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[Display omitted] • PCM energy storage and PV/T coupled multi-source heat pump systems were combined. • The thermal performance, energy efficiency, and economy of the system were analyzed. • The performance of paraffin C17 and water as energy storage materials were compared. • The performance of six low-temperature PCMs applied to the system were analyzed. • Compared to the existing system, it saves 56 % of energy and 27.7 % of operating costs. To improve the application of renewable energy in the heating zone, as well as to address the limitations of air and water source heat pump. The study presents a PV/T (photovoltaic/thermal) coupled air–water source heat pump system integrated with phase change energy storage. A theoretical analytical model and TRNSYS simulation model of the system were developed to evaluate the thermal performance, energy efficiency and economics of the system. The performance of phase change energy storage was compared with that of water storage, and the effect of different phase change materials on the system characteristics. The results show that the coupled system achieves a seasonal performance factor of 2.3, a 56 % reduction in energy consumption, and a 27.7 % reduction in operating costs compared to a conventional gas boiler system. Comparative analysis with the water storage system showed that the system equipped with phase change materials performed well in terms of energy consumption, operating costs and heating stability. In addition, the density of the phase change material has a biased effect on the overall performance of the system. This paper can provide a reference value for the study of renewable energy heating systems in cold zone. [ABSTRACT FROM AUTHOR]

The concept of shared energy storage in power generation side has received significant interest due to its potential to enhance the flexibility of multiple renewable energy stations and optimize the use of energy storage resources. However, the lack of a well-set operational framework and a cost-sharing model has hindered its widespread implementation and large-scale development. This paper introduces three distinct cost-sharing methods, namely the uniform allocation method, the predictive weighted allocation method, and the dynamic weighted allocation method, which are laterly applied to develop a combined operational and cost distribution model. The objective is to improve the efficiency of the power generation system by incorporating shared energy storage assistance and allocating the associated costs based on the use of various renewable energy stations. Furthermore, the viability of the suggested operational framework for shared energy storage and the methods for allocating costs are confirmed through numerical simulation. The findings indicate that the uniform allocation method represents the most straightforward approach for distributing costs evenly. In contrast, the second model introduces a cost allocation method that addresses the issue of fairness by considering the predicted generation level of each renewable energy plant. However, the third model takes into account the actual generation level of the plants when determining their respective costs. Sensitivity analysis is further conducted to offer valuable insights into cost-saving policies for four representative regions in China. The proposed operation and cost-sharing model is anticipated to serve as a useful reference for the widespread implementation of shared energy storage in power generation side. • Design three cost-sharing methods to allocate costs among various entities. • Formulate a combined operational and cost allocation model. • Optimize operational and cost allocation strategies for various entities. • Reduce total costs by up to 36% through the dynamic weighted allocation method. [ABSTRACT FROM AUTHOR]

• Battery transport and logistics to increase renewable use and system flexibility. • Full train transport and carpooling to improve the economics of battery use. • Levelized cost of energy of battery transport & logistics is $0.045/kWh averagely. High share of variable renewable energy is challenging to the traditional power system technically and economically. This calls for a significant increase to the system flexibility, which might result in the costs associated with energy storage and costly upgrades to the traditional transmission and distribution system. This paper presents a multi-stage battery transportation and logistics optimization method to increase the renewable energy consumptions, economics, and mobilities of the battery utilization. A new approach is proposed in which the batteries are charged in the renewable power plants and transported back and forth by railways between the renewable power plants and cities. Based on the forecasts of battery supplies/demands, multiple optimization stages (full train transport and carpooling) are designed by the branch-and-bound algorithm and genetic algorithm respectively. The proposed battery transportation and logistics concept and model are performed using the Beijing-Tianjin-Hebei region in China as an example. The results show that the levelized cost of energy of the battery transportation and logistics model is $0.045/kWh averagely. Also, by the use of mobilized batteries, the proposed battery transportation and logistics model increases the system flexibilities and renewable energy deliveries to the end users without the reinforcement of transmission and distribution system and any constraint from a highly penetrated power system. [ABSTRACT FROM AUTHOR]

• Solar photovoltaics stored by using cheap and abundant materials. • The Calcium-Looping process is integrated as electricity stored system (40% efficiency) • Electric-to-electric performance of the whole system reaches 57%. • A notable cost reduction could be achieved as alternative to batteries. Solar photovoltaic plants are today a competitive alternative to power plants based on fossil fuels. Cost reduction in photovoltaics modules, scalability and ease of installation of these plants are enabling a rapid worldwide expansion of the technology. Nevertheless, dispatchability still remains as the major challenge to overcome due the intrinsic variability of solar energy. Most of the current solar photovoltaic facilities at large scale lack energy storage while those with storage systems rely on expensive batteries. Batteries are based on elements such as nickel, lithium or cadmium whose scarcity hinder their sustainability for storing energy in the large scale. This manuscript presents a novel concept to integrate thermochemical energy storage in photovoltaic plants. Furthermore, the concept is also directly adaptable to wind power plants to store surplus energy. The paper analyses the suitability of the Calcium-Looping process as thermochemical energy storage system in solar photovoltaics plants. The system works as follows: part of the power produced in the solar plant provides electricity to the grid while the rest is used to supply heat for calcination of calcium carbonate. After calcination, the products of the reaction – calcium oxide and carbon dioxide- are stored separately. When power production is required, the stored products are brought together in a carbonation reactor wherein the exothermic reaction releases energy for power production. The overall system is simulated to estimate the process behaviour and results show that storage efficiencies of ∼40% can be achieved. Moreover, an economic analysis is developed to compare the proposed system with batteries. Due to the low price of natural calcium oxide precursors, such as limestone, and the expected longer lifetime of equipment as compared to batteries, the Calcium-Looping process can be considered as a potential alternative for improving dispatchability in solar photovoltaic plants. [ABSTRACT FROM AUTHOR]

Highlights • The complex EH model can be divided into several simple EH models. • The complex MES is highly decoupled. • The nonlinearity of a complex EH model caused dispatch factors can be eliminated. • The energy storage, demand respond and renewable energy are all integrated in the coupling matrix of EH model. Abstract The integration energy and information technology has prompted the development of the multi-carrier energy system. Energy hub model is widely used in the multi-carrier energy system study. However, it is the difficult to formulate coupling matrix and optimize operation state of complex energy hub model. This paper proposes an efficient standardized multi-step modelling method and linearized optimization method for the energy hub model. Firstly, a complex energy hub model is separated into several simple energy hub models based on nodes arrangement and virtual nodes insertion methods; then the coupling matrix of each simple energy hub model can be easily modelled; the coupling matrix of the complex energy hub model can be obtained by multiplying the coupling matrix of each simple energy hub model. In addition, energy storage, demand response and renewable energy are considered and integrated in the energy hub model. Further, the nonlinear optimal operation model of energy hub is reformulated to a linear programming problem by using variable substitution in each simple energy hub model. Cases study is performed on a resident district in a city of China on a typical summer day with the energy storage devices, demand response and renewable energy considered. Compared with the traditional calculation method, the computational burden is significantly reduced based on the proposed calculation method, which can guarantee the global optimal operation decision. [ABSTRACT FROM AUTHOR]

The concept of off-grid hybrid wind energy system is financially attractive and more reliable than stand-alone power systems since it is based on more than one electricity generation source. One of the most expensive components in a stand-alone wind-power system is the energy storage system as very often it is oversized to increase system autonomy. In this work, we consider a hybrid system which consists of wind turbines, photovoltaic panels, diesel generator and battery storage. One of the main challenges experienced by project managers is the sizing of components for different sites. This challenge is due to the variability of the renewable energy resource and the load demand for different sites. This paper introduces a sizing model that has been developed and implemented as a graphical user interface, which predicts the optimum configuration of a hybrid system. In particular, this paper focuses on seeking the optimal size of the batteries and the diesel generator usage. Both of these components are seen to be trade-offs from each other. The model simulates real time operation of the hybrid system, using the annual measured hourly wind speed and solar irradiation. The benefit of using time series approach is that it reflects a more realistic situation; here, the peaks and troughs of the renewable energy resource are a central part of the sizing model. Finally, load sensitivity and hybrid system performance analysis are demonstrated. [ABSTRACT FROM AUTHOR]

This paper examines both the potential of and barriers to grid-scale energy storage playing a substantive role in transitioning to an efficient, reliable and cost-effective power system with a high penetration of renewable energy sources. Grid-scale storage is a term that describes a number of different technologies with a wide range of characteristics. This versatility leads to the use of storage to perform a number of grid-services. We first enumerate these services, with an emphasize on those that are best suited to mitigate the effects of uncertainty and variability associated with intermittent, non-dispatchable renewable energy sources. We then provide an overview of the current methods to evaluate grid-integrated storage, summarize key findings, and highlight ongoing challenges to large-scale adoption of grid-scale energy storage. We focus on one particular area that is critical to both the efficient use of energy storage in the power grid and its long-term economic viability: the conflict between the technical benefits of this resource, which can provide both power and energy related grid-services (in some cases simultaneously), and the economic challenges of compensating these services within the current market structures. We then examine recent progress in addressing these issues through regulatory changes and other initiatives designed to mitigate previous market failures. This discussion is followed by some remarks about ongoing regulatory and market design challenges. The paper closes with a summary of the ideas presented and a discussion of critical research needs. [ABSTRACT FROM AUTHOR]

This paper presents the geological resource potential of the compressed air energy storage (CAES) technology worldwide by overlaying suitable geological formations, salt deposits and aquifers. For this study, the world is divided into 145 regions, which are aggregated to 9 major regions. The potential of CAES in each region is assessed and a relevant map is provided. Three constraints have been implemented, allowing for 1%, 5% and 10% of the selected area to be considered for CAES. Among all major regions, in the most conservative constraint (1% of the total area), North America is the leader with 0.26% suitability of its total area, followed by Sub-Saharan Africa and South America at 0.20% and 0.19%, respectively. A sensitivity analysis is implemented to evaluate the validity and reliability of the results. Three scenarios are considered: Optimistic, Moderate and Pessimistic. Underground natural gas storage data for the US is used due to freely and publicly available data. The natural gas storage site is assumed to have the same structure as CAES. The sensitivity analysis shows that the accuracy of the findings lie in the range of 66–85% and 63–82%, depending on the scenarios and reservoir types. The results clearly reveal that CAES is a promising energy storage technology for electricity supply in most of the regions. This research presents the groundwork to identify the untapped potential of CAES, which can be also utilized for the second generation of CAES such as adiabatic CAES and isothermal CAES. [ABSTRACT FROM AUTHOR]

Renewable energy (RE) penetration growth without energy storage system (ESS) is restricted due to its poor dispatchability. Compressed air energy storage system (CAES) is one of the promising ESS technologies. But, low energy density and high mechanical inertia confined its application as a bulk ESS. In this paper, a novel hybrid thermal-compressed supercritical carbon dioxide energy storage (T-CCES) system is proposed to address CAES shortcomings. In this system, a stratified water thermal energy storage (TES) is employed to store both released heat of compression process and high-frequency reluctant power of a wind farm (which cannot be followed by CCES) using electrical heaters. A dynamic simulation is performed to evaluate system characteristics in steady wind generation condition and in a real wind generation condition. Stochastic simulation of the proposed system integrated with a real wind farm is also fulfilled to assess its characteristics and performance by considering uncertainties using sparse polynomial chaos expansion. Additionally, global sensitivity analysis via Sobol’ indices is conducted to identify the most important parameters of the system. Results show that the system can store wind power during off-peak hours and smoothly releases it into the grid with 57.55% round-trip efficiency (RTE) and 84.1 kWh/m 3 energy density. Uncertainty quantification results indicate that the system can properly work under uncertainties with standard deviation of 55.72–58.16% RTE and 83.7–86.5 kWh/m 3 energy density. Moreover, results show that the random production of wind turbine has a negligible effect on performance characteristics of the T-CCES which makes it a promising solution for integration with wind farms. [ABSTRACT FROM AUTHOR]

• An improved operation strategy for decentralized A-CAES is proposed. • TES behavior and its effects on A-CAES performance are analyzed. • Characteristics and capacity limitations of HES's components are considered. • A parametric study showed an optimum value for the system's design parameters. • Improved operation strategy reduced the ramp-up /down rate by around 4% /11%. Adiabatic compressed air energy storage (A-CAES) has shown great application potentials in integrated hybrid energy systems (HES) in recent years. The integration requires A-CAES to store intermittent renewables power to meet the fluctuating load demand. Therefore, the operation of compressors and turbines must be adjusted by renewable power output and load demand, respectively. This paper presents an improved energy management operation strategy (I-EMOS) to enhance the A-CAES system's utilization for decentralized applications. In doing so, besides integrating thermal energy storage (TES) unit into CAES, several limitations of an A-CAES unit, such as its conversion process mode, dynamic characteristics, power input/output constraints of compressor/turbine train, air pressure constraint, and thermal storage capacity limitations are considered. An HES consisting of PV, A-CAES, and grid to answer the building's electric demand is simulated. The results are validated against data from an existing A-CAES pilot. It is concluded that adopting features and capacity limitations of the A-CAES system's power conversion unit in operational strategies contributes to improved management of energy flow in HES. It is observed that for certain air tank volume and maximum/minimum pressures under I-EMOS, an enhanced performance can be achieved. This analysis presents a feasibility assessment approach for decentralized A-CAES integrated with renewables implemented and tested in a real-world case study. [ABSTRACT FROM AUTHOR]

Exploiting renewable energy is a critical greenhouse gases reduction strategy for China, especially in areas where new power plants are needed. Challenges in energy storage, however, always complicate the design of renewable energy-dominated power generation systems. This study attempt to provide a solution to the energy storage problem through the synergy of both the power supply and demand sides. Based on local natural energy resources endowments, this paper applies the hybrid optimization model for multiple energy resources and load types to analyse the feasibility of satisfying energy demand. To verify the model’s technological and economic feasibility, this research applies its synergy model to a 2.8 km 2 isolated island in the South China Sea. The simulation results demonstrate that the cost of energy and net present cost of the power supply system are $0.212/kW h and $127 M when hydrogen energy storage equipment is used, and $0.178/kW h and $101 M when traditional-battery energy storage equipment is utilized. This study also reveals that using flywheels to supplement the hydrogen and traditional-battery energy storage equipment could reduce the cost of energy by 5.6% and 3.4%, respectively. In addition, power system demand-side management can further reduce the cost of energy by approximately 20% for all technology scenarios considered in this study. A carbon emissions analysis demonstrates that the carbon reduction rates of the proposed power systems are between 87.7% and 95.1% compared with a fossil-energy based power system. In brief, this study indicates that solar and wind energy combined with appropriate energy storage equipment can meet the energy demand of the island. [ABSTRACT FROM AUTHOR]

• Hydrogen storage systems enable flexible energy conversion and scheduling. • Hydrogen storage cost accounts for the largest proportion of system cost. • The hydrogen energy storage system has less demand for energy storage space. With global energy consumption increasing year by year, the industrial sectors of the world's countries have never been more urgent in achieving carbon reduction. Renewable energy plays a crucial role in the industrial decarbonization process. As the most mature renewable energy technology, wind and photovoltaic power generation have made significant progress in recent years. However, the intermittent characteristics hinder the efficient use of renewable energy. Existing research provides sufficient support for the flexible scheduling of large-scale renewable energy. Hence, this paper proposes a combined energy system composed of wind power-photovoltaic-energy storage salt cavern with hydrogen as the energy scheduling carrier. The system mainly realizes energy conversion through electrolytic water equipment and fuel cells. Then, Qianjiang City, Hubei Province, is taken as the analysis object, and the working conditions of each component in the system are optimized with the help of an improved particle swarm optimization algorithm. According to the results, the system's contribution to the energy system is discussed, and the system's economy and carbon reduction effect is studied. The analysis proves that the improved particle swarm optimization algorithm has a stronger solving ability. The combined energy system can effectively improve the economy and renewable energy utilization rate, meet the regional electricity demand, and significantly reduce carbon emissions. The economic analysis of the system shows that the operation and maintenance cost of hydrogen storage salt caverns accounts for the largest proportion of the total cost, about 60 %. Compared with several existing large-scale energy storage technologies, it is found that the energy efficiency of the whole system is only about 40 % due to the limitation of technology maturity. Nevertheless, the flexibility of the hydrogen storage system layout is relatively high. The required underground space volume is only equivalent to 1/6 and 1/2 of pumped storage and compressed air storage with the same scheduling capacity. The system will provide a theoretical support for the optimization of energy pattern and layout. [ABSTRACT FROM AUTHOR]

This work presents a smart microgrid consisting of diesel, photovoltaic (PV), and battery storage plants. One of the key features of smart grid is to provide a redundant high quality power for the consumers. In islanded microgrid, the under frequency and/or voltage collapse, caused by power deficiency, can lead to power outage. The current practice is to shed the load demand until the frequency and voltage are restored. However, the redundancy in supplying power has no meaning as long as the loads are shed. The main objective of this paper is to propose a power management system (PMS) that protects the microgrid against the load shedding. PMS is able to control the microgrid in both centralized and decentralized fashions. To prevent under frequency load shedding (UFLS), this work proposes using battery energy storage system (BESS) to compensate for the power mismatch in the islanded microgrid. A method is presented to estimate the rate of change of frequency and to calculate the power deficiency. The approximated value is exploited as the set-point to dispatch BESS. PV and battery plants are supposed to share the reactive power demand proportionally and thus regulate the voltage at the load bus. This work also suggests two outer control loops, namely, frequency restoration loop (FRL) and difference angle compensator (DAC). These loops ensure microgrid smooth transition from islanded mode to grid-connected mode. The microgrid is configured to investigate the effective utilization of exiting solar PV plant connected to distribution network in Sabah Malaysia. The microgrid is implemented in PSCAD software and tested under different scenarios. The microgrid with PMS shows operational stability and improvements in comparison with the original system. The results indicate that PMS can effectively control the microgrid in all operating modes. [ABSTRACT FROM AUTHOR]

The paper aims to demonstrate the improvement of power dispatchability that can be achieved with a suitable integration of Concentrating Solar Power (CSP) and Concentrating Photovoltaic (CPV) plants to mitigate the effects of the variability and intermittency of solar energy. In particular, the CSP–CPV plant analyzed here refers to the design data of the Ottana Solar Facility, which is currently under construction in the industrial district of Ottana (Sardinia, Italy). Since it is very difficult to know the power curves that are going to be required during the operation phases of the hybrid CSP–CPV plant, the present study has been carried out by assuming a reference daily power output curve, which is simply represented by a constant power output. Moreover, two different energy management strategies, fully integrated (F-INT) and partially integrated (P-INT), are analyzed and compared. The results of this study show the advantages of using an integrated management strategy to satisfy a constant power output curve. Optimization of the CSP and CPV power share leads to an effective use of the dispatch capabilities of the CSP plant owing to the TES section, while the CPV plant is fully exploited, especially during the hours of high solar radiation. Comparison of the results achieved with the F-INT and P-INT control strategies demonstrates that the F-INT one leads to better performance both in terms of annual energy production and hours of potential time duration. [ABSTRACT FROM AUTHOR]

Photovoltaic and wind power generations are currently seen as sustainable options of in rural electrification, particularly in standalone applications. However the variable character of solar and wind resources as well as the variable load demand prevent these generation systems from being totally reliable without suitable energy storage system. Several research works have been conducted on the use of photovoltaic and wind systems in rural electrification; however most of these works have not considered other ways of storing energy except for conventional battery storage systems. In this paper, an energy dispatch model that satisfies the load demand, taking into account the intermittent nature of the solar and wind energy sources and variations in demand, is presented for a hybrid system consisting of a photovoltaic unit, a wind unit, a pumped hydro storage system and a diesel generator. The main purpose of the developed model is to minimize the hybrid system’s operation cost while optimizing the system’s power flow considering the different component’s operational constraints. The simulations have been performed using “fmincon” implemented in Matlab. The model have been applied to two test examples; the simulation results are analyzed and compared to the case where the diesel generator is used alone to supply the given load demand. The results show that using the developed control model for the proposed hybrid system, fuel saving can be achieved compared to the case where the diesel is used alone to supply the same load patters. [ABSTRACT FROM AUTHOR]

Solving power system scheduling is crucial to ensure smooth operations of the electric power industry. Effective utilization of available conventional and renewable energy sources (RES) by tri-generation and with the aid of energy storage facilities (ESF) can ensure clean and energy efficient power generation. Such power generation can play an important role in countries, like Saudi Arabia, where abundant fossil fuels (FF) and renewable energy sources (RES) are available. Hence, effective modeling of such hybrid power systems scheduling is essential in such countries based on the available fuel resources. The intent of this paper is to present a simple model for tri-generation based hybrid power system scheduling for energy resources rich area in presence of ESF, to ensure optimum fuel utilization and minimum pollutant emissions while meeting the power demand. This research points an effective operation strategy which ensure a clean and energy efficient power scheduling by exploiting available energy resources effectively. Hence, it has an important role in current and future power generation. In order to illustrate the benefits of the presented approach a clean and energy efficient hybrid power supply scheme for King Saud University (KSU), Saudi Arabia, is proposed and analyzed here. Results show that the proposed approach is very suitable for KSU since adequate solar power is available during its peak demand periods. [ABSTRACT FROM AUTHOR]

The paper presents results of design parameters optimisation of a wood chips fired steam boiler based heat and power block in a sample project of coal fired municipal heating plant modernisation. The project assumes the conversion of the heating plant into a dual fuel heat and power plant. The problem that is presented is selection of cogeneration block structure and thermodynamic parameters taking into account financial support mechanisms for cogeneration and renewable energy technologies. There are examined energy conversion and financial performances of the project. The results show that without the financial support the project is not profitable although it generates savings of primary energy of fossil fuels. If an administrative incentives are applied the optimal technical solution is different than suggested by energy conversion efficiency or fossil fuel savings. Financial calculations were performed for Polish marked conditions in the years 2011 and 2014 showing the impact of relatively short term variations of prices and support intensity on optimal plant design parameters. [ABSTRACT FROM AUTHOR]

• A novel multi-objective optimization model is proposed for a biogas-solar-wind IES. • A multitasking multi-objective optimization algorithm, MO-MFEA-II, is proposed. • Digester heating is applied to improve the efficiency of biogas production. • Online parameter estimation technology is used to boost the efficacy of MO-MFEA-II. The optimal operation of integrated energy systems (IESs) is of great significance to facilitate the penetration of distributed generators and improve its overall efficiency. A grid-connected IES is proposed in this paper for the synergetic interactions of electricity, thermal and gas energy flows, in which the biogas-solar-wind complementarities are fully considered and the digester heating is applied to provide an appropriate temperature for biogas production from anaerobic digestion. Its multi-objective optimization (MOO) model is constructed to optimize the operational cost, carbon dioxide emission and energy loss while considering digesting thermodynamic effects for anaerobic digester and uncertainty of wind and solar power, which is then compared to that of a natural gas-solar-wind IES. Thereafter, we develop an improved realization of multitasking paradigm within the domain of MOO to simultaneously solve the multi-objective operation optimization of the two IESs. In the associated multitasking algorithm, the underlying similarities of distinct optimization tasks are learned online to mitigate the harmful inter-task interactions and thereby facilitate improved convergence characteristics. The efficacy of the proposed multitasking algorithm has been comprehensively assessed on a novel biogas-solar-wind IES and a natural gas-solar-wind IES. Simulation results validated that the proposed IES can be operated in a more cost-efficient and environmentally friendly manner by comparing to the natural gas-solar-wind IES; the developed multitasking MOO algorithm can provide a better performance than other state-of-art multitask and single-task optimization algorithms. [ABSTRACT FROM AUTHOR]

• Mechanical energy storage systems are very efficient in overcoming the intermittent aspect of renewable sources. • Flywheel, pumped hydro and compressed air are investigated as mechanical energy storage. • Parameters that affect the coupling of mechanical storage systems with solar and wind energies are studied. Mechanical energy storage systems are among the most efficient and sustainable energy storage systems. There are three main types of mechanical energy storage systems; flywheel, pumped hydro and compressed air. This paper discusses the recent advances of mechanical energy storage systems coupled with wind and solar energies in terms of their utilization. It also discusses the advances and evolution in each type and compares them in terms of performance, capacity, response and utilizations. The reviewed studies exhibit all parameters that affect the performance of each storage type in which the configuration of the system has the major effective role. Choosing the suitable mechanical storage type depends on the requirements of each application such as using the flywheel for short duration applications. If long duration is needed, then it is preferred to use either pumped hydro or compressed air storage systems, knowing that the former has higher efficiency while the latter provides a faster start up. For the sake of the environment, it is recommended to use the adiabatic or isothermal compressed air storage. In all cases that combine MESSs with solar or wind energy, the series connection is preferred in order to provide stability and better control strategy. [ABSTRACT FROM AUTHOR]