The manufacturer of the Stirling engine for those submarines, Kokums, is the source of the engines used for a dish-Stirling solar energy system I worked on for a licensee of Stirling Energy Systems[1]. It was a concentrating solar energy system consisting of a parabolic mirror focusing sunlight onto a heater head atop the Stirling engine. Quite efficient at around 30% conversion of direct sunlight to electricity - each unit generated about 25kW under clear skies. Quite a simple system - just a big mirror, sun tracker, Stirling engine and generator. Super reliable - no nasty combustion products. And not very expensive - BOM cost about the same as a mid-size car. But dropping PV prices ended up killing it.
[1]https://en.wikipedia.org/wiki/Stirling_Energy_Systems