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[en] Highlights: • Mode 4 has the highest exergy efficiency. • Mode 2 has the largest exergy density. • Second heat exchanger has the largest exergy destruction. - Abstract: Advanced adiabatic compressed air energy storage system plays an important role in smoothing out the fluctuated power from renewable energy. Under different operation modes of charge-discharge process, thermodynamic behavior of system will vary. In order to optimize system performance, four operation modes of charge-discharge process are proposed in this paper. The performance difference of four modes is compared with each other based on energy analysis and exergy analysis. The results show that exergy efficiency of mode 4 is the highest, 55.71%, and exergy density of mode 2 is the largest, 8.09 × 106 J m−3, when design parameters of system are identical. The second heat exchanger has the most improvement potential in elevating system performance. In addition, a parametric analysis and multi-objective optimization are also carried out to assess the effects of several key parameters on system performance.
[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: • Heat transfer for PCHE in TEG was investigated in detail by 3D CFD analysis. • Experimental data for a 200-W TEG implemented with PCHEs are newly presented. • Power density of the TEG was sufficiently high at low temperature. • Reduction of TEG flow rate requirements from use of PCHEs is estimated. - Abstract: Printed circuit heat exchangers (PCHEs) are employed to improve the compactness of a thermoelectric generator (TEG). PCHEs allows miniaturization of the heat exchanger without excessive additional cost, and permit high temperature and pressure (up to 1100 K and 600 bar) of working fluid, which enable high thermoelectric conversion efficiency. To investigate the pressure loss and thermal resistance of a PCHE in detail, three-dimensional computational fluid dynamic (CFD) analysis is conducted. Experimental results of the proposed TEG with PCHEs are newly presented. The TEG provides power density of 233.1 kW/m3 at inlet temperatures of 448.15 K (hot side) and 293.15 K (cold side), which is the highest value in literature for a low-temperature TEG (<505.15 K hot side). Based on the models of friction and heat transfer in a PCHE validated by the experiment, it is noted that the flow rate required for the heat exchangers in a TEG producing a given amount of electrical power can be reduced by adaption of PCHEs. Such novel results on the TEG with PCHEs might be helpful for more compact design and expands the applicability of TEGs for waste heat recovery.
[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: • 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: • Triplex loop heat pump system for ventilation heat recover is proposed. • Mass flow rate in heat pump system can be improved by triplex loop system. • COP of triplex loop is increase with the decrease of outdoor temperature. • The performance of triplex system is higher than traditional system in most cases. - Abstract: Ventilation heat recovery is an important means of effectively reducing the energy consumption of buildings. To improve the performance of a heat pump heat recovery system under large temperature difference conditions in winter, a triplex loop heat pump system, which contains three independent heat pump cycles, is proposed in place of its single loop counterpart. Operating characteristics and system performance were analyzed while indoor temperature was constant at 20 °C and as outdoor temperature dropped from 15 °C to −20 °C. Results showed that with the decrease of the outdoor temperature, the mass flow rate and temperature effectiveness of the triplex loop heat recovery system decreased whereas the heating capacity and the coefficient of performance (COP) increased. Under the experimental conditions, the COP of the triplex loop system had an advantage over the traditional heat pump system when the outdoor temperature was below 2.5 °C. When the outdoor temperature was −20 °C, the COP of the triplex system could reach 9.33, which was 23.1% higher than that of the traditional system.
[en] Highlights: • A novel integrated system of solar energy and air source heat pump was proposed. • The novel system was compared with other two typical existing systems. • I-T diagram was proposed to divide the optimal working condition ranges. • Effect of different factors on the dividing lines in the I-T diagram was analyzed. - Abstract: Integrated systems consisted of solar energy and air source heat pump have been a hot research topic in recent decades due to their high efficiency and low environmental pollution. Recently, much attention has been paid to the performance characteristics of these systems, however, scarce of attention has been paid to indicate which kind of integrated systems have the optimal performance under different working conditions. For the integrated system of solar heating independently, the solar collectors have high heat-collecting temperature and high heat loss to ambient, so it has advantages in high solar radiation. For the integrated system of solar energy used for the low temperature heat source of heat pumps, the solar collectors have low heat-collecting temperature and low heat loss, so it has advantages in low solar radiation. But for the condition of medium solar radiation, both the above existing two types of systems may not be the optimal ones. Therefore, in this study, a novel integrated system was put forward for this condition. The characteristics and optimal working condition range of this novel system were comparatively studied by the simulation method. By comparison with the above existing two types of systems, the results proved that for most conditions of medium solar radiation, the novel system has the optimal performance, and its COP can be about 55% higher than that of the two types of existing systems when the outdoor temperature is −25 °C. An I-T diagram was proposed in this study to quantificationally divide the optimal working condition ranges of the three types of systems. This study can effectively guide the selection of optimal systems under different working conditions.
[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.