Leaching via Weak Spots in Photovoltaic Modules

Abstract

This study identifies unstable and soluble layers in commercial photovoltaic modules during 1.5 year long-term leaching. Our experiments cover modules from all major photovoltaic technologies containing solar cells from crystalline silicon (c-Si), amorphous silicon (a-Si), cadmium telluride (CdTe), and copper indium gallium diselenide (CIGS). These technologies cover more than 99.9% of the world market. We cut out module pieces of 5 × 5 cm2 in size from these modules and leached them in water-based solutions with pH 4, pH 7, and pH 11, in order to simulate different environmental conditions. Unstable layers open penetration paths for water-based solutions; finally, the leaching results in delamination. In CdTe containing module pieces, the CdTe itself and the back contact are unstable and highly soluble. In CIGS containing module pieces, all of the module layers are more or less soluble. In the case of c-Si module pieces, the cells’ aluminum back contact is unstable. Module pieces from a-Si technology also show a soluble back contact. Long-term leaching leads to delamination in all kinds of module pieces; delamination depends strongly on the pH value of the solutions. For low pH-values, the time dependent leaching is well described by an exponential saturation behavior and a leaching time constant. The time constant depends on the pH, as well as on accelerating conditions such as increased temperature and/or agitation. Our long-term experiments clearly demonstrate that it is possible to leach out all, or at least a large amount, of the (toxic) elements from the photovoltaic modules. It is therefore not sufficient to carry out experiments just over 24 h and to conclude on the stability and environmental impact of photovoltaic modules.

Comment on Nover et al. Leaching via Weak Spots in Photovoltaic Modules. Energies 2021, 14, 692

“…In the later studies, the pH 3 leaching solution consisted of 15.4 g/L citric acid, buffered with 2.8 g/L disodium hydrogen phosphate. As a result of the buffering, pH remained almost constant at 3 throughout the study [1,2].…”

“…An important difference between the authors' initial research on milled PV modules [3] and the later studies on PV module pieces [1,2] is the use of buffered aqueous solution.…”

“…In their recent publication on "Leaching via Weak Spots in Photovoltaic Modules" [1], Nover et al have extended their previous long-term leaching study on photovoltaic (PV) modules [2], by increasing test duration and by examining a larger set of elements (Al, Cd, Cu, Ga, In, Mo, Pb, Se, Te, Zn) and mechanisms of delamination. Based on their results, the authors argue for prompt replacement of damaged modules and complete recycling of end-of-life modules.…”

Towards a successful re‐use of decommissioned photovoltaic modules

“…For modules with intact glass, this risk is virtually zero, but upon frame removal or afterwards, the tempered glass plate will very likely become shattered, which enables leaching of toxic materials. This is an important issue, as has been shown by researchers that investigated the rate of leaching from solar modules for different module technologies 9,10 …”

“…This is an important issue, as has been shown by researchers that investigated the rate of leaching from solar modules for different module technologies. 9,10 Of course, the absence of local recycling facilities is also a concern for the installation of new PV modules in these regions, although for these modules there would be more time left to still create local waste treatment facilities. Apart from local recycling, another solution could be to first collect a huge number of modules locally before shipping these modules to a recycling facility elsewhere in a large batch to be more efficient.…”