Photovoltaic (PV) technology is crucial for sustainable energy generation, but the performance of PV systems in real-life conditions is closely associated with the material quality, degradation and the climatic conditions. While conventional poly-Si modules are already widely installed, Elkem Solar Silicon (ESS®)-based multicrystalline silicon modules are more sustainable owing to energy savings in silicon production. But little field data is available on their behaviour in the hot Indian climate. Thus, the field performance of ESS® multicrystalline silicon and conventional poly-Si modules after one year of installed operation in a rooftop grid-connected 6.71 kWp PV system at BVRIT, Telangana, India is assessed. The demonstration system comprises 28 modules (organized in four rows of seven, with 14 ESS® modules and 14 conventional poly-Si modules). Performance analysis was carried out using field-based energy yield, I–V and P–V characteristics, peak power degradation, electrical mismatch, as well as electroluminescence imaging of the modules. The findings show that both technologies had minimal degradation, with an average annual power loss of 0.3% for ESS® modules and 0.4% for conventional poly-Si modules. ESS® module technology showcased 1-1.5% higher energy yield than conventional poly-Si modules, mainly because of better high-temperature operation. At the module level, it was detected that the majority of the changes in power were due to variations in current (Isc and Imp) rather than in Voc = 37.56 V and Vmpp = 30.23 V. Electroluminescence image analysis showed only minor defects from handling, but no defects caused by material. The results confirm that ESS® modules offer higher energy yield and are more suitable for sustainable grid-connected PV systems.