A review of high-temperature selective absorbing coatings for solar thermal applications

Xu, Ke; Du, Mingliang; Lei, Hao; Mi, Jin‐Xiao; Yu, Qinghe; Li, Shijie

doi:10.1016/j.jmat.2019.12.012

Cited by 133 publications

(73 citation statements)

References 167 publications

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“…Another approach is to deliver the concentrated solar power directly to the converter by using a selective absorber. (A selective absorber is a material with carefully-designed spectral emissivity (or absorptivity) [20][21][22][23]). We emphasize that our model will be equally valid for other types of heat source, too.…”

Section: Energy Balance Efficiency and The Self-consistent Iterativmentioning

confidence: 99%

Harvesting solar thermal energy with a micro-gap thermionic-thermoelectric hybrid energy converter: Model development, energy exchange analysis, and performance optimization

Rahman

Nojeh

2020

Energy

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We present a comprehensive analysis of a dual, micro-gap thermionic-thermoelectric hybrid energy converter by developing a detailed theoretical model of the system. The Space-charge and near-field effects in thermionic conversion and the temperature-dependent effects in thermoelectric conversion are considered while studying the energy flow through the cascade system. The temperatures and energy exchange channels in the different parts of the system are quantified with a self-consistent iterative algorithm considering the energy balance condition. The model is deployed to simulate the hybrid system performance when energized by a constant heat flux source which could, for example, be concentrated solar irradiance. The effect of solar radiation intensity on the combined system efficiency, and the dependence of the thermoelectric generator performance on the waste heat released from the thermionic top stage, are illustrated with several examples. Based on these analyses, a performance optimization of the hybrid system is carried out. The findings presented in this work offer

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Section: Energy Balance Efficiency and The Self-consistent Iterativmentioning

confidence: 99%

Harvesting solar thermal energy with a micro-gap thermionic-thermoelectric hybrid energy converter: Model development, energy exchange analysis, and performance optimization

Rahman

Nojeh

2020

Energy

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“…To realize an SSA with an emissivity curve close to the ideal one, different designs have been analyzed by several authors in the past years [13,14]: nanomultilayer [15], ceramic and metal structures (known as cermet) [11], multilayers [16][17][18], photonic designs [19], structured graphene metamaterial [20], multi-layered cermets [10]. However, a very sharp transition was never obtained and recently Yang et al [21] studied the effect of non-ideal SSA properties on the overall performances in a Concentrated Solar Power (CSP) system: their simulated SSA has a finite constant slope in the cut-off transition (instead of the ideal step function) and a not ideal SSA emissivity.…”

Section: Introductionmentioning

confidence: 99%

Efficiency of Selective Solar Absorber in High Vacuum Flat Solar Thermal Panels: The Role of Emissivity

Maio¹,

D’Alessandro²,

Caldarelli³

et al. 2020

Preprint

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This study refers to the optimization of a Selective Solar Absorber to improve the Sun-to-thermal conversion efficiency at mid temperatures in high vacuum flat thermal collectors. Efficiency has been evaluated by using analytical formula and a numerical thermal model. Both results have been experimentally validated using a commercial absorber in a custom experimental set-up. The optimization procedure aimed at obtaining Selective Solar Absorber is presented and discussed in the case of a metal dielectric multilayer based on Cr2O3 and Ti. The importance of adopting a real spectral emissivity curve to estimate high thermal efficiency at high temperatures in selective solar absorber is outlined. Optimized absorber multilayers can be 8% more efficient than the commercial alternative at 250 °C operating temperatures and up to 27% more efficient at 300 °C. Once the multilayer has been optimized the choice of a very low emissivity substrate such as copper allows to further improve efficiency and to reach stagnation temperature higher than 400 °C without Sun concentration.

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“…The core component in a solar thermal collector is the Selective Solar Absorber (SSA). The idea was first introduced at the end of '50, and since then, several works have been devoted to study and to optimize SSA [9][10][11][12][13][14][15][16][17][18][19][20][21][22]. The ideal SSA should efficiently absorb solar radiation (solar absorptance α=1), whereas its thermal emission should be minimal (emissivity =0).…”

Section: Introductionmentioning

confidence: 99%

“…The ideal SSA should efficiently absorb solar radiation (solar absorptance α=1), whereas its thermal emission should be minimal (emissivity =0). Its spectral emissivity is assumed to be a step function from 1 to 0 [11,23,24] and the wavelength where the transition happens is commonly named cut-off wavelength (λ cut-off ) [23,24]. The formal definition of λ cut-off leads to energetic considerations: it is chosen in order to maximize the absorber thermal performance and it depends on the working temperature and on solar incoming power (i.e.…”

Section: Introductionmentioning

confidence: 99%

“…To design a solar selective coating, various architectures are available: they include intrinsic absorber, semiconductor-metal tandem, dielectric-metal multilayer, cermet, surface texturing, and photonic crystal. They have been periodically summarized in review papers [10,11,23,24,27,28]. Also very recent works developing new idea in SSA such as 3D structured graphene [21], multi-layered cermet [13], nanomultilayer [29] or high entropy alloy [9] use λ cut-off as defined in [10].…”

Section: Introductionmentioning

confidence: 99%

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Efficiency of Selective Solar Absorber in High Vacuum Flat Solar Thermal Panels: The Role of Emissivity and Cut-Off Wavelength

Maio¹,

D’Alessandro²,

Caldarelli³

et al. 2020

Preprint

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A multilayer structure on a metallic substrate has been optically simulated and the optimization procedure aimed at obtaining Selective Solar Absorber (SSA) is discussed. This study refers to flat high vacuum thermal collectors and the overall Sun-to-thermal conversion efficiency has been evaluated using analytical formula and numerical thermal model. Both methods are in agreement and they have been validated using experimental results on a commercial absorber. The importance of a low emittance value to obtain high thermal efficiency at high temperatures and high stagnation temperature in selective solar absorber is highlighted. Optimized absorbers can be 8% more efficient than the commercial alternative at 250 °C operating temperatures and up to 27% more efficient at 300 °C. A stagnation temperature higher than 400 °C can be reached without Sun concentration if the proper design is adopted.

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A review of high-temperature selective absorbing coatings for solar thermal applications

Cited by 133 publications

References 167 publications

Harvesting solar thermal energy with a micro-gap thermionic-thermoelectric hybrid energy converter: Model development, energy exchange analysis, and performance optimization

Harvesting solar thermal energy with a micro-gap thermionic-thermoelectric hybrid energy converter: Model development, energy exchange analysis, and performance optimization

Efficiency of Selective Solar Absorber in High Vacuum Flat Solar Thermal Panels: The Role of Emissivity

Efficiency of Selective Solar Absorber in High Vacuum Flat Solar Thermal Panels: The Role of Emissivity and Cut-Off Wavelength

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