Non-immersion ultrasonic cleaning for heliostats

Soiling and dust accumulation in reflectors for concentrating solar plants (CSP) decrease their reflectance and, as a consequence, the solar field efficiency [1]. Most widely used cleaning methods are based on pressured water jets and rotary brush cleaners. Each method has its own advantages and drawbacks. On one hand, pressured water jets can reach up to 97% of relative reflectance [1] without any kind of physical contact, but it supposes a great amount of demineralized water consumption. On the other hand, brush cleaners consume less water and give higher cleaning efficiency (almost 100% of relative reflectance) but because of the physical contact between the brush and the surface of the mirror, which is full of hard dust particles, mirror’s surface is exposed to abrasion that reduces its reflectivity permanently. The present paper describes the work done on the development of a novel cleaning method based on the same principles of the well known ultrasonic cleaning. This method has demonstrated to be the most efficient one in the market but it is limited to objects that can be immersed. The cleaning of a heliostat would not be feasible with this technology. Most part of the work of the present research has been focused is the development of an ultrasonic device that needs no immersion and, of course, no contact. The system has been tested on real mirror probes at different process conditions and it has been compared with conventional pressured water jet cleaning. It has demonstrated be able to obtain better cleaning results (up to 99% of relative reflectance) with about 600 times less water.