Stirling engines for the third world

[bptdude___2569]

good to hear somebody is starting to move forward.

the most difficult part of design is always what made Rev Stirling famous in the first place, the "economiser", the piece that goes between the hot side and cold side. If somebody made a breakthrough there, you could make low cost Stirling engines out of recycled Harley engines or something.

Also, while CHP units take fuel that would just be lit on fire for heat, and run then through an engine to get useful work for the fuel burn { no idea why this took so long to come about }, taking a conventional internal combustion engine the needs to run anyways, and making heat recovery useful seem another good idea, if it could become cost effective.

For Nigeria, and many nations most needing something to get them up off the economic floor, whatever PC term people agree to use, many have one resource in plenty, sunshine. Semi-conductor solar energy is advancing nicely, and high priced projects with Stirling are being rolled out. I often wonder why places like Nigeria don't use trough solar collection, and take the resulting super-heated oil and make power from steam, as has been proven and actually running since the '70s at a test site in the USA.

I know of certain evacuated tube solar collectors that can generate 400 degree F temperatues even in temperate northern USA. But steam generators are too dangerous and expensive for home use. A Stirling engine would be popular for the same reason Rev Stirling created one, because it was safer then a steam boiler.

I know I'm not helping with actual engineering input. I would love to try out, test, document a Stirling engine electrical generator I could run on a wood furnace. While not as eco-friendly as the evacuatd tube solar energy collection, at least the hot side of the Stirling would be a lot hotter, and that should make design parameters easier to make practical.

I'm here if somebody has one! I am guessing there would be many many people who would also be interested in trying.

Joe
bptdude@hotmail.com

[dai.davies]

Joe

Apologies for being techno dumb but think you can appreciate I am coming at this from a slightly different angle – am not looking for a use for a Stirling engine… I got a societal/welfare/development problem that a Stirling powered generator just might be able to solve. First I heard of this ‘economiser’ issue – can you explain?

I haven’t ruled out Steam in fact it was my first choice as the original idea occurred to me while watching a very small model steam train pull a large number of people around a fairground. But you have hit the point... was advised that steam had a safety issue… high pressure… but am still not convinced this is a real prob just modern attitudes.. Have travelled around Africa for the last 25 years and the evidence of steam being used as late as the 50’s and 60’s for irrigation and crop processing is quite common. With the fall of colonialism and the rise of oil I guess the technology was abandoned… Maybe steam I the answer – I guess it’s a factor of power requirement – not sure how much these model engines produce but I guess they must be pretty safe… and surprisingly engineering skills aren’t a problem… despite the usual perceptions I have had diesel engines overhauled and gearboxes fixed in some pretty remote locations..

CHP I looked at… for me it means using the heat directly for secondary benefit... been lot of theories about using it for communal cooking but like the solar cooker it a good idea that doesn’t really take off. I am more interested in using the ‘waste’ heat for water purification… waterborne diseases still by far the biggest killer… beats malaria, HIV/aids and all the other more trendy issues together… also helps defer the cost element… seems to be a recurring criticism of Stirling/steam but when you build in the social benefits the math changes.

You are partly right about getting them up off the economic floor (although better if they have a means to get themselves up) and that’s one of my interests – not only immediate benefits but if sufficient power is made available then it would facilitate/stimulate local industry – taking it a stage further – the RE business itself is ideally suited for small scale rural and semi-rural locations – part of this is to create awareness of the overall commercial opportunity.

Glad you mentioned alternatives especially sunshine – solar and wind and indeed micro-hydro all have their uses but they depend on climate and topography, and with the exception of hydro need battery backup... never mind the location problems or the ‘bangs per buck’ set up costs there are real problem with batteries.. They are a hidden fuel cost. I worked on a solar powered medical lab in Sierra Leone… big unit… batteries cost 40K USD and had expected life of 5 years. Some form of mechanical or fluid storage might be a solution but I am digressing.

I chose the Niger Delta for this project because it’s the worst case scenario. Like other big river delta areas throughout the world it is very densely populated, (estimated 30M) flat and although lots of river very slow flow rates. It’s in the tropics so the insolation factor is about the same as northern Europe… lots of cloud for lots of the year… solar only about half as good as it says on the can! There are a few solar installations – LED street lighting is becoming popular but not very practical in terms of light/cost – plus security is a problem… panels are easily stolen. Wind is maybe a little better but again climate is not ideal except in a few coastal locations you get either 0 for most of the time and force 10 sometimes but no steady supply.

I looked at solar/steam although not familiar with the term ‘trough’??

Biomass is the obvious answer – and there are plenty of sustainable natural resources plus crop waste and even a few suitable sources for bioliquid – again an opportunity for agro-development…

Just a quick note on efficiency/output – not really the initial priority here… efficiency is relative and as anyone who has lived in the tropics will tell you it gets dark at 6pm every night of the year so just being able to produce sufficient power and by using fluorescent or LED to light a community centre or a school would make a dramatic difference to the physical quality of life. Hopefully with the right components this could be bettered but I don’t think it’s an engineering problem per se…. the ‘bits’ have been around for quite a while it’s just a matter of finding the right ones...

I could easily justify using a system that produced only between 1-5 KW to prove the application benefits so should I look at ‘mini’ steam or can you buy commercially produced sterlings that give you this range…. By the way am about a knowledgeable on stem as I am on Stirling so any info/contacts welcomed


Dai

[bptdude___2569]

Dai,

Here are answers to some of your questions.

economiser

"Robert Stirling's innovative contribution to the design of hot air engines of 1816 was what he called the 'Economiser'. Now known as the regenerator, it stored heat from the hot portion of the engine as the air passed to the cold side, and released heat to the cooled air as it returned to the hot side. This innovation improved the efficiency of Stirling's engine enough to make it commercially successful in particular applications, and has since been a component of every air engine that is called a Stirling engine." - Wiki definition

We know the Stirling brothers did things like pressurized their engine, eventually, and had a business secret of thier economiser design that made it practical for their time. It is not known what they did, and people later trying to recreate the engines have failed. The engines were real enough, well documented to have run in production environments for years.

This is the magical part of the Stirling engine. Current industrial engines add a lot of complexity and cost to their designs and also keep this part of the engine hush. But it is known, nobody really has a good design yet. The problem is that making a good regenerator is an engineering conflict, having it function well to increase power, robs from the engine power.

Yes, steam engines from locomotives were quite effective, in both small size and large. People with practical expertise would be very hard to find. Somebody must know how to still do this. Steam was put out of business by low lost diesel and gas engines. Since low cost diesel and gas is not so available, you would think it would be possible to revert back one phase to steam.

If waterborne diseases are really the biggest killer, then purification is a matter of large scale life and death. Solar heat and cool running even dirty water, some crafty people, elbow grease, and access to low cost scrap metal should be able to yield village size water stills. Even really nasty waste water could be made into pure clean water.

Awareness? If the water was whiskey they could sell bootleg for cash, you can be sure somebody would find a way to make a giant still from what they found at the dump. Why people don't do this for water for thier kids, is something on your end to deal with.

Batteries are stupid to even think about using for storing power. People who argue against solar, saying it only works in daytime are horribly deceptive. There are a number of answers, but the absolute best is to convert the power to hydrogen, and store in presurized tanks. And you don't need fuel cells to use it, another massive deception. It is well known as a simple low cost conversion to any automotive gasoline type engine, to run on hydrogen, instead of gas.

Here is a news article about an African nation building out solar to export electricty to Europe.

http://www.cbsnews.com/stories/2007/08/ ... 8809.shtml

Africa has enough sunshine, mabye not exactly where you picked to work, but enough on the continent to supply the world's energy needs a half dozen times over, using currently known technologies. Talk about an awareness issue?

Although way out of your price range, here is a turnkey system built by Honda, that is built and running, that takes sunshine,and has it stored and ready for a car to fill up. These could be built a little furhter north than you, where the sun shines bright, to fill up hydrogen trucks, that themselves could run on hydrogen. Remember, forget the part about expensive fuel cells, and think converted old gasoline engines.

http://www.ieahia.org/pdfs/honda.pdf

Trough?

Here is a link to a U.S. government project that collects sunshine and make electricity using troughs that heat oil in a tube, to make steam, to spin turbines. There is a fully functional plant running successfully since the 1970's oil crisis. Again, this is not rocket science, and there is nothing special about materials used to build. This is very practical modern use of solar to steam.

I know these are big ticket items, but Africa sure has the need, cheap labor, and lots of sunshine. You might also find more of a friend in the U.S. government than you think. The whole Kyoto Protocol Treaty is crap in my personal opinion, because it is trying to allow "developing nations", like China to be exempted from using available capital to create modern green solutions. Smaller nations that may only have one shot at a new energy structure would be committing economic suicide to think they are getting a good deal, and fall for this. If you were to pitch that you want to build out a totally green, renewable, solar to hydrogen production cycle, not to sell to Europe, but to help desperately needing African nations, you might find the answer you seek.

http://www.nrel.gov/csp/troughnet/

- Joe McLean

[bptdude___2569]

Dai,

I just read my own posting.
I am very sorry in advance for being so harsh about the awareness issues, especially about the water purification. It was heartless of me, please forgive.

Still, the edge of the Sahara shoudl be looked at like the edge of a giant waterfall, as in a unimaginable source of power that needs to be coverted into hydrogen, and used to help Africans, not just sold to other nations for profit of corrupt small groups.

Here is a link to the U.S. government lab PDF file on the Stirling engine supported by the company this supports this discussion group.

http://www.energylan.sandia.gov/sunlab/ ... r_dish.pdf

It produces 25 KW under good conditions, fed by sunshine. It is not cheap, but one of these could be translated into number of gallons of purified water for a village.

Regards,
Joe McLean

[hislop]

Sorry to be a party pooper, but forget Stirling engines for generating power from biomass in developing countries, unless your target market is a small group of enthusiasts with lots of time, fuel and technical expertise. We started our company in the early 1980s with the same purpose in mind as the correspondents to this blog. We saw the Sunpower ST-5 in action in Bangladesh, and although it was a brave effort, it was clearly not going to provide the desired solution – too large, inefficient and expensive, difficult to maintain, and very difficult to get the heat in without sooting up. I later visited the factory in Chennai (ex-Madras) where about 100 ST-5 engines were produced, and talked to the Indian Government agency who put them into villages. A couple of years later, 1 was still working, run by a real enthusiast – otherwise, they just gave too many technical and economic problems, and the factory was shut down. Resources were not the only problem. So we decided to develop our own engine.

We built a 1 kW and a 7.5 kW engine in the UK, and the latter in particular ran very well (it had 5 internationally granted patents) with a Beale number of 0.15 straightaway (highest recorded after many years development is 0.22). However, we could see that there were still too many problems to be solved, particularly in the heat exchangers and regenerator, for the engine to be commercialised, whether in developing or industrialised countries. We have come up with heat exchanger solutions using new technology from outside the Stirling industry, and are working on a new engine with a different cycle that is simpler than the Stirling cycle.

A few fundamentals will put everyone’s ambitions in context. The Stirling cycle is at first sight very simple, but putting it into practice it is extremely complex. Companies have been trying to commercialise the modern Stirling since the late 1930s, including the US Navy, Ford, General Motors, Philips, the major Japanese industrial groups and many, many others. None has succeeded: Whispertech has come closest to it in the niche market of auxiliary CHP systems for yachts. The UK, Germany and the Netherlands are field testing Stirling-based domestic CHP systems: the UK’s Carbon Trust has just published a very thorough study of these trials and shown that with present technology efficiencies (electricity out/fuel in) are mainly in the 4-8% region. This is admittedly with fairly high cold end temperatures, but even so, these efficiencies are extremely low.

Do not be fooled into thinking efficiency is not important in developing countries. It is important if you are going to use wastes and other biomass fuels. Our experience in South and South East Asia is that what may be a very low or even zero-cost waste suddenly becomes valuable once somebody finds a use for it. If you are going to use a fuel grown specifically for power generation, then in most parts of the world you will want to use as little land as possible – again, efficiency is important. The highest recorded Stirling engine efficiency is about 60-65% of Carnot, from an extremely large and sophisticated United Stirling engine in the 1980s. More modern small engines achieve way below 50%. To expect 80% of Carnot from an engine to be built and used in developing countries, as suggested by one correspondent, is, I fear, unrealistic.

Another major constraint on the rural biomass Stirling is getting the heat into the engine. Direct combustion of the fuel will, even if it is suitably sized and with low moisture content, tend to foul the heater tubes. Technical University of Denmark minimise this problem with very large tubes, but the penalty is high weight and costs, and high internal volume, which reduces power output. In our view gasification is a better option, but again, this is difficult and expensive on a small scale, although there are reports of successful biomass gasification for diesel engines in India.

Which brings me to the question: what to do instead. The simple although often unpalatable answer is to use a diesel engine, even if fuel is expensive. Diesel can be obtained wherever a truck can get through, which is nearly everywhere. Why foist technical ideas on poor people in developing countries that have not been proved and used commercially in our own developed countries? If we want to help with local energy problems in this sort of way, then liquid biofuels used in a diesel engine are a better bet, and will continue to be so unless and until something better is developed. We are working on it, but without any illusions. The same applies to Solar dish Stirlings. A US report in 1989 (Dish Stirling Commercialisation Workshop, Electric Power Research Institute, Atlanta) noted that all that the technology required for commercialisation was an efficient, cost effective Stirling engine: it was right and it is still waiting.

Drummond

[cchagnot]

How easy it is to make judgements about something with only a superficial view and no
real understanding of what's actually going on. Judging a book by its cover is never a great
idea.
I think it's unfortunate that some are willing to simply blankly dismiss the Stirling Engine's
potential.

The ST-5 project was indeed started in Bangladesh and Merrick Lockwood led the
implementation efforts there. He took the design in his own direction while Stirling
Technology did their own design and set up a joint venture in Madras to try and produce
the engine. The Madras venture was seriously under capitalized and the early engines put
out were improperly made and not followed up on in terms of service. Kilosker Cummins
got involved for a short time as we made an effort to come up with funding but essentially
killed the project and not because the engine wasn't working.

The ST-5 demonstrated approx. 25% efficiency for the engine. The very simple burner with
minimal heat recovery resulted in an overall efficiency of roughly 12%. We paid attention to
the total system in our efficiency calculations and produced pump sets pumping about 3
times the amount of water with the 5 HP produced by the ST-5. We have engines made
twenty years ago that we reworked at our facilities in the States to design spec that are
running still today with thousands of hours on them.

At the time of production in Mardas the total cost of producing the engine and burner was
less than $1000.

We're currently working in Korea to get a large scale project going aimed at developing
countries. You can see a short video of an engine running by going to this link on youtube.
Fuel is sawdust.

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

I should know. I was there. Bangladesh, India and now Korea

Catherine Chagnot

[bptdude___2569]

well, people are talking about Stirlings again.
An ST-5 does sound like something I would like to play with.
I'll stay tuned!

Meanwhile, something I am looking to get put in my real home, here in a nice developed country, is a home CHP by Honda. It runs on natural gas feeding a hot water home heatings system, but will soon be converted for retail use for propane and hot air heating system.

If American Stirling or somebody can get something like this to run on firewood or wood pellets, maybe by using a Stirling engine, this would make a lot of rural people very very happy. And, of course, could be used in developing nations.

http://www.climate-energy.com/products.asp

http://corporate.honda.com/GovRelations ... elease.pdf

http://world.honda.com/news/2007/c07040 ... werSystem/

http://www.ecrinternational.com/secure/ ... nt/698.pdf

http://www.hondanews.com/categories/1048/photos/13645

Of course, a scaled down version of their solar-to-hydrogen system that feeds this CHP that is converted to run on hydrogen would probably be more popular than free beer!



- Joe

[cchagnot]

Joe,

The closest anyone's come to a high tech Stirling CHP is probably Sunpower's 1 KW engine.
Microgen was formed in the UK to put a gas fired system into place usine the engine but
closed down early this year. Sunpower is working on getting the engine into mass
production but I don't quite know where they are in the process at the moment. You can
check out this link to learn a little more about it.

http://www.green-trust.org/2000/enginet ... iowatt.htm

Catherine

[hislop]

The answers to the ST-5 defence are (i) don't shoot the messenger (ii) I also was there - India, Thailand, Bangladesh, Sir Lanka, Nepal and many others - steam engines, gasification and diesels, Stirlings, micro-hydro - the lot and (iii) I know the book, having been involved since the early 1980s, having put a large amount of my own time and money in to the development, and having been helped in funding by the UK government. As I said, the ST-5 was a brave effort, but in retrospect neither it not its competitors were or are appropriate in concept or technical performance. There are better answers than the Stirling coming along, and, in the meantime, what is wrong with the diesel engine? Unless and until the developed countries can show that they are using small biomass-fuelled power system that are commercially successful, we should be extremely wary of encouraging those with fewer resources than those of the developed countries to use technologies that we are not prepared to use ourselves. A few well-supported aid projects are one thing; to suggest that the technology they use is the answer to the rural power problem is unrealistic.

Drummond

[stan.hornbaker]

Thanks to Catherine Chagnot and Drummond Hislop for providing some much needed up to date information on the state of power producing Stirling engines.

The American Stirling Co. provides and maintains these forums for discussions in relation to Stirling and sometimes Hot Air engines. The company sells demonstration LTD, Low Temperature Difference, Stirlings that run on the heat from a cup of coffee, or one that runs on the heat of your hand, and a third college level laboratory Stirling for students to investigate the parameters of operation.

Please note that American Stirling Co. does NOT manufacture nor sell power producing engines of any kind.