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Abstract The world’s key renewable power markets are generally challenged by wind and solar power curtailment. Research on the influencing factors of curtailment improvement can provide a reference for the further penetration of renewable energy (RE) into the power system. Based on the logarithmic mean Divisia index (LMDI) method, this paper analyzes the factors influencing the wind and solar power consumption rate in China from 2015 to 2018, and four typical provinces are discussed in detail. By decomposing the consumption rate into six factors (transmission structure, generation proportion, power self-sufficiency, resource development, resource utilization, and power consumption), and focusing on the transmission structure factors, this paper further clarifies the contributions of local use, ultra-high-voltage (UHV) transmission, and conventional transmission to the improvement of curtailment. The results reveal the following. (1) At the national level, the power mixing effect and the resource development effect have played major roles in the change of the consumption rate, but the influences of these two effects have been decreasing. (2) The UHV power lines provide a robust resource for the inter-provincial deployment of renewable power (such as the RE power transfer in Inner Mongolia and Gansu), but the role of UHV transmission has not yet been fully utilized. (3) The impact of the electricity consumption effect on renewable power consumption is increasing year by year, but the local consumption capacity remains insufficient (both at the national level and in the four typical provinces analyzed), so it is necessary to further increase the share of renewable electricity in UHV power transmission and the local consumption capacity. (4) The expanding development of wind and solar power may be the reason for the curtailment in Shaanxi, and a reasonable renewable power development plan must be further formulated.

Abstract This paper presents the parameter influence of upstream deflector on the performance of vertical axis wind turbines (VAWTs). For this purpose, two counter-rotating straight-bladed VAWTs and the upstream deflector have been simulated via three-dimensional (3D) computational fluid dynamics (CFD), which is validated against experimental data. Parameter Influence of upstream deflector on VAWTs output power is investigated in this study. From the CFD results, it is observed that when the turbine is positioned outside the near-wake region, the aerodynamic power can increase significantly.) This research indicates that performance of VAWTs can be greatly improved by properly choosing parameters of the deflector.

Abstract In this work, the effects of heating rate on fast pyrolysis behavior and product distribution of Jerusalem artichoke stalk (JAS) were investigated fist by TG-FTIR (heating rates: 20, 30, 50, 100, 300, 500 °C/min) and then via Py-GC/MS (heating rates: 100, 1000, 5000 10000 °C/s). The results showed that with the heating rate increased, TG and DTG curves obviously shifted toward the high-temperature range, and the number of peaks in DTG curves reduced from three to two. The model-free method indicated that the apparent activation energy of JAS pyrolysis was 286 kJ/mol at the low heating rate and increased to 351 kJ/mol at the high heating rate. The distributed activation energy model showed that the value of pre-exponential factor increased with the heating rate increased and the kinetic compensation effect was obvious during the conversion from 0.3 to 0.7. Total 44 compounds were identified by GC/MS. Acid, phenol and carbonyl compounds were the major products groups. With the heating rate increased, the relative contents of acid increased whereas the relative contents of phenolic substance decreased. The yield of carbonyl compounds was maximum at the heating rate of 5000 °C/s.

Abstract Hydrothermal liquefaction (HTL) of biomass into biocrude is attractive but the biocrude themselves are poor fuels, which need to be upgraded for further utilization. Compared with the traditional catalytic upgradation process, a non-catalytic method for biocrude upgrading in the aqueous waste (HTL-AW) derived from HTL of cornstalk was proposed. Optimal reaction conditions of upgradation process were obtained at 356 °C (temperature), 37 min (reaction time) and 19 mL/g (HTL-AW/biocrude) based on the response surface methodology. The biocrude was effectively upgraded in the HTL-AW and a high hydrogen to carbon effective (H/Ceff) ratio of 1.07 with a higher heating value of 36.94 MJ/kg was observed. The energy recovery of ∼80% from biocrude to upgraded biocrude was feasible. GC–MS analysis showed that the contents of phenols and ketones were decreased from 65.61% to 48.38% and 22.39%–16.78%, respectively, while the contents of nitrogen-containing compounds n-hexadecanoic acid were increased from 2.25% to 10.15% and 9.56%–22.23%, respectively. The high H/Ceff was attributed to the promoted deoxygenation by alkali and alkaline earth metals as well as H+ enriched in the HTL-AW. This study demonstrates the feasibility of improving the H/Ceff of biocrude in the HTL-AW under a relatively mild reaction condition.

Abstract Effective utilization of solar energy resource enables to improve the thermal performance of solar evacuated tube. In present work, the back side of solar vacuum tube was coupled with mini-compound parabolic concentrator (mini-CPC). The thermal characteristics of the presented mini-CPC solar vacuum tube were analyzed theoretically and experimentally. A mathematical model of heat transfer for the mini-CPC vacuum tube was established according to the energy conservation, and solved by iterative calculation based on home-built C programming language. The obtained numerical solutions fit in well with the experimental results. Furthermore, analysis indicates the vacuum interlayer plays a crucial role in hindering heat transfer. The thermal-convection resistance (Rco-air,conv) dominates the heat loss from cover tube to ambient rather than thermal-radiation resistance (Rco-sky,rad). The measured final temperature increment of working water for the mini-CPC and ordinary evacuated tube can reach 63.4 K and 49.8 K, respectively. An experimental result also reveals that the thermal efficiency of the mini-CPC vacuum tube is increased by 24.3%–29.2% compared with that of vacuum tube without mini-CPC, considering various weather conditions. Consequently, the designed mini-CPC evacuated tube shows a preferable performance, which may provide a certain reference in technology for engineering applications.

Abstract The sale of value-added byproducts from hydrogen-generating reactions is a strategic approach to lower the costs of hydrogen fuel in order to realize a truly sustainable hydrogen economy. Metal hydrolysis is a chemical process that produces hydrogen together with a metal hydroxide species; however, this reaction is rarely observed without chemical additives or extreme reaction conditions. Previously, we demonstrated that hierarchical nanoporous aluminum can create hydrogen at standard conditions for temperature and pressure via hydrolysis without any additives. The advantage of this method is the co-production of pure aluminum hydroxide (Al(OH)3). Here we explore the transformation of this Al(OH)3 hydrolysis byproduct into valuable materials to elucidate strategies in reducing the overall cost of hydrogen generated. In particular, we demonstrate in this work that (i) the synthesis of hierarchical nanoporous aluminum is scalable to meet the needs of large-scale production for a hydrogen economy, and (ii) the Al(OH)3 hydrolysis byproduct can be transformed to create high surface-area “activated alumina” (Al2O3) as a commercially viable product.

Abstract Microbial fuel cells (MFCs) are potentially used for electricity generation, but their low power output hinders their practical application. This study presents novel, porosity binderless PPy–CS–CNT hydrogel materials, which were prepared using Fe(NO3)3 as an initiator. It can be seen from the results of SEM and swelling ratio that the prepared material had a uniform structure with rich three-dimensional porosity and showed good water retention performance. Electrochemical tests showed that the charge transfer impedance (Rct) of PPy–CS–CNT anode displayed a reduction in comparison with PPy anode (1.06 Ω vs. 2.20 Ω). And the power density of MFC with PPy–CS–CNT anode reached 364 mW m−2, which was 1.36 times as much as that of MFC with PPy anode. High-throughput sequencing results showed that the PPy–CS–CNT hydrogel bioanode exhibits good biocompatibility and selective enrichment of electrogenic bacteria. The dominant genera on PPy–CS–CNT hydrogel anode are the electroactive bacteria, Rhodopsedomonas (47.69%) and Geobacter (8.47%). Therefore, the PPy–CS–CNT hydrogel anode showed a potential for improving the electricity production performance of MFCs.

Abstract In this study, three types of biomass including corn stover, radiata pine wood and rice husk in the form of pellets were gasified with steam as gasification agent in a 100 kW dual fluidised bed gasifier. Tar formation in initial devolatilization stage and its correlation to the final tar concentration in the producer gas were investigated. In addition, the yields and composition of the producer gas for each type of biomass were also examined. In the gasification experiments, operating temperature was controlled, respectively, at 700 °C and 800 °C. Silica sand was used as the bed material with an inventory of 30 kg. For simulation of the initial devolatilization stage in the steam gasification, N2 was used as fluidization agent. From this study, it is found that there was a positive correlation between tar contents in the devolatilization product gas and those in the final producer gas from gasification. In the devolatilization stage, radiata pine biomass yielded more phenols, while corn stover generated more toluene. Based on the results of this study, tar formation mechanism was proposed which is verified by the observation that more naphthalene was present in the producer gas from gasification of radiata pine while gasification of corn stover produced more biphenyl. The experimental results also show that at gasification temperature of 700 °C, the producer gas yield was the highest for corn stover followed by rice husk and then radiata pine wood. However, for gasification at 800 °C, the trend was reversed with radiata pine having the highest yield followed by risk husk and the corn stover. At both 700 and 800 °C, the radiata pine biomass produced a producer gas with higher contents of H2 and CH4 while the producer gas from rice husk had a higher content of CO and that from corn stover had a higher content of CO2, C2H4 and C2H6. These differences are closely related to the chemical composition of the biomass which was also analysed in this study. Radiata pine had a higher content of lignin (31.96 wt%), rice husk had a higher content of hemicellulose (25.30 wt%) while corn stover was rich in cellulose (69.85 wt%).

Abstract In this paper, the control problem of pumped storage unit (PSU) has been studied. A nonlinear generalized predictive control (NGPC) method has been applied to design the controller for a PSU. The NGPC controller is designed based on instantaneous linearization model of the control system, and the parameters of the linearized model are identified online by the recursive least square method (RLSM). Besides, in order to minimize the modelling error on initial state, a prior-knowledge learning method has been proposed to get the initial parameters for control model estimation. To verify the effectiveness of the NGPC controller, we chose a pumped-storage hydropower plant in China as the experimental subject and the simulation experiments respect to the control system are designed. The processes of start-up and speed disturbance under no-load condition have been simulated to testify the robustness and efficiency of the NGPC controller. Comparative experiments have been conducted, while the NGPC controller, a PID controller and a fractional order PID (FOPID) controller have been compared. Experimental results show that the designed NGPC could effectively restrain the oscillation of rotational speed in different working conditions of PSU and demonstrates higher robustness and stability than both the PID and FOPID controllers.