Techno-economic optimization of string sizing in utility-scale Photovoltaic projects: A novel model balancing overvoltage risk, cost and yield

Optimizing utility-scale photovoltaic systems design is crucial for enhancing energy performance and economics, which in turn strengthens bankability for future developments. String size is a key design parameter because it simultaneously governs electrical limits (overvoltage risk and clipping behaviour) and cost structure by improving layout efficiency and refining the material investment. This study conducts a techno-economic assessment that links string-length selection to both capital expenditure and yield outcomes. The analysis quantifies how longer strings reduce cabling, trenching, and mechanical supply while potentially increasing voltage-related clipping. Results are normalized to a project-specific reference and evaluated across ten utility-scale sites with varying climates and layouts. A new decision model, Grupotec Optimum String Size, calculates the optimal string size for each site by balancing the acceptable risk of overvoltage against capital expenditure savings and energy impacts. Across the ten-project portfolio, increasing string size by one module typically lowers total capital expenditure by a range of 0.9–2.3%, and by two modules by approximately 2.2–4.4%, with variation driven by site size and layout geometry. Energy-cost analysis reveals improvements from small to moderately larger strings, including a threshold beyond which photovoltaic systems show a reversal, as overvoltage-induced clipping which erodes the associated economic gains. The evidence demonstrates that controlled increases in string size deliver robust cost reductions and net energy-cost benefits up to a clear, site-dependent threshold. The proposed model operationalizes this trade-off, enabling project-by-project selection of string length under an efficient methodology.