# Making a wood burning or biomass electrical generator



## webbie (May 29, 2007)

OK, all you real engineers and backyard scientists.

The age-old question. How to make a backyard or basement wood burning/Pellet/Bio system that generates electricity? This topic has been discussed for decades, but now that the internet is here, perhaps we can avoid going up the wrong avenues. Seems like the choices are bad, bad and worse. Tell me what you think of this quick summary:

1. Steam Engine - these are only 5 to 8% efficient, so without numerous ways to use the waste heat (heat, dhw), this is not the way to do the job.

2. Stirling Engine, other - solid state and other similar devices - Very expensive and inefficient, and also not very powerful. You can only generate a tiny bit of power.

3. Wood gasification to drive an engine - this is promising, except for the mean time between failure of an engine. There are no reasonably priced engines that can work for thousands of hours without breaking down.
Question: Can you drive a diesel with wood gas? or must it be aspirated gas engine? Either way, the problem of MTBF exists.

4. Given current and projected future technology, it would seem that a wood gasification generator that fed the fuel gas into a fuel cell arrangement might be the best answer.

The above is my opinion from less than 1/2 hour of study on the subject. 
OK, so what is the truth?

PS. I think high pressure turbines are out - they are economy of scale.


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## slowzuki (May 29, 2007)

Right now a company called Woodmizer is working on a product called the biomizer.  It will have an optional generator attachment.  It uses a working fluid in a refridgerant cycle to produce power and dumps its heat into the normal heating circuit.

I have a link on my blog http://www.onthefarm.ca/ somewhere.

I've thought it over too and the only other option I've seen is the thermal bridges used in 12v coolers, the unit can produce power when exposed to a temperature differential.  Ungodly expensive to produce much power at the moment though.

The wood gas fueled engine isn't too bad with an advanced wood gasifier that makes clean wood gas.  The homebuilt jobbies are very dirty generally and kill engines quickly.


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## babalu87 (May 29, 2007)

A water tube boiler with a Super heater (like in a power plant) 
Like you said cost would be an issue but there has to be a way on a small scale.

 I would suspect that someone could "backyard" one. A power plant is big and all but when it comes down to it they take oil/coal and turn it into electricity by using steam. Problem for a homeowner would be supply and demand (storage of the juice) a bank of batteries or a HUMUNGOUS capacitor?

Too bad a BIG company (read research $$$$) wouldnt get behind the idea............. oh, thats right once they sell the unit profits are over.


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## slowzuki (May 29, 2007)

Nobody (companies) wants to get involved with steam as a working fluid, its complicated and expensive, and of course the risk of an explosion is always there like in the early days of steam.  Power plants have engineers and constant maintenance and are still pretty inefficient until you get into big big turbines and boilers.


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## babalu87 (May 29, 2007)

slowzuki said:
			
		

> Nobody (companies) wants to get involved with steam as a working fluid, its complicated and expensive, and of course the risk of an explosion is always there like in the early days of steam.  Power plants have engineers and constant maintenance and are still pretty inefficient until you get into big big turbines and boilers.



Yes, there is always the "idiot factor" companies have to worry about. 
Unfortunately, some things are NOT so easy a caveman can do it.


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## webbie (May 29, 2007)

The more I look at it, the more it seems extremely difficult with current technology. I guess thermal conversion will have to do for now.

Slow is right in that turbines are very high pressure and economy of scale is needed. I will have to look into that refrigerant idea.

In theory, it would seem possible to have a silicon device which turned radiant waves into electric......this would be a good add-on to regular wood stoves. But I guess there is a reason that such products don't exist on the marketplace today.

Honda is probably going in the right direction with their car and home power unit which is all fuel cell and hydrogen powered. It will takes them many years and billions of dollars to get that to market, so I guess I should not expect this to be done so easily.

It takes about 10 cents worth of electric to product 3500 BTU, the amount a pound of wood might produce if your entire process ended up at 45% efficiency (fuel cell system fed from reformer which converts wood gas).

If a cord of wood costs $150, and weighs 3000 lbs, that means a ton is $100, or the wood is 5 cents a pound. So that would only be 1/2 the price of regular electric, probably not a good deal given the cost and complexity. Electric from pellets and corn would be more..in fact, the same price or so as utility electric. So unless you can either use the remaining heat at high efficiency, or else put some simple solid state array next to an existing radiant stove, it looks like an idea whose time may never come!


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## jpl1nh (May 30, 2007)

Sorry Craig, I know this isn't what you mean by backyard biomass generator, but its close to being in my backyard.  Since one of the obstacles to success with a true backyard biomass electrical generator is size, and in following a number of other threads in the green room suggesting the best biomass use might be in the form of energy generation, I thought this link might be of interest. www.psnh.com/Energy/EnergyProject/NWPP/NWPPdefault.asp  I think its a pretty cool project.  Would be good to see more of them.  Now, back to the true backyard generators you're daydreaming about..


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## sstanis (May 30, 2007)

Have researched this topic.  will have to remember what site I saw it on, but some european company sells a residential wood boiler that produces 10kw of electricity.  Ugly looking thing, so perfect for basement.  but you bring up a good point.  With so much wood wasted now a days (ie tree guys dumping in landfill, fallen trees on side of road, etc, etc) why not put it too good use.  We know in vermont they have that 50MW wood fired powerplant.  too small for practical use in bigger states.

My thinking is that gasification with combined cycle turbine is the way to go.  I guess in realistic terms, it would probably be 1 to 2 cents more expensive than coal.  But 1st and foremost, we as a society really need to practice conservation.  There are soo many products available that use less energy, do not cost much more, and save energy in the long run that there is no reason that we cannot cut energy use by 10 to 15 percent.  Suprised that no politicians have lobbied for demand conservation devices on certain high energy draw appliances.  Lets be honest, during one of those crazy heat waves, where on TV they beg you to conserve, you always see people firing up there electric (5KW) dryers and the like.


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## slowzuki (May 30, 2007)

I've done work at the northern wood power station, actually got a tick staying in a hotel in Portsmouth.  Its an interesting boiler.  The advantage of the home power generation is the use of the waste heat, power plants dump enough low grade heat (hot water) to heat entire cities but very few town have district heating.  In Russia many power plants used condenser cooling water to heat houses all winter.

Why don't we do this in many places of North America?

The waste heat is really only good for household heating, there is a huge quanity of heat but the ability to do work with it falls off dramatically as temperature falls.


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## DaveR (May 30, 2007)

Here is something coming along that might be of some interest.  As is often typical the project is the result of military spending funding research into technology that may well migrate into commercial applications for civilian use.  Just one of many projects being worked on at Purdue University and across the country.  You might find other interesting research coming out of Purdue with searches for Biomass, Hydrogen, and Energy.

http://www.physorg.com/news89574820.html



> Scientists develop portable generator that turns trash into electricity
> 
> The "tactical biorefinery" processes several kinds of waste at once, which it converts into fuel via two parallel processes. The system then burns the different fuels in a diesel engine to power a generator. Ladisch said the machine's ability to burn multiple fuels at once, along with its mobility, make it unique.
> 
> ...



Technological innovation to meet need has always been humanity's greatest innate strength and bodes well for the future certain to face new challenges and perils.  That is life in a world certain to change in dramatic and unpredictable ways that put Climate Change in its proper perspective.


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## webbie (May 30, 2007)

District heating is very popular in Denmark. For those who don't know about it, this is hot water (usually) circulated through entire neighborhoods which heats the houses - you have a meter in your house which tells how much you use.

They are trying to build a couple wood burning plants near here, but some locals are trying to shut them down! I saw a letter in the paper the other day and I think I will craft a response. The letter said it would be the End of the World if we built these plants and that they were not Green in any way. How silly! Surely there can be problems...but in my opinion we have to COMPARE it with the existing power generator - the very dirty Mt. Tom coal burning plant. It looks good when you do that.


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## sstanis (May 30, 2007)

believe it or not, in manhattan and other parts of the 5 boroughs of NYC, district heating and cooling is accomplished.  ConED has their power gen stations, they sell off the excess steam to heat buildings in winter, and use that same steam to cool buildings in summer.

I am surprised that no companies have decided to bring back syn gas.   Wood gasification, landfill gas (where feasible) and the like could be purified and sent as methane into the natural gas grid.

To add even better, MICROCHP--all of Europe has it.  Same why can't we.  Craig you hit the nail on the head about drafting a letter in response to the objections to the wood plant.   Go to Learnaboutcleancoal.org  look at the line of BS they are trying to feed everyone.  Not saying that Coal hasn't been a wonderful source of energy, but it is time to put plans into place for its future phase-out, say decreasing amounts over 50 yrs.  Just like TXU tried to get licenses for 11 coal plants in a hurry, b/c they knew in the future that the plants would be grandfathered.


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## begreen (May 30, 2007)

Seattle steam district is switching to woodchips as we speak.


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## scotty (May 31, 2007)

And don't forget about the lowly thermocouple. Connect them in series and you have what is called a "thermopile", which turns a portion of any temperature differential directly into electricity....not much electricity, but enough to measure. Those stove top fans use this principle. Nice thing about a thermocouple is that it couldn't be much cheaper or simpler.  No moving parts and nothing to wear out. And no reason at all why you couldn't have a few thousand of them built right into the top of a stove or into a stove pipe. ...or both. 
          Scotty


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## R&D Guy (Jun 1, 2007)

scotty said:
			
		

> And don't forget about the lowly thermocouple. Connect them in series and you have what is called a "thermopile", which turns a portion of any temperature differential directly into electricity....not much electricity, but enough to measure. Those stove top fans use this principle. Nice thing about a thermocouple is that it couldn't be much cheaper or simpler. No moving parts and nothing to wear out. And no reason at all why you couldn't have a few thousand of them built right into the top of a stove or into a stove pipe. ...or both.
> Scotty



You know I took a bunch of thermopiles from gas pilots, and put them together in series in a flue pipe. From what I remember there was about 30 thermopiles. My original idea was to incorporate the idea into the starter flue of a wood stove, but it was too cool that far away from the flames. The most electricity I ever got was almost 5 volts, but the amps were almost non-existent.


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## webbie (Jun 2, 2007)

Here is a New England company which recently won an award for a 5KW biogas operated fuel cell generator:
http://www.acumentrics.com/79cfcaf6-8ee7-47c9-bc35-5e0402039157/press-releases-release-details.htm


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## scotty (Jun 4, 2007)

"You know I took a bunch of thermopiles from gas pilots, and put them together in series in a flue pipe. From what I remember there was about 30 thermopiles. My original idea was to incorporate the idea into the starter flue of a wood stove, but it was too cool that far away from the flames. The most electricity I ever got was almost 5 volts, but the amps were almost non-existent."

Since the theory is sound, all that remains is the development work, agreed? More couples, more heat, more efficient materials, and maybe there is some way to arrange them geometrically for the best efficiency as well. I keep thinking that there ought to be some downside, but just what it might be doesn't immediately occur to me. Anytime you can convert energy to a more usable form without having to deal with moving parts then that is a huge advantage right there. I hope that someone does something with the idea. 
       Scotty


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## Andre B. (Jun 5, 2007)

While not particularly practical here is some interesting stuff on fluidyne engines, (liquid pistons).

http://vacuum.ramapo.edu/physics/physics-doc/amsci/AmSci01/1985/04/1985-04-body.html
http://www.ornl.gov/~webworks/cppr/y2001/rpt/27113.pdf

A Youtube video of one  running.
http://www.youtube.com/watch?v=J6SjIGWb4zM

This one is of more conventional hot air engines, mostly toy size but near the bottom is a larger one that they claim makes a few hundred watts (I assume that's mechanical shaft power, not out of a generator).
http://www.moteur-stirling.com/modeluk.html


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