Small Steam System

I am adding this link and discussion to the thread as it's relevant to the topic. Those who have read through the thread will understand the relevance.

The link describes a small steam system used to power a small boat. The system uses a small monotube steam generator. The steam generator is made from 40 feet of roughly 1/4" diameter stainless steel tubing. While the system is crude and inefficient (the builder stated elsewhere that he was all about K.I.S.S. and didn't give a damn about efficiency or cosmetics), it shows clearly that a simple length of small diameter tubing can generate quality steam at a surprising rate.

The control system is interesting to me as it's similar in some respects to a configuration I considered independently. The system in the link uses a bimetallic strip exposed to the peak steam temperature supplied to the engine (it's in thermal contact with the steam supply line by mounting the strip to a small copper block clamped onto the steam line). The strip bends in response to the steam temperature changes, and this bending actuates the potentiometer of a Pulse Width Modulating (PWM) controller for a small DC motor. The motor drives the water feed pump for the steam generator. As the steam temperature approaches 600F, then the water is pumped into the coil at the max rate and this cools the coil. Since the the system uses a more or less uncontrolled wood furnace, then this would also increase steam pressure and increase engine output. A simple means to control engine output was devised: an adjustable steam relief valve is placed to manually vent excess steam and drop the steam pressure as required to lower engine output. While wasteful, it does make some sense in this case (uncontrolled wood furnace). The builder states that the steam temperature stays between 550F and 600F during operation, and the pressure is 150-200 psig during normal operation (pressure would be determined primarily by the load on the engine).

More than anything else I just wanted to show that a simple and surprisingly small coil of 1/4" steel tubing can in fact generate steam to run a useful steam engine. In fact, since this system has high thermal losses from the flue (due to the less than ideal shape and placement of the tubing coil), and since the engine design shows low efficiency (simple small counterflow slide valve unit), then it's clear that an efficient system could produce a lot more power with the same steam consumption rate. The engine in the link is described as having an output that corresponds to about 2/3 hp. A good single acting bump valve uniflow engine exhausting to a vacuum (fully condensing) could show twice the efficiency. Add to this a highly efficient steam generator coil and excellent insulation, and the output could approach 2 hp with the same size tubing coil. In any case, the steam generator required for a 1-2 hp steam engine system can be a great deal more compact than most people understand.

Now, the control system I considered also called for using a bimetallic strip to govern steam temperature. However, I considered using it to (1) control a PWM for the small blower fan of a gasification furnace, or (2) control a damper for the air supplied to a rocket furnace. The water feed pump in these cases would be driven mechanically by the engine, and there would be a relief valve on the pump discharge to limit the pressure in the system (this relief should also be able to handle steam just in case). The system would be operating at a constant output that might be adjusted up or down as desired by adjusting the relief valve. An alternative approach would be to set the relief valve at a constant setting, then throttle the steam supply to the engine to vary its output. Other features might include a high flue temperature thermostat to stop the blower fan of a gasification furnace, and a thermostatic damper shut off for high flue temperature in a rocket furnace (both these high flue temp conditions would occur if the engine were to stall while the furnace is putting out).

Hopefully this shows how small scale steam does not require dangerous pressure vessels - and it's not quite rocket science when kept simple.

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.

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.

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.

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.

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.

austin lerwick wrote:Hi,
"WVO Blending with Gasoline to Make Diesel Fuel" I don't understand can you please elaborate and the link is not going on particular topic too.

http://beyondbiodiesel.org/forum/index.php/topic,12.0.html

Just peruse the forum and you might find what you need. Note that I have no experience or real interest in it, I was merely sharing the info for those who might have interest.

http://www.ebay.com/itm/NEW-12V-DC-Micro-Brushless-Magnetic-Pump-High-Solar-Hot-Submersible-Water-Pump-/360881662635?pt=BI_Pumps&hash=item5406392aab

Solar water heating is popular in China. Small dc (12 volt and 24 volt) magnetic drive pumps are manufactured by the millions to meet the demand. They are highly reliable by all accounts I've seen with some models claiming a 30,000 hour life. They are highly efficient, and some models I've seen show impressive performance with fairly high head loads. Of course, any significant pressure differential should use a positive displacement pump - or two mag drive pumps in series could work. However, for transfer of water under modest heads, a dc mag drive pump is unbeatable.

The link provides one example of many.

ronald bush wrote:is there a chart on here, or the web, that gives the amount of usage of electricity by average appliances? seems i would be more apt to conserve if i knew how much it was saving. lol

I've looked and found little that's actually useful. A problem is that usage varies with households, so charts have little value. Those looking to conserve should simply note that using electricity for heating applications or air conditioning will almost certainly be the primary loads. Another big one is air moving equipment like whole house fans, but these are normally associated with space heating and air conditioning usage. I'd say focus on the big ones, then just make sure you're not leaving lights and electronics on unnecessarily, and tackle the "phantom" loads, and you'll be doing well.

Just my $0.02, but I've considered all kinds of thermal storage possibilities, and I keep coming back to water. I tend to agree with the concerns about the high energy required to move air through a packed pebble bed (not to mention ducting). A very low power mag drive pump sending hot water to a fan coil unit seems hard to beat.

Interestingly, the current industrial process for aluminum smelting requires carbon and generates CO2. Basically, the oxygen bonded to the aluminum (in aluminum oxide) is transferred to carbon to drive the process. Funny how this is not mentioned in any of the articles I've seen on this technology. Note that I personally do not consider CO2 production to be cause for concern, but many do - therefore, it should have been emphasized. Gee, I wonder where they're getting the carbon (coal, maybe)? See link:

http://www.balcoindia.com/operation/pdf/Aluminium-Production-Process.pdf - This link shows 13460 KWh of electricity required to process one metric ton of aluminum. That's roughly 13.5 KWh per Kg of aluminum.

http://www.hybridcars.com/renault-nissan-to-use-phinergys-aluminum-air-battery/ - This link shows 4.05 KWh of electricity per Kg of aluminum from the aluminum air battery.

Overall efficiency in electricity storage is roughly 4.05/13.5 - 30%. There is also the energy consumed in transporting the spent battery and reconstituted battery to and from the processing centers. Compared to the efficiency of charging a traditional battery at roughly 80%, then this seems like a substantial loss. Of course, COST is the main consideration. However, I have serious concerns (outright doubts, in fact) about the existing financial system to generate meaningful prices for such comparisons - especially for long term considerations, which matter most. By default, I prefer the system that is both simpler and less centralized. In my opinion, this technology might be suitable only as a range extender for an EV, and this is the targeted application. Basically, the idea is to replace an internal combustion engine driven generator with one of these aluminum air batteries, but rely primarily on a more modest traditional battery to provide the 50 or so mile range normally seen each day. Ideally, the aluminum air battery would be used very rarely. In that setting it seems reasonable. Even so, it's not the most favorable prospect I've seen.

Tessa, I also have considered a cooled space for long term food storage including my wine. The only system I've considered that can produce good results would rely on a vapor compression unit. The simplest configuration would be to place a small chest freezer in the space with the condenser coils outside. Alternatively, the freezer might be outside the space completely. The freezer should be loaded with water bottles that are to be frozen. Duct work is fashioned along with a dc case fan to circulate air in the space through the freezer where it is cooled by the frozen water bottles. Put a timer on the fan so it operates primarily during the day. This would keep the temperature in the freezer above the setpoint while the fan is operating and allow the freezer to be powered directly from the solar array to avoid some battery discharge during most days. Let the thermal mass and insulation of the space carry the unit to the next solar day as this will avoid some unnecessary battery discharge. Also, set the freezer thermostat to the lowest setting since its purpose is only to freeze water - there is no need to take the temperature down any lower than necessary to fully freeze the water.

Wesley johnsen wrote:does anyone know where to find an affordable absorption chiller? i saw they tried to make them with regular refrigerant but never came out with a light weight product that was cheap. i think it would be cool to power an a/c with a pellet boiler. ad solar hot water to it as well.

I can't find them either. I did some experimentation on absorption - just enough to convince myself that I am not willing to risk the resources required to develop a proper unit. The basic principle is extremely simple, but getting a unit with good performance would require a lot of development work - while getting nickle and dimed to death the entire way.

The practical and cost effective solution for off grid air conditioning is to power small electric motor drive vapor compression units with photovoltaics.

There are solar thermal powered adsorption/absorption systems being developed. The problem I see with this option is that the relatively low temperature heat source (solar heated water) either requires additional electricity consumption and even water consumption (using a cooling tower), or a higher water temperature lowers overall efficiency and raises costs due to thermal losses and/or more expensive collectors to compensate. It turns out that a PV array of the same area as a solar thermal array will achieve the same cooling capacity as a well engineered solar thermal adsorption unit, and do so at a fraction of the cost.

OK, that said, there is one configuration that intrigues me. A modern (but modest) off grid home could in principle be powered completed by biomass in the following manner. A slow moving and reasonably efficient piston steam engine powered by small wood splits could generate DC electricity at a low rate to maintain charge on a very modest battery system. The heat from the steam condenser could provide for all heating applications including space heating during the winter months. An adsorption cooling system might by powered by the steam condenser during summer months. I like this prospect for its low tech approach.

Topher Belknap wrote:Perhaps, if you are willing to travel a horse pace. The ELF has a solar panel, but it needs to sit in the sun stopped for hours to recharge a full charge (about 30 miles). A Prius with a solar panel doesn't even bother, it only runs the vent when parked. Solar racers are ALL solar panel, and have drag areas around 1 ft². Solar is diffuse, locomotion requires a lot of power.

Yes, I assumed the OP would be happy with a slow horse pace since he first considered horse power. Horses walk at about 3-4 mph, and oxen slower at around 2 mph (oxen were often used in lieu of horses to pull covered wagons across the plains). Of course, I'm not considering "a solar panel", but a large array of panels (think long and lightweight trailer with panels that can be positioned easily to optimize production). If several thousand watts can be done (roughly 70 square feet per KW - or 11 feet of trailer length per KW for 300 watt panels), then it could be viable (although, I doubt practical as I emphasized before). I sure prefer this prospect over horses. A low rate of travel will not require much power, and it should be a great deal less than the covered wagons of the past due to superior engineering (lighter weight and lower rolling resistance). Also, while the weight of the power system (panels, battery, motor, controls, etc.) would be substantial, it would be significantly less than the weight of draft animals required to pull the same load. Reducing weight as much as possible would be important, and I think the resources available today would be very useful toward this end.

J.S. Turissi, yours is an interesting idea. I do not consider it to be practical. However, for the sake of interest, I will take a gander at possibilities.

I don't like horses. I used to work with them, and my experience has me believing that people in general were very pleased to see the automobile displace the horse. You mentioned a steam engine. I actually think this could be used for motive power at low speeds suitable for long treks along undeveloped terrain. A surprisingly compact and slow moving steam engine can generate extremely high torque, and this would simplify the driving of a large and heavy platform at low speeds. In principle (again, not necessarily practical), a system could harvest biomass while in transit (cutting grass, etc.) and use the heat from the steam condenser to dry the fuel real time before forcing the fuel into a furnace. This same idea has been proposed for a sea going vessel harvesting algae to fuel a modern steam engine system.

Photovoltaics with electric motor drive is another possibility. If travel were restricted primarily to days with reasonably high solar flux, then the demands on a battery system for motive power would be very limited. I suspect travel would deplete a battery system too quickly without a substantial solar flux, so one would be limited in that respect. Of course, one would have to carry around a lot of solar panels. Something like an electric tractor pulling a long trailer with panels mounted on top comes to mind. A backup power source is likely required, and a wood gas engine system for bulk battery charging seems reasonable, and the gasifier can also be a primary source of heat.

Topher Belknap wrote:

That's quite an assertion. Do you have examples (positive and negative) to provide?

Sure. First, note that my argument has several restrictions. Since the OP emphasized selling electricity, then I have not considered the value of "waste heat" for anything other than perhaps wood fuel drying. Also, I am not considering a very large scale that might allow for using highly efficient modern steam power hardware (such as large multi-staged heat regenerative turbine systems). In my opinion, the fuel consumption rates would be too high to support such a system economically.

Basically, my position boils down to considering the most economical alternative at the targeted setting. There exist commercial wood gas engine systems at the low megawatt outputs that can generate electricity at an overall efficiency on the order of 30% (see Jenbacher). There are also small scale units on the order of 100 KW that show 20%+ overall efficiency (google will find them). I know of no commercial steam power system at the targeted scale that can compete with respect to initial and ongoing costs (of which efficiency is a paramount consideration)- with one notable exception. A new company (Terrajoule) has brought back a proven steam engine design known for high efficiency and extreme reliability (the Skinner Universal Uniflow). While designed for solar thermal with thermal storage, this system could generate electricity at a rate of several hundred KW with biomass fuel at an overall efficiency of 20%+. The ability to avoid many gas processing steps combined with the simplicity and extreme reliability of the system should make it a winner in this application.

In short, it's mostly the general lack of steam power hardware suitable for the application that causes me to favor internal combustion.

This thread started on NiFe batteries and went to energy storage in general (electricity in particular). Some problems with NiFe were noted, but the main problem seems to be its high cost. In my opinion, NiFe is simply far too costly to be a practical option. It seems only the zealots (and wealthy ones) remain unconvinced. Don't get me wrong, I like them - they're just too damned expensive.

The most cost effective alternative that I have seen so far is a new forklift battery. I priced a unit recently (see www.giantbattery.com). A 24 volt, 800 amp hour (at 20 hour rate), 1100 pound unit was quoted at $2453 with price including delivery in the continential U.S. There is a 7 year warranty on defects, and the battery is rated for 1500 full cycles. My research shows that 10 years is a conservative estimate for the operational life of these batteries in the off grid renewable energy setting. I've seen several accounts at 15-20+ years. The same company also picks up discarded batteries without charge, so you know they are recycling batteries for compensation. I did not verify, but it seems a significant discount on a new battery could be demanded when presenting a discarded battery in trade, and this should lower costs further.

A lot of lead acid batteries seem to die inside of 5 years in the RE setting. Long term battery costs get very high in that case. If the forklift battery will deliver 10+ years of service, and do so reliably (and all evidence I've seen shows that it will deliver), then it seems hard to beat. If anyone knows of a more cost effective alternative, then please let us all know.

NOTE: On the massive size and weight of a forklift battery, a practical solution for this seems to be placing the unit onto a platform on heavy casters. A battery could be delivered and placed onto the platform, then maneuvered to the desired location. I have moved large safes on several occasions using this approach, and I've found it to be a practical solution.

Richard Hauser wrote:
The last energy storage is the one we are most accustomed to, wood. Wood has 1/3 the energy by weight as gasoline and that statistic still blows me away. To convert wood into usable energy we need to burn it and then use that thermal energy to run a motor: again pneumatics, steam engines, Stirling Engines or Peltier chips. Of the group the most efficient is the Stirling engine. These are generally dismissed as unworkable (the head of the Stirling Society has a diesel engine converted to a steam engine as a backup power source) ...

Just a quick correction. You may be referring to Ken Boak of the UK here. He was once the head of the UK Stirling Society. However, note that he does not use a steam engine, but a Lister Diesel engine converted to run on wood gas.

I second Mike's endorsement of Do the Math. It is outstanding. Read it. You won't be disappointed. A good basic foundation in physics makes it possible to cut through a lot of BS.

http://www.physics.org/featuredetail.asp?id=47

Wesley johnsen wrote:would this be a profitable business to run a few wood pellet industrial sized boilers that heat water to 180 degrees that will be pumped to a lot of organic rankine cycle electric power generators? the electricity would be sold to the grid. also there could be a large compost pile of wood chips with a coil running through the pile to heat the water up to 180 degrees so the pellet boilers would not have to run all the time. solar photovoltaic would be used to power the low energy requirement for the boilers and circulator pumps and controls. i know they have sustainable woody biomass power plants that run on wood pellets and chips but wanted a second opinion. the difference between my idea and the working models is that my idea does not use steam but just hot water.

No. The main problem is the high initial cost combined with the very low overall efficiency in generating the electricity. If you desire to use wood to generate electricity, then the only viable system is a wood gas engine system. Small rankine cycle engines (organic working fluid or steam) will not be viable for primarily generating electricity, but might be suitable where heat is the primary desired product. A sophisticated modern steam engine system might be a different story, but these are not commercially available.

For more information, I recommend you research wood gas engine systems at www.gekgasifier.com and www.driveonwood.com. A fairly large and fairly simple wood gas engine system can be surprisingly efficient at generating electricity when the system is operated under optimal conditions. The larger systems will not only be more efficient, but they can also use fairly large wood chunks (like baseball size) which will lessen the fuel processing requirements of the system. If your goal is to feed the grid, then you're going to need high power along with a helluvalotta wood to be profitable. Wood pellets are a non-starter as they are too expensive. You need access to copious amounts of raw wood resources along with an efficient system of processing the wood fuel for use in the system. Use the heat from the system to dry the fuel.

There are large industrial wood gas engine systems manufactured by Jenbacher. There is a person active on the forum who claims to have experience with these systems. You might contact him (r john) for information.

How about a wood fired steam engine?

http://www.youtube.com/watch?v=ZwxWEUxc1g4

Michael Cox wrote:You can get "grid tied" systems which feed energy back to the grid when not being needed in the house. When the grid goes down for some reason they can keep the house supplied.

A grid-tied solar PV system can be configured to provide electricity during a loss of power, but the vast majority of systems do not provide this feature. Let me be clear: the majority of homes that have installed PV arrays are grid-tie systems. During a power outage (loss of grid power) the vast majority of these systems are completely useless for providing electricity. http://www.wholesalesolar.com/AC-coupling.html

Note that there are new inverters on the market that can allow a grid tied solar system to provide electricity to the home at a limited rate during a loss of grid power. http://www2.buildinggreen.com/blogs/beating-achilles-heel-grid-tied-solar-electric-systems . However, a battery system is required for powering substantial loads during a loss of grid power.

Cooking with electricity can be viable in the off grid setting. Cooking during the day while a PV array is producing could eliminate battery discharge. Also, a wood gasifier stove can be precisely controlled with respect to output. See this for one example: http://www.youtube.com/watch?v=m_jWz3H-48M . Propane was mentioned, and of course this would work, but many do not consider it's use to be "off grid" - I don't know where you stand on this, but it's an obvious solution.

I appreciate and understand the optimism. However, I highly recommend you replace optimism with objectivism. A device such as the one described would be very easy to demonstrate. In other words, it could easily be shown to work. Therefore, if a functional device were available for demonstration, then it would not take long to demonstrate the device and convince a large number of highly qualified individuals who could attest to its functionality. I recommend you find these individuals who can testify to its functionality. If you cannot find the individuals (credible scientists and engineers who have tested the unit first hand), then the rational position is to consider that the unit does not work as claimed - or at least that there is insufficient evidence to make a judgement on the matter.

Marcos Buenijo wrote:Turns out that the steam pressures and temperatures achieved with this system, along with using irrigation water pumped by the system to cool the condenser, will allow for good efficiency. The CEO claims 30% cycle efficiency with 70% concentrator efficiency, and this would allow for 20% overall conversion of solar energy to work. This would be outstanding. However, I am skeptical about the efficiency claim. Their system does not allow for steam reheat or heat regeneration as I understand the configuration. If steam temperature is limited to 600F as the claim, and there is no reheat, then the best efficiency this system would see is the low 20's%. When the concentrator efficiency is considered, then the figure drops to about 15% net conversion of solar energy to work. Now, this is still excellent. More important, the efficiency of the system is not important - it's all about COST. In my opinion, this is where this system shines. I think it's brilliant.

I'm gonna have to reconsider my position here. It turns out that large compounded piston steam engines have shown very high efficiencies in the past. The losses are greatly lessened with large expanders. Croft in "Steam Engine Principles and Practice" shows several large compounded piston steam engines using saturated steam showing well over 60% of Carnot efficiency. A very good compounded uniflow expander like the Skinner design should be better than a counterflow compound. So, I think this system can pull off 30% efficiency with steam at 600F and water cooled condenser down to 100F saturation temperature. Overall efficiency in electricity generation for this system could approach 20% - and that would be AC power.

Video describing the Terrajoule system. The simplicity and effectiveness of this approach is astounding. I love the irony of finding such an effective distributed solar power system with existing mass produced components and old piston steam engine technology. Consider that the more complicated systems are generally the least stable. I believe this approach will catch on.

r john wrote:

Energy density is totally irrelevant. Pumped storage is already commercially viable for storage of renewable energy in UK and Germany using gravity alone. Energy densities are increased many times by using a weighted accumulator. On a local level it could be the weight of the house used as the accumulator but on a country scale this German proposal seems a reasonable proposal given the marble cutting technology used in Italy.

http://blogs.worldwatch.org/revolt/unconventional-“hydraulic-hydro-storage”-system-offers-energy-storage-for-the-grid-on-a-grand-scale/

"On a Grand Scale". Exactly.

r john wrote:

Your road block was solved by Armstrong in the UK in the 1850's see the wicki

http://en.wikipedia.org/wiki/Hydraulic_accumulator

We still have a few weighted accumulators in use in the UK mainly for swing bridges.

Unfortunately, these do not store appreciable energy (low energy density). However, they are useful in some settings because they can deliver energy efficiently at an extremely high rate (high power density). I maintained several very large hydraulic accumulators pressurized to 3000 psig. The purpose of these was to raise an elevator platform weighing more than 250,000 pounds by more than 40 feet in under 10 seconds (aircraft elevators on U.S. Navy aircraft carrier vessels). The system was recharged after each cycle by running four large piston hydraulic pumps powered by electric motors rated at roughly 300 hp. All four pumps working together could recharge the system in roughly 90 seconds. While such a massive storage system at high pressure appears to supply an enormous amount of energy (10 million foot pounds sure seems like a lot), the system actually shows very poor energy density (the figure is about 13000 btu - about one pound of coal). This same amount of energy in the form of electricity (about 3.8 KWh) can be delivered by a fully charged lead acid battery weighing about 250 lbs.

I don't see this as a practical system for appreciable energy storage.

r john wrote:Hydraulic energy densities can be far higher than batteries see below.

http://www.diva-portal.org/smash/get/diva2:373607/FULLTEXT01.pdf

Hydraulics show very nigh POWER DENSITY, not high energy density. Solar energy storage needs high energy density.

I want a green one.

Seriously (well, I was serious), I made a post about this a few months back. I'm pleased to see that momentum is building. It really looks like this will make it to market. I predict (again) that it will be a smashing success, assuming the thing is well engineered and the price doesn't increase substantially. I see a huge market for this kind of vehicle.

http://www.csrail.org/index.php/research-areas/new-steam-locomotive1/cleaner-quicker-cheaper

Particularly good discussion on some benefits of modern steam locomotives.

I'm not necessarily arguing that it's the single best solution. I am arguing that the reader should be willing to think outside the box on this matter.

Chael Givan wrote:I'm not here offering answers but rather I'm here asking questions. I've read that solar systems are expensive, in large part, because of their battery needs to power things when there is no sun out. Why aren't people using panels to pump copious amounts of water into holding tanks, thereby storing potential energy, for use later via outlet gates and water wheels or turbines?

This methodology would apply to metal springs also. It seems to me that a solar system could be broken down into a few motors, springs and solar panels or alternatively, solar panels, a water pump, holding tanks and a water wheel with attached motor. Perhaps it's all just pie in the sky optimism and not practical. I'm asking here to see what others think.

The problem with these prospects is low energy density and high cost. A conventional deep cycle lead acid storage battery weighing about 70 pounds and costing on the order of $120 can deliver about 1 KWh of electricity when fully charged. This represents about 2 million foot pounds of energy. Therefore, when one considers the losses in energy conversion, storing 1 KWh of electricity in the form of water in elevated storage tanks would require a set up that represents about 3 million foot pounds of energy. If the elevation is 10 feet, then one requires about 4800 cubic feet of water. If the elevation is 100 feet, then about 480 cubic feet of water is necessary. In short, this is why a lead acid battery is used in lieu of pumping copious amounts of water into storage tanks.

What I think is that batteries are by far the most practical means to store solar energy in the micro scale, and assuming electricity. Even when used in tandem with a heat engine (such as a wood gas engine system), then a battery is very useful to store energy for low power electrical loads. Now, if the desire is to store thermal energy, then water is a brilliant choice. Also, if the scale is larger, then water is also a brilliant choice even for electricity generation - but I'm not referring to the way you might think. Consider the work of Terrajoule (see http://www.terrajoulecorp.com/). In this case, photovoltaics is not used, but the overall efficiency is higher than conventional PV with battery storage, and a lot less expensive.

william lane wrote:thanks. I figure all my numbers could be off. I'm just parroting what I was told by the engineer next door. It didn't really match what i have read else where on this and other sites, hence the open invite for advice . I have no expectations other than water will turn a wheel and i will build out from there. Maybe he meant if we get another 15 of drop chasing the exit up the hill? 25 foot of drop at 500 gal make 9 horse?

william

You can figure this yourself by knowing the underlying definitions.

One hp is 550 foot pounds per second. If you harness the energy of 550 pounds of water falling a vertical distance of one foot, then this is 550 foot pounds of work energy. If you can deliver this quantity of energy at continual rate of one second (i.e. 550 foot pounds per second), then you'll have one hp.

A gallon of water weighs 8.35 pounds. So, if you have 500 gallons per hour, then you have (500)(8.35) = about 4180 pounds of water per hour. If this water falls over 25 vertical feet, then you have (25)(4180) = about 105,000 foot pounds of work over a period of one hour. Since there are 3600 seconds in each hour, then this provides (105,000) / (3600) = about 29.1 foot pounds per second. Compared to one hp (which is 550 foot pounds per second), this system provides a theoretical maximum of (29.1) / (550) = about 0.053 hp (about 1/20 hp). Since a hp is also 746 watts, then this represents (0.053)(746) = about 40 watts. A real system would see many losses that would take the actual electricity generation down to half this figure at best. So, you can expect a good system to generate electricity from this source at a rate of about 20 watts. So, you see, assuming the numbers are correct with respect to water flow rate and the drop height, then developing this hydro resource is not worth the effort. Of course, as a reliable source of clean water it seems brilliant, and that's a great deal more important.

The fundamentals are both important and not difficult. Feel free to ask questions at any time. It's easier to learn than to unlearn, so it's better to have no knowledge on a topic than incorrect "knowledge".

william lane wrote:Hi! first post! love the site and have lurked around greatly to my benefit. RMH's are in the pipe line on the farm. The farm being the point of this post. I have moved back to the family farm, which is blessed with a natural spring. It flowed 250 gal an hour in the worst drought in 20 years and tops out over 500. It never freezes and has an approximated 9 horse power with ~10 foot of drop. There are definite plans to chase the spring up the base of the hill it flows out of to increase that drop, at which point we will begin to capture that power.

Respectfully, please check the figures you present here as 500 gph over a 10 foot drop represents a very small fraction of 9 hp. The last thing you need is unrealistic expectations.

r john wrote:

Already described on previous thread just do a search for Bellis & Morcom.

I've noted several posts where you mentioned it, and I did a search. I find no resources and no details. If there is available a resource such as a web site that describes your operation, then please provide link. I would like to get as many details as are available. In particular, I'm interested to know if the system is generating useful power and profit... or are these engine part of a museum? Either way, myself and likely others would like to see details of such an impressive operation. Thank you John.

R John, I'm interested to learn more about the operation you have going. Please provide any web resources that describe your operation including pictures. In particular, I'm curious to know how you are making use of such a large steam engine. Are these large steam engines your personal property? Are you involved in a business venture with this engine system and other systems (such as the Jenbacher you mentioned elsewhere)? Is the system generating electricity and revenue? Details please.

To me, it seems crucial to ensure all free oxygen in the primary air is consumed in combustion, and that this heat from combustion is transferred to the fuel to drive pyrolysis. There must be enough surface area of fuel available, sufficient residence time of the gases, and excellent insulation. The simplistic model that I use is to control primary air flow rate, combust all oxygen in the primary air, transfer all heat from this primary combustion to the fuel mass contained in a highly insulated space to drive pyrolysis, transfer the hot pyrolysis gases to a combustion chamber, then mix with sufficient preheated secondary air for full combustion.

A similar process occurs in downdraft gasifiers. In both cases the fuel gas production rate is proportional to the primary air flow rate in a properly designed system:

DOWNDRAFT GASIFIER: Most of the primary oxygen is consumed by combustion with pyrolysis gases. The heat generated by this combustion (1) generates the pyrolysis gases required to keep the process going, (2) is used to drive reduction reactions with charcoal to generate the fuel gas, and (3) is carried out of the hearth with the fuel gas at elevated temperature.

UPDRAFT GASIFIER: By contrast, the updraft unit sees most of the primary oxygen consumed in charcoal combustion. The heat generated by this combustion (1) generates the pyrolysis gases that is fuel gas in this case, and (2) generates the charcoal required to keep the process going (charcoal being generated by the pyrolysis of wood).

These observations are what led me to my design. Really, it's nothing new. I'll be simply trying to achieve dimensions that are ideal for generating hot pyrolysis gas (fuel gas) at my desired rate with the widest possible fuel conditions. I think insulation and the use of highly preheated primary air is the key (hence the grate design that preheats the air), along with controlling primary air flow rate of course.

Len Ovens wrote:I had to look TLUD up, but yes those are the ones I have seen used as cook stoves... that have been natural drafted to burn very quick and were generally less easy to control than the rocket stove, but required less attention than the rocket too. cooking requires lots of attention anyway, so I don't know how bad/good that is.

The forced air furnaces made by SilverFire (http://www.silverfire.us/silverfire-super-dragon) looks like the same thing with fans and control. I like it... for cooking but it would need more attention than I want in a steam genset.

The reason I linked the SilverFire is because it shows that the combustion rate of a biomass furnace can be precisely controlled by controlling primary air flow rate. Actually, the design uses the fan to supply both primary and secondary air. Even better results can be seen by forcing only primary air, or by forcing primary air and secondary air separately. I don't suggest this product be used to support a steam generator. The message I want to emphasize is that a properly configured gasifier furnace will see all primary air consumed - therefore, controlling the primary air flow rate will control the combustion rate by proxy.... and the size of the fuel doesn't matter as long as there is enough surface area, and as long as the fuel is not too small to obstruct air flow.

Len Ovens wrote:I like the idea of a sealed top feeding hopper (after all it is my idea... or at least I have also had it), in fact I used it to feed a rocket. The main thing I don't like about the rocket mass heater is the required attention to the burn process. My findings with this.... are that even with no air, the batch of fuel above the air intake still gets hot (really hot) because the heat from the burn area rises. Mine was not insulated which kept it a little cooler but it was still warm enough that the wood inside, a 4x4 as happens, started to gasify just from the heat. There was tar dripping from the fuel down the inside of the feed hopper (I actually called it a "Cartridge" because I felt I could have more than one prefilled fuel and switch them over when one was empty) The tar was not a problem and just burned up when it fell to the fire, but from my reading about gasification I am guessing I was also producing CH4 and possibly hydrogen gas (though not CO except from the little bit of air that was in there originally, but at least this CO would settle downwards while the ch4 would rise and collect) which while not a problem outside where I was, might be a problem inside if the design is not careful to make sure the seal continues to below the combustion line or at least that all gases end up going through the secondary burner. If this sealed hopper was even opened to add fuel from the top these gases could flash, scorching the person adding fuel.

The tars would have been vaporized in a gasifier design. The combination of no insulation and high air flow rate (rocket furnaces supply both primary and secondary air via the same path) allowed a cool area to condense the tars.

The primary fuel gas in a wood gasifier is CO. H2 is second. There are various hydrocarbons and alcohols, and very little is methane.

The design I considered would keep the sealed hopper under a slight negative pressure since the flue of the combustion chamber provides draft. So, one could safely open the hopper during operation without getting a face full of wood gas. The purpose of the blower fan is primary to meter the primarily air keeping it constant under all conditions.

Len Ovens wrote:This is why I felt having the fuel at the bottom and burning just the top of the fuel at any one time would be better, though I said bring the forced air in from the top, I was still thinking updraft operation. My problem was how to have the air supply follow the gassing part (the top) of the fuel as it burned down. The obvious solution of feeding air from the bottom would move the burn front down faster too. I really do want a long burn time on one load. You may be right that big wood chunks is the way to go. Certainly all of the demos I have seen have used relatively small wood pieces... even the Kimerly has only a small firebox for 8 hours and expects smaller wood (3in dia max or so). Also their fire box is not very deep, they want the secondary burner to take most of the unit so the flame can be fully contained and the heat up the flue is minimized.

I'll describe some details of the design I considered. It's not a TLUD. The reason I referenced the TLUD is because a forced air TLUD shows that combustion rate in a gasifier furnace is determined by primary air flow rate. What I want to do is provide a highly insulated furnace base with a sealed hopper. A grate and shallow ash pan is provided. I would start my system by igniting the fuel at the grate by placing starter material (like paper) in the ash pan, starting the blower fan, igniting the paper, then shutting the access port to the ash pan. The grate is to be made of multiple parallel lengths of black iron pipe capped at one end and connected to a header at the other. The blower fan supplies air into the header, and the bottom of the pipes have small holes drilled along their lengths. The purpose of putting the holes at the bottom is to keep ash and char out of the holes and prevent blockage, and to admit air directly to the ash pan to consume any char that falls through. Admitting air into the pipes serves to (1) preheat the primary air, and (2) cool the grate. Preheating the primary air helps ensure the full combustion of primary air (since hot oxygen is more reactive), and it helps to keep the reaction close to the grate for the same reason (hot char on grate plus hot primary air equals serious temperature). The wood fuel on top of the charcoal will be pyrolysed and any air the gets past the charcoal will be consumed in pyrolysis gas combustion to add more heat for the pyrolysis process... but the main point is that no free oxygen from primary air is going to get to the combustion chamber. The resulting wood gas then moves a short distance to the adjacent combustion chamber to mix with preheating secondary air for combustion (this secondary air is preheated by the walls of the combustion chamber before it moves down into the base to mix with the incoming hot wood gas).

A benefit of this configuration is that the conditions between the grate and the plenum where wood gas moves into the combustion chamber (on the order of 6-8 inches in height) are constant as long as the space below this plenum is filled with wood fuel. So, the furnace can be operated at a constant low rate for a long period after the hopper is filled without fear of conditions changing to affect combustion rate. A problem with combustion at the top of a fuel mass is that the conditions change as the fuel is consumed, and the pyrolysis gases move through the fuel mass to cool down. Any tars that condense would be combusted as the fuel is consumed, but the wood gas that moves into a combustion chamber is cool, and this is not good for combustion. You want hot wood gas mixing with plenty of hot air for good combustion.