?- ABB Ltd.
- Capstone Turbine Corporation
- Caterpillar Inc.
- Siemens AG
- General Electric Company
- Centrica PLC
- Microgen Engine Corporation Holding B.V.
- Senertec Kraft-Warme-Energiesysteme Gmbh (Senertec)
- BDR Thermea Group BV
- Viessmann Werke GmbH & Co. KG