Comparative Evaluation of Bifacial and Monocrystalline PV Systems Using Solis 255 Kw Inverters

Abstract

India’s rapid growth in solar PV (105.65 GW installed by early 2025) has spurred interest in advanced technologies like bifacial modules to boost energy yield. This paper presents a comprehensive performance comparison between two utility-scale (≈255 kW) Solis string inverters – one coupled to Trina Solar monocrystalline monofacial modules (total DC ~313.5 kW) and the other to Trina bifacial dual-glass modules (DC ~307.2 kW). Over 12 months of operation in Gujarat (India), monthly energy readings from each inverter were analyzed for trends, anomalies, and correlation with simulated performance. Simulation modeling (using a PVsyst-based approach) was employed to predict expected output and bifacial gain under local irradiance and environmental conditions, providing context for the experimental data. Results show that the bifacial system consistently outperformed the monofacial system, delivering ~10% higher annual specific yield (≈1770 vs 1600 kWh/kW) under actual site conditions. The bifacial gain varied seasonally – in high-insolation summer months the gain was modest (~5–8%), whereas during diffuse-rich monsoon months it reached ~12–15%. A significant anomaly was observed in one month (monofacial output ~25% below expectation due to a suspected inverter downtime), temporarily inflating the bifacial gain. Excluding this outlier, the bifacial advantage remained aligned with model predictions and literature (e.g. ~13–16% under cloudy conditions vs ~13% on clear days ). Performance ratio (PR) values for both systems were in the 0.75–0.80 range, with the bifacial array achieving a slightly higher PR due to additional rear-side harvest. Simulation results closely matched measured yields (within ~5–8% monthly), validating the modeling approach and assumptions (e.g. ground albedo ~0.25, bifaciality ~0.70). The integrated analysis highlights key factors influencing energy yield: solar irradiance profiles (direct vs diffuse), module bifacial gain, inverter clipping at high DC load, ambient temperature, and soiling/maintenance practices. Design insights are drawn to maximize bifacial benefits – including optimal tilt and spacing to enhance rear irradiance capture, maintaining reflective ground conditions, and ensuring regular cleaning to mitigate soiling losses. This work contributes novel field data from an Indian context, demonstrating that bifacial PV technology can reliably provide ~10% greater energy yield than monofacial systems under real-world conditions, and emphasizing considerations for system designers to harness this advantage in similar climates. The findings are expected to aid solar engineers and researchers in improving PV plant performance and guiding the transition to bifacial modules in large-scale deployments.