Thermo-mechanical stability of lightweight glass-free photovoltaic modules based on a composite substrate

Lightweight PV modules are attractive for building-integrated photovoltaic (BIPV) applications, especially for renovated buildings, where the additional load bearing capacity is limited. This work focuses on the development of a lightweight, glass-free photovoltaic (PV) module (6 kg/m(2)) composed of a composite sandwich back structure and a polymeric front layer. Sandwich structures are usually manufactured with a vacuum bag process and thermosetting liquid glues (e.g. epoxy resin). However, due to the long manufacturing process ( > 24 h), liquid adhesives are not compatible with conventional solar industry processes. This work presents the development of a robust glass-free PV module based on a composite sandwich architecture manufactured with a simple process. To simplify the production, the standard thermoset epoxy is substituted by different PV encapsulant foils (EVA, ionomer, polyolefin). The results show that a particular formulation of polyolefin is the ideal adhesive to produce a stable backsheet structure. The use of this polymer with a high thermal conductive core (aluminum honeycomb) allows a reduction of processing time from 24 h to 30 min. The mechanical properties of the composite sandwich structure showed an excellent stability under thermal cycling and damp heat with only 1% and 3% loss in bending stiffness, respectively. Two-cell lightweight PV modules manufactured with this backsheet show good electrical performance after thermal cycling and damp-heat tests, for which, respectively, an output power loss of only 3% and 2% is observed. This configuration is up scaled to a sixteen-cell module for which a power loss of only 3% is measured after damp-heat.