1,720,980 research outputs found
Multi-Criteria Economic Analysis of a Pumped Thermal Electricity Storage (PTES) With Thermal Integration
Full text linkThe interest toward large-scale electric energy storage technologies is increasing with the large deployment of new renewable capacity. In case of several hours of storage duration, there is no consensus on which technology is the most suited. Several technologies have been recently proposed, among which is pumped thermal electricity storage (PTES), which is a technology based on the idea of storing electrical energy as heat. PTES is usually less efficient than electrochemical batteries, but it is characterized by a lower cost per kilowatt hour, which could make it a suitable alternative for applications with long storage duration. In this study, a recently proposed PTES system based on the use of heat pumps and organic Rankine cycles is investigated from a thermo-economic point of view. The system is powered by both electric and low-grade thermal energy, thus taking advantage of waste heat to increase the electric performance. As the system design both affects efficiency and cost, a trade-off must be found. In this study, this task was performed by means of a multi-objective optimization approach. The relation between electrical round-trip efficiency and system cost is analyzed, and the impact of several design specifications such as boundary conditions, nominal power rating, and storage duration is discussed. Finally, the results are generalized by defining some cost scaling correlations. Large-size configurations (5 MW of charging power for 8 h of storage) may achieve equipment purchasing costs as low as 140 €/kWh and 2,300 €/kW, with an electrical round-trip efficiency of 0.6. These results show that the investigated technology may be suitable in the context of large-scale and long-duration energy storage
Techno-Economic Comparison of Brayton Pumped Thermal Electricity Storage (PTES) Systems Based on Solid and Liquid Sensible Heat Storage
Full text linkTo 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
Energy storage for grid-scale applications: Technology review and economic feasibility analysis
No full textNon-dispatchable Renewable Energy Sources (RES) changed energy production from being centralised and fully dispatchable, to be more decentralised and less predictable. Despite the substantial growth, RES must be increased to fulfil the power production decarbonization targets set by several countries. In several countries, Italy included, RES development must be based on solar PV. Thus, relevant energy quantities will be shifted from day hours to night hours. Such “Load Shifting” is done with energy storage technologies. A few technologies suited for this task are already available, whereas several others have been proposed, but not tested in the practice. In this paper, such storage technologies are reviewed focusing on the performance and costs. Based on the review, current and future storage economic outlooks are assessed by focusing on the Italian scenario. In the paper, the storage operation is optimized at the hourly level to calculate the maximum achievable annual revenue. The optimisation is performed with a linear programming (LP) approach. Since none of the reviewed storage is economically feasible, the energy price modification required to achieve feasibility are estimated. Based on such results, the distance between the current situation and the one favourable to storage is assessed. In this way, the future outlook of each storage technology is discussed
Multi-criteria investigation of a pumped thermal electricity storage (PTES) system with thermal integration and sensible heat storage
Full text linkIn the present paper a multicriteria analysis of a Rankine Pumped Thermal Electricity Storage (PTES) system with low-grade thermal energy integration is performed. The system is composed by an ORC for the discharging phase and a high-temperature heat pump for the charging phase. As previously demonstrated, the low-grade thermal energy can be provided at the heat pump evaporator to boost the PTES performances. As it regards the multi-criteria analysis, a tradeoff is required when electric-to-electric energy ratio ηrt, total exergy exploitation efficiency ψut and energy density ρen, are maximized concurrently. By means of multi-objective optimization, theoretical performances of the system are derived in two different layouts, which are differentiated by the presence, or not, of internal regeneration in charge and discharge subsystems. Results showed that regeneration can be very effective, as it relaxes the tradeoff between the objectives, thus yielding better global performances. Pareto fronts are built and explored to characterize the PTES system. Configurations of interest are proposed, and PTES performances are compared with other storage technologies. Theoretical results showed that, by exploiting thermal energy at temperature lower than 80 °C, ηrt ≈ 0.55 and ρen ≈ 15 kWh/m3 can be concurrently achieved. This can be done at the cost of an inefficient exploitation of the thermal source, as ψut ≈ 0.05. If higher total exergy utilization efficiency is required, storage density can still be maintained high, but ηrt must drop down to 0.4
Rankine carnot batteries with the integration of thermal energy sources: A review
Full text linkThis 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
Off-design of a pumped thermal energy storage based on closed brayton cycles
No full textThe growth of renewable energy source requires reliable, durable and cheap storage technologies. In this field, the Pumped Thermal Energy Storage (PTES), is drawing some interest as it appears not to be affected by geographical limitations and use very cheap materials. PTES is less efficient than pumped hydro and batteries, but it could achieve satisfactory efficiencies, show better economic performance and be characterized by negligible environmental impacts. A PTES stores the electric energy as thermal exergy in solid packed beds, by operating two closed Brayton cycles, one for charging and the other one for discharging. Although PTES thermodynamical behavior is well understood, the interaction between the components is rarely investigated. This study investigates the impact of packed-bed behavior on turbomachines operating conditions. In this way, PTES off-design and part-load performance are estimated. A control strategy especially suited for closed Brayton cycles, i.e.The inventory control, is used to control the system. As it resulted, PTES is characterized by an excellent part-load performance, which might be a significant advantage over the competing technologies. However, the offdesign operation induced by the packed-bed thermal behavior might significantly reduce the system performance and, in particular, that of the discharge phase
OFF-DESIGN CHARACTERISATION OF AN ENERGY STORAGE BASED ON PUMPED THERMAL ENERGY STORAGE AND LOW-CONCENTRATION SOLAR THERMAL COLLECTORS
No full textLong duration storages (i.e. 6+h) could foster the power sector transitions towards renewable energy sources. Among the many technologies proposed for such a task, pumped thermal electricity storage (PTES) recently gained much attention from researchers. A PTES plant based on low-concentration solar collectors, a vapour compression heat pump, and an organic Rankine cycle (ORC) is studied. In the proposed configuration, the solar collectors produce the thermal energy required by the heat pump during the charging phase. The heat pump operates with a reduced temperature lift and upgrades the solar thermal energy to store it at a higher temperature in sensible heat storage. The electric roundtrip efficiency is very high when the thermal energy is discharged through the ORC, thanks to solar thermal energy contribution. In the paper, the system performance in and off-design are analysed. An off-design model is used to map both heat pump and ORC for a set of representative operating conditions. Such performance maps were then used to characterise the system performance when coupled with a solar thermal energy production profile. In this way, the whole system operation was simulated for some representative days of the year. Results show that the average round trip efficiency is between 0.85 and 0.87, and the system can operate in various radiation conditions
High-Temperature Heat Pumps for Electrification and Cost-Effective Decarbonization in the Tissue Paper Industry
No full textThe pulp and paper industry is under increasing pressure to reduce its energy consumption and carbon footprint. This study examines the feasibility of integrating high-temperature heat pumps (HTHP) into tissue paper production to enhance energy efficiency and decarbonization. Focusing on the energy-intensive drying process, the study uses data from a typical tissue paper mill to simulate and optimize an HTHP system producing four tons per hour of nine-bar saturated steam. It also addresses necessary modifications for HTHP integration applicable across the sector. Various refrigerants were analyzed, achieving a maximum coefficient of performance (COP) of 2.01. Results showed that HTHP can reduce energy consumption and emissions by up to 17% and 40%, respectively, based on the European electricity mix. Although steam production costs increase by 55% compared to fossil fuel-based systems, HTHP is more cost-effective than direct electric resistance heating, which raises costs by 196%. With a CO2 price of EUR 100/t, HTHP offers a 12% cost reduction. However, without public funding, capital expenditures may be unsustainable in many regions, though viable in countries with favorable gas and electricity price differentials. The paper underscores the need for advancements in HTHP technology and cost reductions, emphasizing industry adaptation for seamless HTHP integration
Feasibility analysis of a hybrid auxiliary power unit for pleasure boats
No full textTo reduce the pollutant emissions in the naval sector, the use of alternative fuels and new power generator systems are both promising solutions. In this study, the feasibility of replacing a pleasure boat Auxiliary Power Unit (APU) with a hybrid solution is studied from the economic and technical points of view. Several power generation technologies and layouts are considered. Many configurations were investigated, from hybrid battery/diesel generator to innovative layouts including fuel cell with onboard Liquified Natural Gas (LNG) reforming for hydrogen production. Since hybrid APUs may yield significant advantages in terms of both environmental and noise pollution, the opportunity of operating the system for several hours without powering up the traditional generators is also considered. For each configuration, CO2 and NOx emissions, purchasing and operating costs, as well as weight and volume, are estimated. Emissions may be reduced up to 20 % and 60 % for CO2 and NOx, respectively, and fuel cost reductions up to 35 % may be achieved
Energy Storage System for Thermal Load Fluctuation Balancing
No full textCogenerative geothermal power plants can supply thermal energy required by energy-intensive activities, such as greenhouses heating. The required thermal load in these systems usually follows the daily temperature trend, leading to not negligible load fluctuations on the power plant side that need to be managed, in case a constant electric output from the plant is required (e.g. because the energy has been already sold on the dayhead electric energy market). The supplied heat flow rate must be constant to avoid a fluctuating operation of the cogeneration system. This paper investigates the opportunity of using a thermal storage to manage this load fluctuations and keep the system stable. Results show that even an oversized storage tank may not be sufficient to reach the desired set point conditions, especially if the load forecasting is incorrect. For this reason, it is necessary to increase the supplied heat flow rate to reduce energy shortages and use a cooler to dissipate energy surpluses. Results show that it is possible to achieve setpoint conditions by increasing the supplied heat flow rate by 20 % and using a cooler do dissipate thermal energy surplus. This performance worsens when the load forecast is not accurate, though shortening the period with a fixed heat flow rate can be beneficial
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