In this video I show you the investigation into which Stirling engine concept could become the successor to the Rhombic Stirling.

For years I have been trying to support our solar power supply with my selfbuilt Stirling engines fueled by our micro biogas digester.

The Rhombic Stirling has an output of 300 watts, but requires too much maintenance to charge the solar battery around the clock in continuous operation.

That's why I've spent the last few weeks intensively investigating various Stirling concepts for their suitability as a homebuilt combined heat and power plant.

The Thermo Mechanical Generator is a very smart design but unfortunately too complex and underpowered.

I could perhaps imagine a simplified version with a rubber diaphragm and an enlarged stroke.

The design of the Thermal Lag engine is complicated and quite unexplored.

Powerful engines have not yet been developed.

It would therefore be a very risky choice.

The Thermoacoustic Stirling has no moving parts apart from the power generator and seems to offer several advantages.

However, I do not know whether it is possible to develop an engine with a reasonable power output.

The Free Piston Stirling engine does not require a mechanical drive mechanism and is an ingenious simplification of the Stirling principle.

But with the conventional piston and displacer I would have the same problems with friction and wear as with my kinematic Stirling engines.

The calculation of the oscillating system with several masses, spring and damping forces and the thermodynamic effects acting on them is also highly complicated.

Perhaps a lowtech version with a rubber diaphragm would be a realistic option.

A largevolume multicylinder Alpha Stirling engine could reduce the complexity, but the length between service intervals would certainly not be long enough.

An extreme increase in performance could then be considered.

With an output of approximately 2000 watts, the motor would only have to run for around 3 hours a day.

To achieve this, the working volume and correspondingly the heat exchanger surfaces would have to be increased about sixfold.

I have already purchased a corresponding 17 kg diameter 130 mm round material made of 1.4571 stainless steel for the heater head.

Then there are solutions beyond the Stirling principle:

The most obvious option would be to convert an internal combustion engine to run on biogas.

However, I believe that even a highquality small engine with internal combustion would quickly develop major corrosion problems with the relatively dirty biogas or wood gas.

Even with suitable noise protection measures, a combustion engine would still be quite loud.

Producing a gas turbine with reasonable efficiency is probably also very complex and the loud, highfrequency running noise is annoying in the long run.

Steam engines and steam turbines require a large steam boiler that is not without danger.

They are also not very efficient and require a lot of maintenance.

The last option that comes to mind is the use of Peltier elements.

I have experimented a little with them, but the efficiency is probably very low and I can't say anything about their service life.

The remaining candidates for me so far are:

1. The Thermoacoustic Stirling Engine whose only moving parts are the power generator.

2. A LowTech Free Piston Stirling Engine preferably with a rubber diaphragm.

3. A largevolume lowtech Alpha or Beta Stirling engine with high performance and low operating times per day.

4. A conventional combustion engine, whereby I do not estimate the service life in biogas operation to be very long.

What do you think of my selection?

Do you have any suggestions for other or existing concepts?

Please write them in the comments.

Thank you very much for your attention!

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