Direct Thermal Energy Storage Research Articles

Efficiency enhancement in direct thermal energy storage systems using dual phase change materials and nanoparticle additives

The study aims to enhance the reliability of direct thermal energy storage (TES) using phase change materials (PCMs) and nanoparticles, ensuring sustained heat supply even during periods of low or intermittent solar radiation. The study specifically investigates a TES system comprising a double-cylindrical shell container with two distinct PCM types: petroleum jelly or petrolatum with 1 % Al2O3 nanoparticles by volume in the outer shell and wax in the inner shell. Additionally, a redesigned heat exchanger is employed to improve heating efficiency. The study examines two configurations: an open system and a closed system with a storage water tank. The deliberate strategy of augmenting PCM volume is aimed at enhancing heat transfer during both the charging and discharging phases. The performance of closed and open system configurations is compared, with a focus on highlighting the temperature profiles during the charging and discharging processes. The incorporation of 1 % Al2O3 nanoparticles in the PCMs led to a significant enhancement in efficiency, with the two-phase materials case achieving the highest efficiency of 73 %. Furthermore, the utilization of nanoparticles resulted in an improvement in efficiency of approximately 5 %. These findings demonstrate the potential of using dual PCM layers with NPs additives in direct TES systems.

Design a solar harvester system capturing light and thermal energy coupled with a novel direct thermal energy storage and nanoparticles

Design a solar harvester system capturing light and thermal energy coupled with a novel direct thermal energy storage and nanoparticles

Performance investigation of seawater desalination system powered by central receiver concentrated solar thermal plant

Seawater desalination using solar energy is a promising solution for addressing water scarcity in arid and semi- arid regions, as it not only provides a reliable source of fresh water, but also utilizes the abundant solar energy resources in the region to power the desalination process in a sustainable way. For this, the aim of this research is to investigate the performance and economic feasibility of a concentrated solar power plant coupled with a desalination unit for sustainable electricity and freshwater production. Six different coastal sites throughout the Middle East and North Africa region were considered, i.e., Agadir (Morocco), Algiers (Algeria), Sharm el-Sheikh (Egypt), Dammam (Saudi Arabia), Salalah (Oman), and Aden (Yemen). The concentrated solar power facility has a 100 MWe net output with two tanks of direct thermal energy storage using wet cooling with seawater as the cooling agent in the condenser; the solar tower model was validated using the Gemasolar power facility in Spain; and the desalination process include a direct-contact membrane distillation (DCMD) system numerically solved using the MATLAB software®, with experimental data used to validate the model. The findings indicate that large-scale central receiver concentrated solar thermal facilities are more competitive in Sharm el-Sheikh, where annual energy output and capacity factor are expected to be 586.28GWh and 67%, respectively, while the cooling water demand is expected to be 1,793,310 m3. The nominal levelized cost of electricity (LCOEnom) is 11.2 ¢/kWh. Furthermore, water production costs are <0.5 $/m3 in Aden, Damman, Sharm el-Sheikh, and Salalah, but >1.0 $ /m3 in Agadir and Algiers. The results obtained indicate that the combination of these two technologies can be a reliable source of power and fresh water for these locations.

MODELING AND EVALUATING CONCENTRATED SOLAR POWER PLANT PERFORMANCE IN MOROCCO: A PARAMETRIC STUDY

The current paper presents the design and investigation of a 100 MW concentrated solar power (CSP) system composed of a solar tower with a dual-tank direct thermal energy storage system that uses a mixture of molten potassium nitrate and sodium, incorporated with a 111 MWe gross power block composed of a conventional Rankine cycle. The analysis was conducted at Midelt city (Morocco) (32&amp;deg;41'06 latitude and 4&amp;deg;44'42 O longitude). This study aims to evaluate the impact of cooling tower technology on solar tower power plants from a performance and economic standpoint. To achieve this objective, for each cooling tower system, the main parameters were considered: the solar multiple of the system, and the thermal storage hours (TES); their influence on the annual energy generated, the capacity factor, the annual water consumption, and the levelized cost of energy (LCOE) to demonstrate the profitability and the cost-effectiveness of the CSP system on the studied site. The modeling results reveal that in terms of performance and economic perspective, the optimal configuration corresponds to a solar multiple of 3.5 and thermal storage of 16, using the evaporative-cooling system, which resulted in a capacity factor (CF) of 80.47&amp;#37;, and LCOE of 7.68 &amp;#162; per kWh.

Solar organic Rankine cycle—Parametric analysis based on exergy vs energy approaches

Solar thermal electricity generation is one of the encouraging technologies for reducing scarcity of electricity worldwide in a renewable and sustainable manner. Solar organic Rankine cycles (SORCs) are sustainable and an eco-friendly means of power production at low- and medium-heat source temperatures. The proposed system includes a parabolic trough collector based solar system, which operates with Therminol VP-1 oil, a two-tank direct thermal energy storage unit, and an organic Rankine cycle (ORC) operates with a working fluid Toluene. Improvement in efficiencies of components has a cascading benefit in the performance of SORC, operating costs, and payback period. A comparative energy and exergy analysis study is performed to assess the thermodynamic performance of subcritical non-recuperative solar organic Rankine cycle on the basis of heat source temperatures and ORC operating parameters. Iterative procedure is adapted in the analysis to find optimal operating parameters to maximize efficiency. Maximum energetic and exergetic efficiencies of SORC are calculated at various optimal T5 and pevp. Variations of optimal mass flow rate values with respect to time and ηI, ηII with respect to heat source temperatures are plotted. In all, the energy efficiency of the overall system remained almost the same, when the proposed system is operated at the exergy-based vs energy-based optimal operating conditions. However, significant enhancement of 6.61% and 12.42% in exergetic efficiency of ORC and overall system, respectively, are observed when SORC operates at exergy-based optimal operating conditions.

Technical and economic analysis of Brayton-cycle-based pumped thermal electricity storage systems with direct and indirect thermal energy storage

Pumped thermal electricity storage (PTES) systems have attracted increasing attention, owing to high energy density, low cost, flexible adjustable energy storage duration, and lack of geographical restrictions. At present, theoretical research for PTES is relatively deep. Further reduction of investment costs is of great value to its development and application. This paper proposes a 10-MW PTES system with indirect thermal energy storage (TES) (I-PTES). The I-PTES and a PTES system with direct TES (D-PTES) are analyzed and compared in terms of their technical and economic performances. The results show that the I-PTES is advantageous owing to its low installation cost when its electricity storage duration exceeds 6 h, despite bearing some loss in round-trip efficiency. For longer-duration electricity storage, the energy capital cost of I-PTES can be lower than 200 $/kWh, i.e., 40% lower than that of D-PTES, whereas the penalty for its round-trip efficiency can be less than 5% after optimization. For a 10-MW I-PTES system, the optimum round-trip efficiency and energy density can reach approximately 65% and 26 kWh/m3, respectively. This research provides a more economical choice for the long-duration electricity storage, and a theoretical basis for the design and optimization of high-efficiency and low-capital-cost PTES systems.

Thermocline vs. two‐tank direct thermal storage system for concentrating solar power plants: A comparative techno‐economic assessment

This paper concerns the ongoing studies on a Concentrated Solar Power (CSP) plant in operation in Ottana (Italy), comprising a 629 kW organic Rankine cycle (ORC) unit fed by a linear Fresnel solar field. Hexamethyldisiloxane (MM) and “Therminol SP-I” are used respectively as ORC working fluid and heat transfer fluid in the solar receivers. A two-tank direct Thermal Energy Storage (TES) system is currently integrated in the CSP plant, serving as a direct interface between solar field and ORC. With the view of improving the solar facility, two alternative TES configurations were proposed in this study: a one-tank packed-bed TES system using silica as solid storage media and another similar one including encapsulated phase-change material (molten salt). Comprehensive mathematical models were developed for simulating daily behaviour as well as for assessing yearly performance of the various TES technologies. Furthermore, a preliminary economic analysis was carried out. Results showed poorer response of the one-tank TES system to large fluctuations in the ORC inlet fluid temperature, leading to reduction in the mean ORC efficiency (18.2% as against 19.7% obtained with the two-tank TES). Conversely, higher energy storage density and lower thermal losses were obtained adopting the one-tank TES, resulting in about 5% more annual solar energy yield. Invariably, equivalent annual ORC energy production of 0.92 GWh/year was obtained for the three TES configurations. Additionally, adopting a one-tank TES system meant that the purchase costs of a second tank and its storage medium (thermal oil) could be saved, resulting in investment costs about 45% lower and, ultimately, levelized cost of storage about 48% lower than what obtains in the two-tank TES system.

Thermodynamic design and parametric performance assessment of a novel cogeneration solar organic Rankine cycle system with stable output

In areas rich in solar energy, meeting the energy requirement using renewable energy sources can address environmental issues by reducing the use of fossil fuels. In this study, thermodynamic design, simulation, daily and monthly evaluation of a novel cogeneration solar organic Rankine cycle (ORC) system with the capability of electricity and domestic hot water (DHW) production with stable output are performed under transient environmental conditions. The main components of the integrated system are a solar field based on parabolic dish concentrators (PDCs), a direct thermal energy storage (TES) system using two separate tanks, and an ORC power field which was modeled using TRNSYS software. In this system, intending to generate 200 KW of electricity, Benzene fluid in a recuperative ORC indicated a better performance than Cyclohexane, Toluene, and n-Hexane fluids with an energy efficiency of 21.89% and the lowest required inlet temperature for the turbine as 266.1 °C. The highest working hours of the system were obtained in the middle months of the year with an average DHW production of 12.8 h/day (more than 200 m3/day) and 9.1 h of electricity generation. While during the coldest month of the year (December), the system could provide 4.1 h of DHW with 74.5 m3/day of storage. Also, with the annual average of energy efficiency for the solar field as 78.9%, thermal and electric efficiency of the integrated system was calculated as 69.4% and 15.08%, respectively. From the economic analysis of the proposed system, the net annual benefit of the system and return of capital’s period were calculated as 150,815.3 US$ and 7.3 years, respectively.

A two-step procedure for the selection of innovative high temperature heat transfer fluids in solar tower power plants

This work compares with a two-step procedure the performance of different Heat Transfer Fluids (HTF) for high temperature receiver applications (up to 715 °C) in advanced Solar Tower (ST) plants. The most promising molten salts and liquid metals are initially selected and ranked according to their performance, estimated with different Figures of Merit (FoM) available in literature or newly defined. For the best performing fluids, different hydraulic configurations and tube diameters at fixed receiver size are tested. The optimized external tubular receiver configuration for each HTF is then implemented in a ST plant and its performance is assessed through a detailed techno-economic analysis, considering the use of a direct thermal energy storage system and of a sCO2 based power cycle. As a second step, the yearly electricity yield and the LCOE are evaluated for two different sites. Results show NaCl–MgCl2 as the best option for the considered type of plant with a LCOE of 151 $/MWh, which is anyhow 10% higher than the reference Solar Salts case.

Assessing geothermal/solar hybridization – Integrating a solar thermal topping cycle into a geothermal bottoming cycle with energy storage

Geothermal and concentrating solar power (CSP) technologies typically use heat at different temperatures in their commercial deployments. This enables a technically viable hybridization of a solar topping cycle and a geothermal bottoming cycle at locations where both resources are available. In this article, an underperforming geothermal power system based at Burley, Idaho is used as a baseline to investigate the technical and economic potential of such a hybrid cycle. A direct thermal energy storage (TES) system is also integrated to overcome the intermittency of the solar resource. Design and off-design behavior of key components are modelled to simulate the annual performance of the hybrid system on an hourly basis. The sizing of the solar field and thermal storage is investigated and is seen to significantly impact the annual electricity generation and efficiency. Various cost scenarios for the solar field and thermal energy storage are investigated. An economic metric – levelized cost of electricity (LCOE) – is used to optimize the solar field sizing and TES capacity. The hybrid plant converts the additional solar heat input into additional work with an efficiency of 32.9%. Retrofitting a geothermal plant with solar and eight hours of energy storage can achieve an LCOE of 0.136 $/kWhe in current cost scenarios and 0.081 $/kWhe in a future cost reduction scenario. Although the hybrid system cannot directly compete with current PV systems without batteries, it has an LCOE 32% lower than that of a PV-battery system. This paper provides insights into the research and development of the future grid with a high renewable energy penetration and encourages further study of energy hybridization for improved efficiencies and economics.

Multi-mode solid–gas thermochemical resorption heat transformer using NiCl2-SrCl2/NH3

Thermal energy storage is considered as an attractive technology for waste heat recovery and solar energy utilization. A multi-mode solid–gas thermochemical resorption heat transformer for thermal energy storage has been developed. The working principle of three different operating modes, including the direct thermal energy storage and release mode, thermal energy upgrade mode and combined cooling and heating effect mode, is addressed. Performance analysis and comparisons of thermochemical resorption heat transformer are carried out by employing NiCl2-SrCl2/NH3 under the different operating modes. Thermodynamic analysis showed that the lowest and highest heat storage efficiency occur in the thermal energy upgrade mode and the direct thermal energy storage and release mode, respectively. The highest heat storage efficiency obtained is 0.978. Among three operating modes, the thermal energy upgrade mode has the lowest thermal energy storage density, while the combined cooling and heating effect mode has the highest thermal energy storage density. The smallest and largest thermal energy storage density are 1320.66 kJ/kg and 2646.92 kJ/kg, respectively. The developed thermochemical sorption energy storage provides a compact high energy density heat storage approach and therefore can boost the application of thermal energy storage in large-scale industrial processes and renewable energy utilization.

The Ottana solar facility: dispatchable power from small-scale CSP plants based on ORC systems

The Ottana solar facility aims to demonstrate the capabilities of concentrating solar technologies to provide dispatchable power and ancillary services at distribution level. The facility includes a 630 kW Concentrating Solar Power (CSP) plant with thermal storage coupled with a 400 kW Concentrating Photovoltaic (CPV) plant with electrochemical storage. The CSP + CPV plant aims to study the ability of the integrated concentrating solar systems to deliver scheduled power profiles for the following day on the basis of weather forecasting data. The CSP section is based on linear Fresnel collectors using thermal oil as heat transfer fluid and a two-tank direct Thermal Energy Storage (TES) system with a storage capacity of about 15 MWht. The power generation is carried out by a 630 kW Turboden 6HR Special ORC unit. This paper focuses on a description of the CSP plant section and on the analysis of its expected performance. In particular, the control strategy developed for determining the daily power profiles starting from the weather forecasting data is presented. Moreover, the first operating results and the expected performance of the CSP plant are reported and discussed.

Compatibility Study Between Synthetic Oil and Vitrified Wastes for Direct Thermal Energy Storage

Compatibility tests were conducted between synthetic oil and potential solid filler materials in a thermocline tank built at the PROMES-CNRS laboratory. These experiments consisted of placing the oil and the solid materials together in small crucibles (2.3 L) and performing compatibility tests at 300 °C and accelerated ageing tests at 330 °C for 500 h. The mutual influence of the oil and the solid materials was assessed through different measurements: X-ray diffraction and scanning electron microscopy. The influence of the solid on the oil was assessed by measuring thermo-physical and chemical properties. While no significant degradation of the oil is measured at 300 °C, at 330 °C, an increase in the oil degradation rate was observed. Its density, thermal conductivity and specific heat did not change, but its viscosity showed a significant increase. However, after accelerated ageing tests at 330 °C, the oil still shows good heat transfer performance. The solid crystalline structure did not change during the test but some of the samples seemed to absorb oil.

Conceptual Study of Central Receiver Systems with Liquid Metals as Efficient Heat Transfer Fluids

Abstract Concentrated Solar Power plants (CSP) provide several advantages to other energy conversion concepts. However, they are still not competitive in price, compared to conventional power plants. But there is still potential to reduce the cost. The higher heat conductivity of liquid metals leads to very high heat transfer coefficients – ten times higher as with molten salts. This big advantage could increase the efficiency and lower the cost of CSP plants. In order to optimize such a power plant regarding efficiency and cost, detailed information of each component of the system is necessary. This paper shows several system concepts in which liquid metals can be used as heat transfer fluid. In addition, several liquid metal pump types are investigated as well as thermal energy storage concepts. With the assumptions and boundary conditions taken in this model, direct thermal energy storage with liquid metal is prohibitive. But some innovative indirect storage systemswith liquid metals show costs in the same range as with a 2-Tank molten salt storage.

Assessing thermal energy storage technologies of concentrating solar plants for the direct coupling with chemical processes. The case of solar-driven biomass gasification

Dynamic simulation, design improvements and control issues in solar power plants might compete with special considerations on energy storing techniques. In order to provide the stability in production of power or chemical commodities in spite of discontinuity in the source of energy, i.e., sun, overall concerns in the details of solar power plant, competition and comparison of common storing technologies should be taken into account to ensure the effectiveness and continuity of the supply. This research activity is aimed at extending the study from the power generation purpose to the solar-supplied chemical commodities production, highlighting the limitations of certain well-established thermal energy storage techniques when concentrating solar is directly coupled with chemical processes. The (intrinsically dynamic and closed-loop) simulation of solar power plants and direct thermal energy storage technologies is performed for the direct thermal energy storage technologies and, only for the case of thermocline, it is coupled with computational fluid-dynamic (CFD) studies for the proper assessment of molten salt and steam temperature trends. To investigate benefits/restrictions of the storage technologies, the solar steam generation is integrated with the gasification of biomasses for syngas production. Also, first-principles dynamic model for the biomass gasifier is provided.

Thermal energy storage for solar-powered organic Rankine cycle engines

The feasibility of energy storage is of paramount importance for solar power systems, to the point that it can be the technology enabler. Regarding concentrated solar power (CSP) systems, the implementation of thermal energy storage (TES) is arguably a key advantage over systems based on photovoltaic (PV) technologies. The interest for highly efficient and modular CSP plants of small to medium capacity (5kWE–5MWE) is growing: organic Rankine cycle (ORC) power systems stand out in terms of efficiency, reliability and cost-effectiveness in such power-range. In this paper a thorough investigation on thermal storage systems tailored to high-temperature (≈300°C) ORC power plants is addressed first, stemming from the observation that the direct storage of the ORC working fluid is effective thanks to its favourable thermodynamic properties. The concept of complete flashing cycle (CFC) is then introduced as a mean of achieving an unmatched system layout simplification, while preserving conversion efficiency. This is a new variant of the Rankine cycle, whereby the vapour is produced by throttling the organic working fluid from liquid to saturated vapour conditions. The presentation and discussion of a case study follows: a 100kWE CFC system with direct thermal energy storage, coupled with state-of-the-art parabolic trough collectors. The proposed turbogenerator achieves an estimated 25% efficiency, which corresponds to a value of 18% in design conditions for the complete system. Considering siloxanes as working fluids, the estimated values of storage density are around 10kWeh/mstorage3.

Study of Direct Thermal Energy Storage Technologies for Effectiveness of Concentrating Solar Power Plants

Study of Direct Thermal Energy Storage Technologies for Effectiveness of Concentrating Solar Power Plants

Dynamic simulation of concentrating solar power plant and two-tanks direct thermal energy storage

The discontinuous nature of the solar energy forces to study the dynamic behavior of solar plants to characterize their operations, to deepen their process understanding and to improve the performance and maintenance. The present paper focuses on the dynamic simulation and control of concentrating solar plants with the aim to define a reasonably simplified layout as well as to highlight the main issues to characterize the process dynamics of these energy systems and their related energy storages. Detailed first-principles mathematical models of key unit operations are developed, implemented, and integrated into commercial codes to improve the reliability of the plant dynamic simulation as well as the prevision accuracy. The case of Archimede concentrating solar power plant with the related two-tanks direct thermal energy storage technology is investigated.