# The Design Value for Recycling End-of-Life Photovoltaic Panels
## 3 Effective PV Panel Design Methods for Recycling at EoL
### Design for Recycling  
The International Energy Agency (IEA) emphasizes that PV panels must be designed to return the embedded raw materials or, at least, to provide secondary raw materials that can be entirely used for other applications. The requirements assessed as critical by the IEA Photovoltaic Power Systems Programme (PVPS) are functionality, longevity, durability, reliability and cost. The Design for Recycling (DfR) must support and improve these aspects. The first action to be implemented is to eliminate, or at least minimize, the project materials that are difficult to recycle and that are non-reversible adhesives. The composition of the backsheet deserves particular attention, which represents the last layer at the bottom of the photovoltaic solar panel, consisting of a polymer or a combination of polymers. For this, a provision should be made for the use of totally recyclable polymers. The use of encapsulants should be minimized to facilitate the disassembly of the modules. The use of appropriate sealants in the aluminum frame will allow for the separation of the EoL modules without damaging the components. In the second column, Table 2 lists the materials for each PV panel component, identified by the authors, which today are completely recyclable. Table 2 also reports the materials' characteristics of density, Young's modulus, Poisson coefficient, stiffness, thermal conductivity and the specific heat capacity used in the parametric FE panel simulation in the next section. Two main types of PV panels (apart from the PV panels with amorphous silicon that are easily recyclable and that are not treated), which require different recycling approaches, can be traced. Both types, silicon-based panels and thin-film panels, can be recycled using separate industrial processes. Currently, silicon-based panels are the most common [21]. Silicon PV panels are composed mainly of glass, plastic and aluminum, and these are three materials that are recycled in large quantities. The recycling process of silicon-based PV panels initially involves the disassembly of the actual product to obtain separation between the aluminum and glass parts. Almost all glass can be reused (99.5%), and all external metal parts are employed to reshape cell frames. The remaining materials must be treated at 500 \({}^{\circ}\)C in a special heat treatment unit in order to make it easier for cellular elements to bond. Due to the heat, the plastic evaporates, leaving the silicon cells ready to be further processed. The supporting technology ensures that the plastic is not wasted and that it can be reused as a heat source for further thermal processing. After the heat treatment, the hardware is physically separated. As a result, 95% of this can be easily reused, and the rest is further refined. Silicon particles, referred to as \"wafers\", are eliminated with acid. Wafers that become broken are melted to be reused to produce new silicon modules, with a recycling rate of 98% of the silicon material. In Figure 9, the authors summarize a logical scheme of the recycling process of PV modules, considering the mechanical, thermal and chemical processes with which it is  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Layer**} & **Material** & \multirow{2}{*}{**Thickness h**} & **Young’s** & **Poisson** & **Thermal** & **Specific Heat** & **Density** \\  & **(Completely** & **[mm]** & **Modulus E** & **Coefficient v** & **Conductivity** & **Capacity** & **[kg/m\({}^{3}\)]** \\  & **Recyclable** & **[GPa]** & **[-]** & **[W/m \({}^{\circ}\)C]** & **[J/kg \({}^{\circ}\)C]** & **[kg/m\({}^{3}\)]** \\ \hline Frame (1) & Aluminum & 20 \(\div\) 40 & 69 & 0.31 \(\div\) 0.34 & 204 & 996 & 2707 \\ Cover (2) & Tempered & Glass & 3 \(\div\) 7 & 70 & 0.22 & 1.8 & 500 & 3000 \\  & Plasticpossible as well as current technologies used to completely recover all the components at their EoL [22; 23].