Research On Physical Mechanism Of Selective Solar Absorbers

Since the industrial revolution,the burning of fossil fuels has brought a lot of greenhouse gas emissions,resulting in a gradual increase in global average temperatures and more frequent extreme weather.Therefore,governments are paying more and more attention to the use of clean energy.As one of the most abundant and widely distributed clean energy sources,solar energy has received great attention from the government.The solar thermal photovoltaic system proposed in recent years is expected to break through the energy efficiency of the past photovoltaic system,and thus has received extensive attention in the academic community.The selective solar absorber is one kind of broadband metamaterial absorbers,and is also the core component in the solar thermal photovoltaic system.What,s more,it is an important part of improving solar thermal applications.However,some solar absorbers currently proposed have problems such as narrow absorption bandwidth,poor absorption selectivity,polarization sensitivity,and wide-angle absorption,which result in poor performance and hinder their practical application in solar thermal photovoltaic systems.In this thesis,the selective solar absorber is targeted as the research object,and a solar absorber based on fishnet gratings metamaterial and a solar absorber based on photonic crystal metamaterial are designed respectively,and the related physical mechanism is expounded.An anti-reflecion coated two-dimensional vertically-aligned tandem fishnet gratings as solar selective absorber is proposed and studied.The optical properties of the absorber and various electromagnetic resonance modes were simulated using CST software.In the wavelength range of 0.3-1.625 ?m,the absorber has an aborptivity of more than 90%,and in the 0.3-1.53?m,the absorber has an ultra-high absorptivity of over 94.7%,and the average absorptivity in this band is 98%.In the mid-infrared band of more than 2.3?m,the absorber has an emissivity of less than 20%,which exhibits good selectivity.When the incident angle is 50 degrees and the incident wave is TM polarized wave,there is more than 94%absorption in the 0.3-1.5?m band;when the incident wave is TE polarized wave,there is 85%absorption in the 0.3-1.52?m band which shows good wide-angle absorption characteristics.Due to the symmetry of the structure,the absorber is insensitive to polarization.The physics of optical properties associate with anti-reflection mode,cavity resonance,and magnetic polariton.A high-efficiency solar absorber based on dielectric-filled anti-reflection coated film-coupled two-dimensional metallic photonic crystals is proposed and numerically calculated.The proposed solar absorber has a polarization-independent high absorptivity above 95%in the range of 0.33-1.45 ?m with insensitivity to incident light angle as large as 50°.In the range beyond 2.2?m,the thermal emissivity of this structure is below 20%,which shows its strong absorption selectivity.The efficient light harvesting property of the proposed solar absorber can be attributed to the anti-reflection mode,cavity resonance and coupled surface plasmon polaritons.By analyzing the performance of the proposed solar absorber,it can be found that the total solar thermal conversion efficiency is very close to the ideal selective solar absorber,and it is better than several representative solar absorbers.Because of polarization independence,angular insensitivity and broadband wavelength-selective absorption,it is believed the proposed absorber is very promising for real-world applications related with the renewable energy conversion,such as solar thermal heating and solar power generation.