• Energy Research

Abstract Liquid Air Energy Storage (LAES) is a novel energy storage system that stocks up energy by means of air liquefaction and recovers the cryogenic energy when required. The performance of LAES is actually limited both by the inefficiencies of liquefaction and discharge section leading to lower value of round trip efficiency compared to other energy storage solutions. This work investigates the thermodynamic feasibility of an integrated energy system consisting of a LAES system and Organic Rankine Cycle (ORC) in order to recover the waste heat released by the compression phase. To further improve the round trip efficiency of LAES, different integrated LAES-ORC system configurations have been modelled by means of the numerical software EES-Engineering Equation Solver v.10, which allows to compute the thermo-physical properties of the working fluids throughout the whole cycles. The LAES-ORC integrated systems are compared in terms of different performance indices such electric power output, round trip efficiency of stand-alone and integrated systems and recover efficiency of ORC. Moreover, since the potential benefits of waste heat recovery by means of ORC introduces a new capital and operative cost, an economic analysis has been carried out in order to determine the impact of ORC introduction in LAES economy. The results show that a tight integration between LAES and ORC allows to significantly improve the round efficiency (up to 20%) and reduce the pay-back period of stand-alone LAES as high as 6 %.

In this paper, the potential of improving the round trip efficiency of Liquid Air Energy Storage was investigated through modelling and simulations using the numerical software EES-Engineering Equation Solver. Liquid Air Energy Storage is a novel energy storage concept whose performance is actually limited both by the inefficiencies of the charging (liquefaction cycle) and discharging (regasification and expansion) leading to a low value of round trip efficiency when compared to other energy storage solutions. In order to further improve the round trip efficiency, the opportunity to recover the waste heat released during the compression has been considered in this paper. Different integrated energy systems consisting Organic Rankine Cycle and/or Absorption Chiller were compared against a stand-alone Liquid Air Energy Storage used as a baseline. The integrated systems are compared in terms of different performance indices such as electric power output, ORC efficiency, round trip and overall efficiency of the stand-alone and integrated systems and utilization factor of the waste heat recovery systems. The results show that a tight integration between Liquid Air Energy Storage and Organic Rankine Cycle allows to significantly improve the round trip efficiency (up to 20%). Although the introduction of the absorption chiller decreases the specific consumption, the round trip efficiency is not improved due to the lower quality of waste heat available at the LAES discharge phase. The most remarkable results are achieved when the LAES is operated in trigenerative configuration: the introduction of both Organic Rankine Cycle and Absorption Chiller in combination with Liquid Air Energy Storage was found to improve the round trip efficiency by 30% due to a better utilization of the available waste heat.

Concentrating solar power (CSP), also known as solar thermal electricity (STE), is increasing its deployment worldwide. One of the potential ways to decrease costs in CSP plants is the improvement of corrosion resistance between the heat transfer fluid (HTF) and storage materials, and the materials used for pipes, tanks, containers, and receivers. This paper assesses the literature on this topic (290 publications) through a bibliometric analysis, identifying the trends of the research, the topics of most interest to researchers, and literature gaps. Most documents are from Spain, Germany, and the United States of America. Results show that the most recent approaches for corrosion migration are selective coatings and the use of nanoparticles to reduce corrosiveness. The use of nitrates is changing to other salts such as chloride mixtures and potassium compounds. In addition, the techniques used to evaluate corrosion results are dominated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and electrochemical testing, but new dynamic techniques are starting to be used, representing the biggest gap that needs to be filled for the testing of components such as solar receivers.

The adoption of thermal energy storage (TES) systems based on phase change material (PCM) remains limited by their low thermal conductivity, which restricts power density. Existing heat transfer enhancement techniques are often costly or come with significant drawbacks, leaving a gap for an effective and affordable solution. This study highlights metal wool as a promising alternative, offering low cost, ease of application, and retrofitting potential. While previous experiments demonstrated substantial improvements in power density using copper wool, a comprehensive numerical model to further optimize this technique is presented here. The model, incorporating CFD simulations and uncertainty analysis, was validated for bulk PCM and two copper wool-PCM composites before being extended to a wool material analysis. First, possible alternatives to copper as wool material were tested, highlighting aluminum as a viable candidate. Then, the proposed composite was found to match the discharging performance of a PCM with an effective thermal conductivity of 2.5 W/mK, a value rarely achieved by conventional enhancement techniques. Additionally, a techno-economic comparison revealed that copper wool delivered a 14.7-fold increase in thermal conductivity relative to liquid PCM at ¿6 per kg of PCM additivated¿a performance unmet by metal foams and nanocomposites. These findings confirm metal wool as a viable cost-effective and high-performance solution for improving TES systems, partially bridging the gap between efficiency and affordability. A.R. and E.C. acknowledge funding under the National Recovery and Resilience Plan (NRRP), Mission 4 Component 2 Investment 1.3—Call for tender No. 1561 of 11.10.2022 of Ministero dell’Università e della Ricerca (MUR); funded by the European Union—NextGenerationEU. This work was partially funded by the Ministerio de Ciencia e Innovacion’ - Agencia Estatal de Investigacion’ (AEI) (PID2021-123511OB-C31-MCIN/AEI/10.13039/501100011033/ FEDER, UE and RED2022-134219-T). This work is partially supported by ICREA under the ICREA Academia programme. The authors would like to thank the Department de Recerca i Universitats of the Catalan Government for the quality accreditation given to their research group (2021 SGR 01615). GREiA is certified agent TECNIO in the category of technology developers from the Government of Catalonia. This paper is part of the RYC2023-044196-I, funded by MCIU/AEI/ 10.13039/501100011033 and FSE+. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 101036910

The decarbonization of the building sector cannot preclude from the vast diffusion of renewable-sourced polygeneration systems for covering both heating and cooling demand. In this context, this study shows the potentialities of a system based on solar thermal collectors, a biomass boiler and an innovative reversible hybrid heat pump/ORC concept for addressing heating, cooling and domestic hot water demand of residential buildings. The potential is investigated in three cities (Madrid, Berlin and Helsinki), representative of the different European climates. The share of renewables in different seasons and building typologies is presented and the possibility of obtaining a 100% renewable system when the solution proposed is installed in new and renovated buildings is discussed. The results show that in standard multi-family houses, up to 70% of heating demand and 100% of cooling demand can be covered by the system in warmer climates and up to 60% share of renewables can be reached in Northern climates. Moreover, the flexible configuration of the system shows the potential for the application in the future energy system of the EU. This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 814945 (SolBio-Rev). The authors at the University of Lleida would like to thank the Catalan Government for the quality accreditation given to their research group (2017 SGR 1537). GREiA is certified agent TECNIO in the category of technology developers from the Government of Catalonia. This work is partially supported by ICREA under the ICREA Academia programme.

Concentrating solar power (CSP) plants are seen as a key technology to achieve the needed energy transition since its use together with a thermal energy storage (TES) system ensures electricity dispatchability decreasing CSP plants environmental impact and life cycle costs. Latent TES using phase change materials (PCMs) has risen as a very interesting storage technology for such applications. Nevertheless, the selection of the adequate TES system and PCM, is one of the problems researchers and practitioners face to implement such technology. This paper presents a full characterization of fifteen PCMs suitable to work in the temperature range 400-600 ◦C. Melting temperature, melting enthalpy, degradation temperature, and solid-state thermal conductivity are presented, complemented with corrosion behaviour tests against stainless steel and Alloy 20. Moreover, the findings obtained in the characterization of the selected fifteen PCMs highlight the need of these analyses, as notable differences were observed compared to the available data, particularly in thermal stability and thermal conductivity. Furthermore, the compatibility test reveals that out of the fifteen selected PCMs, only two PCMs (binary mixtures of carbonates) are potentially compatible with stainless-steel 314 and Alloy 20 fibres under environmental conditions (air atmosphere). Finally, the results presented will allow researchers and practitioners to have very detailed data on the characterisation of those PCMs. This work was partially funded by the Ministerio de Ciencia e Innovación - Agencia Estatal de Investigación (AEI) (PID2021-123511OB-C31 - MCIN/AEI/10.13039/501100011033/FEDER, UE, and RED2022-134219-T). This work is partially supported by ICREA under the ICREA Academia programme. The authors would like to thank the Catalan Government for the quality accreditation given to their research group (2021 SGR 01615). GREiA is certified agent TECNIO in the category of technology developers from the Government of Catalonia. This paper is part of the RYC2023-044196-I, funded by MCIU/AEI/10.13039/501100011033 and FSE+. Franklin R. Martinez Alcocer thanks the National Doctorate Scholarship for foreign students ANID 2021 Folio 21211932 for the financial support in the research. S. Ushak acknowledges to ANID/PUENTE N° 1523A0006 and ANID/FONDECYT REGULAR N° 1231721 projects.

This paper experimentally investigates the direct integration of 3.15 kg of phase change materials (PCM) into a standard vapour compression system of variable cooling capacity, through an innovative lab-scale refrigerant-PCM-water heat exchanger (RPW-HEX), replacing the conventional evaporator. Its performance was studied in three operating modes: charging, discharging, and direct heat transfer between the three fluids. In the charging mode, a maximum energy of 300 kJ can be stored in the PCM for the cooling capacity at 30% of the maximum value. By doubling the cooling power, the duration of charging is reduced by 50%, while the energy stored is only reduced by 13%. In the discharging mode, the process duration is reduced from 25 min to 9 min by increasing the heat transfer fluid (HTF) flow rate from 50 L·h−1 to 150 L·h−1. In the direct heat transfer mode, the energy stored in the PCM depends on both the cooling power and the HTF flow rate, and can vary from 220 kJ for a cooling power at 30% and HTF flow rate of 50 L·h−1 to 4 kJ for a compressor power at 15% and a HTF flow rate of 150 L·h−1. The novel heat exchanger is a feasible solution to implement latent energy storage in vapour compression systems resulting to a compact and less complex system.