A review on micro combustion powered thermoelectric generator: History, state-of-the-art and challenges to commercialization

The frequent appearance of intense and abrupt weather episodes, geological disasters, and geopolitical instabilities pose challenges to the provision of distributed backup power sources. Such a situation has become even more severe, because the energy system is shifting towards decentralized energy production. Thermoelectric generator (TEG) as a solid-state energy conversion technology with captivating prospects has gained substantial attention due to its inborn nature of miniaturization, structure simplicity, little maintenance, and high energy density. TEG, integrated with fuel oxidation (biomass, hydrogen, and hydrocarbon combustion), becomes a potential distributed backup power source. Although the first concept of combustion powered TEG (CPTEG) was proposed for the first time in the 1950s, subsequent investigations proceeded very slowly, gaining attention again approximately 46 years later in 1996. Indeed, the reality that people increasingly rely on electricity in a society full of chaotic weather and geopolitical instabilities attracts many researchers to discover the TEG's potential. This has brought a growing number of studies on CPTEG and spectacularly increased expectations towards commercialization. This paper provides a detailed research roadmap by categorizing the papers published on CPTEG, showcasing the state-of-the-art, and revealing several important challenges before successful commercialization. Comprehensive discussions and analysis show that there are four interrelated, interactive, and restricted aspects that cause dense fogs of ongoing research and possible commercialization. The abovementioned aspects include combustion organization-capacity-noise, thermal collection-distributionrejection, mechanical design-processing-cost, and electrical conditioning-management-robustness. At present, CPTEGs fueled with hydrogen or hydrocarbon are approaching the upper power generation efficiency, and advanced TE materials must be introduced to furtherly augment the performance. Besides, standalone operation and low noise level are two other aspects that gain less attention and must be solved before commercialization. On the other hand, CPTEGs fueled with biomass are still far from optimal ones, and combustion stability and efficient heat collection are two major technical obstacles.