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Martin, Engineer
Category: General
Satisfied Customers: 4944
Experience:  i'm 41 and i never stopped studying and experimenting
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I am interested in purchasing a Stirling engine, in fact I

Customer Question

I am interested in purchasing a Stirling engine, in fact I found online an engine called the ST-5 built by Stirling Company in Ohio (I think) that looks just right. But when I sent an email inquiring about the price, the email bounced. The ST-5 is supposed to be 5 hp, which would be just about right for my purposes. Do you know of anyone who is actually in business right now making Stirling engines near this size for a reasonable price? Thanks. Bern
Submitted: 5 years ago.
Category: General
Expert:  GeneralistWindylen replied 5 years ago.

windylen :

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windylen :

Hi! AccustrataXXXXX Suite 3102, Tech Ventures Building, College Park, MD ( 301- 314 - 2116 or 240 - 223 - 5400 )

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windylen :

Hi, again. There is an online for the one that you are looking for. Thefind ( )


Thanks for a nice try. I guess you missed the part about 5 hp. The site you listed does indeed have a lot of Stirling kits but they are just toys, basically. I'm looking for one that will actually DO something besides impress people. I'm talking about running a house on it using biomass or solar to power it. Thanks anyway.

windylen :

Oh I am sorry for that. Would you like me to continue working on this?

windylen :

You can try at Stirling Technology, Inc. ( 800- 535 - 3448 ) or visit


Thanks, XXXXX XXXXX have a call in to them waiting for a reply, but it appears they are out of production. I thought you guys might know something I didn't. No, give it up.

windylen :

I do apologize for that.

Expert:  Martin replied 5 years ago.
Hi Bern. I can talk with you about this subject (something i researched and experimented with a lot). What are exactly your purposes? Do you really need a sustained 5KW at all time or do you need peak of 5KW? What do you consider a fair price? Do you want absolutely a Stirling or does any other thermal technology could do?
Customer: replied 5 years ago.
Hi, Martin. I am planning to use it to help power a small homestead off-grid. I really don't know if I need sustained 5 hp or not. I have a gas generator that's 12 hp and generates 5 kw, which will carry a whole house except for drier and range, so I thought I'd need somewhere in that vicinity. The ST-5 was allegedly capable of 3.5 kw, and since my prospective operation will be smaller than our current house, I thought it would likely do the job. I'm also exploring PV arrays (home-built) and wind generation. I expect to put in a battery bank, though I don't know enough about it to say how much battery I need or what I need to keep them charged properly. I could run my current generator but my target is as much free power as possible, so I am very interested in something that can use solar heat or bio-mass.

There is a set of new batteries on eBay described as "24 volt Douglas forklift Batteries 12-125-07 375 Amps," so three of them would equal 1125 Amps, which I interpret to mean amp-hours. I don't know how far that would carry me. If you are familiar with the concept, perhaps you can point me in the right direction. I've been interested in solar power for years but never got into it far enough to get a clue about storage capacities.

Fair price should be somewhere around $3000 to $5000 (less would be acceptable), depending on features. I can buy a 10 kw lp gas-powered generator from Lowes for about $5000 so that seems fair. I have not explored other possibilities so I can't say adamantly I must have a Sterling but I do lean strongly (though perhaps ignorantly) in that direction. I would be interested in hearing what else is out there that might serve the purpose. Thanks. Bern
Expert:  Martin replied 5 years ago.
First on Stirling and why it's so hard to get a usable one. There is 2 kind of manufacturers, the big guys that want to make money from investors and really care little about actually selling any product, then there is small homemade system.

The homemade are unreliable, unproved, untested and can be a scam in many case. the "corporate" ones can also be scam in some cases.

As there is no scale economy because too few are produced, they cost more than equivalent internal combustion engine. The reason why it's like that and will probably stay that way is that those that want them usually have lot of biomass for free, but those are not enough of a market to allow the same selling volume other internal combustion can get (liquid fuel is lot easier to distribute).

The range of prices for a Stirling of the capacity you want is out of reach of your budget. If i take a simple one very similar to the basic principle without too much added gadget:
You are already at 14K (they don't mention the currency buy i assume it's in euro). You may see those as high as 20K.

Another reason why it's expensive is that they assume that the biomass is really cheap compared to liquid fuel so they crank their markup.

A Stirling is also not very efficient, meaning that to produce 5KW of electricity you will need a vast amount of biomass. A steam machine with piston is more efficient (but still cost a lot).


The first thing to do is doing a map of all what is used in time and at what intensity. This will allow you to not overspend on a system. If you heat in winter, every component inside the house producing electricity are also heating unit. Heating ,cloth dryer, oven and water heater can be the easy part of the equation if you have a biomass solution (and in many time solar also). There is no need to convert heat to electricity if you can use it as raw heat in the first place.

Converting many appliance to DC can also save a lot. Everything with a AC to DC converter is not 100% efficient and waste electricity. Same with "vampire appliance" in general (those that still consume electricity even if off, like a TV waiting for the ON command from a remote control).

You can also use a far simpler system if you plan to change your habit of electricity consumption. Sometime it's not just about lowering comfort level, just to to things differently.


Batteries are also a good way to reduce the need to over spec the equipment. Deep cycle lead battery are still the most cost efficient solution in that regard. Again, this is just for pure electricity. If you can keep energy in heat mass or in a big flywheel it can cost less. If you need big peak of power (for power tools) you can use super capacitor banks.


As you are familiar with generator, you could play with the idea of wood gas. Down draft wood gasifier with proper condensation to purify the gas from any source of tar can run a generator on pure wood with few modification. The problem is that those generator are not made for full time heavy duty use like the grid can provide. It can be a good energy support when needed that said.


Solar should definitively be in your strategy. It's low maintenance and even if it does not work at full capacity under cloudy days, you will at least have some power each day (unlike wind that can provide nothing for days).

I like wind a lot but i prefer in in pure mechanical energy transfer, when you add the alternator it start to get expensive. Kept mechanical you can still work pump and many tools.

Dan at his youtube channel really have nice video on lot of trick to be able to operate off-grid:

The post already grew quite a bit :) if you need precision, just ask.
Customer: replied 5 years ago.
I very much appreciate the wealth of information but I do have some questions still. I understand the thought string on the Stirlings, but I have not totally given them up, but they will probably fill a much smaller spot in my system. And let me say here that I grew up in a family of builders and I have a talent for fixing things but I have not been taught about home-built utility systems.

Only reason I don't go for steam, which I was very interested in for awhile, is that finding or building a boiler adequate to run an engine without hovering over it constantly would require a lot of expensive controls and feed mechanisms. Or so I've been instructed.

You mentioned converting AC appliances to DC. How is that done and what appliances can be converted?

I don't use anything with a remote so I got off on that one.

I would like a little more detail on changing electricity consumption habits. Something like hanging clothes out instead of using the drier? Or are we talking about the timing of certain tasks?

I would like a bit more detail about batteries. I mentioned the 24-volt batteries rated at 375 amps. Amps x Volts = Watts. That works out to 9000 watts, but what I'm not clear on is, how long can it put out at that rate? Or even at half that rate. Say I got all three of the forklift batteries I mentioned (27,000 watts). How long would they be able to support a 750-watt refrigerator, 5 26-watt compact fluorescent bulbs, a couple of 780-watt hotplate eyes and a 550-watt breadmaker? And toss in 3 90-watt laptops. That's what I can't get my head around. I would assume you would then have to find adequate generation power to replace the same power usage. But if you can show me how to fit generation systems to storage to usage, you will have earned your fee handsomely.

I considered wood gas but it's quite messy and hard to really get it clean enough to run through an engine. It's kind of like pouring shellac in the gas tank. Used for a cookstove it wouldn't be such a problem because any impurities could be burned with the gas.

Again, with solar I have a hard time figuring what I can expect in practical terms. I see on eBay a set of 550 3x6 PV chips for about $300. I have seen instructions how to solder the chips up and build the panels, but hooking them (and a windmill and occasionally the diesel generator) together with a controller and inverter is another foggy area for me.

Any clarification you can insert here will be very much apreciated. Thanks again.

Expert:  Martin replied 5 years ago.
I am here for all clarification you need.

"You mentioned converting AC appliances to DC. How is that done and what appliances can be converted? "
You can sell some and buy others already made to accept DC. It's easy to do with many equipment that come with external power supply. Essentially you just can bypass the power supply if you have the right DC voltage. This save on the efficiency of the whole operation and also on the cost of AC inverter as you can buy a less powerful one just to power the thing that absolutely need AC. Not every things can be used connected directly to battery. A voltage regulator is often needed to that the 12v (or 5V or 9v...) is constant (for about anything electronic) but it's less a problem for thing like lighting, small motors that would still work OK at 10V instead of their usual 12V.

"I don't use anything with a remote so I got off on that one"
A microwave with a clock (even if it's not set and flash) will continue to consume current. So when possible installing an external switch on all equipment can really save energy int he long run.

"Something like hanging clothes out instead of using the drier? Or are we talking about the timing of certain tasks?"
Yes that kind of things, some just really don't want to change and this may require to over spec lot of component that really don't need to be. The timing is the most annoying part for most. We get used more and more to disconnect from nature, some now can't event handle having to be on front of the TV at a specific time for a TV show now that TV on demand exist. So if you have energy from wind, you may have to put back task until wind come up, same for the sun. When many live in the same house, organizing an energy efficient task/activity list can be a challenge.

"I would like a bit more detail about batteries"
You really need the amp/hour value to know. The most cost efficient are deep cycles lead batteries:
They are easy to get and are fully recyclable.
Covering the science of batteries can be a very long subject, here is a quite complete guide on them:
If you want to make sense of all this, you need to think in joules (a watt is 1 joule per second). This energy in joules make it easy to see energy like a reserve of water. The higher the voltage (the higher the pressure) so water drop faster, the higher the current (the larger is the pipe) so water drop faster. That is how i count them , putting all in joules, yet you will never see that used :) it would be too easy. Use this as a guide

It's hard to tell how much battery bank would be needed as it depend of the usage. You can buy cheap electricity monitor to put on your AC outlet (they are around $15 and you don't need to buy many, just one that you let on an equipment for a whole day). Those can report the total energy consumed in a period of time. With that you would have a nice idea of the battery bank you need. As a trick, you can keep plastic water bottle in freezer and refrigerator to minimize the loss when you open them and also to act like buffer when the energy source is not as abundant (it act like ice pack).

I am not sure about the solar chip you refer too. Perhaps they are solar chip to be used with a solar concentrator. You can get very good 300W solar panel for around $1000 each now. With 3 of those you have quite a good amount of energy.

This guy (Ben Peterson) build quite clean wood gasifier, but i find them expensive at current fuel prices (they are well done that said). He now also sell (he don't build those) turn key solar systems.

Integrating all kind of electricity source is not that simple. There is no good multi-source inverter that i know about. It would be relatively simple to build one that said (for me as i am an electrical engineer). it would require to harvest energy gathered in capacitors banks (one for each power source) really fast, skipping those not yet filled (in case a cloud came on a solar panel). This would be done with FET transistors or IGBT and produce a square wave with a close to 99.9%
that could then be filtered as a flat DC level. Why we can't buy this at Walmart right now i don't know and i still wonder why i don't start to build some :)
Martin, Engineer
Category: General
Satisfied Customers: 4944
Experience: i'm 41 and i never stopped studying and experimenting
Martin and 34 other General Specialists are ready to help you
Customer: replied 5 years ago.
One last thing. You mentioned possibilities other than the Stirling, and you have mentioned steam and wood gas. Are there others within reason or is that the crop? Thanks for a very informative session. Bern
Expert:  Martin replied 5 years ago.
Well, i don't put out the Stirling, it's just that the price is very high for the power you need. It sure can be more possible in the 300W range.

Other possibilities are hydro power if you have a small stream nearby (the higher the better).

At one point horse and cow walking in circle was a common way to generate electricity.

One place where a stilling would do well is with a heat pile (it's also very safe to let unattended, it's long to setup but after wind and sun do not matter:
part 1
part 2

There is also fuel cells (another still expensive solution) that work with hydrogen. Lot of work is currently done to produce hydrogen directly from the sun (photosynthesis) instead of by electricity (electrolysis).

You can also do electricity with the peltier effect, but the efficiency is very low and the cost high.

One relatively inexpensive possibility is storing compressed air. This could complement a purely mechanical windmill.

For heating and cooling you can always look at geothermic. Ground tunnels to heat in winter and to cool in summer. Not really doing electricity but it can reduce the need of hungry electric fan in the summer.
Customer: replied 5 years ago.
It just occurred to me to ask if you know of any source for flash boilers. That might make it easier to set up a steam plant you don't have to babysit.
Expert:  Martin replied 5 years ago.
I sadly don't know any manufacturer making those on a production level. Even when they were used a lot in the last century (for steam cars and boats) it was kinda a prototype run.

Here i receive some publications about forestry. In them (especially when they do a special on biomass) you can find many type of boiler ads. I am always amazed to the number of builders that don't even have a website. They are often very local company. If you can get some of those mag/journal from your local forestry association you may find someone in them that will be willing to build you a tailor made system.
Customer: replied 5 years ago.
Great! That points me in the right direction. Thanks.
Expert:  Martin replied 5 years ago.
Best of luck.