Thermal Energy Storage Efficiency Research Articles

Development and characterization of advanced paraffin plaster composite for building energy storage

Thermal energy storage via phase change materials (PCM) is currently a promising solution for minimizing energy consumption and ensuring thermal comfort in buildings. PCM composites enhance energy efficiency by shifting peak energy loads while maintaining a comfortable indoor temperature. This work aims to develop a novel highly stable form of PCM-based composite and assess its performance in plaster. The composite prepared consists of paraffin (RT27) loaded into expanded perlite (EP). The obtained composite was coated with waterproof SikaLatex adherent (SL). Paraffin loading rate reached 70 % by vacuum impregnation. Composite thermal conductivity was enhanced by aluminum (AL). Compared to other PCM plaster boards, the paraffin coated composite amount reached a greater value of 50 wt% in plaster without friability. Thermal conductivity of plaster containing 50 wt% of RT27/EP/SL/Al composite was 0.56 ± 0.02 W/m.K. Temperature and phase change enthalpy measurements were carried out by Differential Scanning Calorimetry (DSC) analysis. The results revealed that prepared composites stored 107.46 ± 1.89 kJ/kg and 93.77 ± 1.65 kJ/kg respectively without and with Aluminum. These composites were thermally stable even after undergoing multiple heating and cooling cycles. Good chemical compatibility between composite components was shown by Fourier-Transform Infrared Spectroscopy (FTIR) analysis. The resulting plaster composite is a stable, leak-proof, low-cost material with high thermal energy storage (TES) efficiency in buildings.

Influence of MnO2 on the ferroelectric properties, energy storage efficiency and piezoelectric properties of high-temperature Bi3TaTiO9 ceramics

High-temperature BLSFs Bi3TiTaO9 integrated with MnO2, exhibits excellent piezoelectric thermal stability and energy storage efficiency, making it a promising candidate for future wide-temperature pulse power applications.

Heat pump integrated with latent heat energy storage

The heat pump integrated with latent heat storage is an efficient heat decarbonization technology for improving of thermal energy storage efficiency in terms of quantity and quality using renewable energy and off-peak electricity.

Effect of Al2O3 nanoparticle dispersion on the thermal properties of a eutectic salt for solar power applications: Experimental and molecular simulation studies

Thermophysical properties of molten salts aid in determining the storage efficiency of thermal energy storage (TES) systems in concentrating solar power plants. In this research, a novel ternary molten salt (4NaCl–37KCl–59LiNO3, mol%) was utilized as the phase change material (PCM), while Al2O3 nanoparticles (NPs) were employed as a thermal conductivity enhancer. Experimental measurements and molecular dynamics simulations were conducted to confirm that the introduction of Al2O3 NPs as dopants enhanced the specific heat, thermal conductivity, and energy storage density of the eutectic salt. Specifically, at an Al2O3 NP content of 0.5 wt%, the composite PCM exhibited a 44.23 % increase in liquid-state specific heat and a 40.82 % increase in liquid-state thermal conductivity, along with a 15.73 % increase in storage density. This study demonstrates that the enhanced thermal properties of eutectic salts by adding Al2O3 NPs are primarily attributed to the emergence of nanostructures and alterations in atomic potential energy, as evidenced by both experimental and simulated microstructural analyses. These findings offer valuable insight into the selection of thermal storage materials and additives, as well as their implementation in medium-temperature TES systems, with the objective of optimizing the efficient utilization of solar energy.

Dimensionless Thermal Efficiency Analysis for Aquifer Thermal Energy Storage

AbstractSeasonal warm and cold water storage in groundwater aquifers is a cost‐effective renewable energy technology for indoor heating and cooling. Simple dimensionless analytical solutions for the thermal recovery efficiency of Aquifer Thermal Energy Storage (ATES) systems are derived, subject to heat losses caused by thermal diffusion and mechanical dispersion. The analytical solutions pertain to transient pumping rates and storage durations, and multiple cycles of operation, and are applicable to various well configurations and thermal plume geometries. Heat losses to confining layers, its implications for optimizing plume geometries and aspect ratios, and heat spreading due to free convection are also discussed. This provides a general tool for broad and rapid assessment of aquifers and ATES systems. We show that if heat exchange with the confining layers is negligible, the thermal recovery efficiency of thermal plumes with cylindrical geometry is independent of the aquifer porosity and heat capacity C0. Therefore, if mechanical dispersion is negligible as is often the case, the only aquifer property that affects the recovery efficiency is the aquifer thermal conductivity. The field‐scale aquifer thermal conductivity λ can therefore be inferred from the recovery efficiency of a push‐pull heat recovery test. Remarkably, an increase in C0 could either increase, decrease, or not affect the recovery efficiency, depending on the thermal plume geometry. Hence, the analytical solutions reveal that the recovery efficiency is affected by complex interactions between the thermal plume geometry and aquifer properties. Approximate analytical solutions for subsurface temperature profiles over an entire ATES cycle are also derived.

Epoxy composites based on phase change microcapsules with high thermal conductivity and storage efficiency by dispersing with cellulose nanofibrils

The incorporation of microencapsulated phase change materials (MPCMs) into electronic packaging materials has demonstrated the potential to reduce the transient increase in temperature of electronic devices under thermal loading. However, because of their high specific surface area, MPCMs tend to form severe aggregates in polymer matrices, resulting in poor thermal conductivity and energy storage efficiency. Therefore, in this paper, cellulose nanofibers (CNF) were used as dispersants to effectively disperse MPCMs in the epoxy resin matrix to synthesize epoxy composites with superior thermal conductivity and thermal storage properties (referred to as EBM-C). The results demonstrated that the addition of CNF improved the dispersion of MPCMs as well as the thermal conductivity and thermal storage capacity of the composites. The thermal conductivity and energy storage efficiency of the composites with 3 wt% CNF were increased by 100 %, and 97 %, respectively, compared to those of composites without CNF. In addition, the EBM-C composites also had excellent thermal stability and mechanical properties. The experimental results conclusively demonstrate that the EBM-C composites have tremendous application potential as thermal management materials.

Experimental investigation of a thermal energy storage unit integrated with thermoelectric generators under solar radiation

In this present study, a phase change material (PCM) based thermal energy storage unit (TESU) integrated with thermoelectric generators (TEGs) was experimentally investigated under artificial solar radiation. Within the scope of the experiments, a TESU with the dimensions of 15x15x5 cm was designed by assembling nine TEGs connected in series on the TESU. In the design, two types of paraffin based PCM with different thermophysical properties values as PCM in TESU and two models of TEGs with different power were used. Four different TEG/TESU designs with different parameters were made, namely TEC1-12706/P1, TEC1-12706/P2, TEC1-12710/P1, and TEC1-127010/P2. Charge-discharge processes of each design were investigated under radiation intensities of 800, 1000, and 1200 W/m2. According to the results of the experiments, it was observed that as the power of the TEG used increased, the melting time of the paraffin was shortened, and the energy conversion efficiency (ECE) and the thermal energy storage efficiency (TESE) increased. It was determined that the maximum power obtained from the designs with TESU was approximately 11 % higher than that without TESU. The result showed that more efficient TEG systems would be obtained by making the temperature of the cold surface of TEGs more stable with PCM. In addition, it was determined that the melting time decreased and the TESE and ECE increased with the increment of the radiation intensity. The shortest melting time of 135 min, the highest TESE of 80.72 % and the highest ECE of 2.32 % were obtained from the TEC1-12710/P2 design under 1200 W/m2 radiation. The longest melting time of 240 min, the lowest TESE of 64.62 % and the lowest ECE of 2.04 % were obtained from the TEC1-12706/P1 design under 800 W/m2 radiation.

Preparation and characterization of lauric acid-stearic acid/fumed silica/expanded graphite thermally conductive enhanced composites

Fatty acid and fatty acid blend phase change materials (PCM) have issues with easy leakage and low thermal conductivity in thermal storage and exothermic processes. To overcome this issue, a novel low-temperature composite material, Lauric acid - stearic acid - fumed silica - expanded graphite (LA-SA-FS-EG), was fabricated by vacuum impregnation technique using lauric acid-stearic acid (LA-SA) as the phase change material (PCM), fumed silica (FS) as the support material, and expanded graphite (EG) as the thermal conductive material. Leakage tests indicated that the maximum adsorption of LA-SA by fumed silica was 75 wt%. Scanning electron microscopy (SEM) was employed to observe the microscopic morphology of the composites. The crystal structure and chemical composition of the composites were analyzed by X-ray diffraction (XRD) and Fourier infrared spectroscopy (FT-IR). The differential scanning calorimeter (DSC) data indicates that the melting temperatures of LA-SA-FS-EG 3 %, 5 % and 7 % were 33.38 °C, 33.32 °C and 33.13 °C respectively, with melting latent heats of 110.8 J/g, 114.3 J/g and 119.9 J/g, respectively. The thermal conductivity of LA-SA-FS-EG 7 % is improved by 454 % compared to the LA-SA-FS composite without the addition of EG. LA-SA-FS-EG7% composite showed excellent heat storage capacity. LA-SA-FS-EG7% has a 46.1 % increase in heat storage rate and a 59.4 % increase in thermal release rate compared to LA-SA-FS composite. Notably, the LA-SA-FS-EG7% composite retains good thermal properties even after 1000 heating and cooling cycles. Consequently, the LA-SA-FS-EG7% composites produced have potential applications in thermal energy storage and building energy efficiency.

Thermally Conductive Molten Salt for Thermal Energy Storage: Synergistic Effect of a Hybrid Graphite-Graphene Nanoplatelet Filler.

Renewable energy technologies depend, to a large extent, on the efficiency of thermal energy storage (TES) devices. In such storage applications, molten salts constitute an attractive platform due to their thermal and environmentally friendly properties. However, the low thermal conductivity (TC) of these salts (<1W m-1 K-1) downgrades the storage kinetics. A commonly used method to enhance TC is the addition of highly conductive carbon-based fillers that form a composite material with molten salt. However, even that enhancement is rather limited (<9W m-1 K-1). In this study, the partial exfoliation of graphite to graphene nanoplatelets (GnP) in a molten salt matrix is explored as a means to address this problem. A novel approach of hybrid filler formation directly in the molten salt is used to produce graphite-GnP-salt hybrid composite material. The good dispersion quality of the fillers in the salt matrix facilitates bridging between large graphite particles by the smaller GnP particles, resulting in the formation of a thermally conductive network. The thermal conductivity of the hybrid composite (up to 44W m-1 K-1) is thus enhanced by two orders of magnitude versus that of the pristine salt (0.64W m-1 K-1).

Numerical simulations of Darcy-forchheimer flow of radiative hybrid nanofluid with Lobatto-IIIa scheme configured by a stretching surface

Heat transport and energy storage continue to be major issues for manufacturers and scientists. So far, the notion of novel heat transfer fluids has been developed, namely nanofluids and hybrid nanofluids. This investigation examines thermal radiation effect on heat transfer in MHD flow using the hybrid nanofluid. It examines a hybrid nanofluid (SWCNT-Al2O3/H2H6O2–H2O and MWCNT-CuO/H2H6O2–H2O) with H2O water base fluid nature passing through a starching surface with thermal radiation, Biot number and melting phenomena. The suitable similarity transformations are used to transmute the main governing system of equation PDEs and the appropriate boundary conditions for computation with the help of well-reputed shooting technique. The graphical and numerical outcomes against dissimilar flow parameters are computed by the mathematical software MATLAB. The velocity distribution profile is decreased by growing values of the Rotation parameter and porosity parameter. The velocity profile is enhanced by increasing the values of Darcy forchheimer medium. The thermal distribution field is enhanced by rising estimations of the thermal radiation parameter and Biot number. Temperature of the fluid is increasing due to increase in thermal conductivity parameter while decreasing due to increase in Marangoni ratio parameter. The present model hybrid nanofluid of heat transmission is evaluated to see if it has higher thermal energy storage efficiency than standard nanofluids. As a result, these novel findings in heat transport might be advantageous in dealing with energy storage issues in the modern technological environment.

Sandwich Fibrous PEG Encapsulations for Thermal Energy Storage.

Phase change materials (PCMs) textiles have been developed for personal thermal management (PTM) while limited loading amount of PCMs in textiles reduced thermal buffering effect. In this work, we firstly prepared a sandwich fibrous encapsulation to store polyethylene glycol (PEG) with PEG loading amount of 45 wt%, which consisted of polyester (PET) fabrics with hydrophobic coating as protection layers, polyurethane (PU) nanofibrous membranes as barrier layers and PEG-loaded viscose fabric as a PCM-loaded layer. The leakage was totally avoided by controlling weak interfacial adhesion between protection layer and melting PEG. The sandwich fibrous PEG encapsulations had an overall melting enthalpy value ranging from 50 J/g to 78 J/g and melting points ranging from 20 oC to 63 oC by using different PEGs. Besides, introduction of Fe microparticles in PCM-loaded layer enhanced thermal energy storage efficiency. We believe that the sandwich fibrous PEG encapsulation has a great potential in various fields.

The application of magnesium nitrate hexahydrate/hybrid carbon material phase change composites in solar thermal storage

AbstractBackgroundIn this study, a series of phase change composites were developed. Phase change materials (PCMs) are substances with a high heat of fusion, thereby possessing great potential for solar thermal storage. However, their disadvantages, such as low thermal conductivity, phase separation, and supercooling, limit their further applications.ObjectiveIn this study, magnesium nitrate hexahydrate (MNH) was used as the phase change material, and different proportions of photothermal materials were added to improve the thermally conductive property and solar thermal storage efficiency of MNH.MethodsThis study used magnesium nitrate hexahydrate (MNH) as the substrate. In addition, different proportions of photothermal materials (carbon nanotubes, nano‐graphite, graphene, and partially reduced graphene oxide) were added to promote the efficiency of thermal energy storage. Additionally, a fixed ratio of carboxy methyl cellulose (CMC) was added. The phase change temperature and enthalpy change of the phase change material samples were explored and analyzed by differential scanning calorimeter (DSC). In addition, the thermophysical properties, photothermal storage performance, and thermal reliability analysis of the samples were investigated.ResultsThe results showed that the PCM composites prepared with nano‐graphite have higher latent heat and longer time of phase change. However, the composites prepared with carbon nanotubes (CNTs) have lower latent heat and a shorter time of phase change. Therefore, the partially reduced graphite oxide (PRGO)‐containing composites can retain the latent heat storage capacity of nano‐graphite and decrease the time of phase change, thereby improving the photothermal storage efficiency. The results reveal that the solar thermal storage efficiency of the composite with both CNTs and PRGO could reach up to 0.716.ConclusionsMCGOT‐1 and MCGOT‐2 have high latent heat values, and the phase transition time is short. Therefore, the thermal energy storage efficiency can be as high as 0.716. In addition, compared with related literature, the photothermal storage efficiency of MCGOT‐2 increased by about 2 times. Therefore, the environmentally friendly composites developed in this study have a high potential to be used in solar energy storage and energy‐saving systems.

Porous ceramics derived from steel slag/coal gangue mixtures using cigarette butts as the pore‐forming agent

AbstractFabrication of ceramic materials with interconnected pores is necessary to improve thermal energy storage efficiency in high‐temperature infiltration technology. In the present study, industrial wastes such as coal gangue, steel slag, etc., were selected as the raw materials to prepare ceramics with interconnected pores. By adopting 50% cigarette butts as the pore‐forming agent, steel slag–coal gangue mixtures with a mass ratio of steel slag to coal gangue of 1:9 were sintered at 1100°C, and ceramics with interconnected elongated pores were prepared successfully. The highest apparent porosity and lowest volume density of the as‐prepared ceramics were ca. 73% and .74 g/cm3, respectively. Further measurements of the thermophysical properties indicated that no obvious mass loss was observed in the temperature range from ambient temperature to 800°C. The maximum values of specific heat and thermal conductivity were 1.38 J/(g K) and 1.661 W/(m K), respectively, and meanwhile the minimum compressive strength could exceed 3.5 MPa. These research results implied that the as‐prepared steel slag–coal gangue ceramics can provide long‐term service and offer excellent thermal stability over a wide temperature range. Therefore, they should have potential applications in high‐temperature infiltration technology.

Energy conservation performance of a solar thermal and seasonal thermal energy storage-based renewable energy convergence system for glass greenhouses

The utilization of renewable energy sources have gained significant attention in recent years for greenhouse that consumed lots of cooling and heating energy. This study investigated a solar thermal and seasonal thermal-based renewable energy convergence system. This system consists of a solar thermal system, tank- and borehole-type seasonal thermal energy storage, multi-source (i.e., air and water) heat pumps, and ground-source heat pumps. The detailed control logic of the proposed system was implemented, and the system was constructed in a test greenhouse at the Purme Yeoju Farm in South Korea. During the cooling season, the multi-source heat pumps were operated as air-source heat pumps, which showed a coefficient of performance (COP) only 0.5 less than that of the ground source heat pump. The efficiency of the solar thermal system was determined to be 36.6% throughout the investigation period, and the heat storage efficiency of the tank-type seasonal thermal energy storage was 75.7%. Consequently, the proposed system showed a COP of 2.9 during the heating season. The proposed system shows that over 70% of the operating energy can be saved, which is unachievable when using conventional electric heaters.

Fe3O4-Functionalized κ-Carrageenan/Melanin Hybrid Aerogel-Supported Form-Stable Phase-Change Composites with Excellent Solar/Magnetic–Thermal Conversion Efficiency and Enhanced Thermal Conductivity

Impregnating organic phase-change materials (PCMs) into biomass-derived aerogels is regarded as one of the most effective and accessible approach to address the liquid leakage issues of solid–liquid PCMs. However, the inefficient solar–thermal conversion and low thermal conductivity still restrict the large-scaled applications of organic PCMs in solar utilization fields. Herein, novel form-stable PCM composites (CMPCM-Fe) with enhanced thermal conductivity and excellent solar- and magnetic-driven thermal energy conversion and storage efficiency were fabricated by impregnating n-docosane into Fe3O4-functionalized κ-carrageenan/melanin hybrid aerogels (CMA-Fe) through vacuum impregnation. CMA-Fe effectively supported n-docosane and prevented the leakage issue during the phase transition process owing to its strong surface tension and capillary force. CMPCM-Fe exhibited high encapsulated efficiency (88.9–94.6%), satisfactory thermal storage capacity (229.1–246.9 J/g), and excellent reversible stability. The introduction of Fe3O4 nanoparticles enhanced the thermal conductivity (55.3% increased) and solar–thermal conversion efficiency (up to 93.5%) of CMPCM-Fe and endowed it with excellent magnetic–thermal conversion capacity under an alternating magnetic field. The synthesized CMPCM-Fe possesses broad application prospect in mutiresponse thermal management.

Methylated mesoporous silica loaded with 1-octadecanol as a new shape-stabilized phase change material for enhanced thermal energy storage efficiency

Here, a 1-octadecanol (OD)/methylated mesoporous silica (OD/M-MS) shape-stabilized phase-change material (SSPCM) was prepared with enhanced thermal energy storage. The M-MS was synthesized by methylation of low-cost MS with trimethylchlorosilane. Fourier-transformed infrared spectroscopy (FTIR), N2 adsorption–desorption isotherm, and thermogravimetric analysis confirmed successful methylation of MS. OD was then impregnated into the pores of MS and M-MS to form OD/MS and OD/M-MS SSPCMs, and their thermal properties were thoroughly characterized and compared. FTIR result of OD/MS revealed interfacial hydrogen bond (H-bond) interactions between the hydroxyl group (–OH) on the OD molecules and silanol groups (Si–OH) on the MS surface. These interactions prevented the free movement and ordered arrangement of OD molecules for crystallization, thus declining the heat storage capacity. By methylating the MS surface, the H-bond interactions were suppressed and the OD/M-MS could recover the thermal performance. The heat storage capacity increased by 96.8% from 43.5 J g−1 of OD/MS to 85.6 J g−1 of OD/M-MS. Moreover, a test of 400 accelerated thermal cycles proved good thermal reliability for OD/M-MS SSPCM. This work provides an effective strategy to achieve OD/M-MS SSPCM with low cost and high thermal performance, promising for large-scale thermal energy storage applications.

One-way freezing method to construct MWCNTs/BC framework in melamine foam for composite phase change materials applied in thermal management and energy conversion

Latent heat storage (LHS) possesses a great energy storage density, which can reduce the pressure of imbalance between energy consumption and supply. As a commonly used medium for LHS, solid-liquid phase change materials (PCMs) have received growing attentions. However, some inherent defects such as strong rigidity, easy leakage and low thermal conductivity limit further their applications. In this work, a flexible porous framework was constructed using the melamine foam (MF) as the template and the multi-walled carbon nanotubes (MWCNTs)/bacterial cellulose (BC) hybrids as the fillers, then the PEG was encapsulated to fabricate the composite PCMs. Herein, we investigated the microstructure and flexibility of the three-dimensional (3D) porous matrix, and the microscopic morphology, encapsulation capacity, heat storage/release behavior, temperature regulation ability and light to thermal conversion performance of the composite PCMs were also studied. Experimental results suggested that the prepared 3D scaffold had ultra-light characteristics and outstanding resilience performance. The involvement of BC increased the specific surface area of the MF skeleton, thus its adsorption to PEG was more stable. The thermal energy storage efficiency of composite PCMs was as high as 91.5%. Meanwhile, the composite PCMs performed sensitive thermal response behavior and could generate shape memory driven by heat. Furthermore, it also showed excellent light to thermal conversion performance with a corresponding conversion efficiency of 87.9%. This study provides a new strategy for the design and development of advanced composite PCMs, which is expected to expand the applications of PCMs in heat storage, energy conversion, solar energy utilization, and infrared stealth of military targets.Graphical abstract

Novel 3D thermal energy storage materials based on highly porous patterned printed clay supports infiltrated with molten nitrate salts

One of the main drawbacks of phase change materials (PCM) to be employed as thermal energy storage (TES) systems in energy applications, such as concentrated solar power (CSP), is the liquid leakage, which considerably reduces the storage efficiency. To overcome this issue, a novel approach is presented, which is based on the development of three-dimensional (3D) engineered TES structures (3DTES) formed by highly porous patterned 3D printed low-cost clay supports (up to ~85% of total porosity) that are infiltrated with a molten sodium nitrate salt. Expanded vermiculite supports are additive manufactured by robocasting, a direct ink writing technology, using clay aqueous inks with a pseudoplastic behavior. 3DTES are lightweight (~1.8 g·cm −3 ), easy to handle, mechanically robust (~68 MPa) and exhibit high PCM encapsulation capacity (~78%), avoiding the molten salt leakage. Furthermore, they present an enthalpy of fusion of ~136 J·g −1 , excellent thermal stability, and high thermal energy storage efficiency (~80%) and thermal conductivity (1.27 W·m −1 ·K −1 ), which is indicative of a great charging-discharging ability. The results open new opportunities through the 3DTES approach to manufacture promising affordable materials with outstanding performance for CSP applications. • Novel 3D engineered thermal energy storage structures (3DTES) are manufactured. • Highly porous 3D printed patterned clay supports are infiltrated with a molten salt. • 3DTES are light, easy to handle, robust and avoid the molten salt leakage. • 3DTES exhibit excellent efficiency, thermal stability and high thermal conductivity. • 3DTES are promising affordable materials with outstanding performance for CSP.

Study of combined heat and power plant integration with thermal energy storage for operational flexibility

Increasing the share of renewable energy in the future electricity market requires measures to maintain the stability of the grid, owing to the volatility and intermittency of renewable energy. For a combined heat and power (CHP) plant, molten salt thermal energy storage (TES) can be added to improve the flexibility to meet the needs of peak shaving. This paper proposed a novel cascade reheat steam extraction system to adjust the electrical load by using EBSILON software applied to thermal simulation and thermal analysis. A 350 MW supercritical CHP plant was used as an example to analyze the thermal and peak shaving performance under variable operating conditions. Meanwhile, through the static simulation, the change in the load and the efficiency of TES can be calculated during the charging and discharging cycle. The results show that the efficiency of TES is 40–51 %. With an increase in the load, the efficiency of TES is reduced, and the exergy loss range is from 4 MW to 12.4 MW mainly due to the throttling process and the molten salt heat transfer process. Moreover, the thermal efficiency and exergy efficiency of the novel system are higher than those of the traditional CHP plant below 60 % turbine heat acceptance, so it is relatively economical to run for peak shaving under low loads. Finally, depending on the corresponding operating strategy, a reduction of the minimum load by up to 1 % of the rated output electrical load during charging and an increase of the maximum load by up to 2 % of the rated output electrical load during discharging are possible. Overall, the proposed system provides a feasible method for the flexibilization of CHP plants alongside new renewable systems.

Geometry optimisation of an industrial thermocline Thermal Energy Storage combining exergy, Life Cycle Assessment and Life Cycle Cost Analysis

Recently, packed-bed storage has been considered as a promising alternative solution for thermal energy storage especially for waste heat recovery in industrial plants. This work aims to optimise environmental footprint, costs and exergy efficiency of a thermocline thermal energy storage through two optimisation variables. These variables describe the tank shape and the particle grain size. Two solid filler materials are compared: machined ceramic and ceramic from fly ashes. The reference storage is an existing industrial high-temperature air/bauxite packed-bed storage called Eco-Stock®. A one-dimensional two-phase (fluid and solid) model is used to determine the energy and exergy performance of the thermocline tank. For the life cycle assessment, four indicators are selected: cumulative energy demand, global warming potential, abiotic depletion potential and particulate matter. Finally, a life cycle cost analysis is performed to determine levelised cost of energy used as economic criterion. This multi-objective problem is solved by the multi-criteria genetic algorithm available on the Matlab® platform. A Pareto set is obtained, bounded by the single exergy and environmental optimisation solutions. The economic optimisation is found on the Pareto set, close to the environmental optimal solution. Favouring economic performance reduces the environmental footprint of the storage. Despite better exergy performance and smaller tank volume, the exergy-optimised tank increases environmental impacts and costs due to higher pumping work. The environmental and economic optimisations lead to stocky tank shapes while a tapered tank is obtained for the exergy optimisation. According to the TOPSIS method, the economic optimal solution appears to be the best trade-off for both fillers tested. Despite poorer thermophysical properties, the solution with ceramic from fly ashes shows similar exergy and economic performance as the machined ceramic solution (more than 96 % of exergy efficiency for 3.1 c€/kWhth), while the environmental footprint is greatly reduced (61 vs 87 ca.year). This tank has a diameter of 2.6 m and a height of 1.7 m. The particle diameter is 11 mm.