Ole-Hjalmar Kristensen writes:

If you look closer at the technology you will find that the working
fluid is helium.

That's rather obscurely and incompletely explained on the Web site, being
that purveyors of perpetual motion cannot, of necessity, be too specific
about how it is achieved.

But if you're correct about the helium and Stirling, then so much the more
is this made not credible.