| Surface dust is one of the main factors that reduce the generation efficiency of photovoltaic(PV)modules,especially in arid areas.The existing dust removal methods consume a lot of water and have low water utilization rate,which is not suitable for dust removal and cleaning of PV power plants in arid areas.It is found that the surface of PV modules applying a hydrophobic coating(hydrophobic PV modules)is not easy to adhere to dust,and the dust on the surface hydrophobic PV modules can be removed by using a small amount of water.When hydrophobic PV modules are applied in PV power plants in arid areas,in order to provide theoretical basis about coating selection and water consumption regulation for dust removal,the following research is carried out in this paper:(1)Based on the particle adhesion contact mechanics theory,a mechanical model of adhesion between the surface of PV modules and dust particles is established.The relationship between the self-cleaning performance of PV modules and dust particle size and surface properties was calculated.It is found that the surface elastic modulus and friction coefficient are the main factors affecting the self-cleaning performance of PV modules.PV modules coated with hydrophobic coatings with different surface parameters can self-clean dust particles in different particle size ranges.The smaller the particle size of dust to be cleaned,the smaller the optional range of surface parameters of hydrophobic coatings.For example,when cleaning dust particles within the size of 100-250μm,the optional elastic modulus of the surface ranges from 0 to100 MPa,and the friction coefficient ranges from 0.1 to 0.15.When cleaning dust particles in the large particle size range of 500～1000μm,the optional elastic modulus ranges from 100 to 73000 MPa,and the friction coefficient ranges from 0.1 to 0.15.(2)According to the local dust particle size in Lanzhou area,the hydrophobic coatings with suitable surface parameters are selected to prepar the different hydrophobic photovoltaic glasses.A one-month natural dust accumulation experiment is conducted to study the dust accumulation characteristics and visible light transmittance of different hydrophobic photovoltaic glass surfaces in the natural environment.The experiments show that hydrophobic and superhydrophobic PV glasses have certain self-cleaning ability,and the amount of dust accumulation on the surface is reduced by 0.021 g and 0.074 g,respectively,compared with normal PV glass.It is found that bonded dust occurs on the surface of PV glass due to the residue of raindrops,which leads to the reduction of transmittance of PV glass.The contact angle on the surface of superhydrophobic PV glass is high,and the raindrops are not easily retained on the surface,forming less bonded dust accumulation.When the dust accumulation experiment is completed,the visible light transmittance of superhydrophobic PV glass is the highest.Therefore,superhydrophobic PV modules are more suitable for PV plants in Northwest China.(3)Based on the motion law of droplets and the force analysis of droplets and dust particles on the surface of superhydrophobic PV module,a droplet dust removal prediction model is established and a droplet dust removal experimental platform is built.It is found that the droplet on the surface of the superhydrophobic PV module with dust accumulation can maintain the spherical shape and move.With the increase of the amount of dust carried by the droplet and the change of the droplet parameters,the droplet at the later stage of the motion starts to maintain the elliptical shape.As the dust accumulation density increases,the dust removal amount of a single droplet also increases.The relative error of dust removal amount between the simulation and experiment is kept within 22%,which indicates that the prediction model has rationality.The amount of dust removed by a single small droplet is smaller than that of a large droplet.In addition,the experiments find that with the surface wetting droplets will spread into small water puddles sliding downward and stagnate on the surface of ordinary PV glass.So the key to the droplet dust removal of PV module is to constitute a superhydrophobic surface.(4)When cleaning PV modules,the water consumption for small volume droplet dedusting is less than that for large volume droplet dedusting.Under dust accumulation conditions with a dust density of 30 g/m~2,the water consumption for cleaning a PV plant consisting mainly of 270 W superhydrophobic PV modules(1650mm×992 mm×40 mm)with 50μL droplet dust removal is 0.331 m~3/MW.Compared with manual cleaning method and high-pressure water jet cleaning method,the water consumption can be saved about 2.669 m~3/MW and 9.669 m~3/MW respectively.The amount of water required to clean all PV plants in Northwest China with 50μL droplet is about 2.368×10~4 m~3.The water consumption of 10μL droplet cleaning is 0.04m~3/MW.On the basis of 50μL droplet cleaning,using 10μL droplet cleaning can save about 2.085×10~4 m~3 of water for Northwest China.The application of small volume droplets for de-dusting is more suitable in Northwest China. |
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