Elsevier

Energy

Volume 174, 1 May 2019, Pages 932-937
Energy

Replacing commercial thermoelectric generators with a novel electrochemical device in low-grade heat applications

https://doi.org/10.1016/j.energy.2019.02.122Get rights and content

Highlights

  • Presenting a novel replacement for commercial thermoelectric generators.

  • Proposed electrochemical device efficiently converts low-grade heat into electricity.

  • Constructing the proposed device & providing relevant experimental verifications.

  • Output power of the device is extremely more than that of thermoelectric generators.

  • Output current of the device is extremely more than that of thermoelectric generators.

Abstract

A thermoelectric generator (TEG) is a solid-state electronic device. The main defect of a commercial TEG, which makes it useless for most of practical applications such as solar energy harvesting, is its very low power production when the difference of temperature between its two surfaces ranges below 50 °C. The traditional solution is to add some relatively expensive devices such as concentrator, evaporator, condenser and cooling system to TEGs that there is often no technical and economical justification for it. This study provides a new solution by presenting a novel electrochemical device operating based on the thermally regenerative electrochemical cycle (TREC). The proposed device is first analyzed in detail to provide theoretical concepts. A prototype of the device has been constructed, and experimental verifications are given that substantiate the capability of the device in precisely mapping temperature difference between its two cells to its output electric power. A comparison between the proposed electrochemical device and a commercial TEG module TEG1-1263-4.3 is also performed that demonstrates the power production of the electrochemical device is extremely more than that of a commercial TEG module, in particular, in the temperature difference range of 0–50 °C. For instance, 54.5 W of electric power is produced by the device at the temperature difference of 50 °C, while it is only 0.3 W for a TEG module TEG1-1263-4.3. This point explicitly verifies the superiority of the proposed electrochemical device in low-grade heat harvesting. The novelty and originality of this study can be summarized as follows. First, presenting and constructing a novel electrochemical device operating based on the TREC with the size and weight of, respectively, 50×30×32 cm3 and 3.1 kg that makes it portable and suitable for industrial applications. Second, the power production of the constructed electrochemical device is extremely greater than that of TEG modules that considering size, weight and portability is the only alternative technology in low-grade heat harvesting applications. Third, this work presents an electrochemical device which is an industrial TREC based system applicable to industrial applications that is clearly different from small-scale TREC cells reported in the literature, which are only applicable to small-scale experimental applications.

Introduction

A TEG converts heat into electricity, it is a solid-state electronic device without any mechanical moving element [1]. The primary concept of a TEG was firstly introduced by Thomas Johan Seebeck in 1821 [2]. Some applications of TEGs in different areas of engineering such as geothermal energy [3], biomass [4], automotive industry [5] and solar collectors [6] have been reported in the literature. A TEG is composed of two surfaces, a hot-side surface and a cold-side surface. A TEG maps the difference of temperature between its two surfaces to its output electric power. To produce electricity by a TEG, it is necessary to establish a reasonable temperature difference between the two surfaces [7]. As a consequence, for low-grade heat harvesting applications where temperature difference ranges below 50 °C, TEGs cannot be used alone. In this regard, some relatively expensive devices such as concentrators and heat pipes should be also utilized [8]. For instance, to harvest solar energy, different methods which all require peripheral devices can be achieved [[9], [10], [11]]. There are two methods to feed solar heat to the hot-side surface of a TEG; direct method [12] and indirect method [13,14]. In direct method, lens (fresnel) and/or concentrators are required for solar heat feeding [15,16], while in indirect method, heat pipe systems positioned in vacuum glass tubes or the waste heat of PV modules are usually utilized to heat the hot-side surface [[17], [18], [19], [20], [21]]. The TREC is an electrochemical cycle composed of four steps, in which an amount of electric energy is released in the fourth step [22]. Two similar small scale low-power membrane-free and charging-free TREC cells with an efficiency of less than 3.5% were designed and reported in Refs. [23,24]. Some other researches have been carried out to optimize the physical factors of a TREC cell [25].

As mentioned the main defect of a TEG that makes it useless for low-grade heat harvesting is its very low output power. For these types of applications, some extra devices are also required that there is often no technical and economical justification for utilizing them. In this study, utilizing a proposed novel electrochemical device operating based on the TREC is suggested for low-grade heat harvesting applications instead of TEGs. The proposed electrochemical device is theoretically analyzed, and experimental results obtained from the operation of a prototype of the device constructed in this study are presented. The device is also compared to a commercial TEG module TEG1-1263-4 that verifies the superiority of the proposed electrochemical device in low-grade heat harvesting. TEG technology is concisely introduced in Section 2. The proposed electrochemical device is theoretically analyzed in detail in Section 3. The details of the constructed electrochemical device along with experimental results are presented in Section 4, and the paper is concluded in Section 5.

Section snippets

Thermoelectric generators

A TEG is a solid-state electronic device composed of a p-type semiconductor and an n-type semiconductor, one side of the two semiconductors forms the hot-side surface of the TEG, while the other side of them forms the cold-side surface. The open-circuit voltage (Voc) of a TEG is proportional to difference between the temperatures of the two surfaces, and is expressed as:Voc=αT(ThotTcold)where αT is called “Seebeck coefficient”, and Thot and Tcold are the temperatures of the hot-side and

Proposed electrochemical device: theoretical analysis

A TREC cell basically includes a positive electrode and a negative electrode which are separated by an anion membrane. The TREC consists of four processes: heating up, charging, cooling down and discharging as shown in Fig. 3. There is a difference between two voltages charged in the two electrodes during the charging process, so electric power is produced by the TREC cell in the discharging process. The positive electrode is made of solid CuHCF immersed in 6 M NaNO3 aqueous solution, while the

Proposed electrochemical device: construction and experimental results

A prototype of the proposed electrochemical device has been constructed. The dimensions and weight of the built device are, respectively, 50×30×32 cm3 and 3.1 kg that makes it portable, and so, suitable for industrial applications. The photo of the constructed electrochemical device attached on the back of an opaque glass to harvest solar heat is depicted in Fig. 6. The opaque glass was exposed to the sun rays to harvest solar energy as a low-grade heat harvesting application, and the electric

Conclusion

In this paper, a novel electrochemical device operating based on the TREC was proposed to replace TEGs in low-grade heat harvesting applications. The device was theoretically analyzed, a prototype of the device was constructed and experimental results were presented. The comparison between the proposed electrochemical device and a commercial TEG module TEG1-1263-4.3 demonstrated that the output power and current of the electrochemical device is extremely more than that of a commercial TEG

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