Solar stirling engine: a miniature build

[gitPharm01]

Hi, I built a solar-powered miniature Stirling engine system with surprisingly low cost.
The solar power input is from a tiny Fresnel lens which is only 0.0825 square meters (25 cm*33 cm).
Here's the footage:
[bbvideo]https://youtube.com/shorts/xnberSOgnwE?feature=share[/bbvideo]

In this build, I did two things to make sure the engine can be started with this tiny bit of energy.
One is the cone-shaped frame which attaches the Fresnel lens to the engine.
The inside is covered by tin foil to keep as much solar radiation inside as possible.
The airflow near the hot side of the engine is also severely restricted so heat loss is further decreased.
That layer of tin foil also prevents the cone from catching fire.

Another thing I did is painting the hot side with black paint.
This will help converting most of the light into heat.

The system, including the engine and Fresnel lens, costs below 25 US dollars.
Of course, the electricity output is miserable.
But with a larger lens and a better engine, it should be able to generate decent power output.

Most important thing is that by doing two things, a Stirling engine can be started with surprisingly low amount of sunlight:
1.Preventing heat lose.
2.Increase the efficiency of heat convergence.

Yet this model do have some potential flaws.
1.Larger Fresnel lenses are quite expensive.
2.The paint/material which is applied on the hot side must endure high temperature.
In fact, the system I built stopped working shortly after the paint was evaporated.
3.The Fresnel lenses made from glass will suffer from wind erosion and lost efficiency.
If the lenses are made from acrylic, deterioration caused by UV will also be a major issue.

[Tom Booth]

2.The paint/material which is applied on the hot side must endure high temperature.
In fact, the system I built stopped working shortly after the paint was evaporated.

My first thought would be some flat black ceramic paint.

Typically paint (or glaze) used for ceramic are fired in a kiln at about 2000°F and a small bottle doesn't cost too much, maybe $5 from a ceramic supply.

Maybe cover the receiver part of the engine with a cut off end of a test tube for the "greenhouse effect".

Nice work!

I would also have less of the metal displacer tube exposed to heat or light. Leave maybe just 1/2 inch exposed and shield the rest with a mirror or something to reflect light/heat back toward the extremity.

The back end of the displacer tube should be kept as cool as possible I think. You might get better performance.

[Tom Booth]

Maybe just coat the end with soot (lamp black or carbon black) the basis of some black inks and stove polishes.

I've blackened the bottoms of many a cooking pot while simply cooking food in a pot over a campfire.

Sometimes this soot washes off easily but other times it is nearly impossible to scrub off. I'm not sure what the "secret ingredient" is to make it stick well. I was just burning mixed wood, but sappy resinous wood is the most likely culprit.

It may take some experimenting to find a soot that sticks well to the steel engine. But usually the problem is how to get the stuff off rather than how to put it on.

Probably holding the engine over an oil lamp, with too long a wick, for a lot of soot production would work. I've collected carbon by just holding a spoon over a gas stove burner to make ink.

I don't think this can burn off, as it's already burned, but it can sometimes brush off fairly easily, but after many years, I still have some old pots used over a camp fire that are blackened on the bottom with the stuff that I've never been able to scrub off.

https://youtu.be/_UGKxt7Gkx4

Anyway, I suspect your engine may have quit running more due to overheating. (Too much heat on the back end of the displacer) rather than because of the paint burning off.

[Tom Booth]

It appears that the entire displacer, heated and preferably unheated sides as well as the gold colored mounting are at least partially exposed to direct and/or refected sunlight. Which kind of defeats the purpose of the displacer, to shift the air from the heated to the unheated end of the chamber.

Resize_20220924_134503_3965.jpg (100.76 KiB) Viewed 1308 times

Some might say or suggest that the power piston is the "cold side" but that is misleading and inaccurate IMO.

[gitPharm01]

Thanks for your feedback!
I did not know there are so many methods that can help converting radiation energy to heat.
Those heat-resistant paint available on the market can only endure 650 degrees Celsius.
Using ceramic paint may be the choice.

This build has proven my concept, and I'll try to build up another system which integrates 4 lenses.

[Tom Booth]

.

... I'll try to build up another system which integrates 4 lenses.

I'm curious to see what you work out. A difficult challenge.