Wood gas for heat and electricity

Many of us live in forested environments. When I look around me, the resource in great abundance is... wood products! Live trees and brush of course, but also lots of detritus, old logs, branches, lots of pinecones. This woody biomass contains a great deal of stored solar energy. And I want to tap into that efficiently and effectively.

I want to know - NEED to know - if there is a home-scale system that will accomplish these basic parameters:

Input: woody biomass

Output:
- char
- heat (in the vein of RMH)
- electricity (charge batteries via generator)

Being a forest resident, this is my ultimate energy challenge. I suspect that I will pursue the best solution for the rest of my life.

For my purposes, heat and char production are of primary importance. My electricity needs are relatively small and can be met by a stationary bicycle generator, though I understand there's a lot of sweat involved for even small yields, so a cogeneration system is definitely more desirable.

I have been thinking about this for a while and also dwell in the forest.

There are a few commercially available stoves which also produce electricity, one is called the Kimberly, i think. None of them (that i have seen) seem perfect to me.

I'll be watching this thread with interest.

Justin Jones wrote:For my purposes, heat and char production are of primary importance. My electricity needs are relatively small and can be met by a stationary bicycle generator, though I understand there's a lot of sweat involved for even small yields, so a cogeneration system is definitely more desirable.

Why char?

How much heat do you need (i.e. northern climate with harsh winters)? Is space cooling necessary during summer months? What about food storage - a freezer is probably the best thing for long term food storage, and that's a substantial electrical load. It seems you'll be using a laptop computer at the very least - well, what about internet connection? This will require additional electricity. Try to get a realistic estimate on the electrical loads you expect to need, and do not low ball there - if anything, be conservative in the estimates. I don't expect even the most modest off grid homes to get by on less than 3 KWh daily.

In my opinion, solar panels are the most practical means to generate electricity in a remote setting, at least in most settings. If a solar array and battery system can meet your electrical needs most of the time, then it makes practical sense to keep a tank of propane to run a small backup generator (assuming infrequent use - that is, only when required to bulk charge the battery and protect from a dangerously low state of charge). I suggest propane because it stores indefinitely vs gasoline or diesel fuel, and I see your electrical demands as very modest. A small Honda generator is a good choice for a very small system (like an EU1000).

Now, let's assume you want to get away from commercial fuels entirely and use wood for electricity generation. In that case, there are three options (well, only two really). A wood gas engine system, a charcoal engine system, or a small piston steam engine.

1. Wood Gas Engine System - The best example of which I know is the system developed by Ken Boak of the UK. See description here: http://www.powercubes.com/listers.html . Mr. Boak has the system set up to run the engine for part of each day on wood chips. Heat exchangers on the system pick up the heat from the cylinder cooling water and the engine exhaust to heat a large store of water in an insulated vessel. The heat is transmitted to the home using a hydronic heating system (pumping hot water into the home for heating applications). The down side of this is primarily the fuel processing required. A second down side is the necessity to operate the system at a fairly high rate to keep temperatures in the gasifier high enough to generate a clean fuel gas. On this last point, Mr. Boak uses most of the electricity generated in electric space heaters just to load down the engine and help keep the gasifier temps up. It's possible to run a smaller system, but the smaller the system the more fuel processing is required - sort of a catch 22.

This system seems overkill for your application. Also, the fuel processing required to run a system like this for primary heat would be daunting. A better configuration for making use of a wood gas engine system would be to use traditional firewood for heating applications, then process only enough wood fuel as required for use in a small backup generator system - sort of like making small wood chips or chunks for a small engine wood gasifier in lieu of storing propane. However, you would need solar/wind/hydro for primary electricity.

2. Charcoal Engine System - This process entails processing wood to charcoal, but capturing the heat from the process and storing in a thermal mass such as water. The heat can then be used for heating applications, and the charcoal can be stored for use in small engines as required. I don't know of a viable system in operation, at least not on a residential scale, but it's clear that it's possible. Note that charcoal can run very small engines more easily and more cleanly than wood.

3. Piston Steam Engine - Personally, I believe this has the most promise. However, it's not practical due to the lack of hardware. There are decent small engine expanders available that are very durable, but one would have to engineer a steam generator with control system and an efficient small wood gasifying furnace to operate unattended - possible, but not for the faint of heart. The benefit of this system is primarily the ability to use wood with very little processing, and the ease in heat recovery (most of the heat is available at the steam condenser). It can also be very quiet and operate at a low output for long periods. Steam engines have also earned a reputation for longevity.

In my opinion, I say stick with PV/wind/hydro with battery system, and use a small propane fueled backup generator as required. Use wood only for heating applications.

Marcos Buenijo wrote:Why char?

I'd much rather use the carbon skeleton to build soils than burn it for energy production.

Marcos Buenijo wrote:How much heat do you need (i.e. northern climate with harsh winters)? Is space cooling necessary during summer months? What about food storage - a freezer is probably the best thing for long term food storage, and that's a substantial electrical load. It seems you'll be using a laptop computer at the very least - well, what about internet connection?

The winters here in Montana are long and harsh. An efficient wood stove will be essential. Cooling will not be necessary. Food storage is taken care of in the buildings at base camp - so no refrigerator. I have calculated my energy requirements:

- netbook laptop: 30 W x 10 h = 300 Wh
- stereo: 50 W x 5 h = 250 Wh
- modem: 24 hrs x 7 W = 168 Wh

Total: ~720 Wh at maximum usage

Light at night will be provided by candles (which also produce heat). A 12V deep cycle lead-acid battery rated at 130 Ah, discharged to 50%, supplies 780 Wh. With the inverter running at 92% efficiency these power needs could be met with a single battery. I would probably add a second one to cover further inefficiency and reduce strain on the batteries.

Not looking good for the bicycle generator. At 100 Watts production, I'd have to pedal maybe four hours a day just to be able to use my laptop and the modem for six hours.

Please let me know if there are faults in my math.

This is the biomass CHP system I am viewing next week.

http://www.volter.si/biomass-chp-micro-cogeneration-products-en-3.html

Looking in particular at how we can utilise the kiln drying facility.

Justin, the math is fine - but I am wondering about the underlying assumptions. Note that a small inverter is probably more like 85% efficient, but the effective efficiency is often much less when used with low loads. An inverter often has a certain minimum draw that can be a significant proportion of a low load, and this can take the effective efficiency (eff) to much lower levels. Also, it's necessary to consider the inverter loss in addition to the load - so, 720 Wh/eff would be the actual load on the battery since the inverter loss is taken from the battery. More important, I'm wondering about additional loads? Fan(s)? Water pump(s)? These can be DC, so that helps.

Definitely it seems a larger battery is desirable. I suggest sizing the battery for 3+ days capacity. I wouldn't suggest this for a high electrical demand. Otherwise, a very large battery would be necessary. Consider that during an extended period of inclement weather it will be necessary to bulk charge the battery with a small generator when it reaches a low state of charge. This will not be efficient and it will be hard on the battery if it's a particularly small battery, and you would have to do it daily. Also, you want to conserve fuel and labor by avoiding the generator until it's absolutely necessary. A larger battery buys time for solar/wind to start producing. There is also the matter of battery charging being very inefficient while the battery is at a high state of charge. Bulk charging a larger battery is a lot more efficient. A common strategy is to not use the generator until the battery is at a fairly low state of charge, then bulk charge up to absorption - let solar/wind take it to float to avoid fuel consumption. Again, propane would solve a lot of problems, but I am assuming you want to stick with wood fuel. If I were in your position (at least as I understand it), then I would go with a "small" 12v forklift battery or pallet jack battery. One model of which I'm aware stores 8 KWh at the 20 hour rate and is rated for 1500 full cycles. This should buy you several days of zero charging if necessary, and it can go a few weeks without a full charge without significant damage. If you were to only bulk charge such a battery when required to protect against a low state of charge, then get it to float and perhaps a short equalization once a month, then I think this would work out very well. I expect such a battery to last many times longer than alternatives you might have considered.

Back to the original thread - if you are looking to make use of wood for electricity and you desire a commercial product to meet your needs, then I see only a small wood gasifier as a possibility. These products might interest you: http://northernselfreliance.com/get-the-nsr-hardware/isabella-gasifier/ , http://vulcangasifier.wix.com/vulcangasifier#!product/prd15/1585769955/m-series-ii-gasifier-refinery-system . Of course, you would need a small generator, and a Honda is best in my opinion. There is also wood processing equipment required. You could process fairly thin branches by cutting into small chunks. However, I suspect this would get old really fast if you were to rely on wood as a primary source of electricity. For backup power only, and with very low electrical loads, then maybe it would be doable. You would need on the order of 10 pounds of green wood (that must be dried before use) to generate one KWh electricity for end use - assuming a reasonably efficient and very small system, and considering all the losses involved. Most of the heat from the system could be captured for use, so that's a plus. There are no micro scale systems that are turn key, so you would have to develop something (not terribly difficult with the gasifier and engine already had). If you're willing to do this, and if you're dedicated, then you will get something impressive with time.

Now, if you are considering long term prospects, then I suggest a small piston steam engine system as a superior possibility for your particular application. However, that's a more difficult prospect since there's nothing suitable on the market. You would have to do some development work. The reason I consider this prospect to be a good match for your setting is the combination of plentiful wood fuel, low electricity requirements, and high heat requirements. Also, the fuel processing required for a small steam system would be a great deal less than a wood gas engine system. It could be made to use small seasoned wood splits. If you're going to be burning firewood for heat anyway, then a micro steam engine system could give you the heat and the electricity you need.

I, too, have looked for the "Mr. Fusion" of woodgas, just stick anything in from sawdust to firewood and magically get clean power and biochar and heat.

All Power Labs power pallet is the closest turn-key. Does power out of the box, can be tuned for more char production and easily extract domestic heat. Not cheap. but it is the closest you can buy to what you want in one package. Bigger than you want. They are also open-source so if you can weld you can copy the heart of their system. If I wanted an offgrid house with AC or shop in the deep forest and I had the budget, this would be part of the system.

There are lots of smaller experimenter's systems out there, most of them are not very efficient--they are simply too small to keep the temperatures you need, and not that much cheaper when you get it all together (usually way more $/watt).

Bigger problem overall is material handling--to burn all that stuff you have to get it to your machine or your machine to it, you need to get it consistently dry (easier where you are at but still not a given), you need a consistent SIZE--too small will choke the machine and too big won't fit or burn correctly. There are machines to do this at an industrial scale and ways to do it at a hobby scale, but not a great and affordable solution for homestead scale. Wayne Keith's chunker is probably the closest but it only works on specific types of feedstock. Many of the methods take more time or power than you get out of the woodgas. Even when you get past that, just the volume of material you have to deal with is daunting. A pickup load a day, EVERY day, gets old. If you live somewhere wet, you need to be able to dry and STORE your feedstock all the way through the wet season.

Try breaking up the problem. You will want WAY more biochar than you want power, so work on a large biochar reactor and a small woodgas unit.

Make the woodgas unit multipurpose--put it on an old tractor and get a PTO generator. That way you can haul wood or build gardens or charge batteries all with the same tuned engine/gasifier combination. Or put it on a small truck but add high output alternators so you can charge your battery bank quickly.

I have been intrigued by this DIY wood gas generator set up.
http://woodgasifier.org/

If anybody has any personal experience with it, please chime in.

Justin, I lifted this just as one example (see link below). It's a dc voltage booster for using laptops and other electronics from a 12 vdc source. It's designed for automotive use. This should lessen losses. I expect efficiency is on the order of 85% like inverters, but this should be verified. Note that electronics run on dc. So, using an inverter goes from battery dc voltage, to inverter ac voltage, then back to laptop dc voltage. There are unnecessary losses there.

http://www.powerstream.com/Produz10.htm

NOTE: I don't know much about these devices, I am only listing it to make you aware they exist.

Charcoal power might be your best fit.
You want char anyway, a tlud could be set up to charge a rocket stove style adobe bench, or bell,the modifications to the IC engine are ludicrously simple compared to those needed for woodgas,and char has a plethora of other uses.
But for everyday? Solar makes sense to me.

William Bronson wrote: Charcoal power might be your best fit.
You want char anyway, a tlud could be set up to charge a rocket stove style adobe bench, or bell,the modifications to the IC engine are ludicrously simple compared to those needed for woodgas,and char has a plethora of other uses.
But for everyday? Solar makes sense to me.

This discussion has mainly been focused on my specific energy requirements and how best to meet them. I agree that one the scale of a single person, solar is probably the best option for electricity generation.

However I would like to steer this thread in a more general direction, attending to the question of 'What is the best way to generate electricity, at the home scale, from woody biomass?'

It seems that there are two primary candidates: a steam engine, powered by anila-type char/ rocket stove on the one hand, versus a wood gas internal combustion engine on the other hand. This is really what I am interested in exploring.

John Polk wrote:I have been intrigued by this DIY wood gas generator set up.
http://woodgasifier.org/

If anybody has any personal experience with it, please chime in.

Now that's more like it! This is exactly the sort of thing I've been looking for. All the other wood gas engines look much too complex and shiny for any diy potential.

This is exactly the sort of thing I've been looking for.

He has built his on a cart, which makes it quite handy, but if it was mounted on a small trailer, you could even tow it to a more remote site with a truck/tractor/golf cart/ATV. Power tools, anywhere on the site, or at the least, the ability to charge batteries in a remote cabin setting.

I believe that on his older site, he claimed something like a chain saw could produce enough chips in one hour to fuel it for seven hours. If that thing could be operated on waste materials, it could 'pay itself off' real quickly.

I would love to hear a review from somebody that has actually built and used one.
If it performs as claimed, it would be a no-brainer to build one in a wooded region.
In the dead of winter, solar panels may not be enough, but if you could take a 5 gallon bucket of wood chips or pine cones and top off your batteries at any time, that thing would be a godsend.

Justin Jones wrote:What is the best way to generate electricity, at the home scale, from woody biomass?

Wood gas engine system used to bulk charge a large battery system.

While steam has the potential to be better in many respects, there is not suitable hardware available.

I suggest a wood gasifier that can handle fairly large wood pieces to lessen fuel processing requirements (imagine 1-2" diameter branches cut in 1-2" lengths). The larger the chunks, then the less fuel processing required - and the larger the gasifier/engine/battery system required. If your electricity demands are modest, then you could set up a system to charge the battery on a weekly basis. By all accounts I have seen, the forklift battery is the most cost effective battery alternative.

While steam has the potential to be better in many respects, there is not suitable hardware available.

The construction/operation of steam engines is not for the inexperienced.
Without proper training, steam engines can be quite dangerous.

the forklift battery is the most cost effective battery alternative.

I worked on a ship that had electric forklifts for each hold. We were set up for underway replenishment of munitions...no room for error. I was greatly impressed by the amount of work that they could perform before it was time to switch in a new one...not an easy task on a ship at full speed at sea, with about an extra inch of clearance. Those buggers were heavy !

John Polk wrote:The construction/operation of steam engines is not for the inexperienced.
Without proper training, steam engines can be quite dangerous.

I agree. Old school steam systems with their large boilers can be dangerous (and expensive!). Joe Blow shouldn't mess with it. Of course, Joe probably shouldn't be doing anything remotely DIY. Until a commercial system becomes available, or unless an individual is willing to build and test a suitable small furnace and safe monotube steam generator for a low power system, then a wood gas engine system is the only thing going for wood => electricity. Hopefully, there will be a commercial small scale steam option in the near future as it is better suited for micro scale CHP with biomass. Something like this would be ideal: http://uniflowpower.com/.

John Polk wrote:
I worked on a ship that had electric forklifts for each hold... Those buggers were heavy !

Very heavy! Good news is there is a nation wide (U.S.) company (GB Industrial Battery) that manufactures and sells forklift batteries with pricing that includes delivery in the 48 states. They will also pick up a discarded battery free of charge (for the scrap). Even if one must transport the battery, then I still consider it worthwhile due to how long these units seem to last in the stationary RE setting. I've seen many accounts showing 15-20 years, and even 10+ years on some accounts that started with a used battery. More important, they seem to be the most cost effective alternative.

In my opinion, if one desires to generate electricity in a remote setting and using only wood fuel, then using a wood gas engine system to periodically bulk charge a fairly large battery system seems the most practical alternative. I think it could be a reliable and even practical set up when electrical demands are low. Justin, I suggest you take another look at Ken Boak's system. Now, he has a much higher electrical demand than you expect to require. However, his basic configuration is what I suggest. Incidentally, Ken also has a small wood furnace for supplemental heat. He uses a central hot water storage tank and provides most of the heating in the home with a hydronic heating system. I like this idea for use with a low power fan coil unit using a DC mag drive pump and DC fan. Sure, it's an additional load, but if you're running a wood gas engine system to charge a 24 volt forklift battery, then you'll have a little more capacity. The engine system should be used to heat the thermal mass whenever battery charging is done. When additional heat is desired, then a more traditional furnace can be used. One might go with a different thermal mass such as those used in rocket "mass" heaters, and there has been some discussion of using the heat from an engine to charge this kind of mass as well. A benefit of this approach is that the intensive fuel processing required for the gasifier is limited by the electrical demand. A low demand means less fuel processing. So, much or most of the wood fuel consumed can be used for a traditional furnace, and this means wood splits.

I'll provide an estimate on fuel consumption for a good wood gas engine system, assuming it operates at an optimal rate for good efficiency. Expect roughly 15% efficiency in the engine system (fuel to shaft work). Battery efficiency is a conservative 80% (assuming bulk charging at a modest rate from a low state of charge). Alternator efficiency can be 80% with a good permanent magnet unit. Throw in a 0.8 factor as some systems would require a dc converter or small inverter, and there is some battery self discharge. This corresponds to roughly 7.7% conversion of wood fuel to end use electricity. This is a realistic estimate assuming a good system, and it's fairly conservative for a good system running at optimal output while battery charging. Green wood provides roughly 4400 btu per pound, so one needs to prep about 10 pounds of green wood for every KWh of electricity consumed. This is an estimate, of course, but it's based on data that I've gleaned from real world units.

Marcos Buenijo wrote:
I'll provide an estimate on fuel consumption for a good wood gas engine system, assuming it operates at an optimal rate for good efficiency. Expect roughly 15% efficiency in the engine system (fuel to shaft work). Battery efficiency is a conservative 80% (assuming bulk charging at a modest rate from a low state of charge). Alternator efficiency can be 80% with a good permanent magnet unit. Throw in a 0.8 factor as some systems would require a dc converter or small inverter, and there is some battery self discharge. This corresponds to roughly 7.7% conversion of wood fuel to end use electricity. This is a realistic estimate assuming a good system, and it's fairly conservative for a good system running at optimal output while battery charging. Green wood provides roughly 4400 btu per pound, so one needs to prep about 10 pounds of green wood for every KWh of electricity consumed. This is an estimate, of course, but it's based on data that I've gleaned from real world units.

Wow, that is a chilling reality check. Really puts the value of solar into perspective

Justin Jones wrote:

Marcos Buenijo wrote:
I'll provide an estimate on fuel consumption for a good wood gas engine system, assuming it operates at an optimal rate for good efficiency. Expect roughly 15% efficiency in the engine system (fuel to shaft work). Battery efficiency is a conservative 80% (assuming bulk charging at a modest rate from a low state of charge). Alternator efficiency can be 80% with a good permanent magnet unit. Throw in a 0.8 factor as some systems would require a dc converter or small inverter, and there is some battery self discharge. This corresponds to roughly 7.7% conversion of wood fuel to end use electricity. This is a realistic estimate assuming a good system, and it's fairly conservative for a good system running at optimal output while battery charging. Green wood provides roughly 4400 btu per pound, so one needs to prep about 10 pounds of green wood for every KWh of electricity consumed. This is an estimate, of course, but it's based on data that I've gleaned from real world units.

Wow, that is a chilling reality check. Really puts the value of solar into perspective

Its a chilling reality check because it is so way off the mark. If you check out the details of the Finnish CHP system above which I visited yesterday then fuel input is 189kw electric generated 40kw and useful heat 90kw as listed in there sales brochure with actual performance 5-10% better than that due to our strict advertising laws. Woodchip consumption of approx 43 kg per hour running a 6 cyl gas engine.

r john : That is a great system, it is also a great big HUGE system, What do you want with such a big unit ! You could run a small motel, and dump the waste heat into
an olympic swimming pool !

I would be very happy with a 2.5 KWatt per hour plant running 12 -24 Volts directly with some battery back up ! I could live with a unit 1/2 that size with 1 cylinder and
the possibility of the future ability to have a PTO!!

I seriously expect that 1 man would be needed for several hours daily to make sure the wood/biomass fuel was conditioned to burn, and then there is 'hauling the
ashes', and loading the feed box, Watching this leviathan would not be the same as sitting beside a rocket stove and dropping in another chunk or three when the
pitch of the dragons roar changes !

The amount of wood consumed for the rating seems reasonable, if you wanted to both heat and run a machine shop, But it appears to be way over the top for most
of the needs of your Fellow Members !

Just my two cents worth ! Big AL

allen lumley wrote: r john : That is a great system, it is also a great big HUGE system, What do you want with such a big unit ! You could run a small motel, and dump the waste heat into
an olympic swimming pool !

I would be very happy with a 2.5 KWatt per hour plant running 12 -24 Volts directly with some battery back up ! I could live with a unit 1/2 that size with 1 cylinder and
the possibility of the future ability to have a PTO!!

I seriously expect that 1 man would be needed for several hours daily to make sure the wood/biomass fuel was conditioned to burn, and then there is 'hauling the
ashes', and loading the feed box, Watching this leviathan would not be the same as sitting beside a rocket stove and dropping in another chunk or three when the
pitch of the dragons roar changes !

The amount of wood consumed for the rating seems reasonable, if you wanted to both heat and run a machine shop, But it appears to be way over the top for most
of the needs of your Fellow Members !

Just my two cents worth ! Big AL

Allen
We are very fortunate in the Uk in that we get paid by the government for renewable energy. For electricity it is by what they call the Feed in Tariff (FIT) and for heat the Renewable Heat Incentive (RHI). So long as you follow the strict rules then you will be paid for the heat and electric recorded on the meters. The size of the system becomes irrelevant in individual terms as your needs are covered and any excess is exported into the National grid reducing our reliance on fossil fuels. I was looking at the system as a solution for woodchip drying using the German Hook Bin system outlined in the brochure I referred to earlier which there is a link to in the brochure. With respect to time needed the woodchip required for a month takes less than 1 hour to process with a chipper into IBC containers. Refuelling is 5 minutes per day tipping an IBC container into a hopper with a fork lift using a pallet rotator. Monitoring can all be carried out remotely by mobile phone with any error messages automatically sent by SMS text to your mobile and the factory.

Maybe it is a bit OTT for Fellow Members but I am just reporting how much more advanced Europe is in respect of weaning itself of Fossil fuels compared to the power hungry USA.

Nearly forgot in respect of ashes the 45 gallon drum collecting ashes requires emptying on average once every 3 months.

I saw this thread awhile ago. Right now, for various reasons, I'm looking at the alternative to grid electricity. Obviously solar is cool, but not so much in Dec. and Jan. especially. I remember, perhaps after reading the above reply about steam turbines, thinking "it would be cool, when will it be available". So today I googled "microturbine" and found some company in India making them, starting at 1kW capacity with relatively low pressure (5 bar).
http://mizun.trustpass.alibaba.com/product/108351168-0/Micro_Steam_Turbine_Generators_from_1_KW_to_50_KW.html

According to wikipedia, dry wood has an average of 4.5kWh energy per kilogram. I wonder how much of that energy can be captured by a rocket stove for boiling water into steam?

I just googled "rocket stove steam boiler" and found this: http://www.kimmelsteam.com/ryanboiler.html

That website has a ton of information on steam engines from old tractors and cars.

I understand there is some risk of explosion with a boiler, but I wonder why over pressure valves, such as are seen on hot water heaters can't also work for boilers?

Andrew R. : Our Rocket Stove/ Rocket Mass heater Forum Here at Permies.com, and our sister site Richsoil.com have a serious bent towards
safety. None of us want to be guilty of advising on a RMH built to a fellow Member and have a 3rd party come along and due to personal inexperience
attempt a build, or a modification of someones build (as he understands It) and Seriously hurt or kill himself or family !

When water dashes to steam it instantly expands 2700 Xs, this is a tremendous amount of energy released and is generally referred to as Boom-Squish
with you being the Squish !

Think Boston Marathon Bombing with more Deaths, injuries, and full thickness full body burns !

One only has to look at the Frankenstien-like machines of doom called Rocket Mass Heaters by their creators, to wince. With the new posting of a
Video of one of these Abominations we can count on a steady stream of badly built Frankin-clones to follow !

This is where I say U-tube is full of crap ! and climb down off of my soap box ! For the Crafts ! big AL

I must agree with Allen even though I work with steam on a daily basis. There is no such thing as safe steam but there is safer steam which is derived by coils and evaporators rather than use of a boiler. What it means in reality is theres not enough steam within the coils to cause an explosion unlike a typical boiler however it does still have the ability to cause serious burns so needs to be treated with respect.

"I understand there is some risk of explosion with a boiler, but I wonder why over pressure valves, such as are seen on hot water heaters can't also work for boilers?"


Boilers are far more dangerous that water heaters, even though they look and act very similar most of the time. A water heater safety valve isn't designed to deal with the phase change problems of steam. It vents far far before steam is ever produced.

Pressurized steam (to accomplish real work) is a whole different universe.

A gallon of saturated steam at useful working pressures contains about the same potential energy as a stick of dynamite. In the rocket mass heater discussions about hot water, one often hears the phrase, boom-squish. This energy potential is why.

If something bad happens to a steam pressure vessel (say a pipe breaks and the pressure drops suddenly to atmospheric) the result is almost always an explosion.

There is no safety valve in the world that can prevent that explosion when something breaks like that.

Boiler explosions almost universally look like a bomb went off.


Yes, there are lots of worthwhile safety protocols to reduce the risk of catastrophic steam problems. Most of them involve licensed boiler makers, and licensed boiler inspectors, licensed pipe fitters and licensed operators.

I say this as a libertarian who would like to see 80% of our government to go away. We'd still need boiler inspectors.

I have actually built some model steam engines and stirling engines. I have several books describing how to make small scale boilers.

I have considerable welding and fabrication skills. I was actually a licensed pipe fitter for a time.

Yeah, I can't get up the nerve to make a boiler...


This guy sells steam stuff in about the right scale for what is being discussed here:

http://www.mikebrownsolutions.com/mbsteam.htm



On a very good day, steam power with a reciprocating engine at this scale would be less than 10% efficient from fuel to useful electrical output.


Not meant to be discouraging, but don't want anybody to underestimate the risks either.

Quite frankly there is no need in this day and age to operate anything with a conventional boiler. Most countries operate on the requirement that you require a qualified steam engineer to operate a steam boiler this has resulted in many companies investing in hot thermal oil systems which with thermal oil steam evaporators can produce steam on demand and the thermal oil is not held under pressure and therefore there is no requirement to employ a qualified steam engineer. Hot thermal oil typically 230C has its own unique problems but at least with good engineering can produce a very safe working environment.

As for efficiency my girls where the rolls royce of reciprocating steam and achieve about 15% electrical efficiency and 75% overall efficiency.

Just an example of what can happen when all the fail safe devices dont actually work its the 4th video on this site.

http://www.claytonindustries.com/clayton_v1_videos.html

The first video also shows how much safer a coil steam evaporator is on a test to destruction with all safety features removed.

Steam and water under pressure can be a dangerous combination. www.combustionsafety.com/hot-water-heater-explosion-elementary-school/

This item is in almost every househod......a hot water tank.....

One teacher and six children dead....thirty-six injured.....from an 80-gallon hot water tank running at approx 130 degrees Fahrenheit.....due to untrained "maintenance" people and a lack of a PM--preventative maintenance program.  

Another website http://www.stjoechannel.com/news/local-news/hot-water-heater-causes-home-to-explode/162490349

Nobody was killed or injured....the entire house was destroyed and shrapnel from the explosion was found up to 250 feet away.

Just some observations from a certified steam engineer who worked at BC pulp mill boiler rooms and on hi-pressure boilers in the Alberta oil sands.

Hi Justin,

I am in a similar situation about deciding what to do with my electricity situation in an off-grid cabin I'm planning. I figure I need about 1.25 kWh per day of electricity to get by. One solution I have found is these guys,

http://www.devilwatt.com/

They make a little power bar thing that you screw to the top of your wood stove to generate ~ 70 W of continuous power, with no moving parts. You just need to supply cooling water, which could be done by gravity feed from a spring or roof top run off. I haven't seen any reviews of these things, so I don't know how robust they are. Just because they have no moving parts, doesn't mean that they don't break. 1.25 kWh/day is only 52 W continuous power.

If you are running the wood stove anyway then it might be a good solution for the winter months.

Michael Deaves wrote:

I am in a similar situation about deciding what to do with my electricity situation in an off-grid cabin I'm planning. I figure I need about 1.25 kWh per day of electricity to get by.

Hi Michael

You wrote you need 1.25 kilowatts per _hour_ per day.  In  a 12-hour day that would be a consumption of 15 kilowatts.

52 watts of continuous power is 52 watts per _hour_.  I am curious to know what you plan to run off the your system.

Hi Jay,

I meant 1.25 kWh, as in kilo-watt-hours, not kilowatts per hour. Kilo-watts per hour doesn't really make any sense, since a kilowatt is a unit of power, which is already a rate of energy consumption, so we don't need to make it a rate again by saying kilowatt PER hour (that makes as much sense as saying MPH per hour). A kilowatt-hour is the energy that is used by running something that has a power of 1 kilowatt for one hour.

I have no idea why battery and solar people talk in kilowatt-hours, it's just confusing to everyone involved. The SI unit of energy is the Joule, that is what should be used. Power is the rate of energy use, or Joules per second. We call this a Watt. So if you are using one Watt your are consuming energy at a rate of one Joule per Second. A Kilowatt is then 1000 Joules per second.

Now comes the weird part. A Kilowatt-hour, is the amount of energy used by running a 1 kilowatt appliance for one hour. Since a kilowatt is 1000 Joules per second, and an hour has 3600 seconds in it, a kilowatt-hour is actually 3600*1000 Joules, or 3600 kilo-joules.

I think the confusion is made worse by the cooling industry, which rates their appliances in BTU-hours, when in reality what they really mean is BTUs PER hour, which is 1055 Joules per hour, which is 0.293 Watts (Joules per second).

So in my post I say that in my home I will need 1.25 kWh per day, which is 4500 kilo-joules of electrical energy. A 52 Watt generator will produce 52 Joules per second, or 4500 kilo-joules in 24 hours.

I hope this makes sense.

Michael Deaves wrote:

Hi Michael

So in my post I say that in my home I will need 1.25 kWh per day, which is 4500 kilo-joules of electrical energy. A 52 Watt generator will produce 52 Joules per second, or 4500 kilo-joules in 24 hours.

I hope this makes sense.

It makes sense...if you are running a 12 volt system and only producing 4.3 amps...that will give you 52 watts of power.

Joules per second....watts...power....equals product of voltage and amperage

You say one kilowatt-hour is 3.6 megajoules, or 3600 kilojoules which is the amount of energy converted if work is done at an average rate of one thousand watts for one hour.
In 24 hours that would be 86 megajoules.... 86 thousand kilojoules.

The requirement is 1,25kWh ..... 4.5 megajoules or 4500 kilojoules produced in an hour.....multiplied by 24 hours is 108 _Megajoules_.....108,000 kilojoules....

Or.....back to Ohms law...1250 watts of power needed---on a 12-volt system that would be 104 amps...on a 24-volt system-- 52 amps...on a.36-volt system--35 amps....

The Devilwatt stovetop thermocouple 70 watt unit produces a maximum of 18 volts at 4 amps

What you plan to run off the your system?

Check out this "Direct carbon fuel cell", a simple fuel cell that converts carbon directly into electricity.  (Note: There are also ways to use the water-gas shift reaction to trade-off between Carbon and Hydrogen fuels by reforming/recycling the gases, and especially at higher temperatures as is done in the "Molten carbonate fuel cell".)  This "Molten hydroxide fuel cell" operates at only a moderately high temperature.

The following is a summary of this old patent:
http://www.google.com/patents/US555511

The melting point of sodium hydroxide (NaOH) is 318 °C (604 °F; 591 K).  
(Using an electrolyte of potassium hydroxide (KOH) is also possible.)

In a vessel of pure iron (or low-carbon steel) containing molten sodium hydroxide heated to around 400 to 500 °C, immerse a piece of carbon (of any type that is electrically-conductive), and bubble pressurized air into the molten sodium hydroxide in order to fill it with oxygen and circulate the electrolyte.  The iron serves as the positive electrode, while the carbon forms the negative electrode.  The carbon is gradually converted into CO2 / carbonic acid, which mostly bubbles up through the electrolyte and escapes.

In the following side-reaction, a portion of the carbonic acid combines with a portion of the sodium hydroxide to form sodium carbonate
(2NaOH + CO2 --> Na2CO3 + H2), and this, together with any ash from the carbon fuel residue, slowly contaminates the electrolyte, and in the course of time lessens its efficiency. The efficiency may however be maintained by periodically refreshing the electrolyte.  The contaminated electrolyte may be purified by "simple well-known processes".

The contamination of the caustic soda by its union with carbonic acid may be reduced, and its life consequently prolonged, by adding a small percentage of magnesium oxide catalyst.  The inventor's conception of the magnesium oxide is that the free carbonic acid combines with it
(MgO + CO2 <---> MgCO3) in preference to the sodium hydroxide, and that the reaction is reversible so the resulting magnesium carbonate formed is quickly decomposed into carbonic acid, which escapes as CO2, making the magnesium oxide catalyst active again.  Thus the magnesium oxide serves as a carrier to convey the carbonic acid / CO2 through the electrolyte.  

Interesting.....

1. What volume of air or pure oxygen is needed?

"Instead of using the air as a source of oxygen supply, it is evident that I may use oxygen artificially prepared by
any of the well-known methods, and, as might naturally be supposed, the chemical action takes place more rapidly with
pure oxygen than when the oxygen is diluted, as in air. "  

2.   And I guess this is why they are not made for use today:                                                                                                                                                                                                                                    

"The volume of current from such a generator as I have described is very large, but the voltage is smaller than
is demanded for most commercial purposes. Greater voltage may of course be obtained by coupling any desired
number of such generators in series, or the voltage from a single generator may be increased at the expense of
the volume of current by Well-known methods of transformation."

I wonder how many cells {"generators"} you would need to get 12 volts...and how big of a firebox you would
need to heat the battery up to operating temperature.

"F is a furnace surrounding the generator and used to keep the generator and the inclosed electrolyte at the proper
temperature, (say 400o to 500O centigrade.) "

to convert--degrees in Centigrade multiplied by 9/5 and add 32 to equal degrees in Fahrenheit

400 deg C equals 752 deg F
500 deg C equals 932 deg F

You might be able to design a square wave circuit to conver tthe direct current of the cell to the alternating current
needed for the transformer, but to be usable, it depends on how much current the cell initially generates.  It would
be an inverse ratio  eg:  1 volt at 12 amps would becomes 12 volts at 1 amp

The patent says that air works, you don't need pure oxygen.  I'm not sure how efficient this one is, but other fuel cells can be 50-60% efficient.  When you compare that to other ways of generating electricity that are 5%-15% efficient, maybe 20% for a small Diesel or Stirling engine, then you get a feel for the amount of air required.  Although I might target a similar efficiency, so it would use about the same amount of air and woodgas as you'd put in a (small) engine.  

I think the difficult part about this particular design is that molten sodium hydroxide is dangerous if spilled and is extremely corrosive.  It will dissolve any organic material.  That's a problem.  For that reason maybe this isn't practical if it can't be handled safely, although maybe substitutes for the NaOH could work.  (For example, maybe a Molten carbonate fuel cell running at around 425 °C (800 °F) could work, maybe other carbonates could run at lower temperatures, maybe Magnesium carbonate, MgCO3 could be tried instead of lithium carbonate... I don' t know it's just a guess.
http://www.nfcrc.uci.edu/3/TUTORIALS/EnergyTutorial/mcfc.html
http://en.wikipedia.org/wiki/Molten_carbonate_fuel_cell
Or maybe there's a way to use some other low melting point salt like sodium nitrate or potassium nitrate.

If one was willing to sacrifice high efficiency and high power, at least initially, it might be possible to make a simple system akin to something like a TEG (thermoelectric generator) but hopefully costing less than $2/Watt.

A glowing-hot piece of charcoal is highly-active chemically, makes an excellent catalyst and is a common low-cost, non-toxic when used appropriately, "disposable" fuel and material used in wood fires all over the world.  It can also be made in many different forms.  If a piece of bread is made into charcoal it forms carbon foam.  Something like that could make a low cost disposable, high-temperature gas-electrode.  Feed your woodgas (H2 + CO) into it.  Have the electrode immersed in a bath of a suitable conductive molten salt.  It might work assuming some of the engineering design issues could be worked out.  I'd suggest not get distracted with chasing high power and high efficiency but instead just focus on keeping it simple, relatively safe, and DIY accessible.  As in the design of Rocket Mass Heaters for example, if high-temperature refractory ceramic materials are used instead of metals, it can avoid a lot of the problems with metal materials failing due to oxidation and corrosion.  Graphite and Magnetite (Fe3O4) are two examples of low-cost, non-toxic, DIY-friendly, electrically-conductive, high-temperature refractory materials that conceivably might be used to help make simple, high-temperature fuel-cell electrodes.  

Michael and Jay, there are different schools of thought or concept that derive the same answer.... every time.

I really dont care what time it is at Greenwich! The engineers and suppliers of energy convert and sell kilowatt-hours, because somewhere in there, time matters to or has effect on the use of the equation.

Operation time, storage time, delivery or conversion over time.

I failed all math courses, have no diplomas and design reliable systems that are in use all over the territory. I do have an "A" grade in industrial engineering from a professor of industrial engineering at Kettering University, where the prof at the conclusion of a foundation funded geothermal heating project that serves a greenhouse operation, says in front of the international class of graduating engineers, ' i can tell immediately the students grade, he is a "B", she an "A" them, "D", you, you are an "A"!

His class did wonderful maths and had wide knowledge, they failed utterly at applying concepts and observation to detail required to engineer what was being asked for.... and see beyond joules.

When designing from off the shelf equipment we use name plates as a reference and no day is usefully being expressed in jouels, even if you could equate waves are particles and particles waves... its all just a joule and has no reference for time, we do, though use it to pace our day and machines to great effect, ask the slave trading, railroading, clock makers at Greenwich.

A Solar energy conversion and storage designers main hurtle is not units of energy, it is average sun-hours per day vs average use, both widely variable at any point in time within the system and a electrical generation engineers problem is fuel consumption over operating hours and efficiencies of conversion and delivery over time.

You can put all the joules you like on a white paper and it will not change this concept.

So, unless Michael needs all his days power or recharge requirement at one instant, 104 (12v) amps or 1250w will never happen aside from a direct short or potential in storage and the battery cannot accept it over that timeframe anyway, 5 amps battery charging for 12-14 hours of the day (even the heat energy is quite variable unless automated) will provide the required kilowatt-hours with a storage capacity which reflects useful intervals between firing for heat and production of char, likely days or hours and possibly seasonal.

That seasonal thing could (could) exclude a TEG, but may not, depending... i like the TEG over engines, but my concept is to eliminate engines, possibly even the wood stove/heater (and its fuel requirement) which is also our indoor clothes dryer and de-humidifier aside from being a gathering place with a window into the fire for ambiance.

What is a "Tesla"? Can it be expressed in Joules? Does it matter (or is it matter) if we have no other values to apply?

Express it any way you like, ive never been without electricity while operating off grid and without an engine.

Michael will not ever require 104 amps charge or discharge current and will not charge at 18v either.

Not everybody is standardized and he who spins the gold sets the price and terms. That was easier.  

frank li wrote:Michael will not ever require 104 amps charge or discharge current and will not charge at 18v either.  

A lot of people, when they go off-grid, want to run a laptop, use a chest freezer with external thermostat as a fridge, and
perhaps a couple of LED lights.  Frank--How much amps would a person need--using a 12-volt supply?

In Michael's case, I do not know what he wishes to run on a system....I'm just using the average desired load as an example.

R Jay wrote:

frank li wrote:Michael will not ever require 104 amps charge or discharge current and will not charge at 18v either.  

A lot of people, when they go off-grid, want to run a laptop, use a chest freezer with external thermostat as a fridge, and
perhaps a couple of LED lights.  Frank--How much amps would a person need--using a 12-volt supply?

In Michael's case, I do not know what he wishes to run on a system....I'm just using the average desired load as an example.

You are correct to point this out. I was working with the info below, and i remembered distinctly, the guy needs 100w or less with everything on, but it was erronious and was the usage profile of Justin, the original poster of this thread which i confused with Michael Deaves 1.25kwh requirement per day and was thinking, "what in the world is so mistaken about proposing to use a 70w TEG for this?"

["The winters here in Montana are long and harsh. An efficient wood stove will be essential. Cooling will not be necessary. Food storage is taken care of in the buildings at base camp - so no refrigerator. I have calculated my energy requirements: 

- netbook laptop: 30 W x 10 h = 300 Wh 
- stereo: 50 W x 5 h = 250 Wh 
- modem: 24 hrs x 7 W = 168 Wh 

Total: ~720 Wh at maximum usage 

Light at night will be provided by candles (which also produce heat). A 12V deep cycle lead-acid battery rated at 130 Ah, discharged to 50%, supplies 780 Wh. With the inverter running at 92% efficiency these power needs could be met with a single battery. I would probably add a second one to cover further inefficiency and reduce strain on the batteries. "]

True, energy usage for a cabin or other building can differ wildly, day to day and i do not know how Michael would use it exactly. Maybe he uses 2500w for 30 minutes or however many newtons can be moved one meter in metric land, or perhaps he uses 75,000w for one minute.

As an average, it would be roughly 4.3 amps at a nominal 12v over a day. If he uses all his energy in 4 hours while home and not sleeping, it would be about 26 amps.

I do stand corrected. Got lost in the thread.

My issue was SI as the only expression and per, per, per, which is actually not the case when using kilowatt-hours as an expression of an average derived unit of energy.
Sorry, im not making a switch to kilometers, its not in our culture, just as joules is not in common use in the technical language of the electricity industry.

So, joules may be perfect grammar and poor lingo at the same time, depends on the culture and technical language evolves rapidly and adapts what it needs to in order to function, acceptance is key.

It just hit me as kind of grammar nazi stuff, where Michael made no mistake, it was good linguistics as he fully understood that he was correct, while also not using the international standard unit or metric. Unless we are trying for a phd in physics, most people have any relative knowledge of what a joule is and they buy no monthly joules, not that its not there somewhere, but kilowatt-hours are what are produced, bought and sold in the industry and market.

Justins prospect system will never require 104 amps charge or discharge current... if he stays within design limits  produced by his stated requirement, but it doesnt matter, wrong response from me.

So if i were to re-do and specify a charger, i would have to say there is no reason to call Michaels concept into question. He was on a good road with the 70w TEG as a rough figure and his use of language was fine.

Devil watt does make a 100w mover of medium sized apples over a meter and my system is capable of converting 4.5 terra perms per average sunny day for storage, where a perm (P) is the amount of heat absorbed by a hair on the back of Paul Wheatons hand while basking in 100w incandescent lamplight with a distance of 2.5 feet from the tip of his mouse finger and in a room at 50° F (F, for the purists) ambient air temperature and his desk and walls re-radiating sunlight from the day before!

Of course the whole thing is out the window, if the lamp reflector surfaces facing the hair are not up to operating temperature.... we are going metric with delta-wheatons, where we measure the temperature of the coffee cup handle within 45 seconds of activating the lamp and convert that to incident gastrointestinal cob dust digestion rate where poultry is not being housed and a pound of collard greens were eaten an hour before.

Which means, i get the point. Standard units are great. To make communication easier and with more numerous people, they are not always used and are not required if you find any suitable way to explain what we are talking about and people acknowledge it.

Most are technicians, not engineers although some may be both. I am a technician proficient in pv system design.
We can all talk as long as we meet somewhere in the middle to help each other out.

R Jay wrote:

Michael Deaves wrote:

Hi Michael

So in my post I say that in my home I will need 1.25 kWh per day, which is 4500 kilo-joules of electrical energy. A 52 Watt generator will produce 52 Joules per second, or 4500 kilo-joules in 24 hours.

I hope this makes sense.

It makes sense...if you are running a 12 volt system and only producing 4.3 amps...that will give you 52 watts of power.

Joules per second....watts...power....equals product of voltage and amperage

You say one kilowatt-hour is 3.6 megajoules, or 3600 kilojoules which is the amount of energy converted if work is done at an average rate of one thousand watts for one hour.
In 24 hours that would be 86 megajoules.... 86 thousand kilojoules.

The requirement is 1,25kWh ..... 4.5 megajoules or 4500 kilojoules produced in an hour.....multiplied by 24 hours is 108 _Megajoules_.....108,000 kilojoules....

Or.....back to Ohms law...1250 watts of power needed---on a 12-volt system that would be 104 amps...on a 24-volt system-- 52 amps...on a.36-volt system--35 amps....

The Devilwatt stovetop thermocouple 70 watt unit produces a maximum of 18 volts at 4 amps

What you plan to run off the your system?

I keep getting 4.5 mJ and double checked myself and then doubled with 2 different online calculators.. i have failed to find any fault in Michael's explaination that should draw skepticism nor in his consideration of a 70w TEG as a workable solution. He probably is better at math than both of us and seems to have total understanding of theory, law and application here.

frank 11 wrote:
So in my post I say that in my home I will need 1.25 kWh per day, which is 4500 kilo-joules of
electrical energy. A 52 Watt generator will produce 52 Joules per second, or 4500 kilo-joules in 24 hours.

i have failed to find any fault in Michael's explaination that should draw skepticism nor in his consideration
of a 70w TEG as a workable solution. He probably is better at math than both of us and seems to have total
understanding of theory, law and application here.

Frank--you're right....somewhere I  lost it....my bad....kilowatt hours is the product of watts and time,then
divided by 1000......

so.....52 watts times 24 hours gives almost 1250 watt hours---then divided by 1000....equals 1.25 kWh

and yes...a 70 watt TEG will be more than sufficient