Current, Projected Performance and Costs of Thermal Energy Storage

The technology for storing thermal energy as sensible heat, latent heat, or thermochemical energy has greatly evolved in recent years, and it is expected to grow up to about 10.1 billion US dollars by 2027. A thermal energy storage (TES) system can significantly improve industrial energy efficiency and eliminate the need for additional energy supply in commercial and residential applications. This study is a first-of-its-kind specific review of the current projected performance and costs of thermal energy storage. This paper presents an overview of the main typologies of sensible heat (SH-TES), latent heat (LH-TES), and thermochemical energy (TCS) as well as their application in European countries. With regard to future challenges, the installation of TES systems in buildings is being implemented at a rate of 5%; cogeneration application with TES is attested to 10.2%; TES installation in the industry sector accounts for 5% of the final energy consumption. From the market perspective, the share of TES is expected to be dominated by SH-TES technologies due to their residential and industrial applications. With regard to the cost, the SH-TES system is typically more affordable than the LH-TES system or the TCS system because it consists of a simple tank containing the medium and the charging/discharging equipment

Experimental Analysis of Heat Transfer in Passive Latent Heat Thermal Energy Storage Systems for CSP Plants

Abstract Thermal energy storage is a key factor for efficiency, dispatchability and economic sustainability of concentrated solar plants. The latent heat storage systems could ensure a significant reduction in construction costs and environmental impact, because of its high storage energy density. In LHTES, the heat transfer between the heat transfer fluid and the storage system is strongly limited by the reduced thermal conductivity of the storage media. For operating temperatures between 200 and 600 °C, the most used storage media are salts. In order to evaluate solutions which promote the thermal conductivity, by increasing the exchange surface and/or the addition of nanoparticles to the storage media, Enea set up a small facility to test some storage concepts. In this facility, a diathermic oil flows through three elementary "shell-and-tube" storage systems, connected in series, reaching a maximum temperature of about 280 °C. The elementary storage systems are filled with a mixture of sodium and potassium nitrates salts, which melt at about 225 °C. Moreover a small percentage of alumina and silica nanoparticles were added to this mixture. The results of the experiments show an increase of the thermal diffusivity of the medium not only for the presence of fins on the heat transfer tubes but also because of convective flows within the melted fraction were established. These phenomena strongly reduce the charging times of the system (by about 30%). Instead, the presence of nanoparticles increases the thermal capacity and the thermal conductivity of the storage system but seems not to have a relevant effect on the thermal diffusivity of the mixture. This behavior depends on the type of used nanoparticles, which can significantly change over time some characteristics of the storage medium, in which they are dispersed, leaving other characteristics unchanged, according to mechanisms which are still to be well understood

Hybrid solar-biomass combined Brayton/organic Rankine-cycle plants integrated with thermal storage: Techno-economic feasibility in select Mediterranean areas

This paper presents a thermodynamic analysis and techno-economic assessment of a novel hybrid solar-biomass power-generation system configuration composed of an externally fired gas-turbine (EFGT) fuelled by biomass (wood chips) and a bottoming organic Rankine cycle (ORC) plant. The main novelty is related to the heat recovery from the exhaust gases of the EFGT via thermal energy storage (TES), and integration of heat from a parabolic-trough collectors (PTCs) field with molten salts as a heat-transfer fluid (HTF). The presence of a TES between the topping and bottoming cycles facilitates the flexible operation of the system, allows the system to compensate for solar energy input fluctuations, and increases capacity factor and dispatchability. A TES with two molten salt tanks (one cold at 200 °C and one hot at 370 °C) is chosen. The selected bottoming ORC is a superheated recuperative cycle suitable for heat conversion in the operating temperature range of the TES. The whole system is modelled by means of a Python-based software code, and three locations in the Mediterranean area are assumed in order to perform energy-yield analyses: Marseille in France, Priolo Gargallo in Italy and Rabat in Morocco. In each case, the thermal storage that minimizes the levelized cost of energy (LCE) is selected on the basis of the estimated solar radiation and CSP size. The results of the thermodynamic simulations, capital and operational costs assessments and subsidies (feed-in tariffs for biomass and solar electricity available in the Italian framework), allow estimating the global energy conversion efficiency and the investment profitability in the three locations. Sensitivity analyses of the biomass costs, size of PTCs, feed-in tariff and share of cogenerated heat delivered to the load are also performed. The results show that the high investment costs of the CSP section in the proposed size range and hybridization configuration allow investment profitability only in the presence of a dedicated subsidy framework such as the one available in the Italian energy market. In particular, the LCE of the proposed system is around 140 Eur/MWh (with the option to discharge the cogenerated heat) and the IRR is around 15%, based on the Italian electricity subsidy tariffs. The recovery of otherwise discharged heat to match thermal energy demand can significantly increase the investment profitability and compensate the high investment costs of the proposed technology

New Trends in Designing Parabolic trough Solar Concentrators and Heat Storage Concrete Systems in Solar Power Plants

Energy availability has always been an essential component of human civilization and the energetic consumption is directly linked to the produced wealth. In many depressed countries the level of solar radiation is considerably high and it could be the primary energy source under conditions that low cost, simple-to-be-used technologies are employed. Then, it is responsibility of the most advanced countries to develop new equipments to allow this progress for taking place. A large part of the energetic forecast, based on economic projection for the next decades, ensure us that fossil fuel supplies will be largely enough to cover the demand. The predicted and consistent increase in the energetic demand will be more and more covered by a larger use of fossil fuels, without great technology innovations. A series of worrying consequences are involved in the above scenario: important climatic changes are linked to strong CO2 emissions; sustainable development is hindered by some problems linked to certainty of oil and natural gas supply; problems of global poverty are not solved but amplified by the unavoidable increase in fossil fuel prices caused by an increase in demand. These negative aspects can be avoided only if a really innovative and more acceptable technology will be available in the next decades at a suitable level to impress a substantial effect on the society. Solar energy is the ideal candidate to break this vicious circle between economic progress and consequent greenhouse effect. The low penetration on the market shown today by the existent renewable technologies, solar energy included, is explained by well-known reasons: the still high costs of the produced energy and the \u201cdiscontinuity\u201d of both solar and wind energies. These limitations must be removed in reasonable short times, with the support of innovative technologies, in view of such an urgent scenario. On this purpose ENEA, on the basis of the Italian law n. 388/2000, has started an R&D program addressed to the development of CSP (Concentrated Solar Power) systems able to take advantage of solar energy as heat source at high temperature. One of the most relevant objectives of this research program (Rubbia, 2001) is the study of CSP systems operating in the field of medium temperatures (about 550\ub0C), directed towards the development of a new and low-cost technology to concentrate the direct radiation and efficiently convert solar energy into high temperature heat; another aspect is focused on the production of hydrogen by means of thermo-chemical processes at temperatures above 800\ub0C. As well as cost reductions, the current innovative ENEA conception aims to introduce a set of innovations, concerning: i) The parabolic-trough solar collector: an innovative design to reduce production costs, installation and maintenance and to improve thermal efficiency is defined in collaboration with some Italian industries; ii) The heat transfer fluid: the synthetic hydrocarbon oil, which is flammable, expensive and unusable beyond 400\ub0C, is substituted by a mixture of molten salts (sodium and potassium nitrate), widely used in the industrial field and chemically stable up to 600\ub0C; iii) The thermal storage (TES): it allows for the storage of solar energy, which is then used when energy is not directly available from the sun (night and covered sky) (Pilkington, 2000). After some years of R&D activities, ENEA has built an experimental facility (defined within the Italian context as PCS, \u201cProva Collettori Solari\u201d) at the Research Centre of Casaccia in Rome (ENEA, 2003), which incorporates the main proposed innovative elements. The next step is to test these innovations at full scale by means of a demonstration plant, as envisioned by the \u201cArchimede\u201d ENEA/ENEL Project in Sicily. Such a project is designed to upgrade the ENEL thermo-electrical combined-cycle power plant by about 5 MW, using solar thermal energy from concentrating parabolic-trough collectors. Particularly, the Chapter will focus on points i) and iii) above: - loads, actions, and more generally, the whole design procedure for steel components of parabolic-trough solar concentrators will be considered in agreement with the Limit State method, as well as a new approach will be critically and carefully proposed to use this method in designing and testing \u201cspecial structures\u201d such as the one considered here; - concrete tanks durability under prolonged thermal loads and temperature variations will be estimated by means of an upgraded F.E. coupled model for heat and mass transport (plus mechanical balance). The presence of a surrounding soil volume will be additionally accounted for to evaluate environmental risk scenarios. Specific technological innovations will be considered, such as: -higher structural safety related to the reduced settlements coming from the chosen shape of the tank (a below-grade cone shape storage); - employment of HPC containment structures and foundations characterized by lower costs with respect to stainless steel structures; - substitution of highly expensive corrugated steel liners with plane liners taking advantage of the geometric compensation of thermal dilations due to the conical shape of the tank; - possibility of employing freezing passive systems for the concrete basement made of HPC, able to sustain temperature levels higher than those for OPC; - fewer problems when the tank is located on low-strength soils

Numerical simulation of a complete charging-discharging phase of a shell and tube thermal energy storage with phase change material

Abstract Numerical simulations of a shell and tube energy storage device based on a phase change material (PCM) in vertical position are performed. The heat transfer fluid (HTF) is a diathermic oil and the PCM, made by molten salts, is confined within a closed shell surrounding the tube where the HTF flows. The energy loss through the external wall is included. The test has been carried out within the experimental activity performed by ENEA. A complete cycle is considered: the initial stabilization, the charging phase and the discharging phase. Details of flow behavior within the molten PCM are described highlighting its influence on the device performance

Investigation into the Coupling of Micro Gas Turbines with CSP Technology: OMSoP Project☆

Abstract Solar power generation has been gaining worldwide increasing interest by virtue of its ability to meet both the growing energy needs and the increasing concerns on the carbon dioxide emissions. One of the most promising Concentrated Solar Power (CSP) technologies under development uses a parabolic dish to concentrate solar power into a focal point, raising thetemperature of a working fluid which is then used in a thermodynamic cycle to generate electricity. In the OMSoP project, funded by the European Commission, it is proposed to use a Brayton cycle in the form of a micro-gas turbine (MGT), which replaces the more conventional Stirling engine,with the aim of increasing the ratio of the electric power generated to the solar energy collected and improving the operability in relation to solar energy short time fluctuations. To achieve these objectives, research and development will be conducted in all aspects of the system leading to a full scale demonstrative plant to be located at the ENEA Casaccia Research Centre.The present work deals with the activities carried out so far by ENEA, which is principally involved in the development and experimental characterization of the dish component, and in the integration of the complete system, both in terms of modelling and realization

Thermal-fluid flow within innovative heat storage concrete systems for solar power plants

Mini-symposium Computational methods for heat and fluid flow. Santa Fe, USA. Invited Lectur