I have found something of interest to those who like Stirling Engines.
Did you know there is RIGHT NOW in the market refrigerators Freezers that use stirling engines to run them and they do not have a compressor, nor do they use freon???
These cost $9,000 and up.
I have seen a portable unit that is going for just over 1,000$
I would believe because they have so little to fail this would be a very very reliable freezer. And for being off grid would be worth it.
That is interesting but I suspect you could buy a normal refrigerator and the solar PV system to run it for far less than $9000
Right you don’t buy a diesel train engine to run your house but you can buy a diesel engine to run your tractor. They do make smaller units, and less expensive.
As always the right tool for the job, these go down to - 80 deg.
Refrigeration and power generation are very different even if a Stirling “engine” is used in each.
Power generation is efficient when the hot and cold side are as different as possible. In practice that means a very hot, hot side and an ambient temp cold side with temperature differences of many 100s of degrees.
For refrigeration, things are efficient when the hot and cold side are as similar as possible. In practice this means an ambient temp hot side and a freezing or modestly below freezing cold side… maybe not even 100 degrees C or <200 degree F separating the two halves. The materials and configuration are totally different for refrigeration and power generation because of the temps involved.
If you want refrigeration off grid… just get an efficient regular electric appliance and power it as you see fit. Maybe DIY some extra insulation and maybe add some supplementary cooling on the evaporator…
EcoRenovators has a great thread on DIY heat pumps that might serve for inspiration but we are still talking about repurposed electric refrigeration compressors.
Yeah, the main point I wanted to say is that here is a freezer that uses a stirling engine. The fact that it is a commercial product blew my mind, and the fact that it is used for medical and lab grade freezers also.
What you said about keeping the temp closer on both sides of the stirling was exactly what was said in this video.
I like working with 3d printers, and I have a friend who has built a stirling engine. I am looking at the question is it worth building this myself, or… can I just buy the stirling engine off the shelf, or buy a used fridge, what is the best use of time…
My standard fridge is doing a great job, I am always looking to do better… I do tend to end up doing the conventinal way, but I do explore new paths…
Thanks for your input.
They really did some fine engineering on this…
Improvements to stirling engine…
Id like to see this integrated into the rotary motor. Might improve the energy density for the sterling design. Liquid Piston has a design that may work with some mods.
Watching this video again now I understand why he pressurized the engine for more power.
Some Stirling engine rabbit holes to explore:
Ohio University has been active in Stirling Engines with a number of papers and patents-
This guy designed that refrigerator mentioned above, also from ohio-
This is the design “bible” more or less as produced for NASA/DoE. Very extensive…
This is a pretty advanced DIY effort on a small stirling engine-
http://diystirlingengine.com/sv-2-stirling-engine-generator/
And you’ll find the Philips MP1002C coming up over and over. That is worth some research, research that is pretty easy to find.
There is a “simple” spreadsheet floating around that will estimate engine performance based on various design parameters such as gas pressure, stroke and bore dimensions, cycle frequency, etc. I don’t have it handy but it’s worth grabbing a copy if you come across it.
I’ve been down all these rabbit holes and more. My conclusion was that I can’t buy or make a suitable stirling engine but maybe someone else will figure it out.
Your last line conclusion is the best, most realistic statement AnthonyB.
Here is a cross-reference video proof of that:
A full teardown and salvage inspection of the last 50 years evolved improved production
Mazda Wankel engine.
Enable the CC and translate to really hear the very experienced opinions of this engine parts salvage man. (They all lose compression by 100K miles. Conventional engines hold compression into multiple 100’sK miles.)
My points:
in the 50 years Mazda invested improving this engine design for real world production application; they themselves had to reverse course and go back to IC piston engines to survive as as a selling production company. And they had to also design invest into those IC pistons engines to make compliant, and effective competitive engines to install and sale.
Ha! HA! They made a lot more money on Miata’s produced and sold with four cylinder conventional engines than RX fancies.
2011 when they had stopped diverted engineering the Wankle and shifted their efforts over to their Skyactiv systems is where they have really gotten true world class “Zoom-Zoom”.
Dead horse beaters do not go far.
Steve unruh
This is where I think both technologies combined together would make each other shine. It would be very easy to seal a rotary engine for use with the sterling concept as it will be closed loop instead of an open loop. No piston rings to bleed into a crank case.
Liquid Piston is a new company that just came out and they have solved most the issues with apex seals.
I’ve been following Liquid Piston. I think their apex seal equivalent is still proving troublesome but the geometry has a chance to be more wear resistant than Mazda’s wankels with further development.
They have some military funding which makes sense because high specific power and high fuel efficiency has lots of field applications. If the engine only lasts 1000 hours it may not matter so much. With time maybe Liquid Piston can get the longevity up?
I have read it runs on 50:1 oil mix, so emissions could be trouble for us civies that have to follow such rules.
Apex seals I dont believe would be a problem in a sterling there is not internal combustion processes, rendering carbon and high temperature that destroy the seals. I know very little about the sterling but I imagine the temps are much lower than a combustion cycle so those seals could probably be made of better materials to resist wear. The beauty of this is can be sealed unlike a reciprocating engine. So those apex seals may not be a big deal if they seep a little bit its still in a closed loop.
AC systems use oil in the system to lubricate internal parts. This is a closed loop system as well so the oil can not go anywhere it just gets recycled through the system over and over. So the dynamics of the rotary completely change now. You could do this same thing here the oil is not going anywhere as it along with the working fluid will just get recycled through the processes over and over again.
I like Liquid Piston, as they have a product and you can test the results. I do love the concept of so much horsepower with so little weight. I would love to see it running on wood gas 
Watching the videos of the Stirling Engine advancements was a true mind blowing experience for me as I had no idea anyone had taken it as far as it is.
Yeah Ive never had any interest in the sterling until I saw that last vid you posted. That got the gears turning. Now Im wondering what happened to that guy? His videos are from 2018 and then nothing. What happened did it not output? Did something g wrong raising the pressure?
If you could combine this with a stove technology, you could run that engine for basically nothing. 750 watts around the clock is 18,000 watt hours that is huge!!
At some point I will be converting my manual mill into a machining center and I just might start prototyping. If anything it will be a fun learning experience.
I just found that video, what impressed me was how quiet it was 700 watts being that quiet would be amazing.
Yeah imagine this in a rotary, it would be silent!! Did he put a power load on it? Im wondering if it made the power or not and maybe he just abandoned this thing. It makes no sense to put all that time, money and development into that beautiful machine to just stop.