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[Display omitted] • Various carbon nanotube-based devices are developed for solar energy utilization. • The water evaporation system can generate freshwater (1.28 kg m−2h−1). • The solar-thermoelectric system can output a voltage and charge a cellphone. • The supercapacitor performs an areal specific capacitance of 19.6 mF cm−2. • The hybrid energy system can produce freshwater, generate and store electric power. Nowadays, multi-functional systems driven by solar energy have been explored to alleviate the crisis of energy and freshwater scarcity. However, it remains a great challenge to integrate multi-functions into one hybrid system with a monolithic material, which can harvest, convert and store solar energy synergistically. Here, we firstly propose a multi-functional carbon nanotube paper, which starts from a material level to solve these problems. The carbon nanotube paper is fabricated by vacuum filtration. It exhibits high efficiency of solar-thermal conversion. Secondly, three types of energy conversion/storage systems (e.g., solar-thermal evaporation system, solar-thermoelectric generation system, and supercapacitor) are constructed based on the carbon nanotube paper, which extend the research to a device level. The solar-thermal evaporation system shows an evaporation rate of 1.28 kg m-2h−1 under simulated sunlight irradiation of 1 kW m−2. The solar-thermoelectric generation system demonstrates a stable electric power generation with an output voltage of 100 mV under light irradiation of 1 kW m−2. The supercapacitors perform the energy storage function with an areal specific capacitance of 19.6 mF cm−2. These devices and systems can be used in freshwater generation (0.84 kg m-2h−1, sunlight irradiation of 1 kW m−2), water purification/desalination (inorganic ions rejection larger than 99.9%) and portable solar charging system (maximum output voltage of 5 V). Finally, a hybrid energy system is innovatively proposed from the system level to simultaneously produce freshwater, generate and store electric power. Through the synergetic coupling of solar conversion and storage technologies, the hybrid energy system can supply sustainable freshwater and electricity for remote areas in daily life, highlighting the superiority of multi-energy (thermal energy, electrical energy, and electrochemical energy) complementary. [ABSTRACT FROM AUTHOR]

Medium and long-duration energy storage systems are expected to play a critical role in the transition towards electrical grids powered by renewable energy sources. ACAES is a promising solution, capable of handling power and energy ratings over hundreds of MW and MWh, respectively. One challenge with ACAES is achieving the required highly efficient operation in the compressor over the range of conditions encountered in the system as the pressure in the air store changes. In this paper, an application-oriented axial-flow compressor is designed, aiming towards efficient operation throughout the operation range, whilst also associating the performance prediction to a practical compressor geometry. A two-step design methodology based on inviscid, axisymmetric flow conditions has been implemented, leading to the flowtrack, blade-row geometries and the compressor performance map. The compressor model is integrated into an ACAES model, including two compression spools, two expansion stages with preheat, a constant volume high pressure storage operating between 5.5 and 7.7 MPa and two separate Thermal Energy Storage units. While the existing ACAES literature either ignores the transient off-design operation or uses generic numerical correlations (which are not associated to a particular geometry), the key novelty of this paper is the application of a detailed design method for turbomachinery to ACAES. The results indicate that the designed compressor requires 33 stages over the two spools, and is able to operate efficiently over the storage pressure range, showing that if the application-oriented design procedure is applied to the compressor, it does not stop ACAES reaching 70% round-trip efficiency, outputting 35MW for approximately 15 h. Importantly, the specific ACAES requirement of conserving heat at higher temperatures has been fulfilled by decreasing the number of intercoolers. Finally, it is recommended that a similar level of scrutiny is applied to the other components (i.e. expanders, heat exchangers and TES units), keeping in mind the unique set of operational requirements of ACAES. This work is an important step towards removing the common misconception that off-the-shelf components can be easily be used in typical ACAES designs. • ACAES imposes unique conditions on its components, aiming system reversibility. • The compressors must run efficiently and keep the airflow temperature high. • This paper develops an axial-flow compressor geometry and performance map for ACAES. • The compressor is integrated into an ACAES model, operating within 5.5 and 7.7 MPa. • The ACAES system results indicate the system reaches 70% RTE after stabilisation. [ABSTRACT FROM AUTHOR]

• Linear planning models of two types of compressed air energy storage are proposed. • A novel electricity-gas coupled energy hub for cascade utilization is structured. • Comparisons between energy-based and capacity-based energy storage are analyzed. Large-scale long-duration energy storage (LDES), like compressed air energy storage (CAES) and liquid air energy storage (LAES), is promising for high-penetration renewable energy consumption in the city-scale integrated energy system (IES). Due to high installation costs and challenges in decentralized control of distributed energy storage, this paper proposes an optimal planning model for an urban electricity-gas coordination hub (UEGCH) with centralized energy storage using large-scale LDES. Firstly, the UEGCH with energy cascade utilization is designed, where process-based linearized models of advanced adiabatic compressed air energy storage (AACAES) and LAES are established to make a trade-off between solving accuracy and speed. Then, a city-scale integrated electricity and gas system (IEGS) is constructed with multiple regions considering line-packing. Finally, a multi-scenario planning method is proposed based on X-means for scenario reduction, and the global optimum is obtained through linearization. Results show that compared with traditional gas storage tank (GST) in the UEGCH, the utilization of AACAES and LAES requires as little as 7 % and 0.7 % of the construction volume with lower carbon emissions and can be cost-competitive in terms of future advancement. As for different EESs, in contrast to the energy-based energy storage (EBES) (i.e., battery (BT)), the levelized cost of energy (LCOE) of the capacity-based energy storage (CBES), which includes AACAES and LAES, can be reduced by nearly 0.1 $/kWh, bringing an annual economic benefit of $ 3 million. Besides, the discharge duration of CBES can be increased to 13 h, demonstrating the application prospect in 100 % renewable consumption and islanding operation. Compared with AACAES, LAES can reach 11.67 times the energy density, with a drop of 6.11 % in operating cost. The abilities of EBES and CBES to locally consume renewables are respectively weaker and stronger than that of power-to-gas (P2G) combined with line-packing. Meanwhile, this paper further analyzes the impacts of temperature, discharge duration, renewable penetration, energy tariff, and demand on the operation and sizing of centralized energy storage. [ABSTRACT FROM AUTHOR]

• A new multi-energy combined system utilizes abundant wind/PV to produce hydrogen. • The refined coupling model of the system is simulated and realized. • The judgment matrix method is used to evaluate the system performance. • The optimal capacity of pumped storage achieves the system stability and economy. To achieve "carbon neutrality", clean energy such as wind and solar energy is being developed, but due to the random and intermittent characteristics of wind energy and photovoltaics, the instability of grid connections and the abandoning wind and photovoltaics need to be addressed urgently. This paper proposes a method to solve the problems of grid connection and abandonment in wind and photovoltaic generation systems, that is, to establish a combined pumped storage/wind/photovoltaic/hydrogen production system through the pumped storage and hydrogen production system. The system consists of a pumped storage/wind/photovoltaic complementary subsystem and a hydrogen production subsystem. First, different models in the system are modelled using Simulink and the characteristics of the models are analysed. Subsequently, the wind turbine model and the PV model are simulated to derive the wind-PV complementary characteristic curves, and it is found that the load demand cannot be met by relying on wind-PV complementary power generation alone. To achieve system stability and economy, pumped storage is configured to smooth the output of wind power and PV. After comprehensive consideration, the optimal pumped storage capacity is determined to be 1000 MW. Then, through the simulation of the pumped storage/wind/photovoltaic system, it is found that even though pumped storage can absorb the wind and photovoltaic outputs, there is still a surplus when the wind and photovoltaic outputs are in excess. Therefore, this surplus energy is used for hydrogen production and the configuration of the hydrogen production system is optimized using a particle swarm algorithm to minimize the cost per unit of hydrogen production. After particle swarm optimization, it was determined that the unit cost of hydrogen production was minimized to 3.54 CNY/ Nm 3 for the configuration of 55 electrolysis tanks of 4 MW and 219 lead-acid tanks of 1 MW/2 MWh. Meanwhile, the electrolysis tank simulation model and the lead-acid battery simulation model were used to obtain maps of their operating conditions, hydrogen production and hydrogen storage tank pressure. In view of the addition of an energy storage system to the wind and photovoltaic generation system, this paper comprehensively considers the two energy storage modes of pumped storage and hydrogen production, and proposes a corresponding capacity optimization configuration scheme, which has reference value for improving the consumption and stability of wind and photovoltaics and realizing the sustainable utilization of clean energy. [ABSTRACT FROM AUTHOR]

• Brayton Pumped Thermal Energy Storage integrated in urban energy district. • Deep-decarbonization scenarios by integrating PV production. • Mixed Integer Linear programming for day-ahead optimal scheduling. • Multi-energy mode reduces operational costs up to 10 % compared to the electric one. • Multi-energy mode brings to 3–10 % unavoidable thermal curtailment losses. Energy storage systems play a crucial role in supporting the integration of renewable energy sources. In this framework, Brayton Pumped Thermal Energy Storage is an emerging technology thanks to many positive features, including geographical and raw materials independence, long lifetime, and peculiar sector-coupling capabilities. By storing electric energy as thermal exergy, this technology offers the flexibility to discharge energy directly for heating or cooling applications or convert it back into electricity as needed by the grid. This dual functionality fits well with the multi-energy intrinsic nature of urban districts in which electrical and thermal energy carriers are involved. This paper aims then to evaluate the potential economic benefit due to the usage of a Brayton based Pumped Thermal Energy Storage as multi-energy device instead of a solely electric-to-electric. An urban district with thermal and electric requirements is used as a case study to investigate the techno-economic performance of the mentioned storage capacity when coupled to photo-voltaic plants to simulate deep-decarbonization scenarios. The system day-ahead optimization, performed through a Mixed Integer Linear Programming approach, aims to minimize the operational cost computed over a 24-h horizon. The results highlight that operational yearly cost savings are 5–10 % when using the multi-energy storage functionalities compared to the standard electric-to-electric operation. Despite the cost reduction, allowing only direct heating causes unavoidable thermal curtailment losses in the 6–10 % range. However, these losses can be reduced to 3 % by introducing the additional direct cooling functionality, bringing the best performances from the economic and thermodynamic standpoints. [ABSTRACT FROM AUTHOR]

• Design a hydrogen energy storage system-carbon capture and utilization system-based micro energy grid. • Proposed a carbon emission-green certificate equivalent interaction mechanism for multi-energy conversion and storage system. • Construct a two-stage optimal dispatching framework including day-ahead robust dispatching model and real-time rolling model. • Proposed an entropy-Shapley-based benefit allocation method considering multi-dimension impact factors. • Carried out the effectiveness and applicability analysis for the proposed dispatching scheme and benefit allocation strategy. To fully utilize the abundant renewable energy resources in county-level areas of China, this paper designs a novel structure of micro-energy grid integrating hydrogen energy storage (HES) system and carbon capture and utilization (CCU) system (HES-CCU-based MEG). And a carbon emission-green certificate equivalent interaction mechanism is established. Then, a two-stage optimal dispatching framework is proposed for mitigating the impact of uncertainty variables, including a day-ahead robust dispatching model and a real-time rolling optimization model. Thirdly, an entropy-Shapley-based benefit allocation method is constructed to allocate the benefits in dimensions of energy conservation, carbon emission reduction, and renewable power consumption among various devices. Finally, a micro-energy grid in Henan province, China, is selected as an example for case study. The results show that: (1) HES could transfer surplus renewable power and low-priced power to periods with high power prices, while CCU could achieves the cycle and utilization of CO 2 , leading to a decrease in power purchase costs and carbon emissions by 7.85% and 0.47%, respectively. (2) The two-stage optimal dispatching model gives full play to the flexibility adjustment ability of each device, mitigates the deviations caused by uncertainty variables, and formulates the optimal dispatching strategy. (3) The entropy-Shapley-based benefit allocation method could evaluate the contributions of each device in different dimensions, effectively, ensuring the rationality of benefit allocation results. Overall, the proposed model and method could utilize renewable energy resources in county-level areas, which is better to promote the clean and low-carbon transformation of the overall energy structure. [ABSTRACT FROM AUTHOR]

[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]

Highlights • Graphene used in energy conversion and heat transfer are classified and compared. • Performances of energy equipment made of graphene products are investigated. • Further application of graphene products in the field of energy is summarized. • Heat transfer applications of nano-graphene and graphene coatings are discussed. Abstract Along with the chic fad energy industry field, the graphene application in energy conversion and management does bring about some benefits in terms of the energy transfer and storage development, the achievement it exerts on the multifaceted innovate approaches. Both current and previous studies on energy conversion, energy storage and energy transfer development, many research results are sufficient to show that all graphene products including graphene paper, film, foam and fiber have a significant role in improving performance. In the energy conversion research on the graphene paper, it has been recently demonstrated that putting the graphene into triboelectric nanogenerators practice possesses higher output performance than traditional generator, which has a maximum strain as large as 200% without evident degradation of the electrical properties. In terms of energy transfer, the graphene fiber application on the battery can significantly increase the charge and discharge rates with enhanced storage capacity of 763 F g−1. On the energy storage research, the graphene foam can enhance a high density of solar thermal storage up to 269.8 kJ kg−1 for long-term. Nano-graphene and graphene coating provide feasibility for the miniaturization of energy storage equipment which inspired the possibility for portable and foldable devices. The work done in this paper can effectively help promote the application of graphene in energy field. Based on our work, the researchers can choose graphene products (graphene paper, graphene film, graphene foam or graphene fiber) efficiently according to the research object in the future. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Energy storage systems for series hybrid excursion ships are studied. • CO2 emission are avoided during the casting-off and the docking maneuvers. • Full model using Energetic Macroscopic Representation (EMR) is described. • 1.39 kg of CO2 during the casting-off/docking maneuvers can be avoided. • Global consumption and emissions can be reduced by 20%. Abstract Ecological areas visits require appropriate management of key ecological features. In protected reserves innovative systems should be developed to facing problems of pollution, exhaust fumes and noise. These underlying conditions lead to special challenges for excursions ships. The switching to a cleaner, safer and quieter transport system seems to be a sustainable long-term solution for the problems of ecological areas, where more electric ship can be an important part of the solution and principally for the last mile. This paper presents a design approach of a hybrid Energy Storage Systems (ESS) for new generation of series hybrid excursion ship devoted to ecological areas to avoid any emission during the casting-off and the docking maneuvers. The main purpose of the paper is to show that, even if the hybrid ESS plus series-hybrid propulsion were already used to other vehicles, the gain for a ship with no regenerative capability is not evident. The proposed hybridization is built upon a fully-active parallel topology with battery and supercapacitors. The sizing methodology and the configuration of the ESS are detailed. For a real mission profile in Alster Lake (Hamburg, Germany) it is shown that a small battery pack of 2 kWh with a supercapacitor bank of 0.54 kWh are necessary to have zero-emission maneuvers. The graphical formalism Energetic Macroscopic Representation (EMR) is used to describe the model and to establish an energy analysis tool. An inversion-based control scheme is then deduced from the EMR and simulation results are provided to validate the proposed methodology. The usage of hybrid ESS avoids 1.39 kg of CO 2 during the casting-off and docking maneuvers despite increasing consumption of 0.2 l (+8%). However, the plug-in capability can be introduced and a recharge of the battery when the ship is docked could reduce the global consumption and emissions by 20% in comparison to the original ship. [ABSTRACT FROM AUTHOR]

Highlights • An overview of methodology on how to model material and energy flow in industry. • Comprehensive summary of government, private, and trade association databases. • An overlook of connection between material/energy flow and energy purchased/sold. • Synopsis of activity-based process models to create historical pattern for industry. • An outline of key energy end uses including process related and non-process related. Abstract The manufacturing sector has been one of the most significant energy consuming and CO 2 emitting sectors over the past three decades. Therefore, it is important to have energy flow models of manufacturing processes to identify efficiency improvement and waste heat recovery opportunities with very specific targets. One of the best methods to pinpoint such locations is by referring to manufacturing process step models. Such models can be created on a large scale per industry and on small scale per process within an industry branch. Industry level modeling provides energy saving contingency by large magnitude where the impact on the economy and environment can be observed more visibly especially when sequential trends are identified. The methodology, reviewed in this paper, describes how to model energy flows on an industry scale by deriving the connection between key energy conversion activities on the one hand – including energy purchased/sold and onsite electricity generated, and the key end uses on the other hand. Industry-level energy flow model, referred to in this work, does not assume any specific system. That feature makes it scalable and allows analysis of manufacturing at various levels starting with single processes and finishing at sector and national economy levels. A combined analysis of the procedure is described in detail for creating process step models of manufacturing processes. The availability of U.S. national databases to calibrate these models is discussed and the challenges that arise in finding and using such databases are identified and analysed. In addition to addressing generic data issues associated with energy flow models, the paper also focuses on energy and material models and presents several examples of energy-intensive manufacturing processes, producing industrial gases, textiles, pulp and paper. Finally, importance of water use in onsite energy conversion and process end uses in various industries is addressed along with the sources of where this important data can be found to complete the energy flow modeling. [ABSTRACT FROM AUTHOR]

Graphical abstract System output power along with solar irradiance and SWP power. Highlights • Isolated continuous power generation system at constant voltage using solar energy. • A novel technique using PHES with solar photovoltaic system for reliable and quality power. • Power generation absolutely unaffected by variations or absence of solar irradiation. • System is suitable for rural as well as other areas having open well or other water sources. • Mathematical modelling and simulation using real solar irradiation for performance evaluation. Abstract A novel off-grid small power generation system using locally available sources is proposed in this paper for the areas, where the open-wells or the permanent sources of water are available. Although, the system can be installed anywhere, but its installation in remote and rural areas, where there is no access of electricity, can be an interesting application. The proposed system comprises of a solar photovoltaic (SPV) system, solar water pump, pico-hydro turbine-generator and pumped-hydro energy storage system. Its operation is quite different from all other existing SPV power generating systems. In this paper, an innovative power generation technique is developed, due to which the output power of the proposed system is absolutely unaffected by the changes that occur in solar irradiation. The proposed system does not require the use of batteries, inverter, transformer, and charging or controlling circuits at all. The attractive features of the system are simplicity, reliability and ability to generate continuous power at constant voltage irrespective of variations or absence of solar irradiation. The mathematical model of the proposed system has been developed in the paper. The simulation is carried out using real solar irradiation for performance evaluation of the proposed model. [ABSTRACT FROM AUTHOR]

The Conferences on Sustainable Development of Energy, Water and Environment Systems (SDEWES) at the beginning of the 21 st century have become a significant venue for researchers to meet, and initiate, discuss, share, and disseminate new ideas in various disciplines of sustainable development. In 2002, the first conference was organised in Dubrovnik, Croatia and since then, 10 more successful conferences were realised. Following the success of international conferences in Dubrovnik, the organizing committees decided to organize the main conference and regional conferences all over the world in even years. In 2016, the second regional SDEWES conference, namely the 2 nd South East European Conference on Sustainable Development of Energy, Water and Environment Systems, was held June 15–18 in Piran/Portorose, Slovenia while the 11 th SDEWES conference was organised in Lisbon, Portugal on September 4–8. There were 10 special sessions dedicated to various sustainability topics organised in both conferences. This special issue is based primarily upon a collection of 35 papers selected from among 538 scientific contributions presented at the 2 nd SEE and 11 th SDEWES Conferences. Moreover, this editorial summarises SDEWES published articles that have addressed and identified problems or provided the background for the research that is reported in the current special issue. The main topics of the selected papers address sustainable combustion technologies, renewable energy sources and sector integration, including the integration of renewable technologies in the urban environment, the integration of heat, cold, electricity and fuel production in buildings and industrial applications, heat exchangers and heat exchanger networks, the development and integration of energy storage for concentrated solar power plants, and sectorial integration of bioenergy resources and biorefineries with a particular focus on system integration for efficient and low-carbon systems. [ABSTRACT FROM AUTHOR]

• Sunbelt countries can develop reliable solar-dominant grids in the absence of wind. • Policymakers should be highly sceptical of low solar technical potential estimates. • Zero energy emissions Malaysia requires about 0.7 TW solar, 2 TWh pumped hydro. • Sarawak-Peninsular Malaysia interconnection reduces storage needs, but not costs. • Inclusion of about 0.4% hydrogen or synthetic methane reduces storage needs and cost. Three-quarters of the global population lives in the sunbelt region (±35o latitude) with excellent access to solar resources. Wind resources at the equator are very limited, while supply chain and permitting delays are slowing wind deployment at a global scale. This paper investigates the potential for solar photovoltaic-dominant 100% renewable grids to be developed in sunbelt countries through a case study of Malaysia. It was expected that the technical potential for solar photovoltaics and off-river pumped hydro would be far in excess of what is required to decarbonise Malaysia's electricity grids. A Geographic Information System analysis determined that Malaysia has the potential to deploy approximately 8.5 Terawatts of terrestrial photovoltaics and 25 Terawatts of marine floating solar on calm oceans. There are roughly 450 Terawatt-hours of energy storage available in the form of off-river (closed-loop) pumped hydro energy storage. A least-cost, 16-year hourly energy balance model was used to determine that an affluent, fully electrified, highly interconnected Malaysia could greatly reduce emissions through the deployment of 660 Gigawatts of photovoltaics and 2200 Gigawatt-hours of pumped hydro, supported by small amounts of hydrogen-based gas peaking. All-in costs for such a fully decarbonised energy system were modelled to be in the range of 95–103 USD per Megawatt-hour. A Sarawak-Peninsular Malaysia interconnected grid could produce a similar electricity cost to two separate grids while reducing the long-term energy storage needs by approximately 33%. Inclusion of about 3 Terawatt-hours (0.1% of average annual generation at 20 Megawatt-hours/capita/year demand) of hydrogen, synthetic methane, or legacy fossil fuels could further reduce long-term energy storage needs by about 30% by helping to ride through occasional prolonged cloudy periods. Policymakers in sunbelt countries should be highly sceptical of technical potential estimates that suggest limited area for solar photovoltaics. Sunbelt countries can comfortably proceed with the development of cheap, reliable solar-dominant grids primarily supported by pumped hydro energy storage and inter-regional transmission. [ABSTRACT FROM AUTHOR]

In this paper a dynamic simulation model and a thermo-economic analysis of a novel polygeneration system are presented. The system includes photovoltaic/thermal collectors coupled with a solar-assisted heat pump, an adsorption chiller and an electrical energy storage. The modelled plant supplies electrical energy, space heating and cooling and domestic hot water. The produced solar thermal energy is used during the winter to supply the heat pump evaporator, providing the required space heating. In summer, solar thermal energy is used to drive an adsorption chiller providing the required space cooling. All year long, solar thermal energy in excess, with respect to the space heating and cooling demand, is used to produce domestic hot water. The produced electrical energy is self-consumed by both user and system auxiliary equipment and/or supplied to the grid. The system model includes a detailed electrical energy model for user storage and exchange with the grid along with a detailed building model. This study is a continuation of previous works recently presented by the authors. In particular, the present paper focuses on the real electrical demands of several types of users and on the analysis of the comfort of building users. Differently from the works previously published by the authors, the present work bases the calculations on measured electrical demands of real users (fitness center and offices). The system performance is analyzed with two different electricity supply contracts: net metering and simplified purchase/resale arrangement. Daily, weekly and yearly results are presented. Finally, a sensitivity analysis is performed in order to determine the system performance as a function of the system main design/control parameters and to evaluate the minimum Simple Pay-Back period. The results outlined a share of the electrical energy storage system on the self-consumed electrical energy of about 20%. The economic profitability is better in case of net metering contract compared to the simplified purchase/resale arrangement one. Moreover, a Simple Pay-Back of about 15 years is achieved for the best configuration, decreasing to 5.6 years in case of capital investment incentive of 65%. The best system configuration, in terms of solar field area, for the fitness center user ranges from 250 to 300 m 2 . [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel hydrogen energy storage system with PEMEC and SOFC is proposed. • Electrochemical compression instead of mechanical compression of hydrogen. • The PEMEC cathode produce high pressure hydrogen in asymmetric operation. • Avoid the carbon accumulation of SOFC with full utilization of hydrogen. • Comprehensive analysis including energy, exergy, and sensitivity is implemented. Accessing energy storage systems at the grid or renewable energy sources can effectively solve the problem of unstable renewable energy generation. Hydrogen is considered as a potential energy storage medium due to its high energy density and environmental friendliness. In this paper, a novel hydrogen energy storage system is proposed to solve the problem of grid volatility caused by renewable electricity. The system consists of asymmetric PEMEC and SOFC. Asymmetric PEMEC produces high pressure hydrogen directly by electrochemical reaction without mechanical compressor. This will simplify the system structure and improve the stability of the system. Hydrogen-fueled SOFC and ORC-sCO 2 waste heat recovery systems enable efficient power generation with no carbon emissions. On the basis of the thermodynamic modeling of the system, the energy analysis, exergy analysis and the sensitivity analysis were performed. The results show that the round-trip thermal and exergy efficiencies are 54.29% and 50.34%, respectively, and the energy storage density is 367.92 kWh·m−3. The sensitivity analysis revealed that the PEMEC hydrogen production rate and SOFC operation temperature are the main influencing parameters for the system energy efficiency. Increasing the PEMEC hydrogen production rate will reduce the charging time, but the system energy efficiency will be significantly reduced. SOFC operation temperature increased from 700 °C to 1100 °C, the system round-trip exergy efficiency increased by 12.02%. PEMEC operating pressure has a slight impact on system energy efficiency, so it is not considered as a main influencing parameter. But, increasing the PEMEC operating pressure can significantly increase the system energy storage density, which is beneficial for energy storage system. In summary, the novel hydrogen energy storage system proposed in this paper provides theoretical guidance and new ideas for the practical application of hydrogen energy storage system. [ABSTRACT FROM AUTHOR]

• A comparison method between energy-only and energy and reserve model. • Higher revenue for flexible technologies was achieved for joint model. • The down reserve proved to be more required in high RES systems. • The study showed significant difference in operation between two models. The requirements for ancillary services in energy systems are growing as the amount of renewable energy sources such as solar and wind increases. On the other hand, the system can benefit from extra sources of flexibility thanks to the increased digitalization that enables successful integration of demand response and energy storage. The majority of recent energy system analysis research did not consider the regulation markets. As a result, these investigations preclude the ability to fully evaluate the advantages of energy storage and flexible cooling loads. With the method outlined in this paper, it is possible to compare the two strategies and assess the advantages of energy storage and flexible cooling loads for each strategy. In addition to the energy storage systems, the case study in this paper focuses on flexible cooling loads as a significant consumer in the system. According to the findings, the system's operating costs increased by 19.4% when reserve limitations were placed. Furthermore, the findings demonstrated that when flexible assets were permitted to participate in the reserve market, they generated significantly higher incomes. According to the findings, mechanisms that will allow energy storage and demand response to provide reserve capacities as well as the growth of reserve markets are both necessary. [ABSTRACT FROM AUTHOR]

This paper presents the comparative study of two hybrid energy storage systems (HESS) of a two front wheel driven electric vehicle. The primary energy source of the HESS is a Li-Ion battery, whereas the secondary energy source is either an ultracapacitor (UC) or a flywheel energy system (FES). The main role of the secondary source is to deliver/recover energy during high peak power demand, but also to increase battery lifetime, considered among the most expensive items in the electric vehicle. As a first step, a techno-economic comparative study, supported by strong literature research, is performed between the UC and the FES. The design and sizing of each element will be presented. The comparison criteria and specifications are also described. The adopted approach in this paper is based on an academic non-oriented point of view. In a second step, each of the HESS will be integrated in a more global Simulink model which includes the vehicle model, the traction control system (TCS), the regenerative braking system and the vehicle actuators. Simulation tests are performed for an extreme braking and vehicle starting-up operations. Tests are realized on two different surface road types and conditions (high and low friction roads) and for different initial system states. In order to show the most appropriate storage system regarding compactness, weight and battery constraints minimization, deep comparative analysis is provided. [ABSTRACT FROM AUTHOR]

Solar Aided Power Generation is a technology in which low grade solar thermal energy is used to displace the high grade heat of the extraction steam in a regenerative Rankine cycle power plant for feedwater preheating purpose. The displaced extraction steam can then expand further in the steam turbine to generate power. In such a power plant, using the (concentrated) solar thermal energy to displace the extraction steam to high pressure/temperature feedwater heaters (i.e. displaced feedwater heaters) is the most popular arrangement. Namely the extraction steam to low pressure/temperature feedwater heaters (i.e. non-displaced feedwater heaters) is not displaced by the solar thermal energy. In a Solar Aided Power Generation plants, when solar radiation/input changes, the extraction steam to the displaced feedwater heaters requires to be adjusted according to the solar radiation. However, for the extraction steams to the non-displaced feedwater heaters, it can be either adjusted accordingly following so-called constant temperature strategy or unadjusted i.e. following so-called constant mass flow rate strategy, when solar radiation/input changes. The previous studies overlooked the operation of non-displaced feedwater heaters, which has also impact on the whole plant’s performance. This paper aims to understand/reveal the impact of the two different operation strategies for non-displaced feedwater heaters on the plant’s performance. In this paper, a 300 MW Rankine cycle power plant, in which the extraction steam to high pressure/temperature feedwater heaters is displaced by the solar thermal energy, is used as study case for this purpose. It was found that plant adopting the constant temperature strategy is generally better than that adopting the constant mass flow rate strategy. However, if rich solar energy is available, adopting the constant mass flow rate strategy can achieve better performance. [ABSTRACT FROM AUTHOR]

Energy production is changing in the world because of the need to reduce greenhouse gas emissions, to reduce the dependence on carbon/fossil sources and to introduce renewable energy sources. Despite the great amount of scientific efforts, great care to energy storage systems is necessary to overcome the discontinuity in the renewable production. A wide variety of options and complex characteristic matrices make it difficult and so in this paper the authors show a clear picture of the available state-of-the-art technologies. The paper provides an overview of mechanical, electrochemical and hydrogen technologies, explaining operation principles, performing technical and economic features. Finally a schematic comparison among the potential utilizations of energy storage systems is presented. [ABSTRACT FROM AUTHOR]

The Conferences on Sustainable Development of Energy, Water and Environment Systems – SDEWES conferences at the beginning of the 21st century become a significant venue for researchers to meet, and initiate, discuss, share, and disseminate new ideas in various disciplines of sustainable development. In 2002, the first conference was organised in Dubrovnik, Croatia and following the tradition for odd years, the 10th SDEWES Conference again took place in Dubrovnik, Croatia from September 27th to October 2nd 2015. The total number of 1204 submitted abstracts resulted with 551 accepted manuscripts bringing 538 participants from 65 countries that participated in a number of oral and poster presentations, panels, invited lectures, and special events. Moreover, 17 special sessions were organised including 166 invited speakers. This editorial is based primarily upon 32 papers selected from among 551 contributions presented at the 10th SDEWES Conference but it also provides a wider picture on the contributions from previous SDEWES conferences. It summarises SDEWES published articles that have addressed identified problems or provided the background for the research that is reported in the current special issue. The main topics of these papers address sustainable combustion technologies, heat exchangers, waste heat recovery, sustainable buildings, campuses and communities, renewable energy technologies and sources, as well as energy system flexibility and energy storage. [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]

Hydrogen is considered one of the key pillars of an effective decarbonization strategy of the energy sector; however, the potential of hydrogen as an electricity storage medium is debated. This paper investigates the role of hydrogen as an electricity storage medium in an electricity system with large hydropower resources, focusing on the Swiss electricity sector. Several techno-economic and climate scenarios are considered. Findings suggest that hydrogen storage plays no major role under most conditions, because of the large hydropower resources. More specifically, no hydrogen storage is installed in Switzerland if today's values of net-transfer capacities and low load-shedding costs are assumed. This applies even to hydrogen-favorable climate scenarios (dry years with low precipitation and dam inflows) and economic assumptions (high learning rates for hydrogen technologies). In contrast, hydrogen storage is installed when net-transfer capacities between countries are reduced below 30% of current values and load-shedding costs are above 1,000 EUR/MWh. When installed, hydrogen is deployed in a few large-scale installations near the national borders. [Display omitted] • High-fidelity models of Swiss electricity sector and hydrogen storage technologies. • No significant hydrogen storage is required in Switzerland under most scenarios. • Large hydropower resources reduce the need for hydrogen storage significantly. • Hydrogen storage becomes relevant with reduced electricity net transfer capacities. • Hydrogen storage is used for high self-sufficiency ratios to avoid load-shedding. [ABSTRACT FROM AUTHOR]

• Energy density and load response are considered in optimization simultaneously. • Multiple indexes are integrated into an evaluation result. • Normalized optimization variables extend the applicability of the proposed method. • The method demonstrates high effectiveness in improving economics and reliability. System component sizes and their energy densities impact the long-term ship energy efficiency and economics, whereas power source load response influences system transient behavior, posing challenges to system design and energy management when clean fuels are used onboard. In this paper, a novel component sizing method is proposed for integrating reciprocating gas engines and energy storage systems (ESS) on ships, considering energy density and load response simultaneously. By specifying gas engine powers and ESS capacities as normalized optimization variables by ship scales, this method optimizes them based on the A. J. Klee multi-index evaluation and single-objective particle swarm optimization (PSO). Energy densities of engines and ESS were introduced to demonstrate the trade-off between the power-splitting and increased system mass and hull resistance. The engine load response was incorporated into the rule-based energy management strategy (EMS) to limit power ramps. This method was examined in the case study by taking four cruise ships as examples. It can be found that implementing the proposed evaluation-based optimization can improve cruise ship energy efficiency while maintaining reliability over the voyage. It is possible to reduce fuel consumption and carbon emissions by up to 17.1% and 14.8%, respectively. The minimum system reliability can be increased from 0.025 to 0.475 during transients. Furthermore, ship life-cycle costs can be reduced compared to the original design method, and the payback period for gas engines, ESS, and fuel tanks can be shortened to less than six years. Among the various cases, the definition of normalized optimization variables broadens the applicability of this method away from a specific ship, allowing it to be applied to ships of various tonnages and types. [ABSTRACT FROM AUTHOR]

[Display omitted] • A monthly operation strategy is presented with consistent output process everyday. • A multiple time-scale nested optimizing model is designed for the hybrid power system. • The hybrid power system can achieve consistent output process for each day of a month. • New energy can further improve to 5000 ∼ 6000 MW with enhance of the storage system. To address the grid connection challenges derived from the high penetration of intermittent new energy sources, some generation companies are trying to use existing cascade hydropower stations to develop "large-scale cascade hydropower energy storage systems" (LCHES). They intend to combine the LCHES with new energy power to become a new type of hybrid power system (the LCHES-WP hybrid power system). For such an emerging hybrid power system, performance in the medium- and long-term operation is more worthy of attention. Therefore, we propose "monthly LCHES-WP operation strategy" and "short-term dispatch strategy for LCHES" to constrain the operation of the LCHES-WP hybrid power system. On this basis, a multiple time-scales nested optimizing model is presented to estimate the performance in the medium- and long-term operation. A case study in the Yellow River Basin in China was presented based on the baseline scenario (1800 MW of hydroturbine, 1200 MW of pump, 2000 MW of new energy, and 0.24 billion m3 of regulating storage capacity). It reveals that (1) the LCHES-WP hybrid power system can achieve a consistent output process every day during a month with low energy curtailment and low energy supply shortage, which indicates that it can meet satisfactory performance in medium to long-term operation. (2) it will significantly increase energy curtailment (controlling the energy supply shortage is as low as the baseline scenario) without the pumping system or sufficient regulating storage capacity. (3) based on sensitivity analysis, it is indicated that the capacity of new energy can further improve to 5000 ∼ 6000 MW. The simulation framework and the result provided in this paper can be referred to by the same research. [ABSTRACT FROM AUTHOR]

• A CCHP system based on solar energy and thermochemical energy storage is proposed. • Increasing the share of solar energy used in combined cooling, heating and power (CCHP) systems. • The 4E analysis and parameter study of the system are carried out. • The SPECO method is done and provides direction for the optimization of the system. • The effects of the main parameters on the system performance were evaluated. The combination of calcium looping and concentrating solar power (CSP) is a promising energy conversion technology that can greatly increase the share of solar energy used in combined cooling, heating and power (CCHP) systems. This paper designs a CCHP system based on solar energy and thermochemical energy storage. The system runs all day through day and night modes. Under basic working conditions, the energy and exergy efficiencies of the system could reach 56.92 % and 35.94 %, respectively. The system is evaluated by multiple approaches including parametric sensitivity analysis and 4E (energy, exergy, economy and environment)) analyses. The results demonstrate that the system could produce 2618.09 MW of electricity, 305.56 MW of heat and 523.88 MW of cooling capacity per day, respectively. At the same time, the reductions of CO 2 emissions and fossil fuel consumption could reach 2222.76 tons and 696.41 m3 per day, respectively. Furthermore, the increasing mass flow of main turbine inlet could increase both the system efficiency and the exergy efficiency. Thus, it is beneficial to reduce the environmental impact but with the increasing investment cost. In the meanwhile, the exergoeconomic factor and exergoenvironment factor of the system were 55.65 % and 0.139, respectively. Besides, as the extraction flow rate of the intermediate pressure turbine increases, the energy efficiency increases but the exergy efficiency descends. This is unfavorable to reducing the environmental impact, yet it could decrease the investment cost of the system. These results reveal that the hybrid system has the characteristics of high efficiency and emission reduction in energy storage, power generation, heating and cooling, and has great development potential. [ABSTRACT FROM AUTHOR]

• A novel volumetric expander is simulated and validated by experiments. • Advanced CFD simulation using real gas and 3D dynamic mesh were developed in ANSYS Fluent. • The isentropic efficiency of SSWE reached the maximum of 71 % and and maximum power output reached 504 W. • The deviation between CFD simulations and experiments mainly due to heat transfer losses, friction losses and side leakage. Compressed air energy storage (CAES) is a promising technology for storing mechanical and electrical energy using the gas power cycle. The expansion device is a critical component of the CAES that determines the overall performance of the system. Standard Wankel expander (SWE) is one of the volumetric expanders which has several advantages including low vibration, ability to produce high power output, low manufacturing cost and less moving parts. However, SWE requires valves for timing the inlet and outlet flow and a balancing system to ensure reliable operation. Static shaft Wankel expander (SSWE) is an attractive solution to enable valves' removal and the need for balancing system. This paper presents a detailed experimental and numerical investigation of an SSWE performance at various operating pressures and temperatures for CAES application. An advanced computational fluid dynamic simulation model taking into account the dynamic motion of the SSWE and utilising real gas air properties. A compressed air test rig was constructed and instrumented with temperature, flow rate, pressure and torque sensors. Experimental testing at temperatures 20 °C to 80 °C and pressures of 1.5 bar a to 3 bar a was conducted and compared to the CFD simulations results. Correlations were developed for the friction power loss. Experimental results showed that the developed SSWE can produce power output of 504 W at 80 °C and 3 bar a and its isentropic efficiency reached 71 % at 60 °C and 2 bar a. [ABSTRACT FROM AUTHOR]

• Two novel hybrid MPPT techniques, ZOA-ANFIS and GTO-ANFIS, are introduced and evaluated for instantaneous maximum power extraction from solar and wind energy sources. • The Hybrid ZOA-ANFIS-based MPPT technique uses Zebra Optimization Algorithm for optimal power point tacking and ANFIS for enhanced tracking precision through a logical control scheme. • The Hybrid GTO-ANFIS-based MPPT technique uses the Gorilla Troop Optimizer algorithm to optimize wind energy system control parameters, accurately tracking its maximum power point. • The integration of various optimization algorithms with ANFIS-based control systems significantly enhances the advancement and effectiveness of renewable energy utilization. • The research provides a detailed analysis of the system structure and modelling, highlighting the potential applications of hybrid MPPT techniques in renewable energy integration. This paper presents an effective hybrid renewable energy system. This system utilizes primary energy sources represented by both photovoltaic (PV) and wind energy conversion system (WECS). In addition, integrating the battery energy storage system (BESS), the hydrogen energy storage system (HESS), and the supercapacitor energy storage system (SESS), as backup sources which providing reliable simultaneous power supply and loading. A new design for a wind energy conversion system based on a hybrid excitation permanent magnet synchronous generator (HEPMSG) is proposed, and then artificial intelligence strategies are utilized to determine the optimal flow of energy when the system is operating immediately. Moreover, new hybrid maximum power point tracking (MPPT) techniques have been proposed including zebra optimization algorithm (ZOA)-ANFIS-based MPPT and gorilla troops optimizer (GTO)-ANFIS-based MPPT to obtain the maximum power of solar panels and wind turbines, which leads to enhancing the performance of these energy sources. The implemented power flow management (PFM) model is designed by MATLAB/Simulink, considering three various operating cases to evaluate the performance and effectiveness of various backup system configurations under different operating scenarios. According to the results, power can be generated, and load requirements can be efficiently met by applying the proposed PFM strategy, and this leads to the system operating at optimal performance. When comparing two optimization techniques, it will become clear that both give robust performance, but ZOA technique significantly outperforms the GTO technique in the computation time (26.17 % reduction) for the photovoltaic system. On the other hand, in the case of the wind energy conversion system, the ZOA technique achieves a significant reduction in calculation time by 35.5 %. The ZOA technique achieves computation times of 1616.80 s and 672.43 s for the photovoltaic and wind energy conversion system, respectively. [ABSTRACT FROM AUTHOR]

• A hierarchical energy management strategy with life balance control is proposed. • A dynamic threshold control of ultracapacitor SOC is designed for optimization. • Life-cycle average operating cost is defined to evaluate the comprehensive economy. • A hardware-in-the-loop platform is built to verify the effectiveness. • The proposed strategy has better life mileage compared with the DP strategy. Fuel cell (FC) is an ideal power source for electric vehicles with high efficiency and little pollution. However, with its weak dynamic reaction, it needs to be used in combination with other energy storage devices, and the coupling of multiple energy sources makes it difficult to fully utilize the system performance. Meanwhile, the cost and durability of FC hinder its commercialization. This paper takes the composite energy storage system composed of FC, battery (BAT) and ultracapacitor (UC) as the research object. In order to improve the system performance, a hierarchical energy management strategy is proposed based on the analysis of the relationship between UC output power and vehicle demand power under dynamic programming (DP) strategy, taking into account the vehicle energy consumption and energy source lifetime. A fuzzy control based on speed prediction and a dynamic state-of-charge (SOC) threshold control optimization algorithm of UC based on working condition recognition are designed to optimize the hierarchical control strategy. In the upper layer strategy, for realizing the online real-time distribution of UC output power, the generalized regression neural network is used to learn the relationship between UC output power and demand power under DP strategy; in the lower layer strategy, the power of the FC and BAT is distributed using an equivalent energy minimization strategy. Based on above strategy, this paper proposes a life balance control strategy for energy sources to maximize the lifetime of the composite energy storage system. Simulation and experimental results show that the proposed strategy has a comparable life-cycle average operating cost to the DP strategy with better life mileage. [ABSTRACT FROM AUTHOR]

This paper presents the comparison between two braking methods for a two-wheel front driven Electric Vehicle maximizing the energy recovery on the Hybrid Energy Storage System. The first method consists in controlling the wheels slip ratio while braking using a robust sliding mode controller. The second method will be based on ECE R13H constraints for an M1 passenger vehicle. The vehicle model used for simulation is a simplified five degrees of freedom model. It is driven by two 30 kW permanent magnet synchronous motor (PMSM) recovering energy during braking phases. Several simulation results for extreme braking conditions will be performed and compared on various road type surfaces using Matlab/Simulink®. For an initial speed of 80 km/h, simulation results demonstrate that the difference of energy recovery efficiency between the two control braking methods is beneficial to the ECE constraints control method and it can vary from 3.7% for high friction road type to 11.2% for medium friction road type. At low friction road type, the difference attains 6.6% due to different reasons treated in the paper. The stability deceleration is also discussed and detailed. [ABSTRACT FROM AUTHOR]

There are many advantages to utilize storages in electric power system. Peak shaving, load leveling, load frequency control, integration of renewable, energy trading and spinning reserve are the most important of them. Batteries, especially redox flow batteries, are one of the appropriate storages for utilization in distribution network. This paper presents a novel, heuristic and practical method for optimal scheduling in distribution network with flow battery storage. This heuristic method is more suitable for scheduling and operation of distribution networks which require installation of storages. Peak shaving and load leveling is considered as the main objective in this paper. Several indices are presented in this paper for determine the place of storages and also scheduling for optimal use of energy in them. Simulations of this paper are based on real information of distribution network substation that located in Semnan, Iran. [ABSTRACT FROM AUTHOR]

This paper is concerned with Operating Modes in hybrid renewable energy-based power plants with hydrogen as the intermediate energy storage medium. Six operation modes are defined according to plant topology and the possibility of operating electrolyzer and fuel cell at steady-power or partial load. A methodology for the evaluation of plant performance is presented throughout this paper. The approach includes a set of simulations over a fully validated model, which are run in order to compare the proposed operation modes in various weather conditions. Conclusions are drawn from the simulation stage using a set of Key Performance Indicators defined in this paper. This analysis yields the conclusion that certain modes are more appropriate from technical and practical standpoints when they are implemented in a real plant. From the results of the simulation assessment, selected operating modes are applied to an experimental hydrogen-based pilot plant to illustrate and validate the performance of the proposed operation modes. Experimental results confirmed the simulation study, pointing out the advantages and disadvantages of each operation mode in terms of performance and equipment durability. [ABSTRACT FROM AUTHOR]

The droop method is an advantageous technique for stand-alone AC supply systems, allowing for power sharing among various inverters with no need for communication cables. However, in stand-alone systems with multiple distributed energy storage units, the conventional droop methods are unable to control the storage unit state-of-charge (SOC) in order to change simultaneously. Existing techniques endeavor to solve this problem by changing the slope of the P – f curve however this solution compromises the power response performance. As an alternative, this paper proposes a new SOC-based droop control, whereby the P – f curve is shifted either upwards or downwards according to the battery SOC. The proposed technique makes it possible to select the time constant for the battery SOC convergence and, at the same time, to optimize the power response performance. The paper also shows how the SOC changes when the ratios between the battery capacity and the inverter rated power are different and how the proposed technique can limit the SOC imbalance. Simulation and experimental results corroborate the theoretical analysis. [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]

Generally, off-grid fossil fuel generators provide energy supply to remote regions. The integration of photovoltaic (PV) plants to battery energy storage (BES) systems potentially increases reliability, the system autonomy and lifetime, reducing the generator working hours and the system environmental impact. PV–BES–Diesel generator hybrid energy systems (HESs) offer technical, economic and environmental benefits compared to traditional off-grid systems. This paper proposes a bi-objective design model for off-grid PV–BES–Diesel generator HESs. The aim is to identify the PV plant rated power, the BES system capacity and the technical configuration able to jointly reduce the levelised cost of the electricity ( LCOE ) and the carbon footprint of energy ( CFOE ) . Furthermore, the comparison of the LCOE and CFOE values of the HES against a traditional diesel generator allows determining the economic and environmental advantages coming from the described system. Despite the proposed model is general and suitable for any installation site and HES configuration, this paper exemplifies its application designing a HES to be installed in a remote village in Yakutsk, Russia. The model takes into account the hourly energy demand, the irradiation and temperature profiles of the installation location calculating the hourly PV plant yield, the battery charge–discharge processes and the required generator energy. Results highlight the technical, economic and environmental feasibility of the system for a context with a medium irradiation level, i.e. ∼1400 kW h/(m 2 year), and relatively low fuel cost, i.e. 0.7 €/l. For the best economic scenario LCOE and CFOE reductions are of about 8% and 28%, respectively. Finally, the most effective trade-off between economic and environmental performances leads to a CFOE decrease of about 48% and a slight decrease of the economic performances (−2%). [ABSTRACT FROM AUTHOR]

• This paper summarizes the principles of storage and conversion of several kinds of energy in hydraulic wind turbines after the addition of hydraulic accumulators, compressed air energy storage, pumped hydroelectric storage technologies. • This paper discusses the functions of the energy storage system in terms of the stabilizing speed, optimal power tracking and power smoothing when generating power from hydraulic wind turbines. • In this paper, the development prospect and potential application of energy storage device in hydraulic wind turbines are predicted. With the intensification of energy shortages and environmental pollution, new energy sources represented by wind and solar energy have received global attention. Although the proposal of hydraulic wind turbines effectively solves the problems of traditional wind turbine transmission impact and complicated installation and maintenance, further exploration is needed on how to solve the randomness and intermittency of wind. The introduction of energy storage technology into wind power provides a way to solve this problem. This article mainly reviews the energy storage technology used in hydraulic wind power and summarizes the energy transmission and reuse principles of hydraulic accumulators, compressed air energy storage and flywheel energy storage technologies, combined with hydraulic wind turbines. It also discusses the functions of the energy storage system in terms of the stabilizing speed, optimal power tracking, power smoothing, and power system frequency modulation when generating power from hydraulic wind turbines. Finally, the development and potential application of energy storage technology in hydraulic wind turbines in the future are predicted. [ABSTRACT FROM AUTHOR]

• A novel green concept of hybrid energy storage system has been proposed. • Three system forms are presented to satisfy different needs in multiple scenarios. • The multi-objective optimization is carried out. • Potential solutions to improve the system economic performances are discussed. A green concept of hybrid energy storage system with hydrogen and compressed carbon dioxide as the energy carrier has been proposed in this paper. The integration of the two energy storage methods leads to a hybrid efficient storage way, which can have higher energy density and lower pressure tank volume compared to the compressed carbon dioxide, and has higher energy storage efficiency compared with the hydrogen one. The ratio of the two energy storage is determined by the hydrogen consumption way. In this paper, the hydrogen fueled gas turbine with carbon dioxide as the working fluid (Allam cycle) is used for large amounts of the hydrogen consumption, and the mass flow rate ratio of hydrogen and CO 2 is 0.0048 at the design point. The combined system can be used for inter-regional power dispatching, peak and frequency modulation and so on. A basic system form is firstly introduced, and the round trip efficiency (RTE) and levelized cost of electricity (LCOE) are 42.41% and 0.2075 $/kWh at the design point, respectively. In addition, two improved types are proposed. The effect of key parameters, including the CO 2 compressor outlet pressure, the CO 2 compressor inlet pressure and the CO 2 mass flow rate, on the system performance is performed. The multi-objective optimization is also conducted. The comparison reveals that the improved form-I performs with a lower LCOE and a weaker RTE. In contrast, the improved form-II owns a better RTE but a higher LCOE. It can be concluded that the improved form-I can improve the economic performance of the energy storage system through the optimization of the compressed carbon dioxide high pressure storage subsystem. And the improved form-II can enhance the thermodynamic performance by adding the transcritical carbon dioxide cycle branch. Potential solutions to improve the system economic performances are also discussed and the results indicate that technology development, subsidies and electricity market transaction premium would be beneficial for the large-scale promotion of the system in practical. [ABSTRACT FROM AUTHOR]

Concentrating solar power plant coupling with thermal energy storage is a popular technology during the solar application process. A multitude of researches focus on improving heat transfer performance of the whole system for getting the higher efficiency and lower cost. In this paper, a new storage tank for concentrating solar power has been designed, and the mathematical model of one-dimensional unsteady state heat conduction in cylindrical coordinates has been established and validated. Also, the charge time and the temperature of the tank have been investigated in the designing conditions based on this model. The results show that the new storage tank has a superior performance for the system in the charge period. The charge time from unsteady state to steady state heat conduction for the tank is about 9923 s. It can be found that there is a relatively good agreement of about 18.9% for the charge time between the mathematical model and the reference. The curve of the temperature versus the charge time for different thermal properties of the materials based on the model of this paper has been investigated. The results can provide a good reference for designing, operating, and energy-saving of thermal energy storage for concentrating solar power plants. [ABSTRACT FROM AUTHOR]

This paper introduces a new electrical model of a PV array by simulating and tests it on one typical Micro-Grid (MG) to see its performance with regards of optimal energy management of Micro-Grids (MGS). In addition, it introduces a probabilistic framework based on a scenario-based method to overcome all the uncertainties in the optimal energy management of MGs with different renewable power sources, such as Photovoltaic (PV), Wind Turbine (WT), Micro Turbine (MT), and storage devices. Therefore, the uncertainty is considered for WT and PV output power variations, load demand forecasting error and grid bid changes at the same time. It is hard to solve MG problem with all its uncertainty for 24-h time intervals, and consider several equality and inequality at the same time. In fact, in order to resolve this issue, the problem needs one powerful technique that although it converges very fast, it escapes from the local optima. As a result, one modern Dolphin echolocation optimization algorithm (DEOA) is defined to explore all the search space globally. The DEO algorithm uses the ability of echolocation of the dolphins to find the best location. Additionally, the proposed modification method will be introduced in this paper. This method makes the algorithm work better and finds the locations faster. The proposed method is implemented on a test grid-connected MG and satisfying results can be seen after implementation. [ABSTRACT FROM AUTHOR]

The development of power converter topologies, with an increased number of components seems to be an interesting option in modern applications, especially in terms of reliability, efficiency, and current or voltage distortions improvement. This paper focuses on AC–AC power converter technologies without DC-link energy storage elements. The presented converter topologies are fully solid state devices with small passive elements, which are implemented to filter off the high frequency current or voltage components. In the paper the converters are categorized into two groups: with constant output frequency, and with variable output frequency. The first group includes topologies of matrix and matrix-reactance choppers. The second group includes frequency converters based on the matrix converter, taking into account indirect (indirect matrix converter, sparse matrix converter) and multi-level topologies (three-level-output-stage indirect matrix converter, indirect three-level sparse matrix converter, multimodular matrix converters), as well as the topology allowing an increase in the output voltage (matrix-reactance frequency converters). Various converter topologies are presented, compared, and evaluated against output voltage and phase control, input power factor control, and number of components. The features of each converter configuration are considered in the context of alternative applications for commonly used converters with DC-link energy storage devices. [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 a study evaluating the effects of charge controller operation and coulombic efficiency on stand-alone hybrid power systems. The model used in the study makes it possible to consider the uncertainty related to renewable resources, fuel cost, the battery bank's lifetime, energy demand, charge controller operation, and coulombic efficiency. As a case study, a hybrid system installed in Zaragoza, Spain, was analysed. The system includes photovoltaic panels, a wind turbine, a conventional diesel or gasoline generator, and a battery bank. First, the impact of charge controller operation and coulombic efficiency was studied through a comparative analysis of both the model presented in this paper and another that does not offer the ability to consider the charge controller operation or the relation between coulombic efficiency and the state of charge. The results show a difference between the models of approximately 33% in the number of hours of operation of a conventional generator, 31% in fuel consumption, and 31% in net present cost for hybrid power system configurations with low storage capacity. However, these differences were reduced when the capacity of the battery bank was increased because the charge currents were reduced, the acceptance of charge by the battery bank was improved, and the effect of the charge controller was minimised. Finally, a sensibility analysis was carried out for different sizes of battery banks, obtaining uncertainty in the net present cost, which depends on fuel cost and uncertainties about the battery bank's lifetime. [ABSTRACT FROM AUTHOR]

In the last years, the technological development and the increasing market competitiveness of renewable energy systems, like solar and wind energy power plants, create favorable conditions to the switch of the electricity generation from large centralized facilities to small decentralized energy systems. The distributed electricity generation is a suitable option for a sustainable development thanks to the environmental impact reduction, the load management benefits and the opportunity to provide electricity to remote areas. Despite the current cut off of the national supporting policies to the renewables, the photovoltaic (PV) systems still find profitable conditions for the grid connected users when the produced energy is self-consumed. Due to the intermittent and random nature of the solar source, PV plants require the adoption of an energy storage system to compensate fluctuations and to meet the energy demand during the night hours. This paper presents a technical and economic model for the design of a grid connected PV plant with battery energy storage (BES) system, in which the electricity demand is satisfied through the PV-BES system and the national grid, as the backup source. The aim is to present the PV-BES system design and management strategy and to discuss the analytical model to determine the PV system rated power and the BES system capacity able to minimize the Levelized Cost of the Electricity (LCOE). The proposed model considers the hourly energy demand profile for a reference year relating the analysis to the hourly irradiation and the temperature trend for the installation site. Furthermore, the proposed model is applied to design the grid connected PV-BES system installed at the new buildings of the Engineering and Architecture School of the Bologna University, Italy. A multi-scenario analysis is assessed varying the PV-BES system rated power and capacity. The results highlight the technical feasibility and the economic profitability of such a system for the proposed context. A reduction of 25.5% of the electricity cost respect to the grid electricity price benchmark is among the key outcomes discussed in the present paper. [ABSTRACT FROM AUTHOR]

• A novel polygeneration liquid air energy storage system is presented. • An alternative strategy for cold energy utilization is proposed. • Hydrate based processes are integrated to coproduce potable water. • Electrical round-trip and exergy efficiencies of 145.57 % and 72.34 % are achieved. • The advanced system has a high positive net present value of 158.17 million USD. Energy management and freshwater production are recent social concerns due to the population explosion. However, conventional liquid air energy storage (LAES) systems and desalination approaches face low efficiency and high energy consumption challenges. The present paper proposes a novel LAES system coupled with LNG cold energy, solar energy, and hydrate based desalination (HBD) to bridge the research gap at the intersection of electricity and freshwater production. The system develops the respective integration of external cold and heat sources in energy storage and release processes to strengthen the operational characteristics. Additionally, the proposed LAES employs HBD systems in LNG regasification and energy release processes, thus taking advantage of underutilized cold energy. The non-dominated sorting genetic algorithm II is developed to obtain the optimum operating parameters regarding peak shaving and water production. The optimized system is thoroughly analyzed from the energy, exergy, and economic perspectives. The results indicate that the system with 2805.26 tons of daily freshwater production has an electrical round-trip efficiency of 145.57% and an exergy efficiency of 72.34%. A high positive net present value of 158.17 million USD is achieved. Overall, the efficient system, with superior techno-economic performance, provides an extraordinary alternative to enhance the energy management-water nexus in grid dimensions. [ABSTRACT FROM AUTHOR]

[Display omitted] • A solar energy system with hydrogen energy storage and alkaline fuel cell is proposed. • An optimization model base minimum life cycle cost is developed by Getopt. • The performance of solar energy system without and with electrical storage device are compared. In this paper, a novel solar energy system with hydrogen energy storage and alkaline fuel cell is developed in TRNSYS. The solar energy system without electrical energy storage and solar energy system with battery energy storage are established as the reference systems. The life cycle cost is chosen as the optimal objective, and different operating strategies are developed for the proposed system and the reference systems. The optimal variables and dynamic analysis can be obtained after optimization. Various evaluation criteria, including electricity coverage ratio, annual carbon dioxide emission and levelized cost of energy, are used to comprehensively assess the overall performance of the proposed system and the reference systems. Beijing and Shanghai, which belong to cold region and hot-summer and cold-winter region respectively, are chosen as the study sites for case study. The results show that the proposed system has the lowest life cycle cost, which is 186,484.36 USD and 261,467.43 USD in Shanghai and Beijing, respectively. The proposed system has the highest electricity coverage ratio (which is more than 0.5 for most time of the year), the lowest annual carbon dioxide emission (which is 19,099.34 m3 in Shanghai and 31,525.96 m3 in Beijing) and the lowest levelized cost of energy (which is 0.12 USD/kWh in Shanghai and 0.08 USD/kWh in Beijing). [ABSTRACT FROM AUTHOR]

• A novel SOFC system with thermal energy storage (TES) is proposed. • Temperature and power change during load tracking are analysed. • The dynamic time of the system during load step-down and step-up has decreased by 93.79% and 80.52% respectively, compared to traditional SOFC. • The output power of proposed system during half load operation is 7.75% higher than the original system. Solid oxide fuel cell (SOFC) is a promising energy conversion device. However, the severe temperature fluctuations and slow load switching caused by huge thermal inertia during load tracking are urgent issues to be solved. In this paper, a novel SOFC system with thermal energy storage (TES) was proposed and studied. The 1D models of fuel cell stack and TES were established based on electrochemical and thermodynamic laws. The output power switch between full load and half load was explored as an example, and the dynamic response of the proposed system and traditional SOFC was compared, which was achieved by step changes in current. The results indicated that the maximum fluctuations in the inlet gas temperature of traditional SOFC stacks under load step-down and step-up conditions were 169.21 K and 95.24 K, respectively. TES could maintain a constant gas temperature at the entrance of fuel cell stack, thereby avoiding severe temperature fluctuations in the stack. The proposed system would significantly reduce the maximum temperature gradient during load switching and half-load operation. In addition, compared to traditional SOFCs, the dynamic response time of the system with TES had been reduced from thousands of seconds to around 300 s, which meant that the load step-down and step-up processes had been shortened by 93.79 % and 80.52 %, respectively. The response time of load step-down was longer than that of step-up, due to heat generation within the fuel cell stack. The output power of the proposed system during half load operation was 0.21 KW higher than traditional system, which meant an increase of 7.75 % in output power. Finally, the ramp current was adopted to solve the problem of fuel definition in step-up condition, and the response time of the power was 41 s longer than the step current. [ABSTRACT FROM AUTHOR]

• 25 kinds of pumped thermal energy storage systems are presented and assessed. • Configuration selection maps for high power-to-power efficiency are developed. • Energy storage density and levelized cost of storage evaluation are carried out. • Higher energy storage density is achieved by employing latent thermal storage. The thermally integrated pumped thermal energy storage possesses the advantages of not being limited by geographical locations and small installation footprint as compared to other large-scale physical energy storage technologies. To promote the power-to-power efficiency of the thermally integrated PTES system, twenty-five kinds of pumped thermal energy storage systems are proposed and evaluated based on thermodynamics and economics. Since the power-to-power efficiency varies much with different system configurations and operating conditions, this paper focuses on developing a kind of configuration selection maps with different thermal storage methods, which can be employed as an effective and rapid decision-supporting tool for a general design of the thermally integrated pumped thermal energy storage system. Furthermore, the energy storage density and the levelized cost of storage of the mapping selected pumped thermal energy storage systems are also investigated. The results indicate that the energy storage density of the PTES with sensible thermal storage is usually lower than 5 kWh/m3, and increases up to 27.7 kWh/m3 when utilizes erythritol as the latent thermal storage material. Whereas the levelized cost of storage is more sensitive to the system configuration than the thermal storage methods, and ranges from 0.35 $/kWh to 0.55 $/kWh under different conditions. In terms of these performance indicators, the PTES system with latent thermal storage employing the double-stage heat pump cycle with flash tank or economizer as charging process and the single stage organic Rankine cycle with waste heat heater as discharging process would be an excellent option. [ABSTRACT FROM AUTHOR]

• An original approach to modeling the CAES charging and discharging process. • Reduced heat exchangers start-up losses by 34% compared to a conventional CAES. • Reduced heat transfer surfaces by 32% compared to a conventional CAES. • Reduced CO 2 emission per output MWh el by 45% compared to a conventional CAES. • Reduced CO 2 emission per input MWh el by 73% compared to a conventional CAES. This paper presents a novel hierarchical gas turbine cycle cooperating with a hybrid compressed air energy storage and thermal energy storage. Conventional compressed air energy storage systems cannot use heat storage because they require recuperated gas turbines to achieve high efficiencies. The novelty of the proposed solution lies in the original combination of compressed air energy storage and heat storage using a system of two gas turbines, the so-called gas–gas system. Moreover, a detailed mathematical model of CAES with TES is presented including an original approach to modelling of CAES charging and discharging processes and recuperative heat exchanger start-up losses. The paper analyses also the influence of the main design parameters, such as electrical power, gas turbine inlet temperature, compressed air storage capacity and discharge time, main heat exchanger mean logarithmic temperature difference, and heat loss in thermal energy storage on machinery and cycle performance. The results of the analysis show, among other: the energy efficiency, carbon dioxide emissions per unit of input and output electric energy, and the main heat exchanger start-up losses during the round trip of charge/discharge cycle. Compared with a reference compressed air energy storage based on a recuperated gas turbine cycle, the proposed cycle achieves 73% less CO 2 emission per unit input electric energy and 45% less CO 2 emission per unit of output electric energy, while the round trip efficiency is lower by 0.8 pp. The start-up heat loss of the main heat exchanger is reduced by 34%. [ABSTRACT FROM AUTHOR]

Abstract: The paper reports guidelines for the efficient design and sizing of Small-Scale Compressed Air Energy Storage (SS-CAES) pressure vessels, including guidelines for pressures that should be used in the SS-CAES system to minimize the cost of the pressure vessel. Under a specified energy storage capacity and specified maximum and minimum operating pressures in CAES, the volume of the vessel(s) can be evaluated. The present study provides guidelines for choosing appropriate shape and size for the vessels that minimize material and manufacturing cost for cylindrical vessels. The two main contributions of the paper are that it provides a methodology to determine: (a) an optimum pressure; (b) the shape, size, and number of vessel to be used in a particular application. Results suggest that pressure vessels with a length to diameter ratio of roughly three are the most economical, and that a system should be designed for a pressure of roughly three times the minimum pressure of the expansion device. [Copyright &y& Elsevier]

• 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]

• Emergy analysis is used to compare three energy storage systems for a wind farm. • Hydrogen energy storage had the highest emergy efficiency (lowest transformity). • Compressed air energy storage had the lowest emergy efficiency. • Liquid air energy storage had the highest sustainability. • The sustainability of these storage systems was very higher than the wind farm. Due to the environmental and economic circumstances, the use of renewable-energy increases every year. The uncertainty, volatility, and difficulty of storing energy in the large scales are obstacles to the more penetration of renewable energies in the market. Energy storage systems can be used as a solution to store energy at a time when energy consumption is lower than the generated energy or at a time when more energy is generated compared to what is demanded. In this paper, a comparison study has been conducted on the three energy storage systems that proportionated for a typical wind power plant with the capacity of 109 MW. The energy storage systems which are investigated in the current study, include a compressed air energy storage, a liquid air energy storage, and a hydrogen energy storage. For this purpose, the power generated from the wind farm, for eight hours (at peak-off times) is considered as an input for the energy storage systems. To explore various factors such as the environmental impact, economic efficiency, sustainability and renewability, a new method based on emergy analysis is employed. The results showed that the transformity of electricity from hydrogen energy storage was much inferior to that of electricity from the compressed air energy storage and liquid air energy storage. This means that the above-mentioned system utilized the lowest emergy to produce a unit of electricity. Emergy yield ratio of hydrogen energy storage power was 1.98. In fact, it was lower than the emergy yield ratio of compressed air energy storage (2.62) and liquid air energy storage (2.92). This finding proved that liquid air energy storage was more efficient at utilizing local resources. Environmental load ratio of hydrogen energy storage (1.02) was much higher than those of compressed air energy storage (0.62) and liquid air energy storage (0.52). Liquid air energy storage had an emergy sustainability index of 5.6, which was preferable compared to two other cases. It also had better ecological performance and environmental sustainability. [ABSTRACT FROM AUTHOR]