Thermo-mechanical characterisation of fluoropolymer films for concentrated solar thermal applications

Abstract

Renewable and clean energy sources are getting more important. Therefore, a resource-saving alternative to conventional solar concentrators has been designed. This pneumatic pre-stressed concentrator is completely made of polymer films. Due to its pre-stressed construction the mechanical properties of the transparent film have a high influence on the lifetime of the concentrator. The dimension stability of the film significantly affects the effectiveness of the systems due to the shift of the focus point of the reflected radiation after deformation. Therefore, special requirements concerning thermal and mechanical properties in the application relevant temperature range have to be fulfilled.The aim of this work is to characterise fluoropolymer films as transparent layers in a pneumatic pre-stressed sun concentrator. Fluoropolymers have been chosen due to their excellent optical and mechanical properties and their extraordinary stability against ultraviolet radiation. A total of five different fluoropolymer films have been selected and their thermal, mechanical and thermo-mechanical properties at application relevant temperatures were characterised. Even though no material complies with the requirements, an ethylene-tetrafluorethylene-copolymer (ETFE) is suggested, with the recommendation to adapt and adjust the film thickness and the production process to influence the morphology and subsequently the thermo-mechanical behaviour of the material.