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[en] Highlights: • A novel methodology to estimate global wind energy potential is proposed. • Wind park suitability is constrained by land use and water depth. • Power production density is derived from energy conservation laws. • Maximum wind potential is dependent on minimum Energy Return on Investment. • Total potential is established between 700 and 100 EJ/year at EROImin from 5 to 12. - Abstract: Looking ahead to 2050 many countries intend to utilise wind as a prominent energy source. Predicting a realistic maximum yield of onshore and offshore wind will play a key role in establishing what technology mix can be achieved, specifying investment needs and designing policy. Historically, studies of wind resources have however differed in their incorporation of physical limits, land availability and economic constraints, resulting in a wide range of harvesting potentials. To obtain a more reliable estimate, physical and economic limits must be taken into account. We use a grid-cell approach to assess the theoretical wind potential in all geographic locations by considering technological and land-use constraints. An analysis is then performed where the Energy Return on Investment (EROI) of the wind potential is evaluated. Finally, a top-down limitation on kinetic energy available in the atmospheric boundary layer is imposed. With these constraints wind farm designs are optimized in order to maximize the net energy flux. We find that the global wind potential is substantially lower than previously established when both physical limits and a high cut-off EROI > 10 is applied. Several countries’ potentials are below what is needed according to 100% renewable energy studies.
[en] Highlights: • Thermodynamic analysis is presented for a LAES system combined with packed bed units. • The LAES system round-trip efficiency is in the range 50–62%. • Cold box inlet temperature and discharge pressure have significant influence on system performance. • LAES system has smaller air storage volume and higher ASED compared with A-CAES system. - Abstract: Energy storage is a key technology required to manage intermittent or variable renewable energy, such as wind or solar energy. In this paper a concept of an energy storage based on liquid air energy storage (LAES) with packed bed units is introduced. First, the system thermodynamic performance of a typical cycle is investigated and temperature distribution in cold boxes is discussed. Then, the effects of inlet temperature of cold boxes, charge and discharge pressures on thermal behaviors of LAES system are analyzed, as well as the system round-trip efficiency. Finally, an overall comparison between this LAES system and an adiabatic compressed air energy storage (A-CAES) system is conducted. The system could achieve a round-trip efficiency in the range 50–62% depending on the values of process conditions. The system round-trip efficiency decreases with the increase of cold box inlet temperature, and increases with the rise of charge and discharge pressures. Although the round-trip efficiency of the present LAES system is a bit lower than the A-CAES system, however, the air storage volume decreases and the air storage energy density (ASED) increases remarkably for the same operational conditions. The main conclusions draw from this work is beneficial for future LAES development in particular the combination with the packed bed units and the fit with the requirements for large-scale energy storage.
[en] Highlights: • It solves the problem of maritime spatio-temporal forecasting for the first time. • A new method EEMD-SOM-BP is proposed for maritime forecasting of solar irradiation. • An asymmetric four-parallel structure of SOM is proposed to mine data features. • Three experiments are performed to determine the optimal settings of EEMD-SOM-BP. - Abstract: Owing to a shortage of fossil fuels and environmental pollution, renewable energy is gradually replacing fossil fuels in the power systems of hybrid ships. To exploit fully solar energy by the successful day-ahead scheduling of ships, this work proposes a new day-ahead spatio-temporal forecasting method. Ensemble empirical mode decomposition (EEMD) is used to extract data features and decompose original historical data into several frequency bands. After the original data are processed, data from the four land weather stations that are closest to the ship and self-organizing map-back propagation (SOM-BP) hybrid neural networks are used to forecast the solar radiation received by the ship in the next 24 h. Multiple comparative experiments are implemented. The results show that the EEMD-SOM-BP spatio-temporal forecasting method can accurately forecast the solar radiation on a ship that is sailing along a navigation route.
[en] Highlights: • Methods is outlined to improve the efficiency of heat-induced solar thermionic converter. • Optimization of materials and structure is summarized for photon-enhanced thermionic converter. • Combined systems with thermionic energy converters is proposed for concentrating solar power. • Roadmap of thermionic energy conversion for concentrating solar power is brought forward. - Abstract: Concentrating solar power (CSP) is a mainstream of solar energy utilization, and thermionic emission is a potential way to convert concentrated solar radiation into power with a theoretical efficiency of 50–70%, surpassing both Shockley-Queisser limit and photo-thermal limit. This literature attempts to provide a comprehensive understanding of and an insight into solar thermionic energy conversion. The fundamentals of electron emission from electrodes and electron transport in vacuum gap are presented, as well as the state of the art of solar thermionic energy conversion technologies, including heat-induced thermionics and photon-enhanced thermionics. The former is driven by thermal energy, whereas the latter takes advantage of both quantum photon energy and thermal energy. Burgeoning research indicates that photon-enhanced thermionic conversion is a promising technology for concentrating solar power due to the high efficiency and simple operating mode. Now, it is important to develop novel materials and coating technologies to facilitate electron emission and reduce space charge effect in interelectrode vacuum. Structural design of thermionic converters and top–bottom configuration of solar-electricity systems are suggested for practical applications.
[en] Highlights: • The energy output characteristics of the solar hybrid CCHP system are defined in a clear perspective. • The particle swarm optimization (PSO) algorithm is adopted to find the optimum design parameters. • The design features and the performance of solar hybrid systems under five different operation strategies are analyzed. • The comparison between the hybrid system and the conventional system is given. - Abstract: The hybridization between conventional combined cooling heating and power (CCHP) systems and solar systems has been considered as a good solution to the urgent energy and environment issues. This study develops the mathematical model of a CCHP system hybridized with PV panels and solar thermal collectors. The particle swarm optimization (PSO) algorithm is adopted to find the optimum values of design parameters. Based on the energy output characteristic of the solar hybrid CCHP system, five operation strategies of the conventional CCHP system are adjusted and applied for the solar hybrid CCHP system. The simulation work of the hybrid CCHP systems based upon a hotel building in Atlanta is carried out to find an appropriate design scheme. The results show that the hybrid CCHP system under the FEL-ECR mode is the best choice. Besides, its PESR, CO2ERR and ATCSR can reach 36.15%, 53.73% and 4.16%, respectively. Compared with a conventional CCHP system, the hybrid CCHP system achieves better energy-saving and CO2 reduction performance. However, the hybrid CCHP system consumes more annual total costs because of its high initial investment.
[en] Highlights: • Integration model is first proposed for dynamic temperature distribution of DHN. • A new integrated heat and power dispatch for wind power integration is proposed. • Integration model is embedded into the IHPD to truly use thermal inertia of DHN. • Stored heat and heat storage rate of DHN are quantitatively calculated. • Supply and return temperature at HS are optimised for operation regulation of DHS. - Abstract: Utilizing the thermal inertia of a district heating network (DHN) for thermal storage is considered an effective energy-saving method for improving the operational flexibility of combined heat and power (CHP) generation units for wind power integration in an integrated heat and power dispatch (IHPD) system. However, to truly utilize the thermal inertia of the DHN, the supply and return temperatures at the heat source are both necessary to regulate the district heating system (DHS) for wind power integration, whereas the heat output of CHP is not able to do that. Therefore, a new IHPD model that considers the thermal inertia of the DHN was formulated to improve the flexibility of CHP units for wind power integration, in which the first proposed integration model was used to completely simulate the dynamic temperature distribution of the DHS. The optimised supply and return temperatures at the heat source were then obtained to guide the operation regulation of DHS for wind power integration in actual engineering applications. Moreover, the stored thermal energy and the thermal storage rate of the DHN were quantitatively calculated to determine the thermal state of DHN. To analyse the effects of the proposed IHPD model, the approach was compared with a conventional heat and power dispatch model through a case study based on a real DHS. The results demonstrate the advantages of the proposed model in terms of wind power integration, energy saving and operation regulation of DHS.
[en] Highlights: • A novel portable solar collector mechanism is optimally designed. • Wireless power transfer is first applied to cooling systems. • A supercapacitor stores electricity and outputs a regulated supply. • The proposed cooling system shows high efficiency in a limited space. - Abstract: As the greenhouse effect becomes increasingly serious, cooling a vehicle cabin parked under the blazing sun without running the engine or using an electric vehicle’s power has received considerable attention. In this paper, we develop a novel portable, renewable, solar energy-powered cooling system with wireless power transfer (WPT) and supercapacitors to cool the vehicle cabin. The proposed system consists of a solar collector mechanism, an energy conduit, and a temperature control and cooling module. First, consisting of folding solar photovoltaic (PV) panels, the solar collector mechanism making the proposed system portable. Once collected, the solar energy is converted into electricity and stored in the supercapacitors through wireless power transfer without breaching the vehicle body. Automatic temperature regulation is achieved with the cooling device via the temperature control and cooling module. The experimental results indicate that a maximum output power of 2.181 W and a maximum WPT efficiency of 60.3% are achieved when the prototype loaded with 3 Ω and 5 Ω respectively. Meanwhile, the simulation shows the temperature inside the cabin is reduced by as much as 4.2 °C in average, demonstrating that the proposed solar energy-powered cooling system is effective and feasible in cooling a hot vehicle cabin.
[en] Highlights: • An analysis-forecast system for wind speed uncertainty modeling is proposed. • Recurrence analysis is developed to study the characteristics of wind speed. • Feature selection is developed to determine optimal system input. • An improved multi-objective optimizer is first proposed to optimize the system further. • The proposed system shows a greater advantage over benchmark models considered. - Abstract: The uncertainty analysis and modeling of wind speed, which has an essential influence on wind power systems, is consistently considered a challenging task. However, most investigations thus far were focused mainly on point forecasts, which in reality cannot facilitate quantitative characterization of the endogenous uncertainty involved. An analysis-forecast system that includes an analysis module and a forecast module and can provide appropriate scenarios for the dispatching and scheduling of a power system is devised in this study; this system superior to those presented in previous studies. In order to qualitatively and quantitatively investigate the uncertainty of wind speed, recurrence analysis techniques are effectively developed for application in the analysis module. Furthermore, in order to quantify the uncertainty accurately, a novel architecture aimed at uncertainty mining is devised for the forecast module, where a non-parametric model optimized by an improved multi-objective water cycle algorithm is considered a predictor for producing intervals for each mode component after feature selection. The results of extensive in-depth experiments show that the devised system is not only superior to the considered benchmark models, but also has good potential practical applications in wind power systems.
[en] Highlights: • A 3D model couples flow and heat transfer processes of DHE, wellbore and reservoir. • The model is validated against experimental data with a maximum error of 8.3%. • The entire temperature and flow fields of DHE system is analyzed comprehensively. • Performances of single U-tube, double U-tube and spiral tube are compared. • Effects of key factors on heat extraction performance of DHE system are studied. - Abstract: The downhole heat exchanger (DHE) geothermal system is commonly used to exploit geothermal energy for space heating. In this paper, a 3D unsteady state numerical model is established to couple fluid flow and heat transfer processes of DHE system. The model is validated by field experimental data. Temperature and velocity fields are analyzed to understand thermal process of DHE system. Heat extraction performances of three different DHE structures, including single U-tube, double U-tube and spiral tube, are compared. Subsequently, cases are studied to investigate how key parameters affect DHE performance. Simulation results depict that spiral-tube has the best heat extraction performance. As working fluid mass flow rate rises, outlet temperature declines and thermal power increases. When inlet temperature ascends, outlet temperature rises while thermal power decreases. Effects of reservoir porosity and tube wall heat conductivity on DHE performance are minor. Higher subsurface water velocity and larger rock heat conductivity can improve DHE performance, but the former has a more significant influence. Besides, subsurface water flow direction has neglected influence on performances of single and double U-tube, but appreciable impact on that of spiral tube. Key findings of this work are beneficial for optimal design and optimization of DHE geothermal system.