Indoor Overheating Risks of PV-ETICS and Dark-coloured Facades: Experimental and Simulation-based Assessment

Building-integrated photovoltaics (BIPV) are gaining attention for improving energy performance and on-site electricity generation. However, dark-coloured PV panels in facade applications may pose a risk of overheating, particularly when integrated into External Thermal Insulation Composite Systems (ETICS) without a ventilation cavity. This study investigates the impact of dark facade plasters and BIPV with external phase change materials (PCM) on indoor overheating in the cold climate of Estonia. A full-scale experimental test wall with PV-ETICS and light-coloured traditional ETICS was constructed and monitored for thermal behaviour. An IDA ICE simulation model was created and calibrated. Using this model, a typical concrete apartment building was analysed for overheating. The results showed that PV-ETICS systems only modestly increased overheating degree-hours — by 3–10 °C·h above 27 °C in the case of a 200 mm thermal insulation layer, while thinner insulations showed more significant overheating. While the overheating effect isn’t severe enough to hinder the PV-PCM ETICS facade concept, it should be considered in indoor climate and energy modelling, especially for insulation levels ≤100 mm. Mitigation can be achieved by using lower g-value glazing or passive shading methods.