20 Years of Outdoor Weathering

F. Ruesch*, S. Brunold

Institut fuer Solarenergie SPF, HSR University of Applied Sciences, Oberseestrasse 10, CH-8640

Rapperswil.

* Corresponding Author, florian. ruesch@solarenergv. ch
Abstract

The outdoor weathering performance of collector glazings was investigated over a time range of 20 years. A variety of 58 glazing types composed of glass and different polymeric materials were included. Five samples of each glazing type were exposed at two Swiss sites with differing climatic conditions. One sample from each type was collected, analyzed and stored following 40 days, 1, 3, 10 and 20 years of exposure.

The weathering properties of PMMA were in the range of glasses or even slightly better. Contrarily, material degradation was observed for PC, PET, PVC and UP. Soiling was strongly dependent on the exposure site and the glazing material. At the sub-urban site of Rapperswil (CH) a significant loss in solar transmittance in the range of 3-15% was measured. For the investigated fluoropolymers surprisingly high losses in transmittance (ETFE) or tendency for soil accumulation (FEP, PVF) was observed.

Keywords: outdoor weathering, ageing, collector glazing, polymeric glazing

1. Introduction

Solar collectors for hot water production provide a great potential for the exchange of fossil fuels with a renewable energy resource. Unfortunately, high investment costs still lower the economic success of this technology. The use of new polymeric collector materials offers a significant potential for cost savings in the installation and production process. In general the most important contribution to flat plate collector weight comes from the tempered glass glazing. A substitution with polymeric glazing could significantly reduce the weight to lower installation effort and cost. To justify the high investments for a solar thermal system, generally a long lifetime in the range of more than 20 years has to be ensured. However, up to now most producers of polymeric glazing materials do not present reliable data on the ageing performance of their products over such a long time period. This study provides data on the ageing and soiling properties of different polymeric materials and conventional solar glasses during 20 years of outdoor weathering. Major attention was turned to the change of the solar transmittance of the glazing materials as this measure is correlated very well to the change of the collector efficiency.