Researchers from the Universidad Carlos III de Madrid (UC3M) have patented a method which makes it possible to reduce energy losses in solar thermal power plants.
Solar thermal energy relies on harnessing solar radiation to produce heat. As with most methods of obtaining electricity, this heat is used to heat a high-pressure fluid, which drives a turbine connected to a generator. The most common solar thermal power plants are referred to as tower technology plants. These plants are composed of thousands of tracking mirrors (heliostats) that concentrate solar radiation onto a receiver located at the top of a tower, which in turn are made up of an array of smaller mirrors, called facets. Salts usually flow along this receiver and are heated and then stored in a tank at temperatures above 550ºC, before being used to obtain steam.
In order to capture as much solar energy as possible, it is essential that these heliostat facets are properly aligned. "An alignment error of just two milliradians in these heliostats produces about a 30 percent loss in a plant's annual energy production," explains Alberto Sánchez González, professor in the UC3M Department of Technical and Fluid Engineering. Currently, there are several techniques to align heliostat facets: on-sun, mechanical and optical. However, these techniques have a number of drawbacks, such as their imprecision, their unique viability under ideal laboratory conditions and/or the large amount of resources required (time and personnel). "The objective of this research has been to create a procedure for aligning heliostat facets in a simpler, more accurate and more cost-effective way than in previous systems," says José Carlos Castillo Montoya, professor in the Department of Systems Engineering and Automation.
The method patented by both researchers uses the reflection of a nearby (reference) heliostat on the target heliostat, seen from a camera located on the back of the reference heliostat. In this way, regular imaging by the camera makes it possible determine if there is misalignment (deviation from the ideal orientation of the target heliostat facets), in which case the corresponding adjustment would be carried out. "The images taken by the camera are compared with those that should ideally be seen in the absence of misalignment. The theoretical optical model, which generates the ideal images, also makes it possible to determine the alignment error in each of the facets", explains Sánchez. "This method is much simpler than similar methods based on placing a camera on the upper portion of the tower, as the distance between the camera and the heliostat is reduced, thus improving accuracy," concludes Castillo.
Castillo Montoya, J. C. y Sánchez González, A. (2022). Procedimiento y sistema para alinear las facetas de un heliostato de un campo solar (ES 2 891 178 A1). Oficina Española de Patentes y Marcas (Spanish Patent and Trademark Office).