solar-only system
as defined in Commission Delegated Regulation (EU) No 812/2013 of 18 February 2013…, Article 2, point (12) (Definitions)
a device that is equipped with one or more solar collectors and solar hot water storage tanks and possibly pumps in the collector loop and other parts, which is placed on the market as one unit and is not equipped with any heat generator except possibly one or more back-up immersion heaters;