Self-excited critical wind speed and uncertainty determinations

Photovoltaic solar energy provides a sustainable alternative to conventional energy sources, addressing the increasing global energy demand. Among available technologies, single-axis solar trackers with horizontal mounting are the most cost-effective for energy production. However, cost-driven reductions in structural stiffness have increased vulnerabilities, leading to catastrophic failures caused by aeroelastic phenomena. This study examines damping-driven self-excited instabilities, particularly stall flutter, in two-dimensional, flat, isolated solar trackers. These instabilities arise beyond a critical wind speed, but a unified criterion to define this threshold remains absent. To address this gap, the study evaluates several methods for determining critical wind speed, including a semi-empirical mathematical formulation and experimental criteria using constant or dynamic thresholds. These thresholds are applied to various statistics (e.g., amplitude or root mean square) and magnitudes (e.g., incremental angle of attack or moment coefficient). The key contribution is the introduction of a new experimental criterion with variable thresholds, dependent on the tracker’s mechanical properties, that replicates results from the semi-empirical formulation. For high-inertia systems, the study proposes an observational approach with results consistent with the mathematical model. The analysis confirms that experimental criteria yield equivalent outcomes across different statistics and magnitudes. Additionally, when comparing different criteria, significant importance is placed on the determination of uncertainties associated with all variables. To address this, existing standards are reviewed, and a method is proposed for estimating uncertainties in regression coefficients for nonlinear fitting. This methodology addresses a notable limitation of the current ISO standard, which does not provide guidance on uncertainty quantification for nonlinear regression coefficients.