Hybrid and Fully Thermoelectric Solar Harvesting PDF
Preview Hybrid and Fully Thermoelectric Solar Harvesting
Springer Series in Materials Science 268 Dario Narducci · Peter Bermel Bruno Lorenzi · Ning Wang Kazuaki Yazawa Hybrid and Fully Thermoelectric Solar Harvesting Springer Series in Materials Science Volume 268 Series editors Robert Hull, Troy, USA Chennupati Jagadish, Canberra, Australia Yoshiyuki Kawazoe, Sendai, Japan Richard M. Osgood, New York, USA Jürgen Parisi, Oldenburg, Germany Udo W. Pohl, Berlin, Germany Tae-Yeon Seong, Seoul, Republic of Korea (South Korea) Shin-ichi Uchida, Tokyo, Japan Zhiming M. Wang, Chengdu, China TheSpringerSeriesinMaterialsSciencecoversthecompletespectrumofmaterials physics,includingfundamentalprinciples,physicalproperties,materialstheoryand design.Recognizingtheincreasingimportanceofmaterialsscienceinfuturedevice technologies, the book titles in this series reflect the state-of-the-art in understand- ingandcontrollingthestructureandpropertiesofallimportantclassesofmaterials. More information about this series at http://www.springer.com/series/856 Dario Narducci Peter Bermel (cid:129) Bruno Lorenzi Ning Wang (cid:129) Kazuaki Yazawa Hybrid and Fully Thermoelectric Solar Harvesting 123 DarioNarducci NingWang Department ofMaterials Science ChineseAcademy of Sciences University of Milano-Bicocca Institute of Soil andWater Conservation Milan Yangling Italy China PeterBermel Kazuaki Yazawa BirckNanotechnology Center BirckNanotechnology Center PurdueUniversity PurdueUniversity West Lafayette, IN West Lafayette, IN USA USA BrunoLorenzi University of Milano-Bicocca Milan Italy ISSN 0933-033X ISSN 2196-2812 (electronic) SpringerSeries inMaterials Science ISBN978-3-319-76426-9 ISBN978-3-319-76427-6 (eBook) https://doi.org/10.1007/978-3-319-76427-6 LibraryofCongressControlNumber:2018935848 ©SpringerInternationalPublishingAG,partofSpringerNature2018 Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpart of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission orinformationstorageandretrieval,electronicadaptation,computersoftware,orbysimilarordissimilar methodologynowknownorhereafterdeveloped. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publicationdoesnotimply,evenintheabsenceofaspecificstatement,thatsuchnamesareexemptfrom therelevantprotectivelawsandregulationsandthereforefreeforgeneraluse. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authorsortheeditorsgiveawarranty,expressorimplied,withrespecttothematerialcontainedhereinor for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictionalclaimsinpublishedmapsandinstitutionalaffiliations. Printedonacid-freepaper ThisSpringerimprintispublishedbytheregisteredcompanySpringerInternationalPublishingAG partofSpringerNature Theregisteredcompanyaddressis:Gewerbestrasse11,6330Cham,Switzerland Preface Thermoelectricity is, on many counts, a solution in search of a problem. Thermoelectricity as a physical phenomenon was discovered in the nineteenth century, and its very first application was provided by Peltier who built a portable cooler just a few years after the discovery of the thermoelectric effect that was named after him. Applications of the Seebeck effect to convert heat into electric power began instead over the first part of the twentieth century, especially in the SovietUnion,butfoundamajoropportunitywithdeep-spaceexploration,wherever sunlight is too weak for solar panels to power spacecrafts. Plutonium oxide radioactive decay was used in Radioisotope Thermoelectric Generators (RTGs) by NASA in many missions including Apollo (along with photovoltaic panels), Pioneer, Viking, Voyager, Galileo, and Cassini—and, quite recently, to power the Curiosity rover on Mars. Although inefficient, RTGs were preferred over alternate technological solutions because of their remarkable reliability and lifetime due to the absence of moving parts. For terrestrial applications, instead, thermoelectric converters still struggle to find their path. As known, efficiency progress of thermoelectric materials and generators have been delayed by the need of separately controlling electron and phonon transport in solids, keeping phonon mean free paths as small as possible while increasing the corresponding quantity for charge carriers—a result partly achieved just over the last decade by the introduction of nanotechnology. Despite their limited efficiency, also for non-space applications, thermoelectric generators have been considered to harvest heat when lack of moving parts and small sizes were at a premium. Deployment of thermoelectric generators to recover heat from car mufflers prompted quite a bit of basic and applied research, stimulating the searchfornovellow-cost,geo-abundantmaterials.Theautomotiveindustry,which waslookingforwaystocontainCO emissionsinthewakeoftheParisAgreement, 2 reported, however, severe problems concerning the economic sustainability of thermoelectric converters. Although paying back their cost over the average car lifetime, they required an extra capital cost for customers that made thermoelectric harvesters a viable solution only for the high-end automotive segment. Furthermore,thevolatilityoftheenvironmentalpolicies(bothinEuropeandinthe v vi Preface USA) along with the advancements (achieved and/or announced) in the making of electric cars turned out to cool down the initial enthusiasm toward thermoelectric harvesters. Thermoelectric generators (either miniaturized or fully integrated) are also consideredaninterestingsupportingtechnologyfortheso-calledInternetofThings (IoT), namely networks of interconnected, distributed devices embedding elec- tronics, software, sensors, and actuators. Although IoT devices are not necessarily wireless, physical autonomy is a key aspect of a large subset of such networks. Thus, unplugged devices would ideally pair with their being wireless as of data exchanges. Batteries may be once again a viable and ready solution. However, especially when device maintenance isinconvenient orimpossible, harvesters may either complement or replace batteries, targeting the making of deploy-and-forget network nodes. Development of suitable thermoelectric harvesters has advanced overthelastyears.Inthiscase,economicalaspectsarearathermarginallimitation, thehurdletobeovercomebeingessentiallythatofthepowerdensityavailableover small (sometimes very small) temperature differences. Body heat harvesters are a good example of this issue. If the IoT might provide a good driver to move thermoelectric generators from niche to bulk application for microharvesting (i.e., power outputs in the order of somemilliwatts),useofthermoelectricitytocomplementthedominatingrenewable energysource,i.e.,photovoltaics,mightplayasimilarroleformacroharvesting.In 1954, when Mária Telkes published her pioneering work on thermoelectric sun power converters, the efficiency of thermoelectric generators (3–4%) was compa- rable to that of the first photovoltaic cells (4–6%). As known, in the following years, efficiency of photovoltaics skyrocketed to two-digit figures, while thermo- electrics could not break the 10–% efficiency threshold till relatively recent times, thereforeleavingtheraceforsolarharvesting.Itcouldre-enteritnow,however,as a partner more than as a competitor. Currently, the photovoltaic market is domi- nated by silicon panels, with efficiencies now leveled off to about 20%. Use of multiple junctions, capable of efficiencies already exceeding 40% is limited by capitalcosts.Also,powercosts,albeitheavilydopedbytaxationandincentivesby publicauthorities,havealsoreachedaplateausincemorethan5years.Thisimplies that,unlessradicallynewfabricationtechnologiesareconceived,capitalandpower costsfor silicon-based photovoltaics maynotbeexpectedtodecreasesubstantially over the next decades. Novel photovoltaic materials have surfaced, instead, cur- rently with lower efficiencies but also with promising lower costs, should they be fully promoted to production. Perovskites are only the most recent example. Differently from silicon, such materials would take significant advantages from being paired to a thermoelectric stage, remarkably increasing the total electric power output of the solar harvester. Furthermore, preliminary economic estimates show that their power costs, payback periods, and capital investments per electric watt would be sustainable. It is therefore not surprising that both fundamental and applied research on hybrid (photovoltaic–thermoelectric) solar harvesters have lately gained a great momentum.Thenumberofpaperscoveringthistopichasincreased,exceeding500 Preface vii articles published in the year 2017 (Data source: Scopus). With a publication rate still increasing linearly at the noteworthy rate of 46 papers/year2 since 2006, the fieldisclearlystillunderacceleratedexpansion.Thisisoneofthemainmotivations behind this book—namely providing a self-consistent yet thorough and in-depth introductiontohybridharvesterstothenewcomers.Thisbookisprimarilythought asaprimertoexperiencedscientistswillingtoenterthislivelyfieldofresearch.Itis meant both for scientistsworking onthermoelectrics andwilling tocatch thebasic physicsofphotovoltaics;andforprofessionalsworkingonphotovoltaicscienceand technologywhoarecurioustoconsidertheapplicationofthermoelectricharvesters to enhance the total efficiency of solar converters. Therefore, further to core chaptersonfullandhybridthermoelectricsolarharvesters,introductorychapterson thermoelectricity and photovoltaics are provided. This turns out to make the book also suitable for Ph.D. students and post-docs, who will use the first chapters to haveanintroductiontobothharvestersbeforemovingtotheirjoinedapplicationsto solar converters. But we also hope that this book may be of some interest to entrepreneurs and public decision-makers looking for an insight into the opportu- nities (and the limits, too) of hybrid solar harvesters. Although all authors of this book are actively engaged in this research field, we did our very best to uncover also what hybridization cannot afford to do. However, as will be shown, premises look as good as promises for this technology, and it seems fair to suggest more attention to the opportunities it might deliver in the short- and mid-terms. Taking a picture of a quickly moving subject is not simple at all, and some blurring is unavoidable. This book is no exception, and it inescapably reflects the viewsandthesentimentsofitsauthors.Wearefullyawarethatwecouldnotcatch all possible approaches to modern hybrid solar harvesters. We then apologize for any promising approach we did not mention or that we insufficiently covered. We did not aim at being exhaustive in a field showing such a rapid growth simply because a catalog of ideas, hints, and strategies would have suffered a too rapid obsolescence, becoming outdated over the time needed just to publish it. Our aim wasinsteadtowriteaself-contained,agileintroductiontothetopic,whichwasyet missing—as an invitation to senior and junior colleagues to join the effort. This said, any suggestion, criticism, and comment from readers on how to update and completeourpicturewillbehighlyappreciated,andmightbeusedforforthcoming editions of this book. Milan, Italy Dario Narducci West Lafayette, USA Peter Bermel Cambridge, USA Bruno Lorenzi Yangling, China Ning Wang West Lafayette, USA Kazuaki Yazawa Acknowledgements Bruno Lorenzi has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No. 745304. ix Contents 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1 Solar Harvesting: Photovoltaics and Beyond . . . . . . . . . . . . . . . . 1 1.1.1 The Emergence of Renewable Energy Sources . . . . . . . . . 1 1.1.2 Photovoltaics: A Technological Success History . . . . . . . . 3 1.2 Aims of This Book. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2 A Primer on Thermoelectric Generators. . . . . . . . . . . . . . . . . . . . . . 11 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 2.2 Fundamentals of Thermodynamics of Thermoelectricity . . . . . . . . 12 2.2.1 Thermoelectricity in Linear Thermodynamics . . . . . . . . . . 12 2.2.2 Thomson Effect. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 2.3 Thermoelectric Efficiency in the Constant-Property Limit . . . . . . . 17 2.3.1 Dirichlet Boundary Conditions . . . . . . . . . . . . . . . . . . . . . 18 2.3.2 Neumann Boundary Conditions . . . . . . . . . . . . . . . . . . . . 25 2.4 Thermoelectric Efficiency in the Presence of Large Temperature Differences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 2.4.1 Thermoelectric Potential. . . . . . . . . . . . . . . . . . . . . . . . . . 32 2.4.2 Comparison to CPL Efficiency . . . . . . . . . . . . . . . . . . . . . 33 2.4.3 Compatibility and Efficiency . . . . . . . . . . . . . . . . . . . . . . 33 2.4.4 Engineering Figure of Merit. . . . . . . . . . . . . . . . . . . . . . . 34 2.5 Finite–Rate Thermoelectric Efficiency . . . . . . . . . . . . . . . . . . . . . 36 2.5.1 Efficiency of Finite–Rate Thermal Engines . . . . . . . . . . . . 36 2.5.2 Application to Thermoelectric Generators . . . . . . . . . . . . . 39 2.6 Thermoelectric Efficiency Under Non-steady State Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 2.7 Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42 xi
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