Structural health monitoring of solar trackers using distributed fiber optic sensors

Abstract

We demonstrate the application of a novel type of distributed fiber optic sensors (DFOSs) to dynamically monitor the effects of wind on solar tracker structures used in photovoltaic power stations. This DFOS is based on the stimulated Brillouin scattering nonlinear optical effect in optical fiber, which can be used to measure the distribution of strain and temperature along a given structure. However, contrary to existing solutions, the sensor provides dynamic real-time measurements with hundreds or even thousands of full simultaneous measurements for all positions in the fiber each second. Moreover, high-precision and high spatial resolution are obtained. This so-called dynamic Brillouin optical time-domain analysis (D-BOTDA) sensor provides real-time monitoring of the bending and torsion of the structure of solar trackers in response to wind load. This helps the solar tracker manufacturer asses and improve the mechanical designs so as to introduce corrective measures and develop cost-effective components that properly withstand the effects of wind at any given location. We experimentally demonstrate the application of a D-BOTDA sensing system to measure distributed bending and, for the first time to our knowledge, also distributed torsion along the stressed beam of the solar tracker. For this purpose, we have developed a procedure to instrument the torsion beam with two optical sensing fibers that are fixed helically wound along the beam in opposite directions, so that any common-mode thermal or bending effects are removed. We initially performed tests in a laboratory facility in which sections of the torsion beam could be subjected to controlled moments. Static and dynamic loads were applied and the measured deformations were compared to those obtained with fiber Bragg gratings, which just provide point measurements of strain. In both cases, full agreement was demonstrated. Finally, the system was installed in an operational solar park.

A Dual-Wavelength Fiber Laser Sensor with Temperature and Strain Discrimination

“…Figure 3 depicts the schematic diagram of the experimental setup carried out to evaluate the laser generation and sensor properties when using this single mode fiber random reflector (SMF-RR) within the resonator acting as a quasi-distributed mirror. Secondly, an ultra-high spatial resolution optical backscattered reflectometer (OBR 4600, from LUNA), commonly used for fiber testing and sensing [21], was employed to retrieve the backscattered optical power, measured as a function of the length of this fiberbased random reflector inscribed into a single mode fiber. To avoid undesired reflections, free termination of the fiber-based reflector was immersed into index-matching oil.…”

“…As Figure 2 shows, the length of the inscription was around 34 mm and this fiber sample was located at 2.39 m from the OBR connector. Secondly, an ultra-high spatial resolution optical backscattered reflectometer (OBR 4600, from LUNA), commonly used for fiber testing and sensing [21], was employed to retrieve the backscattered optical power, measured as a function of the length of this fiberbased random reflector inscribed into a single mode fiber. To avoid undesired reflections, free termination of the fiber-based reflector was immersed into index-matching oil.…”