Stirling engines, like all heat engines, work more efficiently with large temperature differentials: this means advanced materials. External combustion immediately puts you in a weird and unfamiliar engineering place where you have the firey bits outside the piston where you can do the usual things to keep it under control. Cooling is also different from just farting out exhaust and pumping water through the block in a normal engine. If you don't have a large temperature differential you have shitty efficiency and it's not worth doing. Practical Stirling engines which do useful work, whether for heating or cooling, are usually large, have sealed, pressurized helium as working fluids (oh? you don't know about working fluids in Stirling engines?), complicated gearing mechanisms and sometimes even magnetic coupling to the outside world, and have extremely complex and precision machine parts compared to the slop you see in consumer grade items like a Porsche Engine. Ratios in the engine are often tailored to a very specific use case; and will work for shit if your heat spec is outside that very, very narrow use case. Go have a look at what goes into designing a real world Stirling engine for example in .
People don't use Otto/Rankine/Brayton/whatever because of some live-steam or anti-Stirling conspiracy: they use it because Stirling engines, outside of a few mostly unimportant use cases, are usually expensive and shit. The two most widespread industrial uses of the things I can think of were a Chrysler air conditioner and a coleman beer cooler, both using the same Japanese built Stirling cooler. Even in these use cases, which, mind you are using a Stirling engine in reverse from what HN weebs want them for, they didn't exactly cover themselves in glory. They were expensive, heavy, fragile and not as efficient as would justify their bad qualities over a more standard cooling unit.
 https://docplayer.net/40169613-The-reliability-development-o... (I think)
A Stirling engine must have a regenerator which temporarily stores the heat from one stroke to the next. Otherwise it is just a hot air engine which is altogether more ancient.
They specifically mention systems that do 5kw, 25kw, etc (in the next pages).
That aside, there's a kickstarter project for a 1kw Stirling engine from about 6 years ago:
The "updates" tab there seems to have potentially useful info, though the project appears to have stopped updating there.
The project itself still seems to be iterating on new developments, just slowly.
More recent video's of their development:
Mentions here they're intending on making the design OSS:
Currently, I think the Senertec Dachs might be closest to what you're after in size, although it's based on a conventional four-stroke, not a stirling engine. The residential CHP market seems to be shifting to fuel cells.
OTOH, if the exhaust of your AC is hotter than necessary (the unit wastes energy), then the best you could hope for is to recover some part of (depends on temperature differential) the wasted energy. Better get a better AC unit.
You can uses a Stirling engine as a cryocooler, by running it in reverse, and cool your house itself directly. This is only really useful if you're trying to get to low temperatures.
I have two of the Twinbird FPSC Portable Freezers which utilize this technology, nice and quiet and sips electricity.
Some people have proposed this as yet another bulk energy storage system for the grid; giant underground cryotanks of liquid nitrogen. With careful design the same gear could be used in "forwards" or "reverse" mode. The limit is that the Carnot efficiency isn't great.
Both the Stirling engine and the AC unit are using the Carnot cycle (simplification), and going around the expansion-heat-transfer cycle in opposite directions.
(I have no connection with this company or its products)
Talking to the folks that worked at WhisperGen, the wobble yoke design added extra complications and tolerance issues that added to the cost.
A stand alone generator need not be mobile, so it needn't be that light weight. In fact it probably would benefit being integrated with a home's heating and cooling system to utilize waste heat.
What it does need to do is be relatively maintenance free, and run off a variety of heat sources (such as pellets, woodgas or solar thermal). This is where I think Stirling engines shine...you can gasify all of your waste organic matter into dirty gas that wouldn't normally be fit for an internal combustion engine, but work fine for a swirl burner which can be used on an external combustion engine such as steam or stirling.
A stirling engine might not produce enough power to power the wheels directly, but it could produce electricity quite efficiently at constant power output. It's fairly efficient, compact, relatively quiet and simple to build.
The electricity could be stored in fewer batteries and/or supercapacitors. The electricity from these would then power the wheels.