Due to a continuous and inevitable depletion of fossil fuels, in addition to the great challenge of global warming, we nowadays witness an increasing interest towards renewable and sustainable energy sources. One of the main problems with renewables though is its intermittent and unstable nature, which determines an undesired time mismatch between its availability and demand. Energy storage is a key technology to address this issue, thus enabling a much more extensive use and exploitation of natural and green energy resources. In the introductory part of this course, we aim at providing an extensive and up-to-date overview of the disparate technology solutions, which have been developed so far (both those that are already on the market and the ones that are still under investigations) for storing energy under diverse forms. Afterwards, we will specifically focus on thermal energy storage with a special emphasis on low-temperature thermal solar energy for civil applications. More precisely, this course, through a series of theoretical lectures, discussion of case studies, numerical exercises in the labs and experimental activities aims at providing students with all necessary competencies for properly choosing the storage technology for an optimal exploitation of a given intermittent energy source. We expect students to gain the essential know-how and tools for designing, sizing and analysing (from both energy and cost perspective) the main components of storage plants.

First of all, this course aims at providing a wide overview on the different technologies so far developed for addressing the fundamental problem of energy storage, with a special focus on the most effective approaches for storing (low-temperature) heat. Thanks to a number of theoretical lectures, the student has the opportunity of learning the basic principles and notions underlying the main components utilized in the energy storage devices. Those lectures will also help students to have a coherent vision of the matter and make an aware use of design tools that are discussed during the course. In fact, we expect students to acquire the ability of a quantitative design of storage systems (mostly sensible, latent and sorption thermal energy storage). Such an ability is essential for helping student in strengthening their problem-solving attitude (a very desirable skill of engineers). All this will be pursued by: 1) Case study discussion; 2) hands-on sessions during the numerical labs; 3) experiments in the heat storage lab; 4) solution of storage problems selected in collaboration with the lecturer (not mandatory).

Basic knowledge on heat transfer, applied thermodynamics and chemistry.

The course can be sub-divided as follows: 1) Introduction and brief review of basic notions useful to the comprehension of energy storage phenomena (4.5 hours). Brief overview of the course and a short review of the main heat transfer mechanisms, heat exchangers with and without fins. Brief review of some of the most important relationships in applied thermodynamics. 2) Energy storage in general (9 hours). The importance of energy storage. Storage of mechanical energy: Compressed air and pumped hydro-storage plants. Flywheels. Electrochemical batteries. The issue of deep cycling, battery capacity and other main figure of merit of storage systems. Magnetic storage. Supercapacitors. Hydrogen production as an energy storage strategy. 3) Sensible heat storage (10.5 hours). Direct and indirect heat storage plants. Materials and plant lay-out for sensible heat storage. First and second law efficiencies. Optimal size and storage period. Sizing of small sensible systems with water as storage material for solar applications. Common storage tanks. The importance of the temperature stratification. Simple design approaches for rock-beds. Simplified energy and exergy analysis of stratified sensible heat storage. Solar ponds. Numerical examples of sensible storage systems. 4) Latent heat storage (10.5 hours). Classification of the most common materials for latent heat storage applications (organic, inorganic and eutectic). Short discussion on supercooling, segregation and cycling issues. Examples of phase-change-materials (PCM) available on the market. PCM for buildings: A brief discussion on the use of PCM for passive cooling applications. Some analytical and numerical modeling tools for PCM charging and discharging processes. The choice of the optimal PCM material. Numerical examples of latent storage systems. 5) Indirect heat storage: Physical and chemical sorption thermal energy storage - TES (10.5 hours). The notion of inversion temperature. Closed and open sorption TES. Main thermodynamic transformations and relations describing sorption phenomena. Isosteric heat and isosteric field for a sorbent-sorbate pair. Adsorption isotherms. Discussion of ideal and real sorption heat storage cycles. Simplified models for describing sorption phenomena (Dubinin-Astakhov and Langmuir). Numerical examples of sorption heat storage systems. 6) Transport phenomena in energy storage problems (3 hours). A brief discussion on micro-encapsulated phase-change materials for heat capacity enhancement. Basic notions on classical molecular dynamics simulations. Percolating networks of nano-particles with high thermal conductivity for heat storage applications.

All arguments discussed during this course will be covered by a large variety of material directly provided by the lecturer. In addition, the interested student can find below a list of References for possible further readings: - I. Dincer, M.A. Rosen, "Thermal Energy Storage Systems and Applications", John Wiley & Sons, 2nd Edition, 2011; - P. Asinari, E. Chiavazzo, "An Introduction to Multiscale Modeling with Applications", Esculapio, Bologna, 2013; - A. Bejan, "Advanced Engineering Thermodynamic", John Wiley & Sons, 1997; - A. Bejan, A.D. Kraus (Editors), "Heat Transfer Handbook", John Wiley & Sons, 2003; - Matteo Fasano, Masoud Bozorg Bigdeli, Mohammad Rasool Vaziri Sereshk, Eliodoro Chiavazzo, Pietro Asinari, "Thermal transmittance of carbon nanotube networks: Guidelines for novel thermal storage systems and polymeric material of thermal interest", Ren. Sust. Energy Rev. 41, 2015; - Chiavazzo E., Asinari P., "Reconstruction and modeling of 3D percolation networks of carbon fillers in a polymer matrix" Int. J. Thermal. Sci. 49, 2010; - Chiavazzo E., Asinari P., "Enhancing surface heat transfer by carbon nanofins: towards an alternative to nanofluids?" Nanosc. Res. Lett. 6, 2011.

Modalità di esame: Prova orale obbligatoria; Elaborato scritto individuale; Progetto individuale;

Exam: Compulsory oral exam; Individual essay; Individual project;

... For all students, the examination consists in an oral test on the course topics including a discussion of a brief individual report carried out during the semester on one of the numerical labs. The examination takes about forty-five minutes and it is not allowed to use any educational materials for giving answers (in written form). Only those students who optionally carry out the individual project may possibly get an extra-bonus (in addition to the final mark) of max 2 points. The bonus is variable depending on the project quality and discussion during the examination. To pass the exam it is necessary to obtain an overall score greater than or equal to 18/30. Those who choose to be examined only on the basis of the oral test and the brief report on the numerical laboratories will be able to reach a maximum score of 29/30. Students who also carry out the optional project report can reach the maximum score of 30/30 (possibly cum laude). Specifically, the exam aims to assess the achievement of the following objectives: 1. Theoretical knowledge underpinning the functioning of the technologies developed for energy storage and transport. This is established through questions during the oral exam; 2. Ability to select and to perform a preliminary sizing/design of a storage technology suitable for coping with real energy storage problems. This is established either through questions from the oral exam or through the report; 3. Ability to accurately estimate the expected performance of key components for energy storage technologies (with particular emphasis on thermal energy). This is established by carrying out the report on the numerical laboratories.

Gli studenti e le studentesse con disabilità o con Disturbi Specifici di Apprendimento (DSA), oltre alla segnalazione tramite procedura informatizzata, sono invitati a comunicare anche direttamente al/la docente titolare dell'insegnamento, con un preavviso non inferiore ad una settimana dall'avvio della sessione d'esame, gli strumenti compensativi concordati con l'Unità Special Needs, al fine di permettere al/la docente la declinazione più idonea in riferimento alla specifica tipologia di esame.