much pressure differential you can achieve simply by heating air, then running the heated air through a miniature fan.

My intuitive sense tells me that you will not be able to generate enough velocity across the gradient to effectively drive a Wind turbine. Beyond that, on a large scale project it would have  to be very airtight, hard to achieve with these building materials.

The "Reactor Pit" idea though I think is a good one, and you might do better with a closed loop system using a volatile liquid that boils at a low temp, although getting hold of such liquids after TSHTF would be hard.

Overall, I think a Stirling Engine with reflector Solar Concentrators sufficient to Boil Water will do a better job generating electricity.

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Offline roamer

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Re: "Earth Works Energy"
« Reply #3 on: March 10, 2013, 11:22:58 AM »
RE,
Do the math PV=nRT, if you maintain constant volume and raise your temps to 165 deg and exhaust to 60 deg F I predict I'll have ~2.9psia of driving differential pressure, which is actually excessive for most wind turbine blading.  To optimze I will have to have two stages of expansion.  Keeping it airtight is not a big concern, all that needs to be air tight is the main ducting.  The main concern is keeping the building really well insulated.  Its really just a big thermal mass battery and as long as the temperatures near the duct are maintained at 165 deg F the turbine and outlet at 60 deg F it will put out its power output, regardless of wether the building leaks, though if the building leaks it will require more firing of the biomass system so as I said before keeping the thing insulated is paramount.

I've stewed over stirlings, and organic rankine cycles considerable too, they could be done more efficiently but are too complex for SHTF scenarios.  There is one awesome stirling system out there http://www.bsrsolar.com/sv/produkte3_e.html  but it relies on complex fresnel lens arrangement to collect and store hot enough fluid to justify the complex slow speed stirling.  Low temp solar  energy systems will never do what we have gotten used to in the age of oil.  All that I am shooting for is enough electricity to power site communication systems a couple laptops LED's and a refrigerator.  The rest of the power is heat for food systems and heat for homes. 

Prospectus is not going too well at the moment.  I'm cranking through some taxes and trying to see a different angle on attracting financing.  Will post some notes on that soon.

Offline RE

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Re: "Earth Works Energy"
« Reply #4 on: March 10, 2013, 12:03:36 PM »
RE,
Do the math PV=nRT, if you maintain constant volume and raise your temps to 165 deg and exhaust to 60 deg F I predict I'll have ~2.9psia of driving differential pressure, which is actually excessive for most wind turbine blading.

I know the math on the unified gas law.  Issue is that "T" in this law is measured in Kelvins, not Farenheit.

So, 165F=347K and 60F=289K.  Divide 347/289, your Pressure Differential is only 1.2, not 2.9.  This also assumes no gas leakage of the system, about impossible with such a large structure.

That's the math, but like I said, you could build a workshop model to test it.

I think for generating and storing the low power electrical, you are better off wiith the Wind/Gravity system of yanking sandbags up a hill.

The Heat Sink mainly seems good for Heating and perhaps Slow Cooking.

I don't think you need Fresnel lenses for solar concentrating, I think you can do it by Polishing Sheet metal off dead carz and make large concave reflectors.

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Offline roamer

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Re: "Earth Works Energy"
« Reply #5 on: March 10, 2013, 12:29:48 PM »
RE,
I understand absolute temps just fine, 1.2 though is the ratio that pressure increases relative to atmospheric pressure so 1.2*14.6psia -14.6psia gives you your differential pressure which yields the 2.9 psia differential I quoted. 

I do agree though a model is the first place to start. 

The problem with wind is its very very site specific, a good strategy for some areas a worthless one for others.  We have been through the drawbacks of storing energy in gravitational fields (extremely low energy densities). 

Concentrating for high temp thermal issues is also very site specific as it only works with fairly clear skies.  The fresnel strategy on the link i mentioned was actually much more sophisticated than you might think.  The reason they used it is so that the portion of the energy spectrum responsible for plant growth could pass through and help plants grow in the greenhouse, so the fresnel lens accomplished two functions in that setup not just boiling water.


Offline RE

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Re: "Earth Works Energy"
« Reply #6 on: March 10, 2013, 01:02:06 PM »
OK, maybe for the mass heat sink.  :icon_mrgreen:

Also,while energy density is low on gravity systems, weight is infinite in sand and rocks. Long as you set up so that weight is always being pulled uphill while the wind blows,  you store the energy.  All you need to do is gear it right. Say 10 Tonsof Rocks in a Dry Box Trailer.  Hill slope 20 degrees,total altitude displacement 100ft. Windmill driven Winch pulls it uphill inches at a time at 10MPH windspeed.

Said 10 tons of rocks moving back DOWN the hill will easily turn a 3000W alternator, again geared right so the trailer takes a couple of hours to go back down the hill.  It might take a week of light breeze to get it up the hill for 4 hours of 3000W,but that is enough to charge up your laptops and battery bank for the week. One REALLY Windy Day, maybe you can pull10 trailers up the hill.

Same principle for a running stream, or Exercise Bikes everybody rides each day for an hour.

Use ALL the methods together, I am sure you can store all the energy you need to convert to electrical for just communications and basic lighting.

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Re: "Earth Works Energy"
« Reply #7 on: March 10, 2013, 03:42:48 PM »
RE,
I got to admit that sounds pretty fun to build, even if its a bit rube goldberg'ish.  If my math in my head is right your example would give just under 1kWhr of storage.  Enough to run 4 50W laptops for 5 hrs. 

I'd recommend though that the tribe takes a step back and examines with utmost criticality what we actually need electricity for.  I know way too damn well just how hard it is to get a decent EROEI in natural energy systems.  Designing our lives around as minimal electrical consumption as possible is the easiest way to accomplish this.  I see electricty primarly for LEDs, limited laptop use, refrigerator and future communication systems.

Offline RE

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Re: "Earth Works Energy"
« Reply #8 on: March 10, 2013, 08:09:21 PM »
RE,
I got to admit that sounds pretty fun to build, even if its a bit rube goldberg'ish.  If my math in my head is right your example would give just under 1kWhr of storage.  Enough to run 4 50W laptops for 5 hrs.

No more RG than your Earthworks. :P

You could easily triple capacity, since typical Dry Box will carry 30 Tons no problemo.  You also could easily have a 2nd, 3rd trailer etc.  Main limitations are having enough vertical rise on the property and enough windy days.

Quote
I'd recommend though that the tribe takes a step back and examines with utmost criticality what we actually need electricity for.  I know way too damn well just how hard it is to get a decent EROEI in natural energy systems.  Designing our lives around as minimal electrical consumption as possible is the easiest way to accomplish this.  I see electricty primarly for LEDs, limited laptop use, refrigerator and future communication systems.

I agree completely. Honestly, the only real important uses for electricity are the diode lighting and communications toys.  Both quite low power consumption.

Your refrigeration can be done straight mechanical, running your refrigeration pump of the Windmill/Water Wheel.  Insulated Ice House, that actually is energy storage in reverse.  Of course you will need a refrigerant gas for this, which eventually will be unavailable even to scavenge.

Power tools you do all Compressed Air.  Same for Sewing Machines, Spinning Wheels and Looms. etc.

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Offline roamer

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Re: "Earth Works Energy"
« Reply #9 on: March 10, 2013, 08:45:04 PM »
RE, Well hopefully we can do a side by side comparison at some point, but as you point out yourself your setup needs both wind and the right topography to function. Mine is much more universal and has far fewer mechanical parts.

You remind me of an amish place I saw that powered their whole shop off of compressed air from a windmill.  They used old LP tanks as air storage tanks.  Not a bad route to go.  Still though same lesson here applies as with electricity, cut tools and infrastructure to bare minimum.  Old school hand tools and simple infrastructure reduces our need for power tools greatly.

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Re: "Earth Works Energy"
« Reply #10 on: March 10, 2013, 09:01:21 PM »
RE, Well hopefully we can do a side by side comparison at some point, but as you point out yourself your setup needs both wind and the right topography to function.

Well, the latest spot WHD identified definitely has the topography, and said topo is also good for Wind.


Quote
Mine is much more universal and has far fewer mechanical parts.

Yea, but mine doesn't require TRANSPARENT material for light to pass through.  :icon_mrgreen: The Romans could have built it.  Pulleys, rope, some wooden gearing.

Build em both!  :icon_mrgreen:

Quote
You remind me of an amish place I saw that powered their whole shop off of compressed air from a windmill.  They used old LP tanks as air storage tanks.  Not a bad route to go.  Still though same lesson here applies as with electricity, cut tools and infrastructure to bare minimum.  Old school hand tools and simple infrastructure reduces our need for power tools greatly.

All for Hand tools, but if you ever did any Sewing, you know it goes WAY faster with a machine. Also at my age and small energy footprint size, it would be way easier to hit a lever on an air tank to power a wedge down a pneumatic log splitter. Although I suppose I can find some 6'4" 30year old to do the Axe Swinging.  LOL.

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Re: "Earth Works Energy"
« Reply #11 on: March 30, 2013, 07:03:03 AM »
Update: I have a new more efficient lower cost strategy to replace earthworks energy.  It is a low temperature solar brayton cycle that is made out of a simple bellows style pistons. Here is a first crack conceptual picture of a 1kW scale system
Solar Brayton
Solar Brayton

It has thermal storage for 24/7 operation and for auxillarly heating needs.  It can be built with a fair amount of ease and made with very low cost low tech materials.  Efficiencies will be considerable higher (up from 1.5% to 10%) and the footprint, cost and deployment times will be down dramatically from the original earth works idea.  I need to prototype ASAP and can do so for very little cost ~$500.  I will be posting this idea in full here in two weeks time, and will be seeking peer engineering review in other places.  If no unknown insurmountable hurdles are exposed I will proceed with prototyping at the end of April.

 

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