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

Rahman, Ehsanur; Nojeh, Alireza

doi:10.1016/j.energy.2020.117947

Cited by 25 publications

(3 citation statements)

References 31 publications

(37 reference statements)

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“…This second stage can be a thermoelectric, thermophotovoltaic or any other type of heat engine. With such hybrid operation, the conversion efficiency can be comparable to the multijunction and CPV performance and can exceed the Shockley-Queisser limit 38 . This hybrid generation capability is an additional advantage of thermionic and PETE devices due to their high temperature operation.…”

Section: Resultsmentioning

confidence: 99%

Semiconductor thermionics for next generation solar cells: photon enhanced or pure thermionic?

Rahman

Nojeh

2021

Nat Commun

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Semiconductors have been used in solar energy conversion for decades based on the photovoltaic effect. An important challenge of photovoltaics is the undesired heat generated within the device. An alternative approach is thermionics, which uses the thermal excitation of electrons from an emitter to a collector across a vacuum gap. If the emitter is a p-type semiconductor, the photogeneration-induced quasi-Fermi level splitting can reduce the effective barrier for electron emission—a mechanism used by a photon enhanced thermionic emission device. Here, we evaluate the prospects of this alternative solar conversion technology considering different semiconductor materials and thermionic device configurations. We also reveal that whether such a device operates in the photon enhanced or purely thermionic mode, depends on the complex interplay among materials properties, device physics and solar concentration level.

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Section: Resultsmentioning

confidence: 99%

Semiconductor thermionics for next generation solar cells: photon enhanced or pure thermionic?

Rahman

Nojeh

2021

Nat Commun

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“…[ 3,147,182 ] In terms of heat rejection, TECs are well‐suited to serve as topping cycles that pass heat to other thermodynamic cycles, since TEC collectors often maintain elevated temperatures (

T_{normalc} \approx 600

K). Bottoming cycles that receive heat from TECs could include thermoelectrics, [ 210,211 ] Stirling engines, [ 212 ] or steam turbines. [ 132 ] Beyond simply developing better thermionic architectures, additional research should be devoted to engineering systems that can optimally incorporate TECs.…”

Section: Challenges and Recommendationsmentioning

confidence: 99%

Progress Toward High Power Output in Thermionic Energy Converters

Campbell

Celenza

Schmitt³

et al. 2021

Advanced Science

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Thermionic energy converters are solid‐state heat engines that have the potential to produce electricity with efficiencies of over 30% and area‐specific power densities of 100 Wcm−2. Despite this prospect, no prototypes reported in the literature have achieved true efficiencies close to this target, and many of the most recent investigations report power densities on the order of mWcm−2 or less. These discrepancies stem in part from the low‐temperature (<1300 K) test conditions used to evaluate these devices, the large vacuum gap distances (25–100 µm) employed by these devices, and material challenges related to these devices' electrodes. This review will argue that, for feasible electrode work functions available today, efficient performance requires generating output power densities of >1 Wcm−2 and employing emitter temperatures of 1300 K or higher. With this result in mind, this review provides an overview of historical and current design architectures and comments on their capacity to realize the efficiency and power potential of thermionic energy converters. Also emphasized is the importance of using standardized efficiency metrics to report thermionic energy converter performance data.

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“…The performance of a thermoelectric cooler (TEC) under the influence of the Thomson effect, Joule heating, and combined radiation and convection cooling is investigated in this study. In addition, Rahman et al [8] presented a comprehensive analysis of a dual, micro-gap thermionic-thermoelectric hybrid energy converter by using a self-consistent iterative algorithm considering the energy balance condition. The maximum conversion efficiency of the TEG reached 9.52% by optimizing the system.…”

Section: Introductionmentioning

confidence: 99%

Modeling of an Integrated Thermoelectric Generation–Cooling System for Thermoelectric Cooler Waste Heat Recovery

Zhu

Kong

et al. 2020

Energies

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This paper focuses on the problem of thermoelectric cooler waste heat recovery and utilization, and proposes taking the waste heat together with the original heat source as the input heat source of the integrated thermoelectric generation–cooling system. By establishing an analytic model of this integrated thermoelectric generation–cooling system, the steady-state and transient thermal effects of this system are analyzed. The steady-state analysis results show that the thermoelectric generator’s actual heat source is about 20% larger than the intrinsic heat source. The transient analysis results prove that the current of thermoelectric power generation and the cold end temperature of the system show a nonlinear change rate with time. The cold end temperature of the system has a maximum value. Under different intrinsic heat sources, this maximum value can be reached between 1 s and 2.5 s.

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

Cited by 25 publications

References 31 publications

Semiconductor thermionics for next generation solar cells: photon enhanced or pure thermionic?

Semiconductor thermionics for next generation solar cells: photon enhanced or pure thermionic?

Progress Toward High Power Output in Thermionic Energy Converters

Modeling of an Integrated Thermoelectric Generation–Cooling System for Thermoelectric Cooler Waste Heat Recovery

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