Arash Sayyah

Mitigation of soiling losses in concentrating solar collectors

The adverse impact of soiling (dust deposition) on solar collectors, and the mitigation of the related energy yield losses, are the main scopes of this paper. While soiling related losses have been studied more extensively for flat-plate photovoltaic (PV) panels, this study focuses primarily on the impact of dust accumulation on concentrated photovoltaic (CPV) and concentrated solar power (CSP) systems. We report on different methods used for cleaning solar collectors: (i) natural cleaning by rain and snowfall, (ii) manual cleaning by water and detergent, and (iii) an emerging method of dust removal by electrodynamic screens (EDS). Development of EDS technology as an automated, low-cost dust removal method which does not require any water or manual labor is presented.

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

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.Copyright

Performance Analysis of Electrodynamic Screens Based on Residual Particle Size Distribution

Dust accumulation on the optical surfaces of solar collectors causes significant losses in their energy yield. Fine dust particles, compared with coarse ones, contribute significantly more in the performance loss, assuming identical surface mass concentration. This study examines the performance of different electrodynamic screen (EDS) prototypes, operated under different conditions, in removing fine dust particles in the laboratory environment. After going through several cycles of dust deposition and cleaning using EDS, the dust residue left on each EDS prototype is collected and analyzed using a Horiba particle size distribution (PSD) analyzer. The PSD analyses determine which EDS design has performed superior in removing a given size range and in which operational condition. The results are advantageous in the optimization procedure of EDS to attain maximum dust removal efficiency and minimum optical interference.

Electrodynamic removal of dust from solar mirrors and its applications in concentrated solar power (CSP) plants

Concentrating Solar Power (CSP) systems based on parabolic trough and power tower technologies provide inherent advantage of energy storage and high efficiency for utility-scale solar plants. The specular reflectance efficiency of the solar mirrors plays a critical role in the efficiency of electric power generation. The deposition of atmospheric dust on the surface of the mirrors reduces its reflectance efficiency and requires frequent cleaning to avoid energy-yield loss. Electrodynamic screen (EDS) can provide an efficient method for maintaining the specular reflectivity above 90% by removing the deposited dust particles. In this paper, we briefly review (1) electrostatic charging mechanisms involved in EDS, (2) optimization of EDS for high dust removal efficiency, and (3) minimization of cleaning cost and water consumption. Prototype EDS-integrated solar mirrors were produced and tested in an environmental test chambers simulating desert atmospheres. The test results show that frequent removal of dust layer can maintain the specular reflectivity of the mirrors above 90% subjected to dust deposition ranging from 0 to 10 g/m2.

Environmental degradation of the optical surface of PV modules and solar mirrors by soiling and high RH and mitigation methods for minimizing energy yield losses

Utility-sale solar plants are mostly installed in semi-arid and desert lands and are subjected to high dust deposition rate. Dust layer build up on solar collectors causes major energy-yield loss. Maintaining designed plant capacities requires more than 90% efficiency of light transmission or specular reflection for PV modules and CSP mirrors, respectively. The combinations of high relative humidity (RH), high surface temperature, and long residence time of the dust on the optical surface degrades the solar collectors over time. A tenacious mud like coating is formed, which strongly adheres to the PV modules and concentrating mirrors and requires scrub cleaning. If the global solar-power output is to increase from current GW levels to the TW level, as is envisioned, the water cleaning process would result in an unsustainable demand for water. This paper provide a brief review of the application of an emerging technology of transparent electrodynamic screen (EDS) for removing dust, as frequently as needed, from the solar collectors without water. Power output efficiency is maintained greater than 90% compared to that of the panel under clean conditions. Dust removal efficiency (DRE) is more than 90% with test dust samples obtained from different arid zones and energy consumption for EDS operation is less than 0.03 Wh/m2/cleaning cycle. The method is water-free and provides easy retrofitting onto existing panels and has a high potential for a cost-effective large-scale roll-to-roll production, commercial application, and a significant reduction of operation and maintenance costs.

Performance restoration of dusty photovoltaic modules using electrodynamic screen

Dust accumulation on optical surfaces of solar collectors is been known to cause significant losses in energy yield. The most commonly-practiced methods of cleaning solar collectors use water-based agents. This paper, however, addresses the mitigation of soiling losses on a photovoltaic cell using the electrodynamic screen (EDS) in a laboratory environment. A model for the EDS model with two stacked layers of transparent dielectric coatings is developed using finite element analysis (FEA) software, and the behavior of the electric field on the EDS surface is thoroughly examined. For the reported experiments, an EDS sample has been integrated into a PV cell for dust mitigation. Experimental results show the restoration of the short-circuit current (Isc) to more than 90% of the pre-dust value after 10 trials using standard test dust and EDS cleaning. The tests were conducted in an environmentally-controlled chamber at various applied voltages and inclination angles. In some cases, dust coagulations were observed after several cleaning cycles. To evaluate the performance of the EDS in dust-particle removal, we have studied the particle size distribution on the EDS surface after each dust deposition and cleaning cycle using a custom-built dust-deposition analyzer.

Self-Cleaning Solar Mirrors Using Electrodynamic Dust Shield: Prospects and Progress

Parabolic trough and power tower technologies provide inherent advantage of thermal energy storage and high efficiency of the Concentrating Solar Power (CSP) systems for utility scale solar plants. High efficiency CSP power generation with minimal water use is one of the SunShot goals of the US Department of Energy. The specular reflectance efficiency of the solar mirrors plays a critical role in the efficiency of power generation. The optical surface of the mirrors and the receiver must be kept clean for efficient operation of the plant. Some environmental challenges in operating the large-scale CSP plants at high reflectance efficiency arise from high concentration of atmospheric dust, wind speed and variation of relative humidity (RH) over a wide range. Deposited dust and other contaminant particles, such as soot, salt, and organic particulate matters attenuate solar radiation by scattering and absorption. Adhesion of these particles on the mirror surface depends strongly by their composition and the moisture content in the atmosphere. Presence of soluble inorganic and organic salts cause corrosion of the mirror unless the contaminants are cleaned frequently.In this paper, we briefly review (1) source of atmospheric dust and mechanisms involved in degradation of mirrors caused by salt particles, (2) loss of specular reflection efficiency as a function of particle size distribution and composition, and (3) an emerging technology for removing dust layer by using thin transparent electrodynamic screen (EDS). Feasibility of integration of EDS on the front surface of the solar collectors has been established to provide active self-cleaning properties for parabolic trough and heliostat reflectors.Prototype EDS-integrated solar collectors including second-surface glass mirrors, metallized acrylic film mirrors, and dielectric mirrors, were produced and tested in an environmental test chambers simulating desert atmospheres. The test results show that frequent removal of dust layer can maintain the specular reflectivity of the mirrors above 90% under dust deposition at a rate ranging from 0 to 10 g/m2, with particle size varying from 1 to 50 μm in diameter. The energy required for removing the dust layer from the solar was less than 10 Wh/m2 per cleaning cycle. EDS based cleaning could therefore be automated and performed as frequently as needed to maintain reflection efficiency above 90% and thus reducing water usage for cleaning mirrors in the solar field. A comparative cost analysis was performed between EDS and deluge water based cleaning that shows the EDS method is commercially viable and would meet water conservation needs.Copyright

Mitigation of dust impacts on solar collectors by water-free cleaning with transparent electrodynamic films: Progress and challenges

Energy-yield loss caused by soiling of photovoltaic modules and concentrated solar power (CSP) mirrors in utility-scale power plants installed in semiarid lands and deserts would result in unsustainable demands for fresh water needed for cleaning. This paper reviews the progress of the electrodynamic screen (EDS) film technology for frequent water-free cleaning with low-energy requirements. Results presented here, based on laboratory-scale EDS-film-laminated solar panel cleaning, show that the output power can be restored higher than 95% of the initial power under clean conditions. For solar mirrors, the specular reflection efficiency can be maintained over 90% ensuring high efficiency of the CSP plants. Operation of the EDS film for maintaining high optical efficiency of solar collectors requires less than 0.2 Wh/m

Optimization of Electrodynamic Screens for Efficient Removal of Dust Particles

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Analysis of particle size distribution of residual dust in cleaning process using an electrodynamic screen

/cleaning cycle. Principles, optical modeling, construction, lamination of the EDS films on modules and mirrors, and experimental data showing optical efficiency restoration without water consumption are presented. Current challenges in developing electrodes that would meet optical and conduction properties, low-cost production, and meeting long-term outdoor durability of the EDS films are discussed.Energy-yield loss caused by soiling of the PV modules and CSP mirrors in utility-scale power plants would result in unsustainable demands for fresh water needed for cleaning. This paper reviews the progress of the electrodynamic screen (EDS) film technology for frequent water-free cleaning with low energy requirements. EDS-based cleaning would maintain high optical efficiency ensuring long-term sustainability of TW-scale plants located in arid lands. Principles, modeling, construction, and lamination of the EDS films on modules and mirrors and experimental data showing power output restoration are presented. Current challenges in production and meeting outdoors durability of the EDS films are discussed.