Outdoor performance of photovoltaic mini-modules with aesthetic front glass designs on a south-facing vertical façade in summer

Aesthetic front glass improves architectural appearance while partially concealing the solar cells. Such glazings are usually evaluated under standard test conditions (STC), and information on their outdoor electrical behaviour remains limited. Four photovoltaic mini-modules with identical cells, encapsulation and rear construction were fabricated, differing only in the front glass: an antireflection-coated transparent reference, a gray polysilazane-coated glass, and two ceramic-printed glasses of identical pattern and 25% printed coverage differing only in pigment colour. The modules were operated simultaneously at their maximum power points on a south-facing vertical frame during the Korean summer and compared with STC measurements. The three aesthetic glazings were almost indistinguishable in visible light transmittance, 79.2–80.0% against 94.8% for the reference, yet their transmittance over the spectral response range of the cells differed by up to nine percentage points, 73.4–82.3% (reconstructed from witness samples). Outdoors, all modules reached similar temperatures and operated within 0.4% of the reference voltage, so the influence of the front glass was expressed almost entirely through the operating current. Relative to the reference, the aesthetic modules delivered 82.1–84.7% of the output power under STC but 88.6–90.1% outdoors, with operating current ratios of 88.0–91.2% against 82.3–85.7% under STC. Evaluating the ratios within intervals of irradiance showed that this difference is not an averaging artefact. Glazings of equivalent visual appearance can therefore differ substantially in the irradiance they deliver to the cells, and STC measurements did not fully represent relative outdoor performance under the investigated vertical summer conditions.