Willow Coppice Math Fun

We are actively looking in to designing a Community Supported Energy system here in JEfferson County Wisconsin based on a wood chip gasifier powering a small co-gen unit providing roughly 30,000 kWh of electricity and enough BTU’s to heat 10,000 gallons of water for tilapia aquaponics similar to what Growing Power of Milwaukee is doing.  To that end I spend alot of my free time researching the myriad aspects of that system.  Of  late I am focusing on a working the fuel source into the site plan, my thoughts are beginning to coalesce around using willows on a Short Rotation Coppice plan – the willows would then be chipped or pelletized for use in the gasifier.

I found a short Power Point from the Baltic university that has some great shots of willows being grown for coppice.  VERY industrial, but how cool is it to see perennial carbon crops being harvested by combine rather than GMO corn?  


I loved the shot of the willows towering over the people in the shot … after only 5 months!  Wow these buggers grow fast!

Now for the Math Fun:

A hectare is just shy of 2.5 acres, so translated to Ameri-speak that is roughly 60,000#’s per hectare on a three year rotation – 10 tons/acre/year.  1-2 acres so planted would likely run one of our gasifiers for 2000 hours (50 weeks @ 40 hours/wk using 10#’s/hr), but I would rather see it in a mixed planting as windbreaks around CSA food gardens in an integrated Energy/Food farm.   Using a 10′ wide windbreak dividing the gardens into .5 acre plots one could sustainably grow 15 tons of biomass annually on the windbreaks of 4-5 acres of cropland.  For ease of reference 7 acres could produce about 100,000#’s of potatoes equating to roughly 43 million calories at the yields I achieved this past year.  Of course I would never plant that much of one crop!  

The point is to show the possibilities of using about 3-7 acres of land when combining food and energy systems into a permaculture plan specifically designed to produce significant surpluses for the community.  The equipment to make the pellets for the gasifier could also be used to convert virtually any carbon source into pellets using a hammermill to break it up into little bits first.  If you make ethanol on site with the waste heat from the gasifier using various sugary cover crops in your rotations, some of the dried distillers grains not used for the Tilapia can act as the binding agents for the pellets.  

7 acres producing 5 tons of Tilapia, huge amounts of vegetables, ethanol, electricity, and wood pellets while employing several people in full time wages in a system that can be scaled up/down as needed?  This is the rural community planning I want to see as we transition to a brighter, more localized, future!

Be The Change

14 Responses

  1. Beautiful. Could a transition to renewable energy really be that easy?

    I imagine that those willows use a huge amount of fertilizer. This could come from a confinement livestock operation or even sewage sludge if it was separated from the vegetable gardens.

    In our southern climate, mulberry trees have been proposed as a biofuel feedstock. They grow as fast as willows and produce tons of fruit if allowed to mature for 4-5 years.

  2. I’d be interested to see a layout of what something like this might look like.

    this is a fantastic idea.

  3. Hi Rob,

    I don’t understand why you say that the ton used by these people equal 1000 lbs rather than 2200 lbs ?

    I hope you guys will be able to make it, such a big project will probably mean making a loan, I hope you will find a banker that understand your project, goal and support you.

    Have fun with your shovel tomorow as a nice snow “storm” is here in southern minnesota and will be in southern wisconsin later tonight.


  4. I can attest to the quick growth of willows. We’ve got a thicket around our pond that (when not grazed by goats or cow who love them) will grow 10 feet tall in a year, with trunks spaced less than a foot apart. They don’t get any fertilizer, but they do drink lots of water. Ours won’t grow far from the pond’s edges because they are so thirsty.

    I’m actually trying to establish a hazelnut stand along the edge of our property, to serve as a windbreak, as a source of nuts, and for coppice wood. Unfortunately, a very dry year did in many of my little saplings. But they are very cheap when purchased in quantities of 20+.

    I don’t know if they’d match willows in growth rate, but the other benefits are worth it to me. (Plus I’ve already go willows.)

    I have this idea to run the coppiced wood through a chipper, sift out pieces the proper size with some screens, and use them in our corn / pellet stove. But heating takes a lot of volume, so I don’t know if I’d be able to reach that scale or not.

    I’m sure those fast-growing woods aren’t the best for burning, but then I don’t know that they have to be. Everything’s a trade-off in one way or another.

    Great stuff…

  5. Thanks Everyone!

    Matt – I am sure it is NOT this easy, but I think this system could be an incredibly more efficient use than any other 10 acres in the county right now. Two huge gaps are currently in many Energy Descent plans I am aware of: liquid fuels for transport until we get to electric or whatever, and winter heat if you live north of Kansas. I am looking to “function stack” answers to these issues onto my answers for Local Food. As E4 has said, in my experience trees need remarkably little fertilizer other than mulch- after coppicing they have the root structure of a 3 yr old, 20′ tall tree to support a stump. I would “leave” much of the leaves for mulch vs. the 100% take that the ppt shows. Also, the bio-char from the gasifier would be added back to begin building terra preta to stop nutrient leaching.

    Kory – basically I am imaging a 10′ strip of tree wrapping each .5 acre of gardens with holes for paths. 3′ of width could be harvested annually. This is a REALLY young thought so much more needs to be fleshed out on it, but the edges would include flowering native forbs for insectary and medicinal uses.

    Xavier – um, for some reason I had always thought that the English ton WAS the short ton – 50% shorter. Your elucidation just more than doubled the productivity of this system!!!! Congratulations! To start the CSE properly I think I need $350,000 to pay off everything but the shed in cash. It is a BIG deal. I am thinking grants + loans and raising funds for grant matching with a co-op structure. Also my 401k will likely go into this. I will likely have ot do it on half to a tenth of that and keep my day job for awhile- we have a 3 day work week option for the same pay. Sleep may become option during Energy Descent or the early stages of the CSE.

    E4 – check out Pellet Pros for ways to turn your chips into pellets -not that hard ($4000) and it could be a nice side business -we intend to use 100% of the sawdust from a local pallet manufacturer ($6/ton) to make pellets commercially to pay back the equipment. Willow has much lower btu/pnd than say Oak, but I am not sure what that looks like in pellet form where densities would be more equalized. Need to experiment. The Next Big STage of the woodlot plan is to diversify the plantings to add more functions. Willows can make basketry and furniture, but not food.

    I absolutely love your mulberry tree idea for ethanol AND biomass – the beauty of viral brainstorming!!!

  6. You are welcome rob, if I can help you to increase so easily your productivity, I am happy to give a hand.

    I have of course checked wikipedia to make sure that the ton that I was talking was the equivalent of the english ton you were in your comment and guess what yes, this is the metric ton minus a few pound to make the math easier. I always know that somehow my technical background will be helpfull for someone 😉

    3 days a week well if they are hiring in your company let me know, I can even sweep the floor for that and stay warm and cosy at home the rest of the week….

    I don’t understand, are you looking to go in this venture on your own or with your group ? It seems to be a lot of work for a lonely worker

  7. My “real job” is distribution management – the plant runs 24-7 and we have one shift that works 3 -12 hour days, and another (which I am currently on) that works 4 -10’s. I lead a team of 30 in moving hundreds of thousands of boxes from A to B. Having every Monday off helps give me the time to do all the insanity I regale you all with here.

    I am not sure I understand it myself. I am hoping that the CSE will eventually employ at least 3 people – 1 full time, 1 half time, and one part time for admin work. This would be for the Energy Shed (ethanol, gasifier, biodiesel) and Tilapia Aquaponics operations. Lots of sourcing and processing of materials. If we went with a 10 acre system as in this post, much of the 7 acres of garden space would be used for “incubators” for local CSA wannabees and/or interns that would either pay a small rent, profit sharing, or labor sharing. I guess I plan to be one of the 3 employees of my own idea, but who knows? My group’s members are from several municipalities, and there is no reason that a CSE wouldn’t fit in each one. Indeed that is one of the hopes -that it will seed communities across the country with them. Sometimes I think everyone in the group wants to be an employee, and sometimes it feels like many are just there to learn. Who wouldn’t want to quit their day job to do something like this -to get paid for Being The Change?

    For now we are looking to start small in a borrowed shed this first year, but hope to be ready to Go Big should we land a grant or find some land. In fact Monday I am delivering the biodiesel processor components to a friend that has a pole barn and an oil burning furnace. Hope to be running by 2009.


  8. Hey Rob
    i know you’ve been looking at tilapia aquaponics pretty hard but have you reviewed some of the aussie backyard aquaponics systems? The designs may be helpful (see for example http://www.aquaponicshq.com/ ) but also some of the aussie fish species (murray cod, jade perch etc ) may make a higher value crop for you than tilapia if you can get seed stock.

  9. With hemp you could get 10 tons per acre in approx. 4 months.
    An easy solution to our energy and economic problems would be to legalize cannabis, tax the buds and use the remaining biomass for the gasifier.

  10. PS some of the fish mentioned above might ake slightly lower temps for good growth than tilapia which would bring an energy saving….

  11. I am the “head tech” for a 40 acre campground in Missouri. My wife is the owner. I’ve converted her to accepting renewable energy as being practical. But she is the original doubter needing to be shown small demonstrations before writing checks for bigger projects. Thus my prototype gasifiers have been burning trash. Consider it as “Harm Mitigation. she’d merely burn it in an open top trash can as all the farmers for miles around do. So I constructed a downdraft gasifying burner using a shop-vac for draft air. Forced air enters the drum thru a scavenged several foot long piece of car tailpipe. the flange from the cat converter end keeps it from pulling thru the hole at the upper rim opf the drum. A metal plate weighted with bricks is the lid and explosion pressure relief. And the “false bottom is a perfed metal plate at the 1/3 height rib of the 55 gal drum. A welded bung in the side of the drum at the bottom connects a flexible pipe section that curves around to a ragged hole torched in the side of the drum from a past usage. So- a load of burnables gets tossed in the drum- topped with any rancid greases-too cruddy to recycle shop fluids etc and lit.

    The cover plate goes on- air gets turned on- and with a jet engine roar damn clean combustion begins! See- it’s a crudely assemble but lovingly tweaked secondary air and gas reburner interface system. The flame front from the mass burn on the perfed plate tries to go down in search of fuel and expansion of hot gases. Which of course preheats and gasifies the material on the way down. Part of the gas flow goes thru the ash bed and the perfed plate to exit that curved flex. exiting at the side hole where the 2 gas/air streams meet in a clear burning hovering flame. With near zero visible smoke once burning is initiated into reburn mode! What we thought was prolonged smoking a few times was actually steam from large ice chunks in the trash load. Gasifying wood in this beast’s sucessors will be harnessed for thermal application and eventually a gas stream will go to piston engines or an open top heat drum “boiler”

    The reasons for considering wood fuels on a campground? $0 acres of landscape trimming generates enough brush and twig fuel as “waste” to displace a major amount of propane. With the multiplier of showing the finished system off to the mundanes – proving to them them this stuff is not just for Ed Begley’s TV show.

  12. […] a meat packing plant or a commercial greenhouse. Or maybe, just maybe, a co-generation setup like the one Rob’s working on in […]

  13. […] very soon for $1200.  It will handle everything from orchard pruning for compost to shipping coppice wood (small scale) for the gasifier.   Do not think that scaling up to this level is easy ethically […]

  14. I just learned that goats can be fed coppiced tree material, and will remove the leaves and bark, leaving woody material intact.

    I’m sure goats would have other roles to play (clearing land after harvest, managing invasive species in the larger community), but being able to store feed away for them, and have them process it into a form more-suitable for use as fuel, seems enticing.

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