Thermal property of EDS film and its effect on the removal of dust particles as a function of surface temperature

Solar energy is used worldwide. Deserts and semi-arid areas are well suited for solar energy harvesting. High dust concentration in deserts, where many large solar plants are located, causes a loss of energy conversion efficiency by soiling solar collectors. Electrodynamic Screen (EDS) film when laminated over photovoltaic module, works as a self-cleaning technology designed for soiling loss mitigation of solar plants and it requires no water and consumes very low energy. However, the high ambient temperature in deserts leads to a decrease of efficiency of the silicon solar panels, and the EDS film has a potential influence on increasing temperature of the panels. This thesis focuses on the thermal property of EDS film and to determine its effects on the operating temperature of solar panels and its efficiency. A series of experiments are designed to test the performance of solar panels with or without EDS film lamination operations under different ambient temperatures. With a variety of electrodes and optically clear adhesives used in constructing EDS film, we investigated the change in cell temperature with EDS films. The results show the EDS film has minimum effect on rising temperature of solar panel and its effectiveness in dust removal is not diminished

Development of electro-optic systems for self cleaning concentrated solar reflectors

The current demand for energy usage in the world is increasing at a rapid pace; in China alone, the electricity usage has increased by 12% per year from 2006-2010, where more than 75% of electrical power is produced by coal burning facilities. Numerous studies have shown the effects of carbon dioxide emissions on global climate change, and even showing the permanence of high carbon dioxide levels after emissions cease. Current trends away from carbon emitting power facilities are pushing solar energy into a position for many new solar power plants to be constructed. Terrestrial solar energy at AM1.5 is generally given at 1kW/m2, which is a vast free source of energy that can be be harvested to meet the global demand for electricity. Aside from some areas receiving intermittent levels of solar insolation, one of the largest hindrances to large scale solar power production is obscuration of sunlight on solar collectors caused by dust deposition. In areas with the highest average solar insolation, dust deposition is a major problem for maintaining a constant maximum power output. The southern Negev desert in Israel receives on average 17g/m2 per month in dust deposition on solar installations, which in turn causes losses of a third of the total power output of the installation. In these areas, water is a scarce commodity, which can only be used to clean solar installations at a prohibitive cost. To resolve this problem, a cost effective solution would be the application of electrodynamic screens (EDS), which can be implemented by embedding a set of parallel electrodes into the sun facing surface of solar collectors, including concentrating mirrors or photovoltaic (PV) modules, and applying a low frequency pulsed voltage to these electrodes. Three major contributions made in the course of this research in advancing (EDS) for self-cleaning solar mirrors are: (1) development of non-contact specular reflectometer for solar mirrors that allows measurement of reflectance loss as a function of dust deposition, (2) development of a dust deposition analyzer capable of measuring size distribution of deposited dust and provides mass concentration of dust on the surface of the mirror, and (3) optimization of electrode geometry of EDS film for minimizing optical reflection losses caused by the lamination of the film on the mirror surface while maintaining high reflection efficiency with high dust removal efficiency. The non-contact specular reflectometer and the dust deposition analyzer allowed experimental investigation of reflection losses as functions of surface mass concentration of dust on mirrors for validation of the optical model presented in this study

Engineering Support Contract Capabilities Awareness

No abstract availabl

Mitigation of soiling losses in solar collectors: removal of surface-adhered dust particles using an electrodynamic screen

Particulate contamination of the optical surfaces of solar collectors, often called "soiling", can have a significant deteriorating impact on energy yield due to the absorption and scattering of incident light. Soiling has more destructive effect on concentrated solar systems than on flat-plate photovoltaic panels, as the former are incapable of converting scattered sunlight. The first part of this thesis deals with the soiling losses of flat-plate photovoltaic (PV), concentrated solar power (CSP), and concentrated photovoltaic (CPV) systems in operation in several regions of the world. Influential parameters in dust accumulation losses, as well as different cleaning mechanisms in pursuit of restoring the efficiency of soiled systems, have been thoroughly investigated. In lieu of the most commonly-practiced manual cleaning method of using high-pressure water jets, the concept of automatic dust removal using the electrostatic forces of electrodynamic screen (EDS) technology is in a developmental stage and on its way toward commercialization. This thesis provides comprehensive analytical solutions for the electric potential and electric field distribution in EDS devices having different configurations. Numerical simulations developed using finite element analysis (FEA) software have corroborated the analytical solutions which can easily be embedded into software programs for particle trajectory simulations while also providing flexibility and generality in the study on the effect of different parameters of the EDS on the electric field and ensuing dust-removal performance. Evaluation and comparison of different repelling and attracting forces exerted on dust particles is of utmost importance to a detailed analysis of EDS performance in dust removal. Hence, the balance of electrostatic and adhesion forces, including van der Waals and capillary forces, have received significant attention in this dissertation. Furthermore, different numerical analyses have been conducted to investigate the potential causes of observed failures of EDS prototypes that functioned well in a laboratory environment but failed after outdoor exposure. Experimental studies form the last two chapters of this dissertation. Different tests have been conducted on an EDS sample integrated with a PV cell to restore the efficiency of the cell after dust deposition. In order 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 EDS cleaning cycle using a custom-built dust-deposition analyzer. Furthermore, we have pursued several experiments to examine how the geometric and operational EDS parameters affect particle charge via charge-to-mass-ratio measurements

Modeling the particle transport of electrodynamic screens to optimize dust removal from solar energy collectors

Solar energy installations located in dry, arid regions chosen for their availability of sunlight often face the problem of dust accumulation, or "soiling", on their solar collector surfaces, requiring this dust to be cleaned regularly in order to maintain optimal power production. The electrodynamic screen (EDS) is a technology that can clean this dust off the surfaces of photovoltaic panels and concentrating solar power mirrors using no water and a minimum of power. The EDS is a series of conductive electrodes embedded between two thin dielectric layers, where voltages applied across the electrodes create a patterned electric field which directs the motion of charged dust particles off the EDS surface. As the dust in different desert regions across the world have different physical characteristics, a different set of design parameters is required for the optimal EDS for each region. This optimization work could be easily conducted using a computer model of the physics of an EDS and the dust it clears off its surface. In this thesis, a computer model of the EDS system is created using COMSOL Multiphysics. This model simulates the voltages applied across the electrodes and the resulting electric fields, and then use these to simulate the trajectories of the charged dust particles as they move across the EDS surface. This particle tracing work is validated using experimental data from high-speed camera trials and performance data for different EDS designs. This validation work shows both agreements and disagreements between the predicted and observed dust particle motion, and the beginnings of the investigation into this difference is presented. Finally, the ability to further develop this model for EDS design optimization is discussed

Analysis of parabolic through collector cleaning system under adaptive scheduling policy

The purpose of this study is to investigate the effects of stochastic dust accumulations and rain events on the cleaning schedule of the parabolic trough collectors that are used to generate power at concentrated solar power (CSP) plants. The level of cleanliness is proportional to the power produced, and thus it affects the economic pay off at CSP plants. Current practice to address this dust problem, termed as conventional cleaning, is to follow a periodic cleaning schedule that entails a fixed setup cost for each cleaning event. The frequency of cleaning under such conventional (periodic schedule) policy is selected based upon a tradeoff between the set up cost and the payoff from improving the cleanliness factor. The conventional practice is to have a constant and periodic cleaning schedule over an entire season (e.g. either severe or mild combination of the dust and rain over a 180-day cleaning season, with either 8 or 4 cycles scheduled for the severe and mild seasons respectively). This thesis draws upon evidence from recent literature to show that presence of random rain events improves the cleanliness of parabolic troughs in CSP plants. Upon analyzing such evidence, this study models rain event as a compound Poisson process that replenishes the level of cleanliness. In this scenario, it is possible to establish an adaptive threshold policy for scheduling plant cleaning that analogous to the formulation of a (s,S) inventory management policy, subject to random replenishment of inventory. The study offers a review of related literature to establish that such formulations are not amenable to a close form solution. The second half of the thesis describes a numerical study that has been conducted using Arena Simulation package for characterizing the adaptive cleaning policy. The parameter of interest for assessing system performance is the average payoff over the average cost of cleaning for a 180-day cleaning season. Numerical study shows that adaptive cleaning policy outperforms the conventional (periodic) cleaning policy under reasonable assumptions for dust and rain event distributions. As an extension, the simulation study also examines the use of alternative cleaning system, known as electrodynamic screening (EDS), for different rain scenarios that may be used in conjunction with either conventional or adaptive cleaning policies to improve the overall system performance.2019-07-09T00:00:00

Analysis of parabolic through collector cleaning system under adaptive scheduling policy

The purpose of this study is to investigate the effects of stochastic dust accumulations and rain events on the cleaning schedule of the parabolic trough collectors that are used to generate power at concentrated solar power (CSP) plants. The level of cleanliness is proportional to the power produced, and thus it affects the economic pay off at CSP plants. Current practice to address this dust problem, termed as conventional cleaning, is to follow a periodic cleaning schedule that entails a fixed setup cost for each cleaning event. The frequency of cleaning under such conventional (periodic schedule) policy is selected based upon a tradeoff between the set up cost and the payoff from improving the cleanliness factor. The conventional practice is to have a constant and periodic cleaning schedule over an entire season (e.g. either severe or mild combination of the dust and rain over a 180-day cleaning season, with either 8 or 4 cycles scheduled for the severe and mild seasons respectively). This thesis draws upon evidence from recent literature to show that presence of random rain events improves the cleanliness of parabolic troughs in CSP plants. Upon analyzing such evidence, this study models rain event as a compound Poisson process that replenishes the level of cleanliness. In this scenario, it is possible to establish an adaptive threshold policy for scheduling plant cleaning that analogous to the formulation of a (s,S) inventory management policy, subject to random replenishment of inventory. The study offers a review of related literature to establish that such formulations are not amenable to a close form solution. The second half of the thesis describes a numerical study that has been conducted using Arena Simulation package for characterizing the adaptive cleaning policy. The parameter of interest for assessing system performance is the average payoff over the average cost of cleaning for a 180-day cleaning season. Numerical study shows that adaptive cleaning policy outperforms the conventional (periodic) cleaning policy under reasonable assumptions for dust and rain event distributions. As an extension, the simulation study also examines the use of alternative cleaning system, known as electrodynamic screening (EDS), for different rain scenarios that may be used in conjunction with either conventional or adaptive cleaning policies to improve the overall system performance.2019-07-09T00:00:00

Index to NASA Tech Briefs, 1972

Abstracts of 1972 NASA Tech Briefs are presented. Four indexes are included: subject, personal author, originating center, and Tech Brief number