Most solar thermal systems have a separate antifreeze filled loop for protection against freezing and require a new tank fitted with a heat exchanger. When retrofitting, a perfectly good tank (usually copper) needs to be replaced. Soltropy Ltd has developed an innovative solution that allows a domestic water supply to be heated directly without the secondary fluid cycle. This increases the efficiency of the system and reduces capital and installation costs by allowing the system to freeze but cause no damage; this is achieved by incorporating a compressible tube within an outer copper pipe. When the system freezes the compressible tube takes up the expansion due to the ice and prevents pressure build up. As part of this project the thermal connection between the header pipe and the heat pipe in the evacuated tube will modularised, allowing a standard copper pipe to be used as the header with single units clamping over the pipe. This will reduce costs further as the modular connector can be mass produced. In addition the control system will be optimised, simplified and modularised. Tests at Heriot-Watt University to date have shown that the Soltropy system behaves differently from an "old style" system and therefore requires different control strategies.