• Energy Research

Although lithium-ion batteries have gained considerable popularity in renewable energy and electric vehicle applications, their safety still remains a concern under certain voltage, temperature, or state of charge conditions. This can lead to degradation and potential thermal runaway. In order to improve the safety assessment of LIBs based on their operating conditions, it is therefore essential to analyze not only their safe operating area but also their abuse region. This study focuses on the characterization of the abuse region of lithium-ion batteries by proposing a new methodology in which four areas of abuse are identified and experimentally validated using a commercial 3.6 Ah pouch cell. The cell is subjected to overtemperature and overcharge conditions, exploring various states of charge (0 to 200%) and ambient temperatures (25 to 100 °C). The influence of temperature and state of charge on the battery's behavior is thoroughly analyzed to fully characterize the abuse region. Results reveal the limiting temperatures and states of charge that define the boundaries of the abuse areas. By extending the characterization of LIBs behavior beyond the safe operation area with the determination of four areas of abuse, this article contributes to a better understanding of the phenomena and abuse mechanisms produced by overtemperature and overcharge events with an eye to improving battery safety. This work is part of the projects PID2019-111262RB-I00, funded by MCIN/AEI/10.13039/501100011033/, TED2021-132457B-I00, funded by MCIN/AEI/10.13039/501100011033/ and by the European Union “NextGenerationEU/PRTR”, STARDUST, funded by European Union’s Horizon 2020 research and innovation program, HYBPLANT, Spain (0011-1411-2022-000039), funded by Government of Navarre, Spain, and a Ph.D. scholarship (PRE2020-095314), funded by Spanish Ministry of Science and Innovation. Open access funding provided by Universidad Pública de Navarra, Spain.

The energy transition towards renewables must be accelerated to achieve climate targets. To do so, renewable power plants, such as wind power plants (WPPs) must replace conventional power plants (CPPs). Transmission System Operators require this replacement to be made without weakening the frequency response of power systems, so it must be ensured that WPPs match the response of CPPs to grid frequency variations. CPPs consist of grid-tied synchronous generators that inherently react to frequency variations by modifying their stored kinetic energy and their output power, thereby contributing to grid stability. Such response is known as inertial response. By contrast, wind turbines (WTs) are mostly based on either doubly-fed induction generators (DFIG) or permanent magnet synchronous generators (PMSG). Their power electronics interface decouples the electromechanical behavior of the generator from the power grid, leading to a negligible inertial response. Therefore, in order to replace CPPs with WPPs, WTs must be able to react to frequency variations by changing their output power, i.e., emulating an inertial response. Currently implemented inertia emulation strategies in WTs rely on pitch control and stored kinetic energy variation. This paper proposes an alternative strategy, using the energy stored in a supercapacitor directly connected to the back-to-back converter DC link to emulate inertia. Its performance is validated by means of simulation for both DFIG and PMSG. Compared to state-of-the-art techniques, it allows a more accurate emulation of grid-tied synchronous generators, favoring the replacement of these generators by WTs. This work was supported in part by Siemens Gamesa Renewable Energy, in part by the Spanish State Research Agency, AEI/10.13039/501100011033 under Grants PID2019- 111262RB-I00 and PID2019-110956RB-I00, and in part by the Government of Navarre under Grant 0011-1411-2022-000049 through EnVeNA Project.

Nowadays, the reuse of electric vehicle batteries is considered to be a feasible alternative to recycling, as it allows them to benefit from their remaining energy capacity and to enlarge their lifetime. Stationary applications, such as self-consumption or off-grid systems support, are examples of second-life (SL) uses for retired batteries. However, reused modules that compose these batteries have heterogeneous properties, which limit their performance. This article aims to assess the influence of degradation in modules from electric vehicles, covering three main aspects: performance, capacity dispersion, and extended SL behavior. First, a complete characterization of new and reused modules is carried out, considering three temperatures and three discharge rates. In the second stage, intra- and intermodule capacity dispersions are evaluated with new and reused samples. Finally, the behavior during SL is also analyzed, through an accelerated cycling test so that the evolution of capacity and dispersion are assessed. Experimental results show that the performance of reused modules is especially undermined at low temperatures and high current rates, as well as in advanced stages of aging. The intramodule dispersion is found to be similar in reused and new samples, while the intermodule differences are nearly four times greater in SL. This work was supported in part by the Spanish State Research Agency (AEI) under Grant PID2019-111262RB-I00/AEI/10.13039/501100011033 and Grant DPI2016-80641-R, in part by the European Union under the H2020 Project STARDUST under Grant 774094, in part by the Government of Navarra under Research Project 0011-1411-2018-000029 GERA, and in part by the Public University of Navarre under Project ReBMS PJUPNA1904.

Lithium-ion batteries are gaining importance for a variety of applications due to their price decrease and characteristics improvement. For a proper use of such storage systems, an energy management algorithm (EMA) is required. A number of EMAs, with various characteristics, have been published recently, given the diverse nature of battery problems. The EMA of deterministic battery problems is usually based on an optimization algorithm. The selection of such an algorithm depends on a few problem characteristics, which need to be identified and closely analyzed. The aim of this article is to identify the critical optimization problem parameters that determine the most suitable EMA for a Li-ion battery. With this purpose, the starting point is a detailed model of a Li-ion battery. Three EMAs based on the algorithms used to face deterministic problems, namely dynamic, linear, and quadratic programming, are designed to optimize the energy dispatch of such a battery. Using real irradiation and power price data, the results of these EMAs are compared for various case studies. Given that none of the EMAs achieves the best results for all analyzed cases, the problem parameters that determine the most suitable algorithm are identified to be four, i.e., desired computation intensity, characteristics of the battery aging model, battery energy and power capabilities, and the number of optimization variables, which are determined by the number of energy storage systems, the length of the optimization problem, and the desired time step. This work was supported in part by the European Union under the H2020 Project STARDUST under Grant 774094, in part by the Spanish State Research Agency and FEDER-UE under Grants DPI2016-80641-R, DPI2016-80642-R, PID2019-111262RB-I00, and PID2019-110956RB-I00, in part by the Government of Navarra through Research Project 0011-1411-2018-000029 GERA, and in part by the Public University of Navarre under Project ReBMS PJUPNA1904.

Reducing carbon emissions is essential to stop climate change. The grid-share of renewable generation plants is increasing, being wind and photovoltaic plants the most common ones, whereas conventional plants are the only ones that provide the necessary services to maintain the grid stability and keep the generation-demand balance. However, with the aim of achieving carbon-neutral generation, conventional plants are being dismantled. This leads to the imminent need of providing these services with renewable plants. Due to this challenge, this proposal analyses a hybrid plant composed by wind and photovoltaic generation with two types of storage, lithium-ion batteries and a thermal storage system based on volcanic stones. In order to compare both strategies, a technoeconomic methodology is explained that allows to optimally size the plant, using the current prices of each technology. The most cost-competitive proposal turns to be the hybrid plant with thermal storage, composed by 623.9 MW installed power and 21.9 GWh of storage, which could replace a 100 MW, 24/7 conventional power plant, with an LCOHS (levelized cost of hybrid system) of 118.38 €/MWh, providing identical grid services and an equivalent inertia in a way committed with the environment. This is in turn a zero-carbon emissions solution perfectly matched to a second life plan for a conventional power plant. This work has been supported by Siemens Gamesa Renewable Energy, by the Spanish State Research Agency (AEI/ 10.13039/501100011033) under grants PID2019-111262RB-I00 and PID2019-110956RB-I00, and by the Public University of Navarra under project ReBMS PJUPNA1904.

Energy storage systems are playing an increasingly important role in a variety of applications, such as electric vehicles or grid-connected systems. In this context, supercapacitors (SCs) are gaining ground due to their high power density, good performance and long maintenance-free lifetime. For this reason, SCs are a hot research topic, and several papers are being published on material engineering, performance characterization, modelling and post-mortem analysis. A compilation of the most important millstones on this topic is essential to keep researchers on related fields updated about new potentials of this technology. This review paper covers recent research aspects and applications of SCs, highlighting the relationship between material properties and electrical characteristics. It begins with an explanation of the energy storage mechanisms and materials used by SCs. Based on these materials, the SCs are classified, their key features are summarised, and their electrochemical characteristics are related to electrical performance. Given the high interest in system modelling and the large number of papers published on this topic, modelling techniques are classified, explained and compared, addressing their strengths and weaknesses, and the experimental techniques used to measure the modelled properties are described. Finally, the market sectors in which SCs are successfully used, as well as their growth expectations are analysed. The analysis presented herein gives account of the expansion that SC market is currently undergoing and identifies the most promising research trends on this field. This work was supported in part by the Spanish State Research Agency (AEI) and FEDER UE under Grant DPI2016-80641-R and Grant DPI2016-80642-R, in part by the Government of Navarre through the Research Project PI020 RENEWABLE-STORAGE, and in part by the FPU Program of the Spanish Ministry of Education, Culture and Sport under Grant FPU13 /00542.

This paper presents a non-invasive technical analysis of the degra-dation of four lithium-ion batteries (LIBs) used in extreme frigid weather. In contrast to other studies in which the batteries were tested in laboratory conditions, the LIBs studied in this paper were aged in a real application, more specifically in the WindSled project. In this project, an expedition was made using a zero-emission vehicle drawn by kites, covering more than 2500 kilometers on the East Antarctic Plateau. The study performed in this paper aims to quantify the degradation of the LIBs during the expedition. The results show a 5 % capacity fade, a 30 % increase in the internal resistance and no substantial increase in the impedance of the solid electrolyte interface (SEI). Moreover, no evidence of dendrite growth at the anode is inferred by the interpretation of the distri-bution of relaxation times (DRT), incremental capacity analysis (ICA) and differential voltage analysis (DV). Based on these re-sults, it can be claimed that the LIBs used in the WindSled Project can successfully operate under 50 C. Furthermore, since non-invasive techniques were used to characterize the batteries, they can still be used in upcoming expeditions, with subsequent financial and environmental benefits. This work was supported in part by the Spanish State Research Agency (AEI) under Grant PID2019-111262RB-I00/AEI/10.13039/501100011033, in part by the European Union under the H2020 Project STARDUST under Grant 774094, and in part by the Public University of Navarre through the research project ReBMS PJUPNA1904 and a Ph.D. Scholarship.