UK
- British Gas-Microgen. Research abandoned by British Gas in spring 2007, used SunPower technology.
- Microgen Engine Corporation uses Sunpower free piston technology.
- E.ON (was PowerGen) (uses Whispertech technology)
- Baxi Ecogen uses SunPower free piston engine.
- Disenco Energy uses a beta type Stirling engine based on a Sigma Elektroteknisk design with rhombic drive.
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New Zealand
- Whispertech (has ceased trading)
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