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Electricity storage is becoming one of the main challenges for the massive deployment of renewables. Thermal energy storage is gaining momentum, with molten salts-based systems being the state-of-the-art technology. As an alternative, Thermochemical Energy Storage (TCES) is a promising system that can increase the system performance in terms of energy storage density, maximum heat discharge temperature and long-term storage capacity. This work proposes and preliminary evaluates the performance of a novel modular Thermochemical Energy Storage (TCES) system based on the Calcium-Looping (CaL) process. The modularity allows its integration with multiple renewable energy sources into different high-temperature applications, including hard-to-decarbonise applications. Heat for the charging stage is provided by electrical heaters connected either to a Photovoltaic (PV) facility or directly to the grid. Limestone particles are heated, and once they reach their decomposition temperature (∼ 930 °C at 1 bar), the released CO 2 is removed from the reactor, cooled, compressed, and stored. When the stored energy discharge is required, CO 2 is supplied to the reactor to produce calcium carbonate and release the stored heat (∼ 400–875 °C). In the proposed concept, the solids remain in the reactor, and CO 2 is added or removed depending on the stage. As cases of study of the concept, energy storage systems integrated with PV plants of 0.5 and 20 MW e and grid-based storage are considered. An hourly simulation throughout the year is performed. Results show an energy density above 1 GJ/m3, higher than current molten-salt-based systems. The levelized energy storage cost is below 100 €/MWh for the grid-based storage, highlighting its potential to contribute significantly to the global energy transition. • A novel modular thermochemical electricity storage system is proposed. • The levelized storage cost ranges from approximately 85–190 €/MWh. • All analysed cases exhibit a high energy storage density (∼ 1 GJ/m3). • The implementation of an energy arbitrage strategy proves to be cost-effective. [ABSTRACT FROM AUTHOR]

The Calcium-Looping (CaL) process, based on the multicyclic calcination-carbonation of CaCO 3 /CaO, is considered a promising Thermochemical Energy Storage (TCES) technology to be integrated into Concentrating Solar Power (CSP) plants. This work proposes a novel CaL integration that operates at low-pressure calcination under pure CO 2 and a moderated temperature. Low-pressure calcination (0.01 bar) provides a suitable solution to mitigate CaO sintering and its consequent loss of reactivity in the carbonation stage. Since the temperature for quick calcination in a pure CO 2 atmosphere is decreased (from around 950 °C at 1 bar to 765 °C at 0.01 bar), the energy losses at the receiver are minimised. In addition, a reduced calcination temperature allows for the use of metallic receivers already tested at the MW-scale, which significantly increases the CSP-CaL integration reliability. Moreover, multicycle CaO reactivity is promoted in short residence times, allowing the use of a simpler reactor design. Furthermore, there is an increase of 85% in the energy storage density of the system. The proposed plant proposes a smooth integration of the CaL process in CSP plants, with a moderate storage level and supported by a natural gas backup system (solar share higher than 50%). The results show that the solar thermal-to electric efficiency is above 30%. [ABSTRACT FROM AUTHOR]

• The proposed SCC-TCES allows boost the solar share in combined cycles above 70%. • Receiver thermal-to-electric efficiency are in the range 45–50%. • Annual performance is evaluated through four solar radiation clusters from real data. • A 360° heliostats solar field with three cavity receivers (200 m tower) is designed. The present work proposes integrating a high-temperature thermochemical energy storage cycle to boost the solar contribution in solar combined cycles. The main feature of the plant is the possibility of storing solar energy at a very high temperature and releasing it on demand to drive the combined cycle in the absence of solar radiation. Based on the reversible calcination-carbonation of CaCO 3 /CaO, the Calcium-looping process is proposed since it allows power production above 900 °C by using cheap, non-toxic and widely available raw materials (i.e. limestone or dolomite). Based on an air-open and a CO 2 -closed combined cycle, two potential configurations are modelled and analysed, including designing a 360° solar field with a 200-meter tower. The novel solar combined cycle analyzed in the present work enhances the annual solar share above 50%, whilst the current state-of-the-art technology is below 15%. From actual solar irradiation data and clustering analysis, results show overall plant efficiencies over 45% (considering off-design performance) with a very high dispatchability, which justifies the interest in further developing this novel cycle. [ABSTRACT FROM AUTHOR]

• A fully novel High Temperature Storage Solar Combined Cycle (HTSSCC) is proposed. • Thermochemical energy storage allows a 24 h operation without fuel input. • The solar share in the solar combined cycle is highly enhanced (ideally up to 100%). • The base case analysed leads to a net solar-to-electric efficiency of 44.5%. The integration of Concentrating Solar Power (CSP) in combined cycles is a subjects of increasing attention. Combined cycles require high temperature at the gas turbine inlet (typically over 1000 °C), which hinders plant operation in the absence of direct solar radiation using currently commercial storage technologies based on molten salts (with a temperature limit around 600 °C). Thus, solar power share in current Integrated Solar Combined Cycles (ISCC) is typically lower than 20%, while most of the thermal power required is provided by natural gas. The present manuscript proposes the integration in combined cycles of a Thermochemical Energy Storage (TCES) system based on the Calcium-Looping process, which can release the stored energy at temperatures above 1000 °C. The storage charging step uses the heat provided by a CO 2 stream previously heated in a high-temperature solar receiver. The configuration of the solar receiver-calciner is fundamental to determine the amount of storable energy. Results from the conceptual model simulation predict overall plant efficiencies above 45% (excluding solar side losses), suggesting a high potential for the development of this novel integration that would allow enhancing the solar share in combined cycles. [ABSTRACT FROM AUTHOR]

• Validated linear optimisation model for calcium-looping process integrated with CSP. • Multi-objective operational optimisation for hybrid solar power plants with TCES. • Multi-objective optimisation is key to balance competitiveness and dispatchability. • Configurations described as case studies can achieve capacity factors around 70%. • Affordable full-dispatchability possible in locations with excellent solar resource. Energy storage is key to decarbonising the energy sector by reducing intermittency and increasing the integration of renewable energy. Thermochemical energy storage (TCES) integrated with concentrated solar and photovoltaic power plants, has the potential to provide dispatchable and competitive energy. Here we develop a multi-objective optimisation framework to find the best operational strategy of a hybrid solar power plant with a TCES system. The model uses a typical meteorological year to optimise one-year hourly operation. The results demonstrate that the integration of a calcium-looping process as TCES in a concentrated solar power plant provides dispatchability and, when hybridised with photovoltaic, enhances its competitiveness with current electricity prices. The low mismatch between supply and demand, even when a fixed commitment is required throughout the year, together with a high overall efficiency, indicates that the integration of calcium-looping in hybrid solar power plants is an opportunity to increase the penetration of solar energy in the power sector. Through the optimisation framework presented, a seasonal energy storage analysis can be developed, although a second optimisation stage is required to improve the sizing of the main components of the system in order to further reduce the energy costs. [ABSTRACT FROM AUTHOR]

Energy storage is a key factor in the development of renewables-based electrical power systems. In recent years, the thermochemical energy storage system based on calcium-looping has emerged as an alternative to molten salts for energy storage in high-temperature concentrated solar power plants. This technology still presents some challenges that could be solved by integrating the thermochemical energy storage system based on calcium hydroxide. This work studies a novel concentrated solar power system integrating calcium-looping and calcium hydroxide thermochemical energy storage systems. The results show that the combined use of hydration-dehydration cycles in the calcination-carbonation processes of the calcium looping for energy storage could partially solve the issue related to the multicyclic deactivation of calcium oxide. The improvement in the conversion of calcium oxide during carbonation is demonstrated experimentally when hydration-dehydration cycles are combined. Numerical simulations demonstrate the technical feasibility of the integrated process, with efficiencies ranging between 38-46%, improved with the increase in calcium oxide conversion in the carbonator, showing the potential of the proposed integration. • Novel integration of thermo-chemical energy storage systems based on CaO. • High temperature calcium looping as main high-efficiency energy storage system. • Medium temperature calcium hydroxide integrated as secondary energy storage system. • Dehydration-hydration processes enhance CaO multicyclic activity in carbonation. • Combined joint operation with roundtrip efficiencies exceed 45%. [ABSTRACT FROM AUTHOR]

Thermochemical energy storage is attracting interest as a relevant alternative energy storage system in concentrating solar power plants. Efficient, low-cost, and environmentally friendly thermal energy storage is one of the main challenges for the large-scale deployment of solar energy. The reversible hydration/dehydration process of calcium oxide is one of the most promising concepts for energy storage integration at intermediate temperatures in solar plants. The efficient integration of concentrated solar power with a thermochemical energy storage system based on the calcium hydroxide concept, individually or integrated into a hybrid system with sensible heat storage, can be a feasible solution for long-term energy storage. Efficient energy recovery and subsequent power production are crucial. This work presents a novel analysis of the indirect integration of different power cycle configurations to optimise the roundtrip efficiency of the system. Steam Rankine, closed CO 2 Brayton, and organic Rankine cycles are considered. The analyses show power block efficiencies in the range of 38–50%, with a global roundtrip efficiency of 37.1% in the case of the CO 2 supercritical cycle. [ABSTRACT FROM AUTHOR]

This study introduces an innovative solution to address the challenges arising from the volatile natural gas market and the growing integration of renewable energy sources within the industrial sector. The research strives to confront this challenge by including renewable methanol (CH 3 OH) and converting it into methane (CH 4), with an intermediate step involving synthesis gas (CO/H 2) by using concentrating solar power. This approach provides a sustainable and adaptable solution to reduce dependence on natural gas. The process entails a methanol decomposition reaction at moderate temperatures (<350 °C). Subsequently, the synthesis gas is compressed to 40 bar, stored, and discharged through a methanation process that can be conducted at high temperatures (>500 °C). The resulting methane is used as fuel for gas turbines and can also serve as feedstock in the chemical industry. The simulations were conducted in ASPEN HYSYS and yielded overall system efficiencies exceeding 29% and roundtrip efficiencies of 44%. Through techno-economic optimisation of the reaction conditions, competitive levelized fuel costs (LCOF) of €172/MWh and future LCOE values of €145/MWh were achieved. These findings present an innovative strategy for integrating gas turbine cycles and additional conversion pathways for green methanol. • A novel flexible storage system for conventional power generation is proposed. • Green methanol to methane conversion process from intermediate step to synthesis gas. • Overall system efficiencies above 29% and roundtrip efficiencies of 44% were achieved. • Competitive levelized fuel cost of €172/MWh and future LCOE values <€265/MWh are reached. [ABSTRACT FROM AUTHOR]