Thermal Storage Solutions Research Articles

Natural and sustainable thermal storage solution for solar distillation system using sensible fiber material and latent PCM: Enhanced energy storage application

AbstractThe current research work involves the design and performance assessment of a solar still, which is a conventional single‐slope basin‐type solar still (CSSBTSS) and a modified single‐slope basin‐type solar still (MSSBTSS) under the meteorological conditions of Solan city, Himachal Pradesh, India (30.90° N, 77.09° E). The individual and the combined effect of different sample quantities of sensible Himalayan Rambaan fibers (HRFs) and mass of latent paraffin wax (PW) A48 on the performance of MSSBTSS is evaluated and compared with CSSBTSS. The use of HRF material enhanced the evaporation rate significantly and improved the daytime distillates. Besides, different masses of latent PW filled inside the aluminum tubes improved the nocturnal distillates. For the analysis, three cases have been considered which are, namely: Case 1, solar still with sensible HRFs (MSSBTSS‐HRF); Case 2, solar still with latent PW A48 (MSSBTSS‐PW); and Case 3, solar still with sensible and latent material (MSSBTSS‐HRF‐PW). The results showed that the maximum thermal efficiency for Cases 1 and 2 was improved by 30.02% and 42.41% with five sample quantities of HRF material and 5000 g of PW. For Case 3, the maximum energy efficiency was 90.71% with a gain of 45.16% over CSSBTSS. The economic analysis concluded that the cost per liter of distillate yield produced using MSSBTSS‐HRF‐PW and CSSBTSS is ₹1.5 and ₹1.6, respectively. These outcomes showed the great potential of MSSBTSS‐HRF‐PW approach towards enhancing the overall performance and cost‐effectiveness of solar still.

Climate Change and Energy Security: A Comparative Analysis of the Role of Energy Policies in Advancing Environmental Sustainability

This review analyzes the complex relationship between climate change and energy security and their joint impact on global development. It emphasizes the need for sustainable energy solutions to tackle increasing global warming effects and energy demands. A thorough literature analysis highlights the link between energy policies, climate goals, and sustainable development aspirations. Moreover, it examines the effectiveness of energy policies in various national contexts in promoting environmental sustainability and emphasizing regional dynamics, socio-economic factors, and diverse energy planning approaches. The review explains the multifaceted relationship between climate change, energy security, and environmental protection. Key recommendations related to renewable energy transitions are provided as crucial means to address global energy demand and resource constraints while reducing dependence on fossil fuels. The analysis underscores renewable energy’s key role in aligned energy strategies that balance security and sustainability for a low-carbon future. It emphasizes the critical need for coordinated policies, technological innovation, and collaborative action between academia, industry, and policymakers to advance integrated energy systems and thermal storage solutions.

Waste-derived thermal storage solutions for sustainable solar desalination using discarded engine oil and paraffin wax: A techno-environmental feasibility evaluation

The valorization and repurposing of waste materials for sustainable outcomes and environmental mitigation are gaining prominence. This investigation explores the feasibility of repurposing discarded automotive engine oil as a viable means of energy storage in solar thermal desalination applications. A novel approach combining discarded engine oil with Paraffin wax in equal parts by volume is proposed as a composite energy storage (CES) to enhance nocturnal production and efficiency. The experimental findings show that the composite energy storage system has 26.54 % higher thermal conductivity and 44.66 % greater specific heat energy storage capacity compared to pure paraffin wax. Comparing the Desalination System with Engine Oil-based Energy Storage (DSEES) to a Traditional Solar Desalination System (TSDS) without energy storage, considering water and absorber temperatures and distillate production, reveals compelling advantages. DSEES exhibits remarkable temperature increases of 14 % in the basin and 11 % in water, alongside a significant 52.72 % rise in distillate production rates, yielding 3.36 and 3.16 l/sq.mt compared to TSDS's 2.2 and 2.1 l/sq.mt over two testing days. Cost analysis indicates DSEES's 33.7 % lower cost per liter and 33.8 % shorter payback period relative to TSDS. Furthermore, environmental assessment highlights DSEES's 60.8 % greater net carbon credit, indicating reduced ecological impact.

Innovation and advancement of thermal processes for the production, storage, utilization and conservation of energy in sustainable engineering applications

This vision article accompanies a special issue of Applied Thermal Engineering dedicated to the 16th Conference on Sustainable Development of Energy, Water and Environment Systems (SDEWES) held in Dubrovnik in 2021, and summarizes a selection of papers presented at the conference. At the focal point are a range of topics related to thermal processes as these arise in energy production, storage, utilization and conservation, covering fundamental research, the development of technical solutions for diverse sustainable engineering applications, technoeconomic analyses, and issues relating to the potential and integration of technologies from higher-level approaches. Thermal processes are the basis of numerous sustainable engineering applications and their understanding and improvement are increasingly required in the context of improved resource use efficiency and reduced environmental impact. Applications of interest include thermal systems used in buildings, thermochemical processes, seawater treatment, thermal storage solutions and renewable energy resource use. Emerging challenges in this space have given an opportunity to scientists, researchers and engineers to actively contribute to the development of relevant technological solutions, which are covered briefly in the present article.

Development of a latent heat thermal energy storage unit for the exhaust of a recuperated solar-dish Brayton cycle

Solar air Brayton cycles can provide heat and power to small communities with no access to the national grid. However, the temporal mismatch between the energy supply and demand can limit the amount of solar energy successfully transferred to the user. To increase this solar utilization factor, a high-temperature latent heat thermal energy storage unit for temperatures of up to 750 K, dedicated to a solar air Brayton cycle, is designed and tested under realistic operating conditions. The storage unit is charged employing the cycle exhaust and discharged after sunset to serve domestic heating applications. In agreement with the identified operating conditions, four storage material candidates are shortlisted and characterized. Thus, the so-called solar salt was selected as the most suitable material by means of 3D numerical analysis to meet a series of performance, durability, cost, and compactness requirements. The proposed latent heat thermal energy storage device was tested with 151 kg of solar salt and allowed for the storage of up to 17.5 kWh in a 10 h charging time. Overall, the numerical and experimental results reported in this work demonstrate the feasibility of the proposed device as a cost-effective and durable thermal storage solution in small-scale solar air Brayton cycles.

Numerical modelling of lauric acid phase change material using iterative and non-iterative time-advancement schemes

Phase Change Materials are used in different applications as thermal storage solution. Numerical and experimental studies have been performed to investigate and test their properties. But large time consumption of PCM numerical simulation is considered as one of the main limitations that restrict modelling of large dimension 2D and 3D models, in addition to large time scale experiments. Numerical model using ANSYS FLUENT NITA (Non-Iterative Time Advancement) scheme was employed and compared to the default ITA (Iterative Time Advancement) scheme. The comparison included pairs of models at different grid sizes and time-step sizes. It was found that simulation time-saving by NITA scheme exceeded 89 % and reached 96.4 % when compared to the default ITA scheme. The maximum error percentage between them was 0.27 % in the employed model.

Decarbonization potential of integrating industrial excess heat in a district heating network: The Portuguese case

The paper performs an assessment of the decarbonisation potential in utilizing industrial excess heat to meet the baseload heating requirements of a district heating network in Portugal. The excess heat source considered was a municipal waste-to-energy plant located 5 km from a district heating and cooling network. It performed an economical comparison between two integration procedures: (i) extending the existing pipeline to the excess heat source; and (ii) using a continuous supply of portable thermal storage modules. For the excess heat characterization and tecno-economic assessment, the EMB3RS platform was used. The analysis demonstrated the pipeline alternative more economically feasible (with a levelized cost of heat of 17,25 €/MWh), meeting the baseload consumption with a decarbonisation reduction potential of 30%. The higher levelized cost of heat of the portable thermal storage solution is mainly due to the high daily replacement cost for the thermal stores.

Performance of a shallow solar pond coupled with a heat pump cycle for thermal energy in net zero-energy buildings

Refrigerant evaporation, in heat pumping systems, is a particularly complex process. Since the evaporator is subjected to environmental conditions, several factors weigh in on overall system performance, mainly, the additional energy input from the surroundings. This renders the evaporation process especially susceptible to gaps and fluctuations of said energy availability, particularly in solar-assisted setups. Despite the, comparatively, high heat flux associated to this source, these occurrences make them suitable mostly for low-to-medium thermal requirements, especially in regions with more extreme climates. The present work introduces a novel evaporator design, based on solar ponds. The proposed evaporation device incorporates a short-term, passive, thermal storage solution to compensate for gaps in energy availability. A mathematical-thermal model is developed and a performance assessment is conducted based on real seasonal atmospheric and operation conditions. For this study R134a, R152a, R1234yf and R1234ze(E) were used as working fluids. The proposed heat pump configuration is evaluated for hot water production at 55 °C, indoor air heating at 18–22 °C and a combined simultaneous scheme. The results show that this configuration performs well under moderate climate conditions. For hot water production during spring, highest outlet temperature of 68.54 °C for the R1234yf working fluid, were reached and maintained after the first 13 h. Internal thermal capacitor reached an average temperature of 61.88 °C for R1234yf. During winter, these temperatures decrease almost by a third, with 40.6 °C for R1234yf working fluid. However, daily average outlet temperature of 64.8°Care reached within the first 15 h of operation. Despite a lower thermal storage, with average capacitor, the system yielded consistent average outlet temperature of 20.7 °C. For a simultaneous operation scheme, desired outlet water temperature, is reached within the first 16 h of operation, whilst the indoor air temperature reaches comfort levels within the first 12 h. Despite employing part of the energy absorbed to maintain a stable comfort condition within the dwelling, instead of compensating the heat loss of the hot water tank, both goals are achieved. The inclusion of an inner thermal capacitor that collects and stores energy at a much higher rate provides the refrigerant with an additional heat source. This results in a more effective overall energy absorption of the evaporator, which exceeds the rate at which heat is dissipated from the tank/dwelling to the environment. This heat loss buffer lessens, considerably, the thermal demand during periods with lower energy availability, resulting in achievable outlet conditions.

Palm oil-based bio-PCM for energy efficient building applications: Multipurpose thermal investigation and life cycle assessment

This study aims at investigating the potential use of a bio-based phase change material, i.e. expired palm oil from the food industry, as a more sustainable alternative to petrochemical-based organic PCMs. To this purpose, thermogravimetric analysis (TGA) and isoconversional methods (Starink and Miura-Maki methods) are applied and the main thermo-physical properties of the blend are investigated by means of differential scanning calorimetry (DSC) and extensive thermal monitoring in a controlled realistic environment. Finally, a life cycle assessment is used to evaluate the environmental impact of the bio-based material in comparison to the more common petrochemical-based application. Kinetic analysis results indicate the two dimensional phase boundary reaction model as the most reliable scheme for describing the oxidation of palm oil, with an activation energy of about 73 kJ · mol−1. The DSC and the thermal monitoring procedure, showed two separate melting peaks in the ambient temperature range, which globally guarantee a melting enthalpy of about 50 kJ · kg−1, i.e. of the same order of magnitude of the first developed PCMs. Results from the life cycle analysis reveal that the expired palm oil can be considered a promising material for bio-based latent applications.Globally, the palm oil has proved itself as a promising, low cost, and environmentally friendly alternative for passive thermal storage solutions (e.g. building envelope applications) where stability across multiple thermal cycles, low health risks, and low leakage are crucial parameters to be addressed.

Thermodynamic performance of a novel shell-and-tube heat exchanger incorporating paraffin as thermal storage solution for domestic and commercial applications

This article is focused to evaluate thermal performance of commercial grade paraffin in a novel shell-and-tube heat exchanger with multi-tube passes and longitudinal fins as latent heat storage (LHS) system. Thermal performance assessments of latent heat storage system are conducted with respects to charging/discharging power, accumulative thermal energy storage/retrieval, thermal efficiencies and effectiveness, heat transfer characterisation and nature of melt front propagation. The average charging and discharging powers are significantly enhanced by 75.53% and 27.04% with an increase in temperature gradient between paraffin and inlet water from 52 °C to 62 °C and 15 °C–5 °C, respectively. Likewise, the maximum charging and discharging powers are augmented from 2.15 kW to 2.63 kW and 5.18–10.37 kW with an increase in flow rate from 1.5 to 3 l/min, respectively. Furthermore, the average effectiveness, Nu-Ra and heat transfer coefficient are significantly improved with an increase in temperature gradient and moderately reduced with upgrading volume flow rate. The range of Rayleigh numbers for charging cycles have indicated turbulent nature of melt front movement and supportive behaviour of longitudinal fins orientations towards natural convection. Empirical correlations for average effectiveness and Nu-Ra are developed from experimental results to facilitate design estimation for employment of proposed LHS systems in domestic and commercial applications. These empirical correlations, to evaluate feasibility and employability of LHS systems in practical applications such as domestic hot water supply and space heating to maintain control room temperature, have been successfully implemented in real operating conditions.

Numerical simulation of a phase change material melting process

Storage processes are usually integrated in solar energy systems applications due to daily variation of this energy source availability. Among different thermal storage solutions, phase change materials (PCM) lately became more extensively used covering a wide range of operating temperatures. In this regard, a numerical simulation of a PCM melting process is performed under ANSYS CFD environment. A particular configuration is considered consisting in a 2m length annular tube having a 5.48 cm external diameter. The tube is filled with paraffin chosen as PCM. A concentric interior tube of 2.54 cm diameter is used for transporting the heat transfer fluid (HTF) from the solar collector. Heat is transferred through the 1 mm thick pipe wall to the PCM placed all around the HTF tube. The numerical results reveal the melting process of the PCM at different instances and tube sections. The time variation of the PCM liquid fraction is emphasized. The results describe the dynamic behavior of a PCM melting process and might be further integrated in any solar power plant storage charging process simulation.

Performance comparison of latent heat storage systems comprising plate fins with different shell and tube configurations

For design and optimization purposes, understanding the performance characteristics of different configurations of PCM systems during charging and discharging processes is crucial, particularly for thermal storage in CSP. A numerical study using FLUENT has been performed to explore and compare the characteristics and behavior of PCM in different shell and tube configurations; namely counter flow and parallel flow in vertical and horizontal orientations. These designs have been compared with that of an alternative design using plate fins. The main practical advantage of the alternative design is decoupling the PCM location from the path of flow of the heat transfer fluid that reduces the constraints on the materials. Confined heating/cooling pipes in a channel at the bottom of the PCM enclosure makes it more flexible to match the required working pressures, and simplifies the design and material (PCM/plate) selection. This is a significant issue as higher temperatures and pressures are being required for improving the overall solar thermal system performance. Based on the same heat transfer area, amount of PCM and input energy, a performance comparison was determined based on exergy maximization. Using sodium nitrate as the PCM, the results show a higher heat transfer rate for the vertical arrangement of plate fins compared to the counter flow shell and tube configurations, as well as a more uniform heat transfer rate compared to all shell and tube arrangements for both the charging and discharging processes. The proposed design leads to less redundant PCM, as well as a smaller and more cost effective PCM system as a heat storage unit. Overall, the vertical plate fin configuration maximizes the useful heat that can be extracted for a given amount of heat and PCM, which has direct applicability to thermal storage solutions for CSP and other applications. Moreover, its modular design facilitates the selection and optimisation for different scales and applications e.g. as a heat storage for electricity production or as a protection system for a receiver from high thermal stresses in a CSP plant.

Improving an Integer Linear Programming Model of an Ecovat Buffer by Adding Long-Term Planning

The Ecovat is a seasonal thermal storage solution consisting of a large underground water tank divided into a number of virtual segments that can be individually charged and discharged. The goal of the Ecovat is to supply heat demand to a neighborhood throughout the entire year. In this work, we extend an integer linear programming model to describe the charging and discharging of such an Ecovat buffer by adding a long-term (yearly) planning step to the model. We compare the results from the model using this extension to previously obtained results and show significant improvements when looking at the combination of costs and the energy content of the buffer at the end of the optimization. Furthermore, we show that the model is very robust against prediction errors. For this, we compare two different cases: one case in which we assume perfect predictions are available and one case in which we assume no predictions are available. The largest observed difference in costs between these two cases is less than 2%.

A Novel Modular Design Approach to “Thermal Capacity on Demand” in a Rapid Deployment Building Solutions: Case Study of Smart-POD

Designed to address the challenges of a sustainable future and the financial difficulties facing schools, Smart-POD is a unique and innovative research project which provides an alternative to traditional classroom planning. It proposes a rapid deployment building solution, transitory or permanent in its use, modular in design, flexible in set-up and self-sustaining in use, requiring nominal site works and providing for all of its energy demands from renewable energy sources. Its feasibility was tested via a design case study which investigated potential of its novel “thermal capacity on demand” energy performance approach. It combines a modular thermal storage solution capable of balancing heating demand and supply for a low rise, low mass superstructure with renewable technologies and the level of back-up power/services needed. The project team has formed a consortium of stakeholders and consulted on design methodology, performance specification and viability of other markets, the results of which are reported in this paper. The research has, in its final output, established a commercial model based on its design, procurement, financing, supply chain and the manufacturing strategy and is currently negotiating funding for the prototype.

Some problems in storing renewable energy

Difficulties involved in some commonly advocated options for the storage of renewable electricity are discussed. As is generally recognised the most promising strategies involve biomass and pumped hydro storage, but these involve drawbacks that appear to be major limitations on the achievement of 100% renewable supply systems. Neglected aspects of the solar thermal storage solution are detailed, indicating that it is not likely to be able to make a significant contribution. Batteries, vehicle-to-grid, biomass and hydrogen based solutions also appear to have major drawbacks. Although other options not examined here might alter the outlook, the general impression arrived at is that the probability of achieving satisfactory storage provision enabling 100% renewable power supply are not promising. Provision of total energy supply from renewable sources would probably multiply the task by an order of magnitude.

Improved performance in tube-encapsulated phase change thermal energy stores for HVAC applications

Thermal energy stores can be used to shift building peak electric loads for cooling to off-peak hours. Compact, high-density thermal storage solutions are required for buildings that may not have the space necessary for typical thermal storage systems, such as chilled water tanks. Previous studies show that latent thermal stores using polymer tube-encapsulated paraffin-based phase change materials (PCM) yield acceptable thermal performance at low to moderate encapsulation tube packing densities, but that thermal performance falls as tube packing densities climb due to increasingly restricted heat transfer fluid (HTF) flow paths. This paper reports the experimental results found when using a highly conductive encapsulation material to redistribute the thermal energy around the PCM, mitigating the effect of the restricted HTF flow paths and enabling maximum encapsulation tube packing densities. These experiments show a more than two-fold increase in the percentage of recoverable thermal energy over a similar polymer tube based system, providing thermal performance comparable to that of a low density polymer tube encapsulation system while increasing PCM capacity by 111%. Test results are provided in a format suitable for estimating design criteria for larger thermal stores, and a design parameter – the resistance ratio – is proposed to assist in optimizing encapsulation tube parameters.

Experimental Investigation into a Packed Bed Thermal Storage Solution for Solar Gas Turbine Systems

High temperature thermal storage in randomly packed beds of ceramic particles is proposed as an effective storage solution for Solar Gas Turbine (SGT) cycles in the near term. Numerical modelling of these systems allows for optimised thermal storage designs, but such models must be validated against experimental data. In this work an experimental test programme was conducted to generate high temperature heat transfer data for a packed bed operating over the temperature ranges 350-900°C and 600-900°C. These are representative of two potential SGT cycles. Flue gas from a 45kW LPG burner was used to heat a packed bed of Denstone ceramic pebbles and the testing procedure involved preheating the system to achieve the desired temperature ranges. The fluid and solid temperature profiles in the packed bed were measured in the axial and radial dimensions and are compared to a numerical model with reasonable agreement. Potential modifications to the test facility are described and future testing plans outlined.

AN EXPERIMENTAL AND COMPUTATIONAL INVESTIGATION OF A THERMAL STORAGE SYSTEM BASED ON A PHASE CHANGE MATERIAL: HEAT TRANSFER AND PERFORMANCE CHARACTERIZATION

The integration of latent heat storage solutions into modern heating and cooling systems has the potential to enhance overall system performance compared to standard hot water systems (radiators and tanks) due to an augmentation of the stored heat by the latent heat of a suitable material. This paper presents computational predictions complemented by experimental measurements of the dynamic behavior and performance of an active thermal storage system for domestic applications, based on the use of a hydrated salt phase change material (PCM) and a conventional cylindrical storage tank. The thermal storage (heating) and extraction (cooling) rates for this PCM-filled tank are compared to a water-filled tank. Flow and temperature fields are analyzed in a customized storage tank design for heat transfer and performance characterization. Experimental findings show good agreement with full 3-D simulation results. The heat removal characteristic is identified as being the main factor limiting the arrangement's performance when compared to a water-based system, due to the solidification of the PCM onto the pipes, and a significant consequent decrease in heat flux. It is confirmed that the PCM thermal storage solution has the capability to store a large amount of heat effectively, but design improvements are required to eliminate the cooling-limited heat transfer process in the investigated arrangement.

Evaluation of the effect of phase change materials technology on the thermal stability of Cultural Heritage objects

The use of phase change materials (PCMs) in civil buildings as an effective thermal energy storage solution has been well documented in literature and proven in the field. When applied to Cultural Heritage, PCMs’ technology needs to be adapted to specific requirements. Besides the important objectives of economic return and human comfort, the indoor microclimatic conditions have to be suitable for conservation purposes. The application of PCMs’ technology to Cultural Heritage has been investigated within the European MESSIB (Multi-source Energy Storage System Integrated in Buildings) project. Firstly, several methodologies of incorporation of PCMs in different materials were studied and tested. The thermal properties of gypsum panels and silicon coatings incorporating micro-encapsulated PCMs in the form of powder and emulsion were analysed in the laboratory. Then, PCMs incorporated in gypsum panels in contact with a wooden panel were tested and their effect on the thermal behaviour of the wooden panel was evaluated under thermal cycles in a climatic chamber. PCMs incorporated in silicon coatings in contact with a painting were also tested. Moreover, gypsum panels containing PCMs were tested in the S. Croce Museum in Florence, Italy, where the microclimatic monitoring has shown thermal conditions potentially dangerous for the works of art preserved. The research performed both in the laboratory and on the field confirmed the effectiveness of the PCMs as thermal storage solutions, but also gave evidence on an important drawback when the material incorporating PCMs is in direct contact with an object of art.

Thermodynamic evaluation of liquid metals as heat transfer fluids in concentrated solar power plants

Concentrated solar power, and in particular central receiver systems, can play a major role as a renewable energy source with the inherent possibility of including a thermal energy storage subsystem for improving the plant dispatchability. While current commercial projects are dominated by direct steam generation and molten nitrate salt concepts, next-generation systems will require higher operating temperature and larger heat-flux densities in order to increase the efficiency and reduce costs.In that context, liquid metals are proposed in this work as advanced heat transfer fluids that can face those challenges. The main advantages, regarding higher temperature and improved heat transfer performance, are discussed and quantified using simplified models. Indirect thermal storage solutions are proposed for compensating their relatively small heat capacity. Overall, provided that some practical challenges can be overcome, liquid metals present large potential as efficient heat transfer fluids.