To enable the widespread exploitation of intermittent, low-cost, and non-dispatchable renewable energytechnologies, energy storage plays a key role in providing the required flexibility. In the spectrum ofenergy storage systems, one out of a few geographically independent possibilities is the storage ofelectricity into heat, so-called Carnot batteries. For thermal-to-electricity reconversion, depending onthe operating energy storage temperatures, conventional or advanced power cycles can be integratedinto the system, yielding different techno-economic performances. This work proposes a methodologythat enables decision-making in selecting the adequate power cycle and Thermal Energy Storage (TES)type for a wide range of operating temperatures between 200 and 800 °C. To select the optimumcoupling of TES and power block, a techno-economic optimization has been conducted aimed atminimizing the Levelized Cost of Storage (LCOS) for different plant capacities and charging costs. Thestudy explores various power block configurations, including Organic Rankine Cycle (ORC), steamRankine cycle, and supercritical CO2 (sCO2) Brayton cycle. Additionally, it evaluates different TESoptions such as molten salt, particle, and air packed bed TES. Results highlight that, for a charging costof 50 EUR/MWh, the most cost-effective combination of TES and power block involves sCO2 powerblocks with recompression and intercooling, along with particle-based TES operating at temperaturesbetween 600 to 800 °C and a temperature difference of 200 °C. ORCs are suitable for low temperatures(up to 350 °C) and high temperature differences, while the steam Rankine cycle is considered optimalbetween the low-temperature and the sCO2 preferred regions. Air-packed bed TES is suggested as aviable option when TES represents a large share of the capital cost, with low charging costs, low hottemperatures, or low temperature differences. Molten salt TES is ideal when its design temperaturesalign with the operating limitations of the salts. Particle-based TES is the most cost-effective choiceacross a wide range of temperatures, at small (10 MW) and large scales (100 and 200 MW).

This paper presents an update on the status of the EU-funded H2020 project SOLARSCO2OL, with the main target and accomplished project objectives and deliverables. SOLARSCO2OL is dedicated to demonstrating a 2 MW supercritical CO2 (sCO2) cycle utilizing heat derived from molten salts within a solar facility, namely the Evora Molten Salt Platform (EMSP), in Portugal. SOLARSCO2OL will be the first MW scale EU sCO2 power block that will be coupled with an existing molten salt parabolic trough collector system featuring high-temperature molten salt thermal energy storage (TES). The demo plant will include a molten salt electric heater, boosting the salt temperatures before they enter into the salt-to-sCO2 primary heater, ensuring a Turbine Inlet Temperature (TIT) of 565 °C. Successful demonstration of sCO2 power block and molten salt loop components at MW scale, along with complete system integration, marks a pivotal stride toward more competitive and efficient CSP plants in the short term, capitalizing on existing commercially viable molten salt CSP plants. Driven by an industry-oriented consortium, SOLARSCO2OL seeks to advance this concept's marketability by 2030. This is explored through feasibility studies for scaling up, environmental and social analyses, and encouragement of business cases within the EU. The project was initiated in October 2020 but experienced a suspension from March 2022 to February 2023 due to financial constraints. This paper focuses on the engineering, design and integration aspects of the new demonstration plant now located in Evora, Portugal. The initial phase, centered around design optimization, has been successfully completed, and the project's current focus is on tasks like manufacturing, prototype testing, detailed engineering, procurement, and installation. The concluding phase will be the operation of the demo. The demonstration campaign is projected to conclude by the end of 2025.

To enable the widespread exploitation of intermittent, low-cost, and non-dispatchable renewable energy technologies, energy storage plays a key role in providing the required flexibility. This study introduces maps of optimal combination of Thermal Energy Storage (TES) and power cycles, supporting decision-making in power-to-heat-to-power applications. These maps span a wide temperature range from 200 to 1200 °C and are proposed for different charging costs, installed capacities, and storage durations. For thermal-to-electricity reconversion, this study explores power blocks including steam Rankine cycle, supercritical CO₂ (sCO₂) Brayton cycle, Organic Rankine Cycle (ORC), and combined gas turbine with Rankine and sCO2. Results highlight that, in a grid-based plant with a 50 EUR/MWh charging cost, the most cost-effective pairing involves sCO2 cycles with recompression and intercooling, with particle TES at 600–800 °C. Air packed-bed suits scenarios where TES contributes significantly to capital costs or involves low charging costs. Molten salt TES is the optimal choice when the design temperatures align with salt temperature limitations. Particle TES proves cost-effective across a broad temperature range and scales (10–200 MW). For solar-based systems, the integration of molten salt TES with simple sCO2 recuperated cycles demonstrates market potential for southern European locations.

Techno-economic performance simulations play a crucial role in assessing the feasibility, cost-effectiveness, and overall impact emerging renewable energy system designs. Concentrating Solar Power (CSP) is a promising technology for decarbonizing the electricity grid by integrating cost-effective thermal energy storage (TES). However, their development is hindered by their high levelized cost of electricity compared to other energy sources. Hybrid systems that connect with solar photovoltaic (PV) and battery systems are a viable solution to reduce the cost of these plants while maintaining flexibility and guaranteeing firm production despite the intermittence of solar availability. This paper presents MoSES (Modeling of Solar Energy Systems), an open-source techno-economic modeling tool designed to evaluate the feasibility and cost-effectiveness of hybrid PV-CSP plants. While existing simulation tools perform well with established systems, they face challenges when adapting to new components, configurations, and operating strategies. MoSES addresses this challenge by providing a simulation framework and a versatile library of components and control strategies that can be modified to meet end-users’ needs. The tool enables simulation activities to assess the advantages, optimize the design, and benchmark different hybrid PV-CSP plant layouts. This paper outlines the methodology employed to determine system design, costs, and key performance indicators, as well as to estimate operational performance. Furthermore, a case study is presented to illustrate MoSES's effectiveness as a tool for conducting annual simulations despite being in its early stages of development. MoSES provides a valuable contribution to the solar community by enabling the evaluation of the impact of emerging solar-based system designs.

The present work proposes a methodology that enables decision-making in selecting the adequate power cycle and Thermal Energy Storage (TES) type for a wide range of operating temperatures between 380 and 1200 °C. A broad spectrum of power block configurations has been explored including steam Rankine, gas turbine, supercritical CO2, (sCO2) combined gas turbine with Rankine, and combined gas turbine with sCO2. The study also evaluated molten salt, particle, and air packed bed TES to identify the most cost-effective power cycle and TES combination. A techno-economic optimization has been conducted aimed at minimizing the Levelized Cost of Storage (LCOS) for different plant capacities and charging costs. Results show that coupling of a sCO2 power block with recompression and intercooling with a particle TES is the most cost-effective solution for a 100 MWe plant with 12 hours of storage and a charging cost of 50 EUR/MWh. This achieved an LCOS value of 154.7 EUR/MWh at 750 °C with a 200 °C temperature difference. Particle-based energy storage is the most cost-effective option for a wide range of temperature combinations, while an intercooled sCO2 power block with an air-packed bed TES should be preferred when electricity is free, and storage represents a significant portion of the capital cost. Molten salt TES is the optimal choice provided that the design temperatures align with the limitations of the salts.

The present study explores the integration of supercritical CO₂ (sCO₂) power cycles into Concentrating Solar Power (CSP) plants using molten salt, and the hybridization of these plants with solar photovoltaic (PV) systems through electric heaters. Techno-economic evaluations determined the optimal power cycle configuration and subsystem designs for two different scales and locations and then compared them with state-of-the-art solar power plants. The results show that hybridizing PV with state-of-the-art CSP can lead up to a 22% reduction in the Levelized Cost of Electricity (LCOE) compared to standalone CSP systems. This hybridization and the use of electric heaters are particularly beneficial for small-scale installations and locations with low DNI/GHI ratios. By replacing the steam Rankine cycle with a sCO₂ power block, a further 42% reduction in LCOE can be achieved at small scales, even with a simple recuperated cycle. In conclusion, the hybridization with PV and the integration of sCO₂ power blocks provide cost benefits despite the temperature limitations imposed by the molten salt. Hybrid PV-CSP plants with sCO₂ power blocks prove to be a cost-effective solution for capacity factors exceeding 60%. For lower capacity factors, configurations combining PV with battery energy storage or PV with electric heaters, thermal energy storage, and sCO₂ power blocks are preferable options.

The present work performs a thermodynamic analysis of a hybrid CSP – PV plant characterized by a particle tower CSP running a supercritical CO2 power unit and a PV field. The two plants are hybridized by employing a particle electrical heater that allows to store the electricity produced in excess by the PV field as thermal energy in the CSP storage. The PV production is compensated by the CSP plant to achieve the maximum power that can be injected into the grid (25 MW). The main key performance indicators considered in this analysis are the capacity factor, the share of energy wasted, the annual energy yield, the electric heater utilization factor, and the share of TES charged by the electric heater. The influence of the plant solar multiple, storage size, PV nominal size, electric heater efficiency, and electric heater capacity has been assessed through different sensitivity analyses. The results show that it is worth hybridizing the system, indeed the solar power plant operates during summer continuously day and night, exploiting the advantages of the two technologies, while limiting their drawbacks. Plant configurations leading to a capacity factor higher than 81% with a share of energy wasted limited to 5% can be identified. The electric heater capacity and efficiency are shown to be highly important parameters, highlighting the need for further component development.

The integration of compact and high-efficient supercritical CO2 (sCO2) power blocks has been identified as one of the key alternatives for enhancing the economic viability, and the flexibility of Concentrating Solar Power (CSP) plants. The present work aims at identifying and selecting the most promising CSP plant configurations that can be integrated with sCO2 power blocks. Several sCO2 – CSP layouts are identified, classified by the receiver heat transfer fluid and storage design, and benchmarked through a methodology developed by the authors. An analytical approach, based on purposely defined techno-economic criteria, is defined to benchmark each layout with an overall score. The following criteria are considered: maturity, low-cost potential, maximum temperature, safety, and system complexity. The overall score is then derived by combining the mentioned criteria and weighting factors. A comparative analysis is proposed, in which the higher the resulting overall score, the more attractive the layout was deemed. The CSP layout employing molten salts results in being the most attractive one, standing out for its maturity. The air- or particle-based configurations combined with packed beds or particle silos as storage are promising for their low-cost potential and high operating temperatures.

High-temperature receivers are critical for third-generation (Gen3) Concentrating Solar Power (CSP) technology to achieve high system efficiencies, and play the role of converting concentrated sunlight into heat. In this paper, two CSP systems with different working fluids in the receiver are examined in order to achieve identical supply of heat to the power block: a direct high-temperature chloride salt system and an indirect high-temperature sodium receiver with an associated heat exchanger to heat the same chloride salt. The presented numerical model indicates that the indirect sodium-salt system has a 4.37% higher exergy efficiency than the direct chloride salt system. The exergy destruction in the added sodium-salt heat exchanger was only 0.54%, which did not outweigh the performance benefits gained from using a sodium receiver, when compared to the direct salt case with no heat exchanger. Even at lower DNIs, the better heat-transfer characteristics of the sodium are responsible for its improved performance compared to salt in the receivers.

To enhance the economic viability of Concentrating solar power (CSP) plant, recent efforts have been directed towards employing high-temperature working fluid in the receiver and incorporating higher-efficiency power cycles. This work presents a techno-economic analysis of a sodium-chloride salt heat exchanger included in a sodium-driven CSP system with a supercritical CO2 power block. A quasi-steady state heat exchanger model was developed based on the TEMA guidelines, with the possibility of being customised in terms of media adopted, constraints, boundary conditions, and heat transfer correlations. The sodium-salt heat exchanger has been designed aiming at minimising the Levelized Cost of Electricity (LCOE) of the plant. The performance and the design of the proposed heat exchanger have been evaluated via multi-objective optimisation and sensitivity analyses. Results show that advanced CSP systems employing sodium and an indirect chloride salt storage can represent an economically viable solution and can drive towards the future goal of 5 USD/MWh. For a base-case 100 MWe plant with 12 h of storage, a LCOE of 72.7 USD/MWh and a capacity factor (CF) higher than 60% were reached. The techno-economic investigations showed the potential LCOE reduction of 6% as well as the flexibility and robustness of the heat exchanger model. The developed tool lays the groundwork to explore potential improvements of this new generation of CSP systems.