Stirling engine for non-profit rural use.

[raguna]

Hello Everyone,

I volunteer for a small non-profit group who try and help the families who live in the rural parts of Sri-Lanka and I think that stirling engines could really help.
We have built and donated a large number of solar powered lanterns but during the rainy season we don't get enough sunshine for the lights to work for their intended duration.

Temporarily we are solving the problem by having local entrepreneurs charge batteries for the families for a small fee but we feel that this should not be a permanent solution because some need to walk long distances as well as dangerous terrain to reach the charging station. All the families we help have access to kerosene so I thought that they could use this fuel source to provide electricity for their homes by burning it in a pressurised kerosene mantle lamp which burns much hotter than their wick based counterparts. This would also mean that when the batteries start wearing out we don't need to have them replaced.

Something with an output of 5-8 watts should be more than enough. We've looked into using thermoelectrics but their efficiency is less than 5% while stirling engines can reach much higher. Would it be possible for someone on here to develop something which could be built for less than the equivalent of $30? This could also allow us to provide jobs to locals who could put it all together after a bit of training. The materials don't have to be locally sourced, if there are special parts that are needed it's not a huge issue to get items imported for us. I'd also like to know if a pressurised or non pressurised version will be better for our situation.

We're not asking for you to do this for free. For example, I was thinking that for every unit that is made and donated we could give you a small royalty fee of 25 rupees which is $0.20, I know it might not be a lot but we are a donation driven group and we're considering converting around 5000 families so it'll add up.
I also don't mind giving the person who built one $250 out of my own pocket for their help.

As a community which knows much more than me in this area I would also be interested in hearing about any ideas that you may have as well.

Thank you for reading.

[Triangle.Stirling]

Hello Raguna, welcome on the forum!

I think you have a very good idea there.
It is only difficult to find Stirling-engines that can do so. Nonetheless personally i'm certain it is possible.
It would be a very nice application of the Stirling-engine, if it could help people.

You can look on Youtube for video's from Approtechie, he has very nice engines, that are relatively simple builded. He has also one that has 10 Watt output(mechanical, at the shaft). Approtechie also does something with 'technology for development'. Maybe you can try to contact him.

Personally i'd like to help to design such an engine, but it is very difficult to do so. It would cost very much time and effort.
I'm sure other people also would like the idea, but i'm afraid it is not easily done.

Also like to hear the opinion of other, more experienced, people on this forum.

Regards,

Krijn

Where are you based in the world by the way?

[Ian S C]

If you have access to a lathe etc., it would not be too difficult to build an engine with say a 2"(50 mm) bore, and 1.5" stroke for the power piston, this should give some where near the power required.
Don't fool your self about the efficiency of Stirling Engines, 5% is not too bad for an unpressurised engine, it's only when you start building high tech pressurised engines that things get interesting with the efficiency, and power, and the amount of money required.
I think the most expensive motor I'v built cost $NZ35, most of my 17 motors are built from scrap, but I try to use the correct materials, stainless steel for the displacer, and hot cap, cast iron for the power piston, and cast iron(best), or steel for the power cylinder.
If you look on google, you will find reference to a 5hp unpressurised engine developed in USA(I think), to burn rice husks, It was intended for use in Bangladesh, I think there is a book about it. Ian S C

[raguna]

Thanks for taking the time to reply.

Where are you based in the world by the way?

I'm from Sri-Lanka

If you have access to a lathe etc., it would not be too difficult to build an engine with say a 2"(50 mm) bore, and 1.5" stroke for the power piston, this should give some where near the power required.

Yes we do have access to lathes and other metal working equipment. Where should I be looking to get plans for this sort of build?

So a pressurised engine is better for efficiency but bad for price. If we're mass producing, buying in bulk and using local labour couldn't we bring the price down quite a bit. Also, what fluid do people normally use for this purpose.
I personally like the pressurised route because I don't want the people to lose too much money because of efficiency and more than the cost of the actual unit it's the cost of fuel that will add up in the end. Do you think that setting a target efficiency of 10% is asking too much even if the price increased to about $50?

I'm going to send a couple of messages to approtechie and someone called barumman who has built a small pressurised engine.

[Ian S C]

If you go along the pressurised way, air would be the way to go, it's free, and easy to get, other gasses cost money, and in your situation probably quite a lot of money, if you could get them at all.
I'd still recommend an unpressurised engine for simplicity of building, and operating, an engine with the dimensions I suggested would not be very large.
Put Stirling Engine books in the search window at the top of the page, you will find about 6 pages of references to books. Libraries, public or university are another place to look. Ian S C

[bladeattila]

I shared your call with my Stirling builder FB group.
My opinion is, if you have metal machine shop with some good engineer, they can make easily a high performance Stirling for you and your families from scrap materials.
The cost is too low, but your goal is low too. Is an engine with highest power for the closest families not better than a small one for each other?.

[raguna]

Do stirling engines scale? i.e. can power output be estimated using the part sizes of the engine.
For the 2 inch bore and 1.5 inch stroke engine should I be looking at beta designs?

bladeattila, I appreciate you spreading the word.
There are varying densities and distances when it comes to households so if we were to build larger engines we would have to build different versions for different places. Then there is the work of wiring the houses and then maintaining the cables.

[bladeattila]

Your welcome!:)

If it is possible then use big diameter bore what you can make it possible. The simple design atmospheric engines can make usefull power with big bore.
Did you read Andy Ross book from Stirling engines? Basically that is a good starter "kit" for your ideas.
Kind regards!
Blade

[Ian S C]

The engines scale to a certain extent, but as they get larger, heating the air becomes more difficult(air is an insulator, and difficult to heat).
One advantage we have now is LED lighting, we can do away with incandesant lights, other than that, the best use is battery charging. Ian S C

[tentstovenerd]

If you are using Koresene, you can buy inetrnal combustion engine.
I am sure its efficience must be over 30%
By stirling engine we shall aim at waste heat energy.
Most here use LPG is nothing but for hobby.
I am looking for a 5 Watt stirling engine too.
My heat source will be a wood burning tent stove

[Ian S C]

tentstovenerd, I'v heard it said that in rural parts of China bio gas is used for cooking (collected pig dung), maybe in Sri - Lanka something similar could be devised to run a hot air engine. I would recommend looking at the TMG motor in this case as I did when answering tentstovenerd's thread.
Ian S C

[tentstovenerd]

yes dated back to 1970's China government was promoting biogas.
Another booming happened a few years ago.
Government even gave financial support to household in rural area to build biogas pit/tank.
But I can say basically it is a big failure.
More and more labor forces leave countryside to cities to work there.
Rural area is left kids and olds.
To remove waste from pit/tank is a heavy labor burden.
Less and less people are left in rural area and the energy consumption is getting less and less.
Coal is cheap, and transport is better and better.
Rural area either use coal or bottled LPG.
Even by fire wood, as popultion is less and less, it is not a big problem.
Also biogas does not work in winter time, say in Beijing, today is -6C.

in Sri - Lanka if not enough coal/gas, it is most economic to build a steam engine generating station in each village or town.
Fuel can be wood/bamboo.
But a diesel engine generator must be most practical.
Renewable energy sounds great, but more expensive, even worse in poor area.
If local peasant is really poor, TEG must be more workable.
To put TEG on cooking stove. Anyhow each household must cook.
It must be able to generate enough electricity for LED light for 2 or 3 hours per day

What I am seeking is a compact generator used together with a tent stove.
It is not for energy recovery, but for emergency, charging a mobile phone or laptop.
So I do not care efficiency
I care weight and size only
still wanting a solution