Comparative Study of Power Degradation in Five Photovoltaic Technologies Under Outdoor Conditions

This study investigates the long-term performance degradation of five commercial photovoltaic (PV) modules with different technologies - monocrystalline silicon (c-Si), hybrid multicrystalline/amorphous silicon (mc-Si/a-Si), copper indium selenide (CIS), heterojunction with intrinsic thin layer (HIT), and cadmium telluride (CdTe) - under real outdoor operating conditions at the SIRTA observatory (Palaiseau, France). The experimental platform has been continuously recording climatic parameters and PV output characteristics since 2014 (2017 for CIS), providing dense open-access data. To quantify the degradation rates, a dedicated MATLAB routine was developed to extract annual mean values of the output electrical parameters ($\mathbf{P}_{\text {max}}, \mathbf{V}_{\text {mpp}}$, $I_{m p p}, V_{o c}$, Isc), under filtered environmental conditions. The analysis focused on two specific operating points, a lowirradiance condition (GPOA $=400 \mathrm{W} \cdot \mathrm{m}^{-2}, \mathrm{T}_{\text {mod}}=25^{\circ} \mathrm{C}$) and one at high irradiance ($\text{GPOA}=800 \mathrm{W} \cdot \mathrm{m}^{-2}, \mathrm{T}_{\text {mod}}=50^{\circ} \mathrm{C}$). Linear regressions of the normalized maximum power were used to estimate the annual degradation rates $\left(R_{D}\right)$. The results show that higher irradiance conditions tend to mitigate degradation, with all modules exhibiting lower $\mathbf{R}_{\mathbf{D}}$ values under $G=800 \mathrm{W} \cdot m^{-2}$ compared to $G=400 \mathrm{W} \cdot m^{-2}$. Across both scenarios, crystalline silicon technologies (c-Si and mc-Si/a-Si) display the lowest degradation rates, while CdTe exhibits the highest.