Influence of inertia and aspect ratio on the torsional galloping of single-axis solar trackers

Abstract

Single-axis solar trackers are currently one of the cheapest systems for electricity generation. However, they may have to face significant maintenance costs depending on environmental and climatic factors. Weather is believed to provoke approximately half of the damages registered in solar tracker systems, and a large part of them are due to dynamic wind load. Torsional galloping – or, more precisely, flutter with one degree of freedom – is a phenomenon that arises when the wind speed exceeds a certain critical value. It causes the tracker to undergo angular oscillations with increasing amplitude until the structure collapses. The phenomenon is intrinsically linked to geometric and structural parameters, some of which exhibit a wide range of variation in the current market, depending on the configuration and design of the trackers. This article presents an analytical and experimental study on how the onset of torsional galloping is influenced by the inertia of the modules and the aspect ratio of the panel; it also includes the effect of the torque tube stiffness. The analytical study starts from the equation of motion involving the aeroelastic derivatives and the torque equation in differential form. Tests have been conducted on aeroelastic models of the structures of interest. It has been found that the critical reduced velocity of galloping changes with tilt angle, but it is essentially independent of the main structural parameters: torsional stiffness, inertia and aspect ratio. The results are finally presented in a Stability Diagram for the correct and optimal dimensioning of these structures against torsional galloping.