Development of Self-Cleaning Solar Collectors for Minimizing Energy Yield Loss Caused by Dust Deposition

Abstract

Concentrated Solar Power (CSP) systems used for photothermal conversion of solar energy to electricity are capable of meeting a large fraction of the global energy requirements. CSP plants are inherently robust with respect to the availability of materials, technology, and energy storage. However, dust depositions on solar collectors cause energy yield loss annually, ranging from 10 to 50% depending upon their location in the semi-arid and desert lands. Mitigation of energy loss requires manual cleaning of solar mirrors with water. A brief review of the soiling related losses in energy yield of the CSP plants is presented, which shows that cleaning of the CSP mirrors and receivers using water and detergent is an expensive and time-consuming process at best and is often impractical for large-scale installations where water is scarce. We report here our research effort in developing an electrodynamic dust removal technology that can be used for keeping the solar collectors clean continuously without requiring water and manual labor. Transparent electrodynamic screens (EDS), consisting of rows of transparent parallel electrodes embedded within a transparent dielectric film can be integrated on the front surface of the mirrors and on the receivers for dust removal for their application as self-cleaning solar collectors. When the electrodes are activated, over 90% of the deposited dust is removed. A summary of the current state of prototype development and evaluation of EDS integrated solar mirrors and experimental data on the removal of desert dust samples are presented. A brief analysis of cost-to-benefit ratio of EDS implementation for automated dust removal from large-scale solar collectors is included.

Mitigation of soiling losses in concentrating solar collectors

“…Experiments for numerous trials have shown more than 90% reflectivity restoration is possible after EDS activation on the order of a few minutes [19]. …”

Field test and electrode optimization of electrodynamic cleaning systems for solar panels

“…The repulsive forces are first the Coulomb force and then the dielectrophoretic force, which is independent of the particle charge and depends only on the nonhomogeneity of the electric field around the particles. In outdoor operating systems, gravitational and wind force should also be taken into account, which will depend on mounting system and meteorological conditions. During the electrodynamic cleaning process, the dust particles are charged positively by various charge transfer mechanisms such as contact charging when a difference in electronegativity is present between the particles and the surface, tribocharging when particles move over the surface and between each other, and microfilament charging when high space charge is created between the surface and the particles …”

“…The electrode design can vary from standard interdigitated electrical line (in particular for standing wave) to spiral design (Figure A). The voltage difference between electrodes usually varies between 0.9 and 7 kV.…”

“…During the electrodynamic cleaning process, the dust particles are charged positively 16 by various charge transfer mechanisms such as contact charging when a difference in electronegativity is present between the particles and the surface, tribocharging when particles move over the surface and between each other, and microfilament charging when high space charge is created between the surface and the particles. 4,15 When alternated high voltage pulses are applied to only two independent electrodes, a standing wave is formed over the surface, and the particles are moved forth and back due to the variable electric field: in this case, gravity and wind are needed for efficient cleaning over large surfaces. 5 In case of three or more electrodes, a traveling wave can be generated and can move the particles even on horizontal surface (see Figure 1).…”

“…4 Modeling of EDS for better understanding and optimization of the design and process was already done by different institutes. [9][10][11]16,17 The electrode design can vary from standard interdigitated electrical line (in particular for standing wave) 4 to spiral design 15 (Figure 2A).…”