Design Of Solar Absorber Based On Metamaterial-surface Plasmon

In modern society,excessive use of non-renewable traditional energy such as coal,oil,natural gas has led to lots of environmental problems,such as acid rain,smog and global warming.Solar energy,as a substitute for traditional energy,is a kind of abundant and renewable clean energy which is taken seriously by countries in the world.In the development and utilization of solar energy,compared with the traditional photovoltaic system,solar thermal system has been widely concerned by the society because of its higher solar energy conversion efficiency.Solar absorber is core component of solar thermal system,whose absorption performance can directly affect the energy conversion efficiency of the whole system.Therefore,the design of solar absorber with excellent spectral selectivity,high absorption,insensitive to polarization and incidence angle is a hot spot in the field of solar thermal system research.Metamaterial is a kind of artificial unnatural composite structure with extraordinary electromagnetic properties,which can show some unique electromagnetic properties,such as negative refractive index,perfect absorption and so on.By designing the geometry of metamaterial structural unit,surface plasmon effect can be excited to realize local enhancement of electromagnetic wave at sub-wavelength scale,which is beneficial to improve the absorption performance of solar absorber.In this paper,the solar absorbers based on metamaterial-surface plasmon are taken as the research object.Three kinds of spectrally selective metamaterial solar absorbers with high energy conversion efficiency for solar thermal system are designed.1、A solar absorber composed of moth eye structure and square ring structure is proposed.The optical properties are analyzed by finite difference time domain method:the average absorption of the absorber in 280nm～2500nm band is 96.58%,the solar absorption efficiency is 96.14%,which can efficiently absorb sunlight.The energy emissivity is 6.27%at 300K operating temperature and the solar-thermal conversion efficiency is 95.23%when solar concentrating coefficient is 1.When the solar concentrating coefficient is 200,the solar-thermal absorption efficiency of the absorber exceeds 90%at 600℃,indicating that the structure has strong environmental adaptability.When TE and TM polarized waves incident on the surface of the structure vary from 0° to 60°,the solar absorption efficiency of the absorber can be maintained above 90%,indicating that the structure is independent of incident and polarization angle.2、A frustum structure solar absorber is designed.The absorber’s average absorption of TM or TE polarized waves with incident angle of 0～60° is more than 94%at 280nm～2500nm,which has insensitivity to incident and polarization angle.When the incident light is vertically incident on the surface of the structure,the average absorption of the absorber is as high as 99.15%in 280nm～2500nm band,while the absorption of the incident light over 4000nm is less than 10%,showing excellent spectral selectivity.At temperature of 300K,the solar absorption efficiency,energy emissivity and solar-thermal conversion rate of the absorber are 99.14%,3.93%and 98.57%respectively when the solar concentrating coefficient is 1.When the concentrating coefficient is 200,the solar-thermal conversion efficiency of the absorber is still more than 80%at 900℃,indicating that the structure can maintain high absorption performance in different environments.3、A solar absorber with anti-reflective film covering and insulator filled nano-square ring structure is designed.The solar energy absorption efficiency of the solar absorber is 95.75%,and the average absorption is 95.69%in 280nm～2500nm band.When the operating temperature is 300K and the solar concentrating coefficient is 1,the solar-thermal conversion efficiency of the absorber is 94.76%.When the solar concentrating coefficient is 200,the solar-thermal conversion efficiency of the absorber is more than 80%at temperature of 800℃.When the incident light is TE and TM polarized wave and the incident angle varies from 0° to 60°,the solar absorption efficiency of the structure can remain above 95.46%and 93.79%,respectively,showing insensitivity to polarization and incident angle.