Why can't I "just buy" a stirling engine?

[Bumpkin]

Here’s one we’ve been watching a few years — God I hate how I can’t seem to copy and paste anything lately — anyway go to “seftonmotors.com” I’m not touting them or not, but I think they’re real. Seems they’re behind on deliveries, but that’s good news for most kickstart endeavors. Bumpkin

[Tom Booth]

It appears from the literature that these Microgen engines should be able to start generating power (200 watts) at 200°C (400°F) and increase output from there as the temperature increases up to a maximum of about 550°C (or about 1000°F)

So I'm a little puzzled by the statement in the letter:

If you have only 550-600C heat source, you would almost need an infinite amount of kW to get the engine hot side to 1kW and then the 1kW is almost 0% percentage of the offered heat stream..

Anyway, my coal stove should be able to supply 1000°F easily. Anthracite burns at around 2000°F but I'd even be happy with 200 watts continuous through the long winter months.

A TEG cost about $1000 for 100 watts. But will burn out if it gets too hot and they seem to be perpetually sold out.

Looking over the details, these Microgen engines seem horribly inefficient, producing way more hot water than actual electrical output.

My question to Gerwin Lubbers was actually, would the engine be damaged if heated above 550°C as that is as high as the spec charts go. Full output is at about 550 or 600°C so her(?) Answer is that much more perplexing. "Only" 600°C ????

Infinite kw ? 0 heat stream ?

The published specs seem perfectly clear, so what the heck is she talking about?

[Tom Booth]

Here’s one we’ve been watching a few years — God I hate how I can’t seem to copy and paste anything lately — anyway go to “seftonmotors.com” I’m not touting them or not, but I think they’re real. Seems they’re behind on deliveries, but that’s good news for most kickstart endeavors. Bumpkin

Thanks.

Over 8 feet long ? About maybe $3,000 to $3,500 with shipping. 1000 watts max I guess, pressurized ? 200 watts + at low heat, unpressurized.

It is what it is, but also "sold out". Or for a about a $1000 deposit can be put on queue to have one built and ready in 3 to 6 months.

Nice to see. Seems vaguely reasonable. A little Microgen seems more attractive, but if it cost hundreds of thousands of dollars like a Sunpower NASA type engine.

I'm still thinking I might be able to get some power out of a Ringbom conversion.

Like a V twin air compressor for $100 from harbor freight, some pipe leading to displacer canisters.

Something like this:

https://youtu.be/id-NBC6UW2g

Maybe just a one cylinder air compressor would make more sense.

Under $100 for one of these:

Resize_20221206_030257_7209.jpg (94.82 KiB) Viewed 6102 times

If say a certain size attached displacer doesn't produce enough power, it can just be made bigger (the displacer canister that is).

I'm not sure why that wouldn't work.

I'll give it a try though before paying $3,000 for a nine foot long monstrosity.

Unlike gas engines that have a lot of valves and breathers and/or ports and such, requiring considerable modification, a compressor head is already designed to contain pressurized air, and a Ringbom type conversion seems relatively simple.

For under $200 for the compressor and displacer canister materials, (and maybe some balloon helium ?) I'm tempted to give it a try. I just have to find or make time to actually do it.

[Tom Booth]

Well, I got a response. The engines weigh about 130 lb.

For $5,000,000 for 1000 engines there is a bulk discount, otherwise about $10,000 ($9,500) for a single engine "ex works".

Which apparently means the buyer is responsible for picking up the item at the factory and takes the responsibility for shipping charges, clearing customs etc.

That is the 1 kw engine.

The 2 kw (actually 1.8kw) $12,500 USD ex works China.

I did ask what the cost would be for 1 engine delivered. Awaiting a response.

Not actually that bad. Better than $200,000

A typical solar system cost what? 20 - 30 thousand and only really produces power 6 hours a day maybe.

1000 watts 24/7

The price also includes a "starter package" which includes some kind of control panel for grid intertie.

Not exactly an inverter. It controls the engine frequency to match the grid in some way.

I believe there is a special panel for off grid use. I asked about that also.

I think the control panel also manages engine startup and shut down and what not, so pretty sweet in a way IMO., But having to pick the thing up at the factory in China could be a problem.

Back to my compressor/Ringbom conversion for the time being, but something to think about.

With 1000 people willing to chip in ? The cost of 1 engine is cut in half to $5,000.

Does anyone think it worth the money ?

How high is your electric bill ?

50,000 hours unattended operation.

[Tom Booth]

I've been shopping around for compressors that might be suitable for conversion.

There is a ton of these little 3/4 horse cast iron compressors (designed to be driven by a 3/4 horsepower motor that is) being sold on ebay for $89 typically.

In bulk, what looks like it may be the same, or very similar 1 cylinder compressor on Alibaba are advertised for about $25 each (with an order of 50 minimum) don't know about shipping but on eBay, for that compressor, shipping is free.

Ebay compressor:

Resize_20221206_214359_9855.jpg (53.56 KiB) Viewed 6088 times

And Alibaba:

Resize_20221206_213249_9757.jpg (76.77 KiB) Viewed 6088 times

Maybe not the same?

Anyway, I sent for one from eBay, because I only have twin cylinder compressors at the shop to play with and I'd rather start out experimenting with one of these little 1 cylinder compressors, just to test the theory.

I don't suspect the compressor horsepower rating has much to do with potential horsepower as an engine but 3/4 hp translates to about 500 watts.

So, that would make the Stirling conversion worth about what $4,000 ? LOL

Who knows, with my ingenious Ringbomesk design, might even get 1000 watts!

[Tom Booth]

Some additional correspondence regarding the Microgen Stirling engines.

If Microgen is to arrange shipping for the customer, for 1 engine, would be approximately another $2000 more or less. (Or "cost pluss 25%")

Off grid use would, apparently, according to the rep, require the same controller as the grid connect but also an additional user supplied inverter.

This does not make sense to me in that - why would you need to match frequency with a grid that isn't there?

"The engine would be connected to the AC OUT of the inverter charger."

Seems unnecessarily complicated, and how do you charge the batteries the inverter is running on if the engine is coupled with the inverters ac output?

Maybe this makes sense if you already have an off grid Solar system you just want to supplement with the Stirling engine, running off a wood/coal stove or something.

I would probably get a simple rectifier and inverter.

It seems there would also be a lead time.

I went back into my email to double check what the lead time would be, as I recall, up to 6 weeks, but mysteriously that correspondence seems to have evaporated. (Is no longer in my inbox or deleted folder), just gone.

I'm told maybe the email was recalled. Is that possible?

Anyway, the overall cost is creeping up,

9,500 for the engine
2000 shipping
1000 inverter ?

Mostly conservative estimates. But $12,500 for a mere 1000 watts.

Plus, unlike PV where power is supplied by free sunshine, that 1000 watts, unless using concentrated solar, probably has to come from fuel, wood, coal, whatever added to the cost. But there is also, with solar, at least the additional cost of some kind of parabolic dish, but then your back to collecting power for a few hours a day when the sun is shining and it's not cloudy, or snowing or something.

So maybe someone could theoretically, "just buy" a Stirling engine, but it seems the propositions is, as yet, still rather expensive and fraught with difficulties.

But my little compressor is being shipped. Not a high tech "free piston" engine, but I'll see what it can do.

[Tom Booth]

Ok, this makes more sense I think.

Gerwin from Microgen recommended a Vitctron Multiplus or similar inverter.

This is a combination inverter + battery charger.

Basically the inverter would work in reverse using the power from the Stirling engine to charge the batteries.

Interesting.

Latest YouTube video on the Vitctron channel:


https://youtu.be/19BI2UAwRXk

There are probably additional videos and info on the website more specific to the "multiplus" but I kind of like this one as I had been trying to live completely off grid on some land on top of a mountain for about ten years, which is what initially got me interested in Stirling engines to begin with.

[Tom Booth]

I asked if the lost email could be resent.

I was wrong about the lead time.

"If no stock, lead time is 5-7 weeks in our factory in China."

That was about six WEEKS, not six months.

[Tom Booth]

This Microgen engine is looking less desirable, the more I find out about it:

" ...when the engine goes into emergency stop (for whatever reason), the heat flow to the engine must stop immediately, or the engine has to be moved away from the heat source."

Sounds like a $12,000 investment could go up in smoke pretty quickly and easily.

The specification charts don't show the engine going above about 600°C max. After that I guess it's emergency stop?

Can't be used on any unregulated and controlled heat source.

"engine and boiler would not communicate with each other"

Seems it needs continuous water cooling, wood would have to go into a gasifier.

Can't operate without circuitry and software.

I have toy Stirling engines that can handle a propane flame easily (nearly 2000°C)

With such limited heat input and presumably water cooling (the "starter kit" comes with hoses) my nice rugged little Ringbom conversion is looking better and better.

I guess it is the alternator windings, permanent magnets and monitoring circuitry that would be damaged, so close to the heat source in a little bucket size engine.

[Bobsmith]

Hello hello hello

[Stroller]

These generators look good, and the price is reasonable.
You'll have to find a way to import one from Russia though. Tricky in the current circumstances...

https://tecra.pro/elgen

https://www.youtube.com/watch?v=x_NFgNNlk6g

[Stroller]

At 1:57 in this newer video, we see the system hooked up to a cheap Chinese diesel/air heater.
https://www.youtube.com/watch?v=VI92DJT2s6U
Sadly, no fuel consumption or output figures are given, but a fair assumption might be around 330ml/hr being converted to an output of around 140W
That works out around 2.3l/kWhr
In the UK at the moment, that costs around £1.40/kWhr running on kerosene. This is around 3 times the current grid price.

The diesel/air heater I run for background heating in my home uses 200ml/hr for around a 2kW output of hot air. I also recover around 450W from the exhaust using the EGR unit off a road vehicle and a 5W water pump. That's circulated through a large chromed towel rail in my bathroom. I like the idea of a Stirling generator charging a battery bank as needed when there's no sunshine for PV panels.

[Tom Booth]

I was trying to negotiate the purchase of one of those generators, maybe a couple years ago, or even be a US distributor.

There was some trade import/export restriction of some sort, apparently, as I recall. Not sure or the nature of the issue or what country or countries imposed this.

There seemed some possibility of shipping just parts, then assembling them here, but this was still up in the air at the time. Communication was also difficult with the language barrier.

Last I recall, someone was going to get back with me if they worked out, whatever the problem was. I might still have an email or something but that's all I remember.

[Stroller]

There was some trade import/export restriction of some sort, apparently, as I recall. Not sure or the nature of the issue or what country or countries imposed this.

US/EU sanctions imposed on Russia following their invasion of the Ukraine have put the stoppers on trade. But it shows what can be done, and we could do it too. It's a mildly pressurised Alpha with a constant voltage power converter attached, along with some neat refinements for self starting etc.

The nice thing about the Chinese diesel/kerosene heaters is that they're pretty quiet, and the fuel is a lot cheaper than propane. And they come with their own control system (seen in the video), allowing variation in output from 2-5kW. They're reliable and simple to work on too. Mine ran 24/7 for 5 months last winter and just needed a new fan bearing.

[Stroller]

This vid has useful details on construction:
https://www.youtube.com/watch?v=da8VhtGz2Ss
Looks like it's based on a V twin compressor.
Note the slotted heater cap, a la Andy Ross.