Power generation systems are attracting a lot of interest from researchers and companies. Storage is becoming a component with high importance to ensure system reliability and economic profitability. ...A few experiences of storage components have taken place until the moment in solar power plants, most of them as research initiatives. In this paper, real experiences with active storage systems and passive storage systems are compiled, giving detailed information of advantages and disadvantages of each one. Also, a summary of different technologies and materials used in solar power plants with thermal storage systems existing in the world is presented.
Concentrated solar thermal power generation is becoming a very attractive renewable energy production system among all the different renewable options, as it has have a better potential for ...dispatchability. This dispatchability is inevitably linked with an efficient and cost-effective thermal storage system. Thus, of all components, thermal storage is a key one. However, it is also one of the less developed. Only a few plants in the world have tested high temperature thermal energy storage systems. In this paper, the different storage concepts are reviewed and classified. All materials considered in literature or plants are listed. And finally, modellization of such systems is reviewed.
The goal of this study is to implement and to test a thermal energy storage (TES) system using different phase change materials (PCM) for solar cooling applications. A high temperature pilot plant ...able to test different types of TES systems and materials was designed and built at the University of Lleida (Spain). This pilot plant is composed mainly by three parts: heating system, cooling system, and different storage tanks. The pilot plant uses synthetic thermal oil as heat transfer fluid (HTF) and has a working temperature range from 100 to 400 °C. Two different PCM were selected after a deep study of the requirements of a real solar cooling plant and the available materials in the market through literature review and DSC analysis. Finally d-mannitol with phase change temperature of 167 °C and hydroquinone which has a melting temperature of 172.2 °C were used at pilot plant scale. For both PCM, no hysteresis was detected, and at pilot plant only d-mannitol showed subcooling even though both showed it during the DSC analysis. An effective heat transfer coefficient between the storage material and the heat transfer fluid (HTF) was calculated. For the same boundary conditions, the energy stored by d-mannitol was higher than that for hydroquinone. Moreover, d-mannitol has polymorphism that needs to be taken into account when the material is used as PCM, but experiments in this paper showed that polymorphism did not interfere its performance as PCM.
► Different PCM for thermal storage in solar cooling application were studied. ► DSC analysis showed that hydroquinone and d-mannitol were suitable materials to be used as PCM. ► The materials were tested at pilot plant scale in the University of Lleida installations. ► An effective heat transfer coefficient between the HTF and the PCM was defined and calculated.
Thermal energy storage is a key component of solar power plants if dispatchability is required. On the other hand, although different systems and many materials are available, only a few plants in ...the world have tested thermal energy storage systems. Here, all materials considered in literature and/or used in real plants are listed, the different systems are described and analyzed, and real experiences are compiled. The associated heat transfer technologies to support and improve these systems are described and analyzed.
Shell-and-tube latent heat thermal energy storage units employ phase change materials to store and release heat at a nearly constant temperature, deliver high effectiveness of heat transfer, as well ...as high charging/discharging power. Even though many studies have investigated the material formulation, heat transfer through simulation, and experimental studies, there is limited research dedicated to the storage unit design methodology. This study proposes a comprehensive methodology that includes the material assessment with multi-attribute decision-making and multi-objective decision-making tools, epsilon-NTU method, and cost minimization using Genetic Algorithm. The methodology is validated by a series of experimental results, and implemented in the optimization of a storage unit for solar absorption chiller application. A unit cost of as low as USD 8396 per unit is reported with a power of 1.42 kW. The methodology proves to be an efficient, reliable, and systematic tool to fulfill the preliminary design of shell-and-tube LHTES before the computational fluid dynamics or detailed experimental studies are engaged.
The final goal of this study is to implement and to test a thermal energy storage (TES) system using different phase change materials (PCM) for solar cooling and refrigeration applications. A high ...temperature pilot plant able to test different types of TES systems and materials was designed and built at the University of Lleida (Spain). This pilot plant is composed mainly by three parts: heating system, cooling system, and different storage tanks. The pilot plant uses synthetic thermal oil as heat transfer fluid (HTF) and has a working temperature range from 100°C to 400°C. Two different PCM were selected after a deep study of the requirements of a real solar cooling plant and the available materials in the market, finally d-mannitol with phase change temperature of 167°C and hydroquinone which has a melting temperature of 172.2°C were used.
•Experimental study at pilot plant scale of addition of fins in LTES systems.•Comparison of two LTES tanks, with and without fins, during a charging process.•Hydroquinone was selected as ...PCM.•Effective thermal conductivity was compared at different thermal power ratios.•Increase in measured thermal effective conductivity was 4.11–25.83%
Solar cooling is a promising solution to overcome the high energy demand of buildings. Nevertheless, the time dependent nature of the solar source leads to the need of storage systems in order to better match the energy demand and supply. For this purpose, thermal energy storage was considered during last decades as the optimal solution at commercial scale. Latent thermal energy storage offers higher energy densities together with more constant outlet temperature than sensible heat storage, but the low thermal conductivities of PCMs represents the main drawback which limits its applicability. Several studies based on heat transfer enhancement techniques applied in latent thermal energy storage have already been performed. Specifically, the technique of adding fins in storage tanks, which is the most known and studied. However, there are few experimental studies at pilot plant scale focused on this technique and less on the analysis of the heat transfer enhancement through the parameter effective thermal conductivity. This paper presents an experimental study where this parameter is determined and compared using of two identical latent storage tanks, one with 196 transversal squared fins and another one without fins. In this case, hydroquinone was selected as PCM. A set of six experiments was performed at pilot plant of the University of Lleida (Spain), combining three different HTF flow rates and two temperature gradients between HTF inlet temperature and initial PCM temperature. Experimental results showed that the addition of fins can increase the effective thermal conductivity between 4.11% and 25.83% comparing the experiment with highest and lowest thermal power supplied to the PCM, respectively.
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•Summarizes a wide temperature range of Cold Thermal Energy Storage materials.•Phase change material thermal properties deteriorate significantly with temperature.•Simulation methods ...and experimental results analyzed with details.•Future studies need to focus on heat transfer enhancement and mechanical design.•Analyzes applications with technology readiness and more should be explored.
The energy industry needs to take action against climate change by improving efficiency and increasing the share of renewable sources in the energy mix. On top of that, refrigeration, air-conditioning, and heat pump equipment account for 25–30% of the global electricity consumption and will increase dramatically in the next decades. However, some waste cold energy sources have not been fully used. These challenges triggered an interest in developing the concept of cold thermal energy storage, which can be used to recover the waste cold energy, enhance the performance of refrigeration systems, and improve renewable energy integration. This paper comprehensively reviews the research activities about cold thermal energy storage technologies at sub-zero temperatures (from around −270 °C to below 0 °C). A wide range of existing and potential storage materials are tabulated with their properties. Numerical and experimental work conducted for different storage types is systematically summarized. Current and potential applications of cold thermal energy storage are analyzed with their suitable materials and compatible storage types. Selection criteria of materials and storage types are also presented. This review aims to provide a quick reference for researchers and industry experts in designing cold thermal energy systems. Moreover, by identifying the research gaps where further efforts are needed, the review also outlines the progress and potential development directions of cold thermal energy storage technologies.
Thermal energy storage (TES) is nowadays presented as one of the most feasible solutions in achieving energy savings and environmentally correct behaviors. Its potential applications have led to R&D ...activities and to the development of various technology types. However, so far there is no available data on a national scale in Spain and on a continental level in Europe, to corroborate the associated energetic and environmental benefits derived from TES. This is why, based on a previous potential calculation initiative model performed in Germany, this work intends to provide a first overview of the Spanish TES potential as well as an European overview. Load reductions, energy savings, and CO2 emissions reductions are tackled for the buildings and industrial sector. Results depend on the amount of implementation and show that, in the case of Europe for instance, yearly CO2 emissions may get to be cut down up to around 6% in reference to 1990 emission levels.
In the metallurgical industry, large amounts of waste called slag are accumulated besides the production of iron and steel. One part, considered as by-product, is recycled but the other part, ...considered as waste, is still landfilled with potential bad consequences for environment. In this paper, two electric arc furnace slag samples (most common steel production technology in Europe), have been considered and characterized to be used in medium and high temperature thermal energy storage systems. These slags have demonstrated relevant properties to store thermal energy by sensible heat from ambient temperature up to 1000 °C, and their representativeness of the worldwide produced slag in a wide EAF (electric arc furnace) steelmaking process range. The objective is to develop sustainable and low-cost thermal energy storage systems for industry waste heat recovery and in renewable energy applications. At the same time, this new valuable market for slag in the energy field could solve a big part of the waste management problem in the iron and steel sector.
•The valorisation of steel slag as low cost TES material is proposed.•Steel slag is thermally stable at least up to 1100 °C.•Steel slag has appropriate thermal properties to be used as TES material.•Steel slag is suggested as promising material for packed bed storage systems.
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