Search Results (12)

Spain’s energy transition poses the dual challenge of managing renewable curtailment and enhancing the competitiveness of concentrated solar power (CSP) technologies. This study evaluates the suitability of replacing molten salts with solid particles for energy storage and, additionally, explores the storage of surplus electricity from grid in Carnot batteries. Four scenarios were analyzed using a Gemasolar-type plant model: each storage medium was studied with and without the integration of curtailed electricity. The solar field was modeled with SAM (System Advisor Model), while curtailment data from Red Eléctrica de España (2016–2021) quantified the available surplus. Results show that solid particles lead to 7.4% higher annual electricity production compared to molten salts, mainly due to improved power cycle efficiency. The integration of curtailment increased output further, with the solid particle Carnot battery scenario achieving the highest performance (up to 19.0% sun-to-electricity efficiency and 69.7% capacity factor). However, round-trip efficiency for curtailment storage was limited (~25–27%), and although solid particles showed lower LCOE (levelized cost of energy) than salts (192 vs. 211 USD/MWh), the Carnot battery increased costs. These findings suggest that while solid particles offer clear advantages, the economic viability of Carnot batteries remains constrained by current cost and operational limitations. Full article

To fully recover abundant waste heat and reduce the operation cost in liquid-cooled data centers, a Carnot battery consisting of a heat pump (HP) and organic Rankine cycle (ORC) is proposed. Due to the existence of different cycle states for HPs and ORCs, four different cycle combinations are considered. To evaluate and compare their performances, thermo-economic models are developed. Under the design conditions, the optimal working fluid combinations are first determined for each battery. On this basis, thermodynamic and economic performances of the four batteries are analyzed in detail. The results indicate that the system consisting of a subcritical HP/transcritical ORC achieves the highest round-trip efficiency at 76%. Notably, the round-trip efficiency of the system can exceed 100% at low ORC condensing temperatures. Additionally, the system cost is about 767–796 USD/kW∙h, depending on the cycle combinations. Furthermore, the effects of operating parameters on system performances are also investigated. Finally, with the objective of maximum round-trip efficiency, key parameters of four batteries are optimized. The results reveal that the system with a subcritical HP/subcritical ORC attains a maximum round-trip efficiency of 83% after optimization. These research results contribute to the development of green data centers and the reduction of power costs. Full article

This study proposes an innovative system for recovering waste heat from exhaust air after a regenerative thermal oxidiser process, integrating a Carnot battery and photovoltaic (PV) modules. The Carnot battery incorporates an organic Rankine cycle (ORC) with a recuperator, thermal energy storage (TES), and heat pump. Waste heat is initially captured in TES, with additional energy extracted by a heat pump to increase the temperature of a secondary fluid, effectively charging TES from both direct and indirect sources. The stored heat enables electricity generation via ORC. The result of this study shows a heat pump COP between 2.55 and 2.87, the efficiency of ORC ranging from 0.125 to 0.155, and the power-to-power of the Carnot battery between 0.36 and 0.40. Moreover, PV generates 1.35 GWh annually, primarily powering the heat pump and ORC system pump. The proposed system shows a total annual net generation of 4.30 GWh. Economic evaluation across four configurations demonstrates favourable outcomes, with a return on investment between 25% and 160%. The economic evaluation examined configurations with and without the PV system and recuperation process in the ORC. Results indicate that incorporating the PV system and recuperator significantly increases power output, offering a highly viable and sustainable energy solution. Full article

Triple organic Rankine cycle (TORC) is gradually gaining interest, but the maximum thermal efficiencies (around 30%) are restricted by low critical temperatures of common working fluids (<320 °C). This paper proposes a high-temperature (up to 400 °C) TORC system to ramp up efficiency. A near-azeotropic mixture biphenyl/diphenyl oxide (BDO), which has a stellar track record in the high-temperature ORC applications, is innovatively adopted as the top and middle ORC fluid simultaneously. Four conventional organic fluids are chosen for the bottom ORC. A mixing heat exchanger connects the top and middle ORCs to reduce irreversible loss. Thermodynamic analysis hints that the optimal performance is achieved on the use of benzene as the bottom fluid. The maximum thermal and exergy efficiencies are respectively 40.86% and 74.14%. The largest exergy destruction occurs inside the heat exchanger coupling the middle and bottom ORCs, accounting for above 30% of the total entropy generation. The levelized energy cost (LEC) is 0.0368 USD/kWh. Given the same heat source condition, the TORC system can boost the efficiency by 1.02% and drive down LEC by 0.0032 USD/kWh compared with a BDO mixture-based cascade ORC. The proposed system is promising in solar thermal power generation and Carnot battery applications using phase change materials for storage. Full article

The expansion of renewable energy sources and sustainable infrastructures for the generation of electrical and thermal energies and fuels increasingly requires efforts to develop efficient technological solutions and holistically balanced systems to ensure a stable energy supply with high energy utilization. For investigating such systems, a research infrastructure was established within the nationally funded project Energy Lab 2.0 including essential components for generation, conversion and storage of different energy sources. One element includes a thermal energy storage (TES) system based on solid materials, which was supplemented by an electrically heated storage component. Hereby, the overall purpose is to efficiently generate and store high-temperature heat from electrical energy with high specific powers during the charging period and provide thermal energy during the discharging period. Today’s solutions focus on convective electrical heating elements, creating, however, two major challenges for large-scale systems: limited load gradients due to existing systemic inertias and limited operating temperatures of 700 °C in the MW scale. To overcome such restrictions, a novel electrically heated storage component with dual operating modes was developed. The central component of this solution is a ring-shaped honeycomb body based on an SiC ceramic with electrical heating registers on the inside and outside. This configuration allows, in storage operation, instantaneous direct heating of the honeycomb body via thermal radiation. At the end of systemic start-up procedures, an operational change toward a convective heating system takes place, whereby the high-temperature heat previously stored is transferred to downstream components. The simulation studies performed for such a component show, for both operating modes, high operating temperatures of over 800 °C with simultaneous high electrothermal efficiencies of up to 90%. Experimental investigations on a 100 kW scale at the DLR test facility HOTREG in Stuttgart confirmed the feasibility, performance and good agreement with simulation results for a selected honeycomb geometry with a mass of 181 kg. With its successful testing and good scalability, the developed component opens up high use case potentials in future Power-to-Heat-to-Power applications, particularly for Brayton process-based Carnot batteries and adiabatic compressed air energy storage systems. Full article

Research on pumped thermal energy storage (PTES) has gained considerable attention from the scientific community. Its better suitability for specific applications and the increasing need for the development of innovative energy storage technologies are among the main reasons for that interest. The name Carnot Battery (CB) has been used in the literature to refer to PTES systems. The present paper aims to develop an energy analysis of a CB comprising a high-temperature two-stage heat pump (2sHP), an intermediate thermal storage (latent heat), and an organic Rankine cycle (ORC). From a broad perspective, the CB is modeled considering two types of heat inputs for the HP: a cold reservoir in the ground (at a constant temperature of 12 °C throughout the entire year) and a heat storage at 80 °C (thermally-integrated PTES—TI-PTES). The first part defines simple models for the HP and ORC, where only the cycles’ efficiencies are considered. On this basis, the storage temperature and the kind of fluids are identified. Then, the expected power-to-power (round-trip) efficiency is calculated, considering a more realistic model, the constant size of the heat exchangers, and the off-design operation of expanders and compressors. The model is simulated using Engineering Equation Solver (EES) software (Academic Professional V10.998-3D) for several working fluids and different temperature levels for the intermediate CB heat storage. The results demonstrate that the scenario based on TI-PTES operation mode (toluene as the HP working fluid) achieved the highest round-trip efficiency of 80.2% at full load and 50.6% round-trip efficiency with the CB operating at part-load (25% of its full load). Furthermore, when the HP working fluid was changed (under the same scenario) to R1336mzz(Z), the round-trip full-load and part-load efficiencies dropped to 72.4% and 46.2%, respectively. The findings of this study provide the HP and ORC characteristic curves that could be linearized and used in a thermo-economic optimization model based on a Mixed-Integer Linear Programming (MILP) algorithm. Full article

Carnot batteries store surplus power as heat. They consist of a heat pump, which upgrades a low-temperature thermal energy storage, a high-temperature storage system for the upgraded thermal energy, and a heat engine that converts the stored high-temperature thermal energy into power. A Carnot battery is proposed based on supercritical CO₂ Brayton thermodynamic cycles. The low-temperature storage is a two-tank molten salt system at 380 °C/290 °C fed by a field of parabolic trough collectors. The high-temperature storage consists of another two-tank molten salt system at 589 °C/405 °C. Printed circuit heat exchangers would be required to withstand the high pressure of the cycles, but shell and tube heat exchangers are proposed instead to avoid clogging issues with molten salts. The conventional allocation of high-temperature molten salt heat exchangers is then modified. Using solar energy to enhance the low-temperature thermal source allowed a round-trip efficiency of 1.15 (COP of 2.46 and heat engine efficiency of 46.5%), thus increasing the stored power. The basic configuration has a levelised cost of storage of USD 376/MWh while replacing the shell and tube heat exchangers with hybrid printed circuit heat exchangers is expected to lower the cost to USD 188/MWh. Full article

In the current study, a high temperature thermal storage system with a hybrid of phase change material and graphite as the storage materials is designed and evaluated as to its applicability for use as a utility-scale Carnot battery. The design includes an externally heated liquid sodium tank, which is used as the heat transfer fluid. This is used to charge and discharge the storage system consisting of a graphite storage medium sandwiched by two phase change materials. Finally, electrical generation is by way of a supercritical carbon dioxide Brayton cycle operated at 700 °C. Detailed modelling of these designs was conducted by way of a previously validated numerical model to predict performance metrics. Using the aforementioned designs, a preliminary cost estimate was undertaken to better determine applicability. From these results, it was found that while the graphite system was the most effective at storing energy, it was also the highest cost due to the high cost of graphite. In total, 18 storage tanks containing nearly 17,400 tons of storage material were required to store the 1200 MWh_t required to run the sCO₂ power block for 10 h. Under the study conditions, the cost of a PCM-based Carnot battery was estimated to be $476/kWh_e, comparable to other storage technologies. Furthermore, it was found that if the cost of the graphite and/or steel could be reduced, the cost of the system could be reduced to $321/kWh_e. Full article

In this study, exergy and thermoeconomic analyses were performed on a Carnot battery system (CBS) comprising an air heat pump and steam turbine. The Carnot battery technology employed in this study stored electricity as heat for 10 h during night-time, when electricity prices were low, and generated electricity for 10 h with power output of 500 MW during the day, when electricity prices were relatively high. The roundtrip efficiency and the energy density of the CBS were approximately 0.37, and 150.0 MJ/m³, respectively. When the unit cost of electricity supplied to the heat pump system was approximately 23.0 USD/GJ, that of electricity produced by the steam turbine was approximately 70.8 USD/GJ. The thermoeconomic results indicate that the changes in electricity cost flow rate relative to the reference value can be used as an indicator to make purchasing, replacement, and research and development decisions for specific components of the CBS. Full article

The objective of this investigation is to present a novel concept for the optimum exploitation of volatile electricity from renewable energy sources. The idea of the Carnot battery is extended to a general concept for trigeneration which can be called “power to XYZ”. This idea is applied for the building sector where there are needs for cooling production, space-heating production/domestic hot water production and electricity. More specifically, volatile electricity feeds a multi-stage heat pump that produces cold storage at 0 °C for cooling, medium heating storage at 50 °C for space heating and high thermal storage at around 115 °C for future utilization in an organic Rankine cycle for electricity production. The storage is performed in three different temperature levels, with latent storage proposed for proper long-term and efficient storage. The use of ice is suggested especially for cold storage in order to make the design a cost-effective one. This work is a theoretical preliminary thermodynamic analysis performed with a model created in Engineering Equation Solver. The results indicate the system’s maximum exergy efficiency is found at 45.28%, while the respective energy efficiency is found at 322.16%. Moreover, this work includes parametric studies and calculations about the operating margins of the suggested system. Full article

Carnot batteries are a quickly developing group of technologies for medium and long duration electricity storage. It covers a large range of concepts which share processes of a conversion of power to heat, thermal energy storage (i.e., storing thermal exergy) and in times of need conversion of the heat back to (electric) power. Even though these systems were already proposed in the 19th century, it is only in the recent years that this field experiences a rapid development, which is associated mostly with the increasing penetration of intermittent cheap renewables in power grids and the requirement of electricity storage in unprecedented capacities. Compared to the more established storage options, such as pumped hydro and electrochemical batteries, the efficiency is generally much lower, but the low cost of thermal energy storage in large scale and long lifespans comparable with thermal power plants make this technology especially feasible for storing surpluses of cheap renewable electricity over typically dozens of hours and up to days. Within the increasingly extensive scientific research of the Carnot Battery technologies, commercial development plays the major role in technology implementation. This review addresses the gap between academia and industry in the mapping of the technologies under commercial development and puts them in the perspective of related scientific works. Technologies ranging from kW to hundreds of MW scale are at various levels of development. Some are still in the stage of concepts, whilst others are in the experimental and pilot operations, up to a few commercial installations. As a comprehensive technology review, this paper addresses the needs of both academics and industry practitioners. Full article

In both rural and urban areas, two-wheeler vehicles are the most common means of transportation, contributing to local air pollution and greenhouse gas emissions (GHG). Transitioning to electric two-wheeler vehicles can help reduce GHG emissions while also increasing the socioeconomic status of people in rural Kenya. Renewable energy systems can play a significant role in charging electric two-wheeled vehicles, resulting in lower carbon emissions and increased renewable energy penetration in rural Kenya. As a result, using the Conventional and Renewable Energy Optimization (CARNOT) Toolbox in the MATLAB/Simulink environment, this paper focuses on integrating and modeling electric two-wheeled vehicles (e-bikes) into an off-grid photovoltaic Water-Energy Hub located in the Lake Victoria Region of Western Kenya. Electricity demand data obtained from the Water-Energy Hub was investigated and analyzed. Potential solar energy surplus was identified and the surplus was used to incorporate the electric two-wheeler vehicles. The energy consumption of the electric two-wheeler vehicles was also measured in the field based on the rider’s driving behavior. The modeling results revealed an annual power consumption of 27,267 kWh, a photovoltaic (PV) electricity production of 37,785 kWh, and an electricity deficit of 370 kWh. The annual results show that PV generation exceeds power consumption, implying that there should be no electricity deficit. The results, however, do not represent the results in hourly resolution, ignoring the impact of weather fluctuation on PV production. As a result, in order to comprehend the electricity deficit, hourly resolution results are shown. A load optimization method was designed to efficiently integrate the electric 2-wheeler vehicle into the Water-Energy Hub in order to alleviate the electricity deficit. The yearly electricity deficit was decreased to 1 kWh and the annual electricity consumption was raised by 11% (i.e., 30,767 kWh), which is enough to charge four more electric two-wheeler batteries daily using the load optimization technique. Full article