Leaching Hazardous Substances out of Photovoltaic Modules

Abstract

Photovoltaic modules contain hazardous substances such as lead and cadmium. Under normal operation conditions, these materials will not be released into the environment. This study identifies conditions resulting in release. Our worst case study uses milled module pieces of 0.2 mm size. Depending on the pH value of water based solutions, more or less amounts of hazardous substances are leached out. Solutions with low pH values (acidic solutions) yield substantial leaching. Three different solutions simulate different environmental conditions: i) “low mineralized water” conditions, via water containing sodium hydroxide, ii) “sea water” conditions, via water containing sodium hydroxide and sodium chloride, and iii) “rainwater” conditions, via water containing acetic acid. In “rain water”-like solutions with low pH, already after a few days, around 30 % of the cadmium is leached out from milled cadmium telluride module pieces, increasing to 50 % after 56 days! In the same time, more than 15 % of lead is leached out from c-Si module pieces. Tellurium elutes in the range of 30 to 40 % with a weak dependence on the pH value of the solution indicating an instability of the compound cadmiumtelluride out of the cadmiumtelluride modules. Most of the extractions increase during several weeks of measurement. Therefore, the usual one-day-elution test does not give enough information. Meaningful leaching experiments should last for at least ten days.