Preliminary characterization of ST2G: Solar thermionic-thermoelectric generator for concentrating systems

Bellucci, A.; Calvani, P.; Cappelli, E.; Orlando, S.; Sciti, Diletta; Yogev, Ronen; Kribus, Abraham; Trucchi, Daniele M.

doi:10.1063/1.4922563

Cited by 23 publications

(11 citation statements)

References 8 publications

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“…The whole converter has to work under vacuum in order to (1) ensure a sufficient mean free path for emitted electrons and (2) avoid chemical‐physical degradation of active materials when operating at high temperatures. The system internal pressure has consequently to be pumped down to values <10 −5 mbar, since a drastic decrease in emitted current is observed at higher pressures . Vacuum may represent a technological complication (even though commercial vacuum technology already proposes reliable sealing materials, pumps with low power consumption, and efficient getters), but it is connected to considerable benefits, such as avoiding large thermal losses by convection and significantly extending the operating lifetime of materials.…”

Section: Concept Of Solar Thermionic‐thermoelectric Generatormentioning

confidence: 98%

Solar Thermionic‐Thermoelectric Generator (ST²G): Concept, Materials Engineering, and Prototype Demonstration

Trucchi

Bellucci

Calvani

et al. 2018

Advanced Energy Materials

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Concentrating solar technologies represent economically viable alternatives to distributed PV since the optics production cost per unit surface is far lower than that of PV cells. The reduction of the active conversion area allows for expensive multijunction cells with efficiency as high as 45% to be used in concentrating PV (CPV). [1] However, CPV is struggling commercially because high-density arrangements are prevented by issues in excess heat removal. On the other hand, concentrating solar power (CSP) technologies, [2,3] based on transfer of high-temperature thermal energy through a fluid toward thermomechanical engines, are promising for large plants characterized by thermal-to-electric efficiency around 35%, with the important capabilities of energy cogeneration and storage.The solar thermionic-thermoelectric generator (ST 2 G) explored here takes the advantages of CSP and CPV to provide an effective alternative concept for future solar technologies by combining the hightemperature operations, typical of CSP, to the compactness, scalability, reliability, and long operating lifetime of the solid-state converters, typically used in CPV systems. By combining a thermionic energy converter (TEC), operating at high but practical temperatures (<1100 °C) that can be achieved with point-focus solar concentrators and the development of low-work-function materials, with a thermoelectric energy generator (TEG) thermally connected in series, the ST 2 G technology can meet requirements of economic cost-effectiveness guaranteed by high-temperature solid-state converters. [4] The thermionic-thermoelectric solid-state technology, characterized by solar-to-electric conversion efficiency feasibly >40%, is comprehensively proposed and discussed for conversion of concentrating solar power. For the first time, the related solar generator prototype is designed and fabricated by developing advanced materials functionalized for the specific application, such as thermally resistant hafnium carbide-based radiation absorbers, surface-textured at the nanoscale to obtain a solar absorptance >90%, and chemical vapor deposition diamond films, acting as lowwork-function (2.06 eV) thermionic emitters. Commercial thermoelectric generators and encapsulation vacuum components complete the prototype. The conversion efficiency is here evaluated under outdoor concentrated sunlight, demonstrating thermionic stage output power of 130 mW at 756 °C, combined to the maximum thermoelectric output power of 290 mW. The related solar-to-electric conversion efficiency is found to be 0.4%, but, once the net thermal flux fed to the conversion stages is considered, a thermal-toelectric efficiency of 6% is revealed. Factors affecting the performance of the present prototype are analyzed and discussed, as well as a strategy to rapidly overcome limitations, in order to prepare an efficient and highly competitive solid-state conversion alternative for future concentrating solar plants.

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Section: Concept Of Solar Thermionic‐thermoelectric Generatormentioning

confidence: 98%

Solar Thermionic‐Thermoelectric Generator (ST²G): Concept, Materials Engineering, and Prototype Demonstration

Trucchi

Bellucci

Calvani

et al. 2018

Advanced Energy Materials

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“…Both thermionic (TI) and infrared photovoltaic (PV) or thermophotovoltaic (TPV) have been demonstrated to be feasible for many high temperature energy conversion applications. In particular, the research teams participating in this project have already successfully demonstrated these two separate technologies for concentrated solar applications: solar-thermionics at CNR [22] and solar-thermophotovoltaics at IES-UPM [23].…”

Section: Ultra-high Temperature Heat-to-power Conversionmentioning

confidence: 99%

AMADEUS: Next generation materials and solid state devices for ultra high temperature energy storage and conversion

Datas¹,

Cristóbal²,

Cañizo³

et al. 2018

AIP Conference Proceedings

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Starting in January 2017, AMADEUS (www.amadeus-project.eu) is the first project funded by the European Commission to research on a new generation of materials and solid state devices for ultra-high temperature energy storage and conversion. By exploring storage temperatures well beyond 1000 ºC the project aims at breaking the mark of ~ 600ºC rarely exceeded by current state of the art thermal energy storage (TES) systems. AMADEUS Project, through a collaborative research between seven European partners, aims to develop a novel concept of latent heat thermal energy storage (LHTES) systems with unprecedented high energy density. One of the main objectives of the project is to create new PCMs (phase change materials) with latent heat in the range of 1000-2000 kWh/m 3 , an order of magnitude greater than that of typical salt-based PCMs used in concentrated solar power (CSP), along with developing advanced thermal insulation, PCM casing designs, and novel solid-state heat to power conversion technologies able to operate at temperatures in the range of 1000-2000 ºC. In particular, the project will investigate Silicon-Boron alloys as PCMs and hybrid thermionic-photovoltaic (TIPV) devices for heat-to-power conversion. This paper describes the project R&D activities and the main results that have been attained during the first 6 months of work. This includes the first wettability and solubility analysis of liquid Si-B alloys, the numerical simulation of silicon phase-change and heat loss analysis through thermal insulation cover, as well as the first steps for the realization of the two main AMADEUS proof-ofconcept experiments: the TIPV converter, and the full LHTES device.

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“…3 Generally, in order to improve the thermionic device performance, the materials with a low work function ϕ must be selected for both cathode and anode. 4,5 For a TIPV device, the thermionic anode must be developed taking into consideration three specific characteristics: (1) ϕ lower than that of the thermionic cathode; (2) capability to collect the electrons thermally emitted by thermionic emitter; (3) optical transparency for the blackbody radiation from the emitter. A good strategy for this development is represented by the deposition of a functional coating on the TPV surface.…”

Section: Introductionmentioning

confidence: 99%

“…The anode has to guarantee an efficient collection of electrons and the optical transparency to the infrared (IR) radiation emitted by the cathode and absorbed by the TPV cell (made of GaAs or InGaAs) that could convert the absorbed radiation into electricity 3 . Generally, in order to improve the thermionic device performance, the materials with a low work function φ must be selected for both cathode and anode 4,5 . For a TIPV device, the thermionic anode must be developed taking into consideration three specific characteristics: (1) φ lower than that of the thermionic cathode; (2) capability to collect the electrons thermally emitted by thermionic emitter; (3) optical transparency for the blackbody radiation from the emitter.…”

Section: Introductionmentioning

confidence: 99%

Work function and negative electron affinity of ultrathin barium fluoride films

Mezzi

Bolli

Kačiulis

et al. 2020

Surface & Interface Analysis

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Thin films of barium fluorides with different thicknesses were deposited on GaAs substrate by electron beam evaporation. The aim of the work was to identify the best growth conditions for the production of coatings with a low work function suitable for the anode of hybrid thermionic‐photovoltaic (TIPV) devices. The chemical composition and work function φ of the films with different thicknesses were investigated by X‐ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). The lowest value of φ = 2.1 eV was obtained for the film with a thickness of ~2 nm. In the valence band spectra of the films at low kinetic energy, near the cutoff, a characteristic peak of negative electron affinity was present. This effect contributed to a further reduction of the film's work function.

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Preliminary characterization of ST2G: Solar thermionic-thermoelectric generator for concentrating systems

Cited by 23 publications

References 8 publications

Solar Thermionic‐Thermoelectric Generator (ST²G): Concept, Materials Engineering, and Prototype Demonstration

Solar Thermionic‐Thermoelectric Generator (ST²G): Concept, Materials Engineering, and Prototype Demonstration

AMADEUS: Next generation materials and solid state devices for ultra high temperature energy storage and conversion

Work function and negative electron affinity of ultrathin barium fluoride films

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Preliminary characterization of ST2G: Solar thermionic-thermoelectric generator for concentrating systems

Cited by 23 publications

References 8 publications

Solar Thermionic‐Thermoelectric Generator (ST2G): Concept, Materials Engineering, and Prototype Demonstration

Solar Thermionic‐Thermoelectric Generator (ST2G): Concept, Materials Engineering, and Prototype Demonstration

AMADEUS: Next generation materials and solid state devices for ultra high temperature energy storage and conversion

Work function and negative electron affinity of ultrathin barium fluoride films

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Product

Resources

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Solar Thermionic‐Thermoelectric Generator (ST²G): Concept, Materials Engineering, and Prototype Demonstration

Solar Thermionic‐Thermoelectric Generator (ST²G): Concept, Materials Engineering, and Prototype Demonstration