Search Results (13)

This work proposes a pumped thermal energy storage (PTES) integrated into the power block of a concentrated solar power plant. The power block operates under a Hybrid Rankine–Brayton (HRB) cycle using propane as the working fluid. During PTES charging, some thermal energy is obtained from a dedicated compressor (additional to that of the HRB cycle), which is stored. During discharge, both compressors (HRB and PTES) are off, restoring the consumed energy and resulting in about a 13% increase in nominal power output. The system is also able to store thermal energy that would otherwise be rejected through the condenser if the PTES were turned off, leading to efficiency improvements in some cases. Considering the 2022 Spanish electricity market prices, the proposed PTES integration with 4 h of storage is feasible. The levelized cost of storage is calculated and compared to those of other PTES systems, achieving around a 40% reduction compared with an equivalent PTES Rankine. These results encourage future studies where the proposed PTES could be integrated into other power cycles that include a recompression process. Full article

Pumped thermal energy storage (PTES) is a promising long-duration energy storage technology. Nevertheless, PTES shows intermediate round-trip efficiency (RTE—0.5 ÷ 0.7) and significant CAPEX. sCO₂ heat pumps and power cycles could reduce PTES CAPEX, particularly via reversible and flexible machines. Furthermore, the possibility to exploit freely available heat sources (such as waste heat and/or CSP inputs) could increase RTE, making the system capable of an apparent RTE > 100% as well as reducing CAPEX, avoiding the need for two TES systems. This paper analyses the potential valorization of industrial waste heat (WH) to enhance PTES thermodynamic performance as well as increase industrial energy efficiency, valorizing different levels of WH sources in the 100–400 °C temperature range. In fact, the use of additional heat, otherwise dumped into ambient surroundings, may contribute to avoiding the need for a second TES, thus enhancing plant competitiveness. Starting from an assessment of the most relevant industrial sectors to apply the proposed solution (looking at available WH and electric flexibility needed), this paper analyses the feasibility of a specific sCO₂-based PTES case study, where the cycle is integrated into a cement production plant with a WH temperature of around 350 °C. It is demonstrated that the CAPEX of the proposed systems are still relevant and only a robust exploitation of the PTES in the ancillary service market could attract industrial customers’ interest in sCO₂ PTES. 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

In recent years, there has been an increase in the use of renewable energy resources, which has led to the need for large-scale Energy Storage units in the electric grid. Currently, Compressed Air Energy Storage (CAES) and Pumped Hydro Storage (PHES) are the main commercially available large-scale energy storage technologies. However, these technologies are restricted geographically and can require fossil fuel streams to heat the air. Thus, there is a need to develop novel large-scale energy storage technologies that do not suffer from the abovementioned drawbacks. Among the in-development, large-scale Energy Storage Technologies, Pumped Thermal Electricity Storage (PTES), or Pumped Heat Energy Storage, stands out as the most promising due to its long cycle life, lack of geographical limitations, the absence of fossil fuel streams, and the possibility of integrating it with conventional fossil-fuel power plants. There have been a number of PTES systems proposed using different thermodynamic cycles, including the Brayton cycle, the Rankine cycle, and the transcritical Rankine cycle. The purpose of this paper is to provide a comprehensive overview of PTES concepts, as well as the common thermodynamic cycles they implement, indicating their individual strengths and weaknesses. Furthermore, the paper provides a comprehensive reference for planning and integrating various types of PTES into energy systems. Full article

Geological restrictions and the low energy density of compressed air energy storage (CAES) plants constitute a technical and economic barrier to the enablement of variable and intermittent sustainable sources of energy production. Liquid air energy storage (LAES) and pumped thermal energy storage (PTES) systems offer a promising pathway for increasing the share of renewable energy in the supply mix. PTES remains under development while LAES suffers from low liquefaction unit efficiency, although it is at a higher technology readiness level (TRL) than PTES. The most significant element of large-scale EES is related to the discharge features of the power plants, especially the energy storage unit. Here, a novel multi-aspect equation, based on established codes and thermodynamic principles, is developed to quantify the required storage capacity to meet demand consistent with the design parameters and operational limitations of the system. An important conclusion of the application of the multi-aspect equation shows that liquid air storage systems instead of compressed air would reduce the space required for storage by 35 times. Finally, a cost equation was introduced as a function of the required storage volume. Calculations have demonstrated that the use of the novel cost equation, in lieu of the old one-aspect cost equation, for an LAES power plant with a production capacity of about 50 MW makes the costs of installing liquid air storage tanks against the total expenditure of the power plant about six times higher than what was reported in earlier research. Full article

To integrate large shares of renewable energy sources in electric grids, large-scale and long-duration (4–8+ h) electric energy storage technologies must be used. A promising storage technology of this kind is pumped thermal electricity storage based on Brayton cycles. The paper’s novel contribution is in the techno-economic comparison of two alternative configurations of such storage technology. Liquid-based and solid-based pumped thermal electricity storage were studied and compared from the techno-economic point of view. The cost impacts of the operating fluid (air, nitrogen, and argon), power rating, and nominal capacity was assessed. Air was the most suitable operating fluid for both technologies, simplifying the plant management and achieving cost reductions between 1% and 7% compared to argon, according to the considered configuration. Despite a more complex layout and expensive thermal storage materials, liquid-based systems resulted in being the cheapest, especially for large applications. This was due to the fact of their lower operating pressures, which reduce the cost of turbomachines and containers for thermal energy storage materials. The liquid-based systems achieved a cost per kWh that was 50% to 75% lower than for the solid-based systems. Instead, the cost per kW benefited the solid-based systems up to nominal power ratings of 50 MW, while, for larger power ratings, the power conversion apparatus of liquid-based systems was again cheaper. This was due to the impact of the turbomachines on the total cost. The machines can represent approximately 70% of the total cost for solid-based systems, while, for liquid-based, approximately 31%. Since the cost of turbomachines scales poorly with the size compared to other components, solid-based systems are less suitable for large applications. 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

The urgent energy transition needs a better penetration of renewable energy in the world’s energy mix. The intermittency of renewables requires the use of longer-term storage. The present system uses water displacement, in a lined rock cavern or in an aerial pressurised vessel, as the virtual piston of compressor and expander functions in a carbon dioxide heat pump cycle (HPC) and in an organic transcritical cycle (OTC). Within an impermeable membrane, carbon dioxide is compressed and expanded by filling and emptying pumped-hydro water. Carbon dioxide exchanges heat with two atmospheric thermal storage pits. The hot fluid and ice pits are charged by the HPC when renewable energy becomes available and discharged by the OTC when electricity is needed. A numerical model was built to replicate the system’s losses and to calculate its round-trip efficiency (RTE). A subsequent parametric study highlights key parameters for sizing and optimisation. With an expected RTE of around 70%, this CO₂ PHES (pumped-hydro electricity storage) coupled with PTES (pumped thermal energy storage) could become a game-changer by allowing the efficient storage of intermittent renewable energy and by integrating with district heating and cooling networks, as required by cities and industry in the future. Full article

Pumped Thermal Energy Storages (PTES) are suitable for bridging temporary energy shortages, which may occur due to the utilization of renewable energy sources. A combined heat pump (HP)-Organic Rankine Cycle (ORC) system with suitable thermal storage offers a favorable way to store energy for small to medium sized applications. To address the aspect of flexibility, the part load behavior of a combined HP-ORC system, both having R1233zd(E) (Trans-1-chloro-3,3,3-trifluoropropene) as working fluid and being connected through a water filled sensible thermal energy storage, is investigated using a MATLAB code with integration of the fluid database REFPROP. The influence on the isentropic efficiency of the working machines and therefore the power to power efficiency (P2P) of the complete system is shown by variation of the mass flow and a temperature drop in the thermal storage. Further machine-specific parameters such as volumetric efficiency and internal leakage efficiency are also considered. The results show the performance characteristics of the PTES as a function of the load. While the drop in storage temperature has only slight effects on the P2P efficiency, the reduction in mass flow contributes to the biggest decrease in the efficiency. Furthermore, a simulation for dynamic load analysis of a small energy grid in a settlement is conducted to show the course of energy demand, supplied energy by photovoltaic (PV) systems, as well as the PTES performance indicators throughout an entire year. It is shown that the use of PTES is particularly useful in the period between winter and summer time, when demand and supplied photovoltaic energy are approximately equal. Full article

In this work, the integration of a grid-scale ternary-Pumped Thermal Electricity Storage (t-PTES) with a nuclear power generation to enhance operation flexibility is assessed using physics-based models and digital real time simulation. A part of the electricity from the nuclear power generation is delivered to the grid, and the balance is used to power a heat pump that can be augmented by an auxiliary resistive load element to increase the charging rate of the thermal storage. This increases the thermal potential between hot and cold thermal stores (usually solid materials or molten salts inside large storage tanks). The thermal energy is transformed back into electricity by reversing the heat pump cycle. Different transient scenarios including startup, shutdown, and power change for grid-connected operation are simulated to determine the behavior of the hybrid nuclear-t-PTES system operating under variable loads that constitute a departure from conventional, baseload nuclear plant operation schemes. Ternary refers to the three modes operation: (i) heat pump (including heating coil), (ii) heat engine, and (iii) simultaneous operation of heat pump (including heating coil) and heat engine during changeover from pumping to generation or vice-versa. The controllability of t-PTES in the short timescales as a dynamic load is used to demonstrate operational flexibility of hybrid nuclear plants for flexible operation through advanced load management. The integration of t-PTES into nuclear power systems enhances the system flexibility and is an enabler for high penetration of renewable energy resources. Full article

This paper provides an overview of a novel electric energy storage technology. The Thermally Integrated Pumped Thermal Electricity Storage (TI-PTES) stores electric energy as thermal exergy. Compared to standard PTES, TI-PTES takes advantage of both electric and low-temperature heat inputs. Therefore, TI-PTES is a hybrid technology between storage and electric production from low-temperature heat. TI-PTES belongs to a technology group informally referred to as Carnot Batteries (CBs). As the TI-PTES grows in popularity, several configurations have been proposed, with different claimed performances, but no standard has emerged to date. The study provides an overview of the component and operating fluid selection, and it describes the configurations proposed in the literature. Some issues regarding the performance, the ratio between thermal and electrical inputs, and the actual TI-PTES utilisation in realistic scenarios are discussed. As a result, some guidelines are defined. The configurations that utilise high-temperature thermal reservoirs are more extensively studied, due to their superior thermodynamic performance. However, low-temperature TI-PTES may achieve similar performance and have easier access to latent heat storage in the form of water ice. Finally, to achieve satisfactory performance, TI-PTES must absorb a thermal input several times larger than the electric one. This limits TI-PTES to small-scale applications. Full article

A fast-paced energy transition needs a higher penetration of renewables, of heating and cooling in the worldwide energy mix. With three novelties 1-of using shallow high-pressure LRC (Lined Rock Cavern) excavated close to storage needs, 2-of using a slow-moving CO₂ piston applying steady pressure on the hydro part of UPHES (Underground Pumped Hydro Energy Storage) and 3-of relying on inexpensive thermal stores for long-duration storage, CO₂ UPHES coupled with PTES (Pumped Thermal Electricity Storage) could become, at expected Capex cost of only 20 USD/kWh electrical, a game-changer by allowing the complete integration of intermittent renewable sources. Moreover, even though this early conceptual work requires validation by simulation and experimentation, CO₂ UPHES as well as UPHES-PTES hybrid storage could also allow a low-cost and low-emission integration of intermittent renewables with future district heating and cooling networks. Full article

Chile has abundant solar and wind resources and renewable generation is becoming competitive with fossil fuel generation. However, due to renewable resource variability their large-scale integration into the electricity grid is not trivial. This study evaluates the long-term impact of grid level energy storage, specifically Pumped Thermal Energy Storage (PTES), on the penetration of solar and wind energies and on CO₂ emissions reduction in Chile. A cost based linear optimization model of the Chilean electricity system is developed and used to analyse and optimize different renewable generation, transmission and energy storage scenarios until 2050. For the base scenario of decommissioning ageing coal plants and no new coal and large hydro generation, the generation gap is filled by solar photovoltaic (PV), concentrated solar power (CSP) and flexible gas generation with the associated drop of 78% in the CO₂ emission factor. The integration of on-grid 8h capacity storage increases the solar PV fraction which leads to a 6% reduction in operation and investment costs by 2050. However, this does not necessarily lead to further reductions in the long term emissions. Thus, it is crucial to consider all aspects of the energy system when planning the transition to a low carbon electricity system. Full article