Modelling the soiling of heliostats: Assessment of the optical efficiency and impact of cleaning operations

The optical efficiency of the solar field heliostats of a Concentrating Solar Power (CSP) tower plant is a fundamental parameter to assess the productivity of the plant. The optical efficiency is mainly affected by the position of the sun in the sky during the year, and by the cleanliness level of the heliostats, which is related to their reflectance. The reflectance is continuously diminished by the deposition of dust on the heliostat surface (that is, soiling). Natural cleaning events, as rain, are rare in typical locations for CSP plants, so artificial cleaning is the most common technique used to maintain the optical efficiency (heliostat reflectance) as close as possible to its optimal value in order to maximize the overall production and thus the revenues of the CSP plant. This paper provides a methodology to assess the soiling of a heliostat field and then evaluates the impact of artificial cleaning on the optical efficiency, considering different frequencies of cleaning in four different scenarios. The outcome of this study is a considerable step forward towards the optimization of costly cleaning activities to minimize operation costs in solar power technologies