Decision making for sustainable aggregation of clean energy in day-ahead market: Uncertainty and risk Renew. Energy (IF 4.9) Pub Date : 2018-10-17 I.L.R. Gomes, R. Melicio, V.M.F. Mendes, H.M.I. Pousinho
This paper addresses a strategy for decision-making of sustainable aggregation for clean energy participating in a day-ahead electricity market. The clean energy consists of wind turbines, photovoltaic arrays and energy storage, contributing to a better resilience of the system. The power delivered by a wind turbine or by a photovoltaic array is most certainly in deviation from the value associated with the bid accepted at a closing of a day-ahead electricity market. The deviation is due to the unpredicted variable nature of the respective sources of energy, leading to uncertainty and may imply a risk of loss of profit. So, uncertainty must be considered, and the addressed strategy considers uncertainty by scenarios of historical data and risk by the conditional value at risk. The strategy is a unified approach based on a risk-constrained and a two-stage stochastic optimization problem rewritten as a mixed-integer linear programming problem. A case study is presented to illustrate the main result and drive conclusions.
Energy storage based on SrCO3 and Sorbents—A probabilistic analysis towards realizing solar thermochemical power plants Renew. Energy (IF 4.9) Pub Date : 2018-10-18 Laureen Meroueh, Karthik Yenduru, Arindam Dasgupta, Duo Jiang, Nick AuYeung
Performance assessment of a standard radial turbine as turbo expander for an adapted solar concentration ORC Renew. Energy (IF 4.9) Pub Date : 2018-10-17 Michael Deligant, Emilie Sauret, Quentin Danel, Farid Bakir
Organic Rankine cycles are one of the available solutions for converting low grade heat source into electrical power. However the development of plants tends to be very expansive due to the specific design of the expander. Usually, the input parameters for designing an ORC plant are the temperature and power of the heat and cold sources. They lead to the selection of a working fluid, pressures and temperatures. The expander is then designed based on the required operating parameters. Using standard turbine easily available on the market and with well known performances would allow to reduce the development and manufacturing cost. However, the ORC would have to be adapted to make the expander work in its best conditions. For a solar concentrated heat source, the temperature and power can be adapted by adjusting the concentration factor and the total area of the collector. In this paper, a given gas turbine is considered to be used as the expander of the ORC. Knowing the turbine's performances with air, the optimal operating parameters (pressure, temperature, flow rate and rotational speed) of the ORC with different fluids are sought based on similitude rules. The adaptation aims to maintain the same density evolution, inlet speed triangle and inlet Mach number with the working fluid as with air. The performance maps of the turbine are then computed with CFD simulations and showed a maximum isentropic efficiency close to the one with air, about 78%.
Opportunistic maintenance strategy for wind turbines considering weather conditions and spare parts inventory management Renew. Energy (IF 4.9) Pub Date : 2018-10-17 Chen Zhang, Wei Gao, Tao Yang, Sheng Guo
Exploitation of Nannochloropsis gaditana biomass for biodiesel and pellet production Renew. Energy (IF 4.9) Pub Date : 2018-10-17 A. Cancela, L. Pérez, A. Febrero, A. Sánchez, J.L. Salgueiro, L. Ortiz
Risk of penstock fatigue in pumped-storage power plants operating with variable speed in pumping mode Renew. Energy (IF 4.9) Pub Date : 2018-10-16 Guillermo Martínez-Lucas, Juan I. Pérez-Díaz, Manuel Chazarra, José I. Sarasúa, Giovanna Cavazzini, Giorgio Pavesi, Guido Ardizzon
The upgrade of a pumped-storage power plant (PSPP) to allow variable speed operation offer several advantages in pumping and generating modes. However, in pumping mode at part load, both pressure and torque pulsations develop in the pump turbine runner. This paper evaluates the risk of fatigue damage in the penstock of a variable-speed PSPP due to the propagation of the pressure pulsations developing in the pump turbine runner at partial load in pumping mode. For that purpose, a simulation model of a variable-speed PSPP has been developed. The pressure and torque pulsations are generated each from a different set of sinusoidal functions calibrated from the results of a Computational Fluid Dynamic model, which was in turn validated from experimental data. A Monte Carlo simulation has been performed considering different temporal gaps between the sinusoidal functions reproducing the pressure pulsations in one and another pump turbine. The number of stress cycles that may cause fatigue damage in the penstock has been obtained from the results of the simulations and the fatigue curves defined in the Eurocode, and then transformed into the maximum number of hours per year the PSPP can operate at partial load in pumping mode to avoid fatigue damages.
Synthesis and application of Co doped ZnO as heterogeneous nanocatalyst for biodiesel production from non-edible oil Renew. Energy (IF 4.9) Pub Date : 2018-10-15 Manash Jyoti Borah, Anuchaya Devi, Raju Borah, Dhanapati Deka
Exploration of non-edible oil as a feedstock and the use of new heterogeneous nanocatalyst could contribute to bioenergy research. In this regard, the present work is focussed on the use of cobalt doped zinc oxide nanocatalyst for production of biodiesel from Mesua ferrea oil. The synthesized catalyst has been analyzed through X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX), and Thermogravimetric analysis (TGA) techniques. Under optimal reaction condition, maximum biodiesel conversion of 98.03% was obtained in 3 h at 60 °C with 2.5 wt% catalyst loading and 1:9 oil to methanol molar ratio. The produced biodiesel has been characterized using Proton Nuclear Magnetic Resonance (1H NMR), Carbon Nuclear Magnetic Resonance (13C NMR) and Gas Chromatography-Mass Spectroscopy (GC-MS) techniques. Fuel properties of the produced biodiesel have also been determined. The result showed good catalytic activity of cobalt doped Zinc oxide nanocatalyst and could be used for large scale biodiesel production from Mesua ferrea oil by further enhancing its stability.
Optimum design and characteristics of potassium-based sorbents using SiO2 for post-combustion CO2 capture Renew. Energy (IF 4.9) Pub Date : 2018-10-15 Min Sun Cho, Soo Chool Lee, Ho Jin Chae, Yong Mok Kwon, Hyun Ji Kim, Min Young Ryu, Joong Beom Lee, Jae Chang Kim
SiO2 is a common material and is used in various industrial fields. However, the potassium-based sorbents using SiO2 as a support have the low CO2 capture capacities. In this study, the CO2 sorption and regeneration properties of potassium-based sorbents using SiO2 as a support were investigated to determine the cause of the low CO2 capture capacities. In addition, an optimum design method of the potassium-based sorbents using SiO2 as a support having excellent performance was proposed. The CO2 capture capacities of the sorbents decreased as the calcination temperature increased from 500 °C to 700 °C owing to the disappearance of the active material (K2CO3) through the formation of inactive components, such as K2Si2O5 and K2Si4O9. On the other hand, the potassium-based sorbent using SiO2 calcined at 500 °C had a high CO2 capture capacity of 152.3 mg CO2/g sorbent and excellent regeneration properties under the process simulation conditions. Control of the calcination temperature and the mole ratio of K2CO3 to SiO2 was important for obtaining the sorbents with a high CO2 capture capacity. Consequently, SiO2 can be used as a support or additive material in the design of potassium-based sorbents with a high CO2 capture capacity and excellent regeneration properties for post-combustion CO2 capture by controlling the amount of inactive component formed in the calcination process.
Anaerobic co-digestion of sludge cake from poultry slaughtering wastewater treatment and sweet potato: Energy and nutrient recovery Renew. Energy (IF 4.9) Pub Date : 2018-10-15 Felippe Martins Damaceno, Maico Chiarelotto, Juan C. Pires Salcedo Restrepo, Eduardo Luiz Buligon, Luiz Antonio de Mendonça Costa, Jorge de Lucas Junior, Mônica Sarolli Silva de Mendonça Costa
the energy and nutrient recovery of the sludge cake (S) from poultry slaughtering wastewater was investigated by the anaerobic co-digestion with sweet potato (P) within a wide range of S:P of 100:0 to 0:100 (mass ratio). The assay was conducted using batch anaerobic digesters (6L capacity) in laboratory scale operating at room temperature during 145 days. The highest methane yield (0.5032 3 kg VS−1±0.01) was obtained in the treatment S80P20 (68.2% CH4±0.14) indicating that co-digestion of sludge cake and sweet potato at this ratio has provided an optimum environment for microorganism activity due to the balanced nutrient content Concerning the nutrient recovery, the higher the percentage of the sludge cake in the mixture, the higher the concentration of total N and P. Multivariate analysis (Cluster and PCA) revealed that the S:P range of 100:0 to 60:40 represents the higher energetic potential recovery and the higher digestate quality with greater agronomic value without the associated phytotoxicity.
Theoretical and experimental study on the uniformity of reflective high concentration photovoltaic system with light funnel Renew. Energy (IF 4.9) Pub Date : 2018-10-15 Cheng-Long Wang, Gong Jing-hu, Yan Jia-Jie, Zhou Yuan, Fan Duo-Wang
The efficiency of GaAs solar cell was significantly reduced resulting from non-uniformity of energy flux-density on receiver surface, and damage of solar cells was made by “hot spots”. In this paper, a light funnel is added between the concentrator and the receiver to improve the uniformity of energy flux-density on receiver surface, which is designed according to the ray tracing method. The simulation result shows that the uniformity of the energy flux-density on the receiver surface is 92.26%, which agrees with the experimental result (94.64%). According to the maximum output efficiency of GaAs solar cell, the layout range of the cell is determined. The simulation results shown that the cell is arranged in the radius of 58 mm, which is similar to the experimental value (60 mm), and the effective area rate of the photoelectric conversion is 69.4%. At normal operation temperature (20 °C), the photoelectric conversion efficiency is 29.64%, and the total efficiency is about 83%.
Optimal orientation angles for maximizing energy yield for solar PV in Saudi Arabia Renew. Energy (IF 4.9) Pub Date : 2018-10-12 Hassan Z. Al Garni, Anjali Awasthi, David Wright
This paper uses research-quality, ground measurements of irradiance and temperature that are accurate to ±2% to estimate the electric energy yield of fixed solar modules for utility-scale solar power plants at 18 sites in Saudi Arabia. The calculation is performed for a range of tilt and azimuth angles and the orientation that gives the optimum annual energy yield is determined. A detailed analysis is presented for Riyadh including the impact of non-optimal tilt and azimuth angles on annual energy yield. It is also found that energy yield in March and October are higher than in April and September, due to milder operating temperatures of the modules. A similar optimization of tilt and azimuth is performed each month separately. Adjusting the orientation each month increases energy yield by 4.01% compared to the annual optimum, but requires considerable labour cost. Further analysis shows that an increase in energy yield of 3.63% can be obtained by adjusting the orientation at five selected times during the year, thus significantly reducing the labour requirement. The optimal orientation and corresponding energy yield for all 18 sites is combined with a site suitability analysis taking into account climate, topography and proximity to roads, transmission lines and protected areas. Six sites are selected as having high suitability and high energy yield: Albaha, Arar, Hail, Riyadh, Tabuk and Taif. For these cities the optimal tilt is only slightly higher than the latitude, however the optimum azimuth is from 20° to 53° west of south due to an asymmetrical daily irradiance profile.
Study of assessment on capability of wind power accommodation in regional power grids Renew. Energy (IF 4.9) Pub Date : 2018-10-13 Lin Ye, Cihang Zhang, Hui Xue, Jiachen Li, Peng Lu, Yongning Zhao
With the development of large-scale wind power integration, wind curtailment appears around the world, especially in China. It is essential to perform the assessment on capability of wind power accommodation (ACWPA) by calculating the maximum admissible wind power which plays an important role in system planning and operation. This paper proposes a long-term assessment on the maximum level of wind power installed capacity in future years based on peak power regulation, with consideration of potential wind curtailment. Meanwhile, a short-term assessment based on wind power forecasting is developed through day-ahead unit commitment to get admissible zone of wind power in grid operation. In particular, the extreme wind variation scenario (EWVS) calculated by quadratic programming (QP) is applied to optimize upper limit of admissible zone. Case studies are carried out to analyze wind power characteristics in a province in Southern China. Results show that the proposed approaches can effectively and accurately evaluate the capability of wind power accommodation in regional power grids.
Experimental investigation of flows inside draft tube of a high-head pump-turbine Renew. Energy (IF 4.9) Pub Date : 2018-10-13 Xi-De Lai, Quan-Wei Liang, Dao-Xing Ye, Xiao-Ming Chen, Mi-Mi Xia
Due to fast and frequently switch between pumping and generating modes several times daily and continuously increase to operate at off-design conditions, understanding the detail of flows is a prerequisite to the design and safety operation of a pump-turbine. Because complex flow phenomena occur inside the draft tube at different operating conditions, its flow patterns are highly demanding to be accurately investigated with reliable approach. Laser Doppler Velocimetry measurements and vortex ropes visualization inside the draft tube of a high-head pump-turbine with the specific speed nq=24 have been performed at various operating conditions both in turbine and pump modes. Measurements and observations were taken for the speed factor nED=0.21 and 0.19 at loads ranging from 40% to 120% of the rated power at turbine mode, and the possible operating range at pump mode. The distribution of measured axial and tangential velocities, the size of backflow zones and the rotation of vortex rope are all in line with the hydraulic design and model test results. The LDV measurement has been applied to accurately analyze the swirl flow pattern and quantify swirling intensity, the region of backflow and vortex rope, as well as to precisely determine the location of the rope-free zone combining with vortex ropes visualization. Measured instantaneous tangential velocities have been applied to accurately distinguish the processional frequency of a rotating vortex rope inside the draft tube from other fluctuations at part loads. Influence of the splitter blades can be also observed in both time and frequency domain of measured instantaneous velocities. This study can provide rather valuable information for analysis and validation in different operating regimes. The presented methodology and techniques have been demonstrated very helpful to successfully developed high-head pump-turbines for two pumped storage power plants in China.
A novel estimation approach for the solar radiation potential with its complex spatial pattern via machine-learning techniques Renew. Energy (IF 4.9) Pub Date : 2018-10-13 Choongwan Koo, Wenzhuo Li, Seung Hyun Cha, Shaojie Zhang
As a clean and sustainable energy resource with lower environmental impact, the Chinese government encourages the application of solar energy system. The global solar radiation on the horizontal surface in the specific site should be investigated in advance so that the solar energy system could be implemented properly and efficiently. However, the monthly average daily solar radiation (MADSR) in China has complex spatial patterns, and its observation stations are still lacking due to the high cost of equipment. To address these challenges, this study aimed to develop a novel estimation approach for the MADSR with its complex spatial pattern over a vast area in China via machine-learning techniques (i.e. a clustering method (k-means) and an advanced case-based reasoning (A-CBR) model). The MADSR and the relevant information were collected from 97 cities in China for 10 years (from 2006 to 2015). The average prediction accuracy of the proposed approach was determined at 93.23%, showing a promising way. The proposed novel approach is expected to be generalized via the interpolation methods (e.g. kriging method in a geographical information system) so that decision-makers (e.g. construction manager or facility manager) can determine the appropriate location, size and form in implementing the solar energy system.
Investigation of leakage reinjection system for supercritical CO2 power cycle using heat pump Renew. Energy (IF 4.9) Pub Date : 2018-10-13 Hafiz Ali Muhammad, Beomjoon Lee, Gilbong Lee, Junhyun Cho, Young-Jin Baik
Supercritical carbon dioxide power cycle (sCO2) has recently attracted a great deal of interest owing to its compact size and potential for achieving high efficiency over a wide temperature range. However, several challenges still need to be overcome before the sCO2 cycle can be commercialized. One such challenge is leakage at the rotor components. The present paper discusses an innovative heat-pump application that can be used for leakage reinjection. The unique consideration of this leakage supplement system for the supercritical CO2 cycle stems from the high energy density of sCO2 and the high rotational speeds seen in turbomachinery. This paper proposes a heat-pump system that collects CO2 leakage at the turbine and liquefies this gas at the evaporator. The liquefied CO2 is then pressurized to the high pressure required for the main power generating cycle, and subsequently heat from the heat-pump working fluid is transferred to the CO2 in the heat-pump condenser. This heat-pump system offers superior compression performance over conventional methods of reinjection. Thermodynamic analysis reveals that the performance of the heat-pump system is sensitive to the saturation temperature of CO2 in the evaporator and superheating at the heat-pump's compressor inlet. Then, the genetic algorithm optimization module in MATLAB is used to optimize the system for net power consumption. Various heat-pump working fluids are investigated; R290 (Propane) delivers the best performance at 38.9% reduction in net power compared to a base case.
An Experimental Study on the Aerodynamic Performance Degradation of a Wind Turbine Blade Model Induced by Ice Accretion Process Renew. Energy (IF 4.9) Pub Date : 2018-10-11 Linyue Gao, Yang Liu, Wenwu Zhou, Hui Hu
An experimental study was conducted to characterize aerodynamic performance degradation of wind turbine blades induced by dynamic ice accretion process. The experimental study was performed in an Icing Research Tunnel with a turbine blade model under a typical glaze icing condition. Ice structures was found to accrete rapidly over both the upper and lower surfaces of the blade model after starting the ice accretion experiment. Irregular-shaped ice structures were found to disturb the airflow around the blade model greatly, resulting in large-scale flow separation and shedding of unsteady vortex structures from the ice accreting surface. The aerodynamic performance of the blade model was found to degrade significantly. The performance degradation induced by the ice accretion was found to be a strong function of the angle of attack of the blade model with more significant degradations at lower angles of attack. For the test case at the angle of attack of 5.0°, while the lift decreases to only ∼12% of its original value after 600 seconds of the ice accretion experiment, the drag was found to increase 4.5 times correspondingly. The detailed flow field measurements were correlated with the aerodynamic force data to elucidate the underlying physics.
Influences of binderless briquetting stresses on intrinsic bioconstituents of rice straw based solid biofuel Renew. Energy (IF 4.9) Pub Date : 2018-10-11 Sandip Gangil, Vinod Kumar Bhargav
This is the first article, presenting the use of nonaccelerating nodes of thermal degradation of biomaterials to visualize thermogravimetric-reactivity. The transitions of nonaccelerating nodes, during thermal degradation, due to binderless briquetting stresses on rice straw were studied and critically discussed. Intrinsic biopolymeric transformations of rice straw due to binderless briquetting stresses were analysed using thermogravimetry and Fourier transformed infrared spectroscopy. The nonaccelerating nodes in briquetted biofuel shifted towards higher temperature in lignin-related region showing that lignin became less reactive in briquetted biofuel. A pattern similar to the sine wave function was noticed in the tail end segment of the acceleration profile of thermal degradation. This function was at a phase-lag of 180° in briquetted biofuel as compared to raw material. In briquetted biofuel, fluctuations in degradation rate for lignin region subsided revealing consistent and consolidated lignin configuration. The FTIR-node at 1325.06 cm−1 related to characteristic group vibrations of CO (lignin) emerged in briquetted biofuel. Reduction in energy, related to OH-stretching, CH-bending, CO stretching was observed due to briquetting stresses. Due to briquetting stresses, the vibrational energy of CH-stretching, lignin-related CO vibration, and vibrations of lignin related benzene ring, increased. The energy-related to SiOSi FTIR node drastically reduced due to briquetting.
Real-time condition monitoring and fault detection of components based on machine-learning reconstruction model Renew. Energy (IF 4.9) Pub Date : 2018-10-12 Chunzhen Yang, Jingquan Liu, Yuyun Zeng, Guangyao Xie
Reconstruction model is a powerful method for component condition monitoring and fault detection by considering the model prediction residuals. In this article, a new signal reconstruction modeling technique is proposed using support vector regression. Multiple indicators are calculated to recognize slight shift from normal condition, and detect the fault at an early stage. Input variables are selected based on correlation analysis and failure mode analysis. A sliding-time-window technique is employed to incorporate temporal information inherent in time-series data. Residuals between the observed signal and the reconstruction signal are utilized to indicate whether the desired quantity is different from its normal operation condition or not. Three statistical indicators (Deviation Index, Volatility Index and Significance Index) are defined to quantify the deviation level from normal condition to abnormal condition. Health index (HI) of a specific fault is derived from responsive statistical indicators, and the integral health index (integral-HI) of an entire component is composed of all individual health index. An experiment of real-life wind turbine high temperature fault detection scheme is studied. Results show that the proposed approach demonstrates improved performance in detecting wind turbine faults, and controlling false and missed alarms.
Superiority of random inverted nanopyramid as efficient light trapping structure in ultrathin flexible c-Si solar cell Renew. Energy (IF 4.9) Pub Date : 2018-10-12 Quntao Tang, Honglie Shen, Hanyu Yao, Kai Gao, Ye Jiang, Yufang Li, Youwen Liu, Lei Zhang, Zhichun Ni, Qingzhu Wei
Intensiﬁcation of Reutealis trisperma biodiesel production using infrared radiation: Simulation, optimisation and validation Renew. Energy (IF 4.9) Pub Date : 2018-10-12 A.S. Silitonga, T.M.I. Mahlia, F. Kusumo, S. Dharma, A.H. Sebayang, R.W. Sembiring, A.H. Shamsuddin
The environmental benefits and economic impacts of Fit-in-Tariff in China Renew. Energy (IF 4.9) Pub Date : 2018-10-12 Weixian Wei, Yurong Zhao, Jianlin Wang, Malin Song
We employ a dynamic computable general equilibrium (CGE) model that includes Fit-in-Tariff, greenhouse gas (GHG), and air pollutants modules to evaluate the impacts of different subsidy scenarios. Assuming that the subsidies will continue until 2030, our results indicate that the Fit-in-Tariff will have positive effects on real GDP, employment, and emission reductions and that these benefits will increase over time. Such subsidies not only encourage the substitution of clean energy for traditional fossil energy, but also invite investment in renewable energy industries, ultimately benefiting all sectors. A sustained higher subsidy rate can contribute to the abatement of GHGs, and air pollutant emissions significantly, while also stimulating real GDP and employment in the early periods of the policy, yet it will not be conducive to growth over time due to the increasing tax burden. If subsidies continue until 2050, the environmental benefits will become more pronounced while the economic benefits will gradually disappear.
Optimization design of a thermal protection structure for the solar array of stratospheric airships Renew. Energy (IF 4.9) Pub Date : 2018-10-12 Junhui Meng, Siyu Liu, Zhongbing Yao, Mingyun Lv
Renewable power system using solar array is one of the most critical subsystems for stratospheric airships. It is important of thermal protection for the stratospheric airship, because excessive temperature of solar cell may reduce its conversion efficiency and age the envelope material underlaid solar cells. Multi-objective optimization of a thermal protection structure with heat dissipation and insulation layers for solar array of a stratospheric airship is performed in this paper. The optimization process is carried out by a Nondominated Sorting Genetic Algorithm to decrease the sensitivity toward weights or demand levels. The specific temperature difference, which indicates the ratio of temperature reduction and structure density, and the output power of solar array are used to present the optimization aims. Three geometric variables related to the number of fins, width ratio of fins and thickness ratio of dissipation and insulation layer are selected as the design variables. Pareto optimal fronts representing the trade-offs between the performance parameters are obtained at last and optimization results are compared with previous studies and the thermal protection effects and output power of the solar array are both more excellent. Furthermore, the simulation of the thermal protection structure with optimization parameters are carried out at last.
Biogas from a full scale digester operated in psychrophilic conditions and fed only with fruit and vegetable waste Renew. Energy (IF 4.9) Pub Date : 2018-10-12 J. Martí-Herrero, G. Soria-Castellón, A. Diaz-de-Basurto, R. Alvarez, D. Chemisana
Sn doped α-Fe2O3 (Sn=0,10,20,30 wt%) photoanodes for photoelectrochemical water splitting applications Renew. Energy (IF 4.9) Pub Date : 2018-10-12 B. Jansi Rani, G. Ravi, R. Yuvakkumar, S. Ravichandran, Fuad Ameen, S. AlNadhary
One pot hydrothermal route was adapted to synthesis pristine and Sn doped α-Fe2O3 nanospheres successfully. Sharp high intense diffraction peaks obtained from XRD confirmed crystalline nature of rhombohedral hematite. The secondary SnO2 face formation was due to increasing Sn dopant concentration. Raman spectra confirmed intrinsic phonon vibration modes [Eg(1)+Eg(2)+Eu] of hematite nanospheres. 2P3/2(1) → 2P1/2 transition by emission peak at 549 nm confirmed hematite phase formation. Metal oxygen vibration (Fe-O stretching) was confirmed by absorption band situated at 539 cm-1. The noticeable variation in band gap of pristine hematite nanospheres was due to tetravalent Sn4+ dopant concentration. The lowest band gap energy 1.90 eV was found for 10 wt% Sn4+ doped hematite. Highest photocurrent 2.34 mA/cm2 at 0.098 V Vs RHE was obtained for 10% Sn doped hematite nanospheres. The EIS exposed the charge transferring mechanism of synthesized pristine and Sn doped α-Fe2O3 nanospheres. M-S plot evidenced that the lower shift of flat band potential for 10 wt% Sn4+ doped hematite was as -0.35 V. CA study proved the good stability over 4 h of the best performed photoanodes. Sn4+ doping and its dopant concentration on pristine hematite had dominant effect on photocatalytic activity of hematite nanospheres.
Experimental evaluation of nucleate pool boiling heat transfer correlations for R245fa and R1233zd(E) in ORC applications Renew. Energy (IF 4.9) Pub Date : 2018-10-12 Matthias Welzl, Florian Heberle, Dieter Brüggemann
In binary geothermal power plants based on the Organic Rankine Cycle (ORC) typically shell-and-tube heat exchangers are used as evaporators. In the shell-side, nucleate boiling of the working fluid takes place on the external surfaces of tubes. For the replacement of fluids with high global warming potential (GWP) or selection of efficient working fluids, a comprehensive evaluation has to be performed. Therefore, the knowledge about the nucleate pool boiling heat transfer coefficient (HTC) in combination with the electrical power output is necessary. In this study, the focus is led on the experimental evaluation of nucleate pool boiling heat transfer correlations for R245fa and its possible replacement R1233zd(E) in ORC applications. The nucleate boiling HTC on a horizontal tube and the electrical power generation of a 1 kW scroll expander are simultaneously measured with an ORC test rig for both fluids. The thermal input is provided by an electrically heated preheater and evaporator. Nucleate boiling takes place on a plain copper tube with an outer diameter of 32 mm and a heated length of 822 mm. The surface temperature of the copper tube is determined by thermocouples within the tube in consideration of thermal conduction. The obtained measurement results, regarding heat transfer characteristics as well as power output, show that the working fluid R245fa performs better at equal saturation temperatures due to the higher density and saturation pressure, and the lower viscosity. The HTC for R245fa is up to 43.2% higher in comparison to R1233zd(E). The experimental HTC are compared to selected nucleate pool boiling HTC correlations. The evaluation reveals that correlations according to Cooper and Gorenflo et al. show the slightest mean absolute deviations between 4.75% and 15.65% for both working fluids.
Parameter estimation of fuzzy sliding mode controller for hydraulic turbine regulating system based on HICA algorithm Renew. Energy (IF 4.9) Pub Date : 2018-10-12 Zhihuan Chen, Xiaohui Yuan, Yanbin Yuan, Xiaohui Lei, Binqiao Zhang
Global hydropower growth continues to increase with a relative higher rate of total installed capacity in just last 10 years. This expansion means that it is increasingly important to make a further research with respect to various hydropower stations. As the core of hydropower stations, hydraulic turbine regulating system (HTRS) attracts many attentions. In essence, HTRS is a complex nonlinear system that governs the frequency and the electrical power output of hydroelectric unit. The design of the control laws for the HTRS is an important and difficult task. In this study, a hybrid imperialist competitive algorithm (HICA) for the dynamic model of HTRS system is proposed and applied to estimate the parameters of fuzzy sliding mode controller (FSMC). In the proposed approach, sliding mode controller (SMC) is regarded as a robust control technique to the external uncertain load disturbances and fuzzy logic rule provides a better proportional gain and reduces the inherent chattering effect of the SMC controller. The HICA is developed to search optimal values of the control law and the membership functions of fuzzy logic rules. Simulations are carried out to verify the effectiveness of proposed approach, where the results show that compared with parallel PID controller and conventional SMC controller, the designed FSMC controller performs much better in terms of system performance and chattering reduction. Also, the results certify the superiority of the HICA algorithm in estimating the parameters for the proposed controller of HTRS in comparison to other classical evolutionary algorithms, where HICA reduces the value of the objective function by 3.28%, 5.33% and 9.69% compared with ICA, BSA, and PSO under unload condition, and HICA reduces the value of the objective function by 3.69%, 4.01% and 10.70% compared with ICA, BSA, and PSO under load condition.
Economic Analysis of a Field Monitored Residential Wood Pellet Boiler Heating System in New York State Renew. Energy (IF 4.9) Pub Date : 2018-10-11 Kui Wang, Yuanyuan Zhang, Gasper Sekelj, Philip K. Hopke
An economic and environmental benefit analysis have been performed using data from the field monitoring of a 25-kW wood pellet boiler heating system with thermal energy storage (TES) tanks installed in a home using a low temperature heat distribution system and radiant heat emitters in northern New York State (NYS). Pellet fuel demand was a linear function of daily average ambient temperature. It was used to predict total seasonal fuel and heat demand from the beginning of October to the end of April. A cost of heat (COH) analysis was performed considering all costs associated with the system including capital cost, operation, maintenance, other costs, and final system disposal (or salvation) cost. Sensitivity analysis showed that initial capital cost, wood pellet fuel price, and boiler heating system seasonal efficiency were the top three key factors determining the final COH with seasonal efficiency becomes more significant when pellet price increases. A life cycle annualized cost method was used to determine and compare the costs of heat using natural gas, No. 2 fuel oil, and propane. The study found that at the current seasonal efficiency of 75.8% (based on gross heating value), pellet fuel price of 240 $/ton, and maximum government incentives of $10,000, wood pellet boiler heating is able to replace intermediate efficiency (83%) propane heating systems in NYS at current fuel price of 2.48 $/gal. With a 3.6% fuel price increase to 2.57 $/gal, wood pellet heating is comparable with high efficiency (95%) propane heating systems. In addition, a heating oil price above 3.22 $/gal would make it economically possible to switch from oil heating to wood pellet heating in NYS. It was found that major emissions reductions can be achieved by switching from inefficient wood heating technology to wood pellet heating in terms of reductions in CO2, particulate matter (PM), and CO emissions. Greenhouse gas emissions reductions are also achieved when switching from fossil fuels to wood pellets, but PM and CO emissions increased significantly.
The Dynamic Relationship of Renewable and Nonrenewable Energy Consumption with Carbon Emission: A global study with the application of heterogeneous panel estimations Renew. Energy (IF 4.9) Pub Date : 2018-10-11 Arshian Sharif, Syed Ali Raza, Ilhan Ozturk, Sahar Afshan
This present study explores the relationship of renewable and non-renewable energy consumption with carbon emission by using panel data of 74 nations from 1990 to 2015. In doing as so, we apply the second-generation econometrics of panel data to examines the cross-section independence and control the heterogeneity between cross-sections. The CIPS unit root test, Westerlund (2007) bootstrap cointegration, Pedroni co-integration, FMOLS and heterogeneous panel causality techniques have been applied. The outcomes affirm that all variables are integrated over the long-run. The results also show that the nonrenewable energy consumption has a positive effect on environmental degradation whereas; renewable energy has a negative impact on environmental degradation and help to reduce environmental hazards. Similarly, financial development also has a negative and significant impact on environmental degradation. Furthermore, the Kuznets hypothesis are also tested and found its existence. This study provides valuable policy implications for the government and the policy makers.
The technical efficiency of China’s wind power list enterprises: An estimation based on DEA method and micro-data Renew. Energy (IF 4.9) Pub Date : 2018-10-11 Xingang Zhao, Zhen Wei
Promoting wind power is a long-term strategy of China to respond to both energy shortage and environmental pollution. Stimulated by various incentive policies, wind power generation in China has achieved tremendous growth. However, the China’s wind power industry is still in its early development stage and various problems have emerged, seriously challenging the healthy functioning of the industry. Based on micro-data on wind power listed companies, the four-stage Data Envelopment Analysis (DEA) model is used to measure the technical efficiency of China’s wind power enterprises and sketch the development of the wind power industry at the micro level. The results show that there exist non-efficiency problems arising from the diseconomies of scale in China’s wind power industry during 2011-2015. The average value of the efficiency of wind power enterprises is 32.5%. According to the subsample analysis, large-scale enterprises, private-owned enterprises and enterprises taking wind farm conduction and operation as their main business, as well as enterprises located in the three northern area, have the highest efficiency in their respective categories. Drawn on this analysis, conclusions and policy implications are provided at the end of the paper.
CO2-TiCl4 working fluid for high-temperature heat source power cycles and solar application Renew. Energy (IF 4.9) Pub Date : 2018-10-11 D. Bonalumi, S. Lasala, E. Macchi
The application of CO2 power cycles has proved to be particularly advantageous to exploit high-temperature heat sources (500–800 °C) in the case of available low-temperature heat sinks (15–25 °C). Otherwise, the efficiency of these cycles is strongly reduced when cold sink temperatures are higher than 25 °C. This is the case, for example, of solar applications installed in desert areas whose cold sink is represented by available hot air. Due to these high temperatures of the cold sink, CO2 is inevitably compressed in the supercritical phase thus preventing its more efficient pressurization in the liquid phase.One of the solutions envisaged to overcome this problem consists of adding to CO2 a small amount of one or more chemicals, resulting in a mixture with a critical temperature higher than the one of pure CO2 (about 31 °C). This preserves the working fluid compression in its liquid phase, even in the case of cold sinks with temperatures greater than 25 °C.This research aims to show that the addition to CO2 of a specifically selected second component enables to increase the critical temperature up to 45 °C with relevant improvements of cycle efficiency with respect to pure-CO2 power cycles. In particular, after summarizing the most relevant criteria to be accounted for when selecting CO2-additives, the paper warns about the thermodynamic effects deriving from adding to CO2 a second component characterized by a much more high critical temperature, such as the occurrence of infinite-pressure critical points and multiple-phase liquid-liquid and vapor-liquid critical points. Moreover, the paper specifically analyses the thermodynamic properties of CO2-TiCl4 mixtures which, depending on the content of TiCl4, may lead to a mixture characterized by the sought higher critical temperature. While studying this mixture, it has been observed that it presents multiple-phase critical points. For the sake of completeness, the paper also shows how do enthalpy and specific volume change in response to pressure variations in the event of either liquid-liquid or vapor-liquid critical points. This research finally shows the comparison between performances of power cycles which use, as working fluid, either pure CO2 or the specifically designed CO2-TiCl4 mixture. As expected, the TiCl4 addition brings about a significant efficiency gain.
On-line measurement of activation energy of ground bamboo using near infrared spectroscopy Renew. Energy (IF 4.9) Pub Date : 2018-10-11 Panmanas Sirisomboon, Jetsada Posom
On-line measurement of activation energy (Ea) is very important in supporting the thermal conversion process. The main objective of this study was to evaluate the Ea of ground bamboo using near infrared spectroscopy in real time. 80 bamboo samples with different diameters were selected using random sampling. Ea was determined using the Coats-Redfern method, and Ea of reaction order (n) at n=1 and n≠1 was investigated. The performance of on-line measurement predicted by PLS modeling for Ea at n=1 and Ea at n≠1 showed coefficients of determination of 0.781 and 0.714, respectively; standard error of prediction of 5.249 and 6.858 kJ/mol, respectively; and bias values of -1.0628 and -1.871 kJ/mol, respectively. Both PLS models were found to be fair and could be applied toward screening. The results showed that the vibration bands of lignocellulosic components (CH2, hemicellulose, cellulose, and lignin) highly influenced model development. Moreover, internal relationships were identified among Ea, the pre-exponential factor (A), and n, such as A (1/min)=63251×e0.2200×Ea (at n=1), A (1/min) =33719×e0.2267×Ea (at n≠1), and n=0.008×Ea+0.254. These relationships can be used to evaluate A and n if Ea is known. In the case of this study, Ea was forecasted using an NIR model.
Hydropower Revenues under the Threat of Climate Change in Brazil Renew. Energy (IF 4.9) Pub Date : 2018-10-11 Anderson Rodrigo de Queiroz, Victor.A.D. Faria, Luana M.M. Lima, José W. M. Lima
This work analyzes the impacts of climate change in the revenues of hydropower plants. One important input for designing and evaluating investment opportunities in hydropower is the water inflows historical data. Unfortunately, the use of such information alone may not project well the future power generation due to the influence of climate change in the water inflow patterns. This paper introduces spatio-temporal information of the future climate into the operational planning of the Brazilian hydropower system. Global climate models from IPCC are considered along with downscaled regional climate models. Our results at the individual hydro plant level show the importance of taking into account climate change information when performing hydro generation planning studies.
5-Na/ZnO doped mesoporous silica as reusable solid catalyst for biodiesel production via transesterification of virgin cottonseed oil Renew. Energy (IF 4.9) Pub Date : 2018-10-11 Rashi Malhotra, Amjad Ali
Research on a Cost-effective Measure Dedicated to Stabilizing Offshore Wind Farm Crew Transfer Vessels Renew. Energy (IF 4.9) Pub Date : 2018-10-09 Wenxian Yang, Wenye Tian, Kexiang Wei, Zhike Peng, Zhonghua Huang
The rapidly growing offshore wind industry is calling for more crew transfer vessels to deliver increasing number of minor maintenance tasks as about 75% of onshore wind turbine failures are related to the minor errors occurring in the electrical and power electronic systems of the turbines. The situation in offshore wind farms may be worse due to the wet, salty and corrosive air in offshore environments. Due to the limitations of small hull and deck spaces, there is difficulty to apply the proven motion stabilization techniques to wind farm crew transfer vessels. Consequently, the present crew transfer vessels have limited capability in providing safe transfer between the vessel and wind turbines, particularly in rough sea waves. To tackle this issue, a new motion stabilization technique is studied in this paper by using both numerical analysis and experimental testing approaches. Through investigating the vessel’s motions under different wave conditions before and after applying the proposed technique, it is found that the heave, roll and pitch motions of the vessel, especially in its resonant frequency regions, have been successfully constrained after applying the proposed stabilizing technique. Moreover, the amount of motion reduction can be further improved through optimizing the size of stabilizers and their underwater distance.
Machine learning methods for wind turbine condition monitoring: A review Renew. Energy (IF 4.9) Pub Date : 2018-10-09 Adrian Stetco, Fateme Dinmohammadi, Xingyu Zhao, Valentin Robu, David Flynn, Mike Barnes, John Keane, Goran Nenadic
This paper reviews the recent literature on machine learning (ML) models that have been used for condition monitoring in wind turbines (e.g. blade fault detection or generator temperature monitoring). We classify these models by typical ML steps, including data sources, feature selection and extraction, model selection (classification, regression), validation and decision-making. Our findings show that most models use SCADA or simulated data, with almost two-thirds of methods using classification and the rest relying on regression. Neural networks, support vector machines and decision trees are most commonly used. We conclude with a discussion of the main areas for future work in this domain.
BaZrO3 and Cs-BaZrO3 catalysed transesterification of Millettia Pinnata oil and optimisation of reaction variables by response surface Box-Behnken design Renew. Energy (IF 4.9) Pub Date : 2018-10-08 Dipesh Kumar, Bhaskar Singh
Comparative thermo-economic analysis of multi-fuel fired gas turbine power plant Renew. Energy (IF 4.9) Pub Date : 2018-10-09 Godfrey T. Udeh, Patrick O. Udeh
This study compares the performance of a thermal power plant fired by natural gas to that fired by biodiesel blend, from exergetic and economic perspectives. A thermodynamic model has been developed to predict the performance of a running plant and was used to conduct the comparative study. Plant life of 25 years has been used to assess the viability of the gas turbine power plant by analyzing the net present cost and the break-even point for both fuels. The plant specific fuel consumption for natural gas fired and biodiesel blend fired are 0.3151 [kg/kWh] and 0.3884 [kg/kWh] respectively. The system fired by natural gas only, has a payback period of 1.9 years, internal rate of return of 52% and exhaust temperature of 915.74 [K], while that fired by the biodiesel blend has a payback period of 2.4 years, internal rate of return of 60% and exhaust temperature of 858.50 [K]. Nevertheless, biodiesel blend is preferable because it is biodegradable, produces less emissions, and as a consequence, environmentally benign. Biodiesel blend would be more suitable for firing gas turbine engines, if the combustor is redesigned to improve its efficiency. Thermo-economic analysis of gas turbine power plants is essential to improve its thermodynamic and economic performance.
Fault diagnosis of wind turbine based on Long Short-Term memory networks Renew. Energy (IF 4.9) Pub Date : 2018-10-09 Jinhao Lei, Chao Liu, Dongxiang Jiang
Time-series data is widely adopted in condition monitoring and fault diagnosis of wind turbines as well as other energy systems, where long-term dependency is essential to form the classifiable features. To address the issues that the traditional approaches either rely on expert knowledge and handcrafted features or do not fully model long-term dependencies hidden in time-domain signals, this work presents a novel fault diagnosis framework based on an end-to-end Long Short-term Memory (LSTM) model, to learn features directly from multivariate time-series data and capture long-term dependencies through recurrent behaviour and gates mechanism of LSTM. Experimental results on two wind turbine datasets show that our method is able to do fault classification effectively from raw time-series signals collected by single or multiple sensors and outperforms state-of-art approaches. Furthermore, the robustness of the proposed framework is validated through the experiments on small dataset with limited data.
Apparent kinetic and thermodynamic calculation for thermal degradation of stearic acid and its esterification derivants through thermogravimetric analysis Renew. Energy (IF 4.9) Pub Date : 2018-10-09 Shengli Niu, Hewei Yu, Shuang Zhao, Xiangyu Zhang, Ximing Li, Kuihua Han, Chunmei Lu, Yongzheng Wang
Thermal degradation properties of stearic acid and its esterification derivants of methyl stearate and ethyl stearate are investigated through thermogravimetric analysis. Based on experiments, which are conducted at the temperature heated rates of 10, 15 and 20 K min-1, the iso-conversional methods of Kissinger-Akahira-Sunose and Flynn-Wall-Ozawa are used to calculate the apparent activation energy. Further, the Avrami theory is used to estimate the apparent reaction order. Apparent thermodynamic parameters of the apparent enthalpy change, apparent Gibbs free energy change and apparent entropy change are calculated. Calculations of apparent kinetic and thermodynamic parameters illustrate that thermal activity of stearic acid is distinctly heightened after esterification and the derived derivants are more easily activated. Meanwhile, influences of alcohol type on esterification products are weak. Conclusions from this study make more comprehensive understanding of the thermal events of biodiesel to be favor for its commercial application.
Multi-step wind speed forecasting based on a hybrid decomposition technique and an improved back-propagation neural network Renew. Energy (IF 4.9) Pub Date : 2018-10-09 Zongxi Qu, Wenqian Mao, Kequan Zhang, Wenyu Zhang, Zhipeng Li
Precise and reliable wind-speed prediction is vital for wind-farm operational planning. However, wind speed series usually have complex features, such as non-linearity and volatility, which makes the wind energy forecasting highly difficult. Aimed at this challenge, this paper proposes a forecasting architecture based on a new hybrid decomposition technique (HDT) and an improved flower-pollination algorithm (FPA)-back propagation (BP) neural network prediction algorithm. The proposed HDT combines the complete ensemble empirical mode decomposition adaptive noise (CEEMDAN) and the empirical wavelet transform (EWT), which is unique, since the EWT is specifically employed to further decompose the high frequency intrinsic mode functions (IMFs) generated by CEEMDAN to reduce prediction complexity. And then an improved BPNN with the flower-pollination algorithm is applied to forecast all of the decomposed IMFs and modes. To investigate the forecasting ability of the proposed model, the wind speed data collected from two different wind farms in Shandong, China were used for multi-step ahead forecasting. The experimental results show that the proposed model performs remarkably better than all of the other considered models in one-step to five-step wind speed forecasting, which indicates that the proposed model is highly suitable for non-stationary multi-step wind speed forecasting.
Steady and transient operation of an Organic Rankine Cycle power system Renew. Energy (IF 4.9) Pub Date : 2018-10-09 Shuang Cao, Jinliang Xu, Zheng Miao, Xiulong Liu, Ming Zhang, Xuewang Xie, Zhi Li, Xiaoli Zhao, Guihua Tang
The Organic Rankine Cycle (ORC) driven by low-grade energy can operate in off-grid mode. Here, we report the steady and transient characteristics of an ORC system. A single screw expander and a synchronous generator convert mechanical power to electricity. A lamp array simulates the variable external loads. The quality parameters including electric frequency, electric power and effective voltage are measured by a power meter. We show that at setting frequency of 50 Hz, the maximum system efficiency can be reached when the external load is not larger than the ORC power capacity. The expander isentropic efficiency is above 80% for the vapor superheating of 5-10 K at expander inlet. A control strategy is proposed to achieve better system performance under varied heat source and environment conditions. By use of residual frequency and adjusting pumping frequency, the vapor pressure at expander inlet can be automatically adjusted to reach the optimal value. Transient tests indicate that the electric quality is insensitive to the step change of external loads and heat/cold sources parameters. The thermohydraulic parameters are self-adapted to the change of external parameters. This work provides a self-adapting strategy for ORC operation at varied heat/cold source parameters.
Study on active disturbance rejection control with actuator saturation to reduce the load of a driving chain in wind turbines Renew. Energy (IF 4.9) Pub Date : 2018-10-09 Lina Ren, Chenhong Mao, Zeyu Song, Fucai Liu
In this study, nonlinear uncertainty and actuator saturation characteristics are investigated with respect to the issue of reducing the load of a wind turbine drive train. A method of active disturbance rejection control (ADRC) with actuator saturation is proposed to reduce the load on a wind turbine drive chain when the wind speed is below the rated wind speed. A tracking differentiator is designed to arrange the transient process for the error of the torsional vibration angle of the control system. An extended state observer (ESO) is used to estimate the strong non-linearity and “unknown disturbance”, and this is compensated by a linear controller in real time. The actuator saturation is applied to prevent over-saturation of the actuator (generator) and thereby to protect the complete system. Both convergence of the extended state observer and stabilization of the closed-loop system are discussed in this article. Finally, simulation results are detailed to demonstrate the effectiveness and robustness of the proposed control method.
Effect of lanthanide ion doping on Mg−Al mixed oxides as active acid−base catalysts for fatty acid ethyl ester synthesis Renew. Energy (IF 4.9) Pub Date : 2018-10-09 Jessika de Souza Rossi, Olavo Micali Perrone, Marcos Rechi Siqueira, Diogo Paschoalini Volanti, Eleni Gomes, Roberto da Silva, Mauricio Boscolo
Euonymus maackii Rupr. Seed oil as a new potential non-edible feedstock for biodiesel Renew. Energy (IF 4.9) Pub Date : 2018-10-09 Ju-Zhao Liu, Qi Cui, Yu-Fei Kang, Yao Meng, Ming-Zhu Gao, Thomas Efferth, Yu-Jie Fu
In this study, Euonymus maackii Seed oil (EMSO) was exploited and evaluated for the ﬁrst time as a new non-edible oil feedstock for preparation of biodiesel. The EMSO yield was 41.06 ± 2.68 wt%. The fatty acid compositions of EMSO involved palmitoleic acid (2.01%), palmitic acid (14.5%), stearic acid (3.1%), oleic acid (49.8%), linoleic acid (29.3%), 11-Eicosenoic acid (0.1%) and arachidic acid (0.07%). Microwave-assisted transesteriﬁcation with methanol provided a high conversion yield in short duration under low temperature. The 2.0 wt% of catalyst amount, 10:1 of methanol/oil molar ratio, 40 min of reaction time and 60 oC of temperature were found to be the optimum process conditions for the maximum biodiesel yield of 94.74 ± 2.09%. Using pseudo first-order kinetic model, the reaction rate constants were 2.145 × 102, 3.550 × 102 and 6.447 × 102 min-1 for 40, 50 and 60 °C, respectively. The thermodynamic property for biodiesel preparation was determined as activation energy = 47.67 kJ mol-1. The fuel properties of the biodiesel product were evaluated and comparable to ASTM D-6751 and EN 14214 standards. Overall, this study revealed and confirmed the potential of Euonymus maackii seed oil as the appropriate alternative feedstock for biodiesel production.
Performance assessment of a solar parabolic dish for domestic use based on experimental measurements Renew. Energy (IF 4.9) Pub Date : 2018-10-09 Augusto Bianchini, Alessandro Guzzini, Marco Pellegrini, Cesare Saccani
The paper deals with extensive monitoring of a solar thermal parabolic dish system. It was carried at the outdoor development center HEnergia of HERA S.p.A. in Forlì (Italy). HEnergia has a small-scale parabolic dish of 11.5 kW thermal peak which has been realized with a commercial concentrating unit. Parabolic dish plant is remotely monitored and data on environmental conditions, module temperature, cooling fluid flowrate and temperatures and thermal power production are continuously acquired and stored by a PC. Parabolic dish plant performance can be measured on-site and compared in relation to different environmental conditions. On the basis of experimental data, the paper also shows a simplified method to evaluate parabolic dish performance.
Application of pulse electric field pretreatment for enhancing lipid extraction from Chlorella pyrenoidosa grown in wastewater Renew. Energy (IF 4.9) Pub Date : 2018-10-09 Song-Fang Han, Wenbiao Jin, Qian Yang, Abd El-Fatah Abomohra, Xu Zhou, Renjie Tu, Chuan Chen, Guo-Jun Xie, Qilin Wang
Comparative study of standard engine and modified engine with different piston bowl geometries operated with B20 fuel blend Renew. Energy (IF 4.9) Pub Date : 2018-10-08 Manjunath Channappagoudra, K. Ramesh, Manavendra.G
Preparation of phosphotungstic acid based poly(ionic liquid) and its application to esterification of palmitic acid Renew. Energy (IF 4.9) Pub Date : 2018-10-08 Yongqiang Wang, Dan Zhao, Guanyi Chen, Shejiang Liu, Na Ji, Hui Ding, Jianfeng Fu
Pleasure is the profit - the adoption of solar PV systems by households in Finland Renew. Energy (IF 4.9) Pub Date : 2018-10-05 Sami Karjalainen, Hannele Ahvenniemi
Decentralized energy production offers households considerable potential to support the attainment of climate targets. This study focuses on solar photovoltaic (PV) adoption in Finland, where the adoption of solar PV systems is still at a low level. The study asks how adopters have overcome the barriers to adopting solar PV systems. A special interest lies in the user experience of solar PV systems. Twenty-eight semi-structured interviews were conducted to obtain an understanding of the experiences of Finnish pioneer households. The results show that the adopters have overcome the barriers to adoption with the help of trustworthy information and advice from experts and from other adopters. The adopters are very satisfied with their PV plants even though economic profitability is not particularly good. The adopters actively monitor their energy production and are highly engaged in domestic energy matters. Many have enlarged their solar PV system or plan to do so, or are highly interested in upgrading their energy system with an electric car or advanced home automation. The adopters find pleasure in producing pollution-free energy effortlessly and being able to deliver information about clean energy production to others through their own installations.
The expansion and changing cropping pattern of rapeseed production and biodiesel manufacturing in Poland Renew. Energy (IF 4.9) Pub Date : 2018-10-05 Anna M. Klepacka, Wojciech J. Florkowski, Cesar Revoredo-Giha
Measurements and analysis of the thermal properties of a sedimentary succession in Yangtze plate in China Renew. Energy (IF 4.9) Pub Date : 2018-10-05 Jin Luo, Yu Qiao, Wei Xiang, Joachim Rohn
A geological stratum is a rock or soil layer that has internally consistent characteristics and is distinguishable from adjacent layers. A stratigraphic section contains reference information for the strata of an associated sedimentary area. In this paper, the thermal properties of 36 rock formations in a succession of the Yangtze plate in China are studied. Thermal properties are analyzed with an emphasis on rock formations, rock lithological types and dry/saturated conditions. The results show that thermal conductivity varies dramatically with different rock lithological types, which range from 0.72 W m−1 K−1 to 4.49 W m−1 K−1. The analysis of biochemical sedimentary rocks shows that silicate has the highest thermal conductivity, followed by dolomite and limestone; this variation is due to the differences in rock-forming minerals. The thermal conductivity of the clastic rocks is mainly determined by the type of minerals, the porosity and the water content. Compared to dry samples, the thermal conductivity and volumetric heat capacity of saturated samples are higher. Moreover, the thermal conductivity data of nine other locations in the Yangtze plate are compared with the stratigraphic data. This analysis shows that thermal conductivity matches very well for most of the geological formations, with the exception of sandstone, which exhibits a significant deviation across formations. Finally, the thermal properties for the Yangtze plate are mapped for insight on their spatial distribution.
How to measure flexibility – performance indicators for demand driven power generation from biogas plants Renew. Energy (IF 4.9) Pub Date : 2018-10-06 Martin Dotzauer, Diana Pfeiffer, Markus Lauer, Marcel Pohl, Eric Mauky, Katharina Bär, Matthias Sonnleitner, Wilfried Zörner, Jessica Hudde, Björn Schwarz, Burkhardt Faßauer, Markus Dahmen, Christian Rieke, Johannes Herbert, Daniela Thrän
Flexible power provision from biogas can significantly contribute to energy systems with high shares of renewables. However, the characteristics and demands for this flexibility are not clearly defined or measured. In this paper eight indicators are defined to shape “flexibility” and perform a downstream investigation of eight research projects focusing on flexible energy provision of biogas plants. The indicators are structured in three dimensions (1) velocity (ramps) by which the system can be modulated, (2) power range (bandwidth) and (3) duration for specific load conditions. Based on these indicators bottlenecks for the flexibility potential were identified. One crucial result shows that short-term flexibility of biogas plants is mainly driven by properties of the combined heat and power unit (velocity and bandwidth). The long-term flexibility depends mainly on gas storage, mode of operation and ability for modulation of the target gas production.
Effectiveness of Recyclable Aluminum Cans in Fabricating an Efficient Solar Collector for Drying Agricultural Products Renew. Energy (IF 4.9) Pub Date : 2018-10-06 Sameh S. Kishk, Ramadan A. ElGamal, Gamal M. ElMasry
The shortages in conventional fuels along with the continuous rise in their prices have led to an increased emphasis on using solar energy as an alternative source of energy. However, establishing reliable and affordable solar collectors for different applications is a great challenge. Therefore, this study aimed to design and fabricate an efficient and cheap solar air collector from recyclable aluminum cans. Two dryers of different configurations (closed and open modes) were then constructed and examined for drying tomatoes under different operating conditions. The results revealed that the thermal efficiency of the designed solar collectors increased considerably from 25 to 63% when the air-flow rate increased from 15 to 45 m3h-1. In comparison to the conventional method of open sun drying, the designed solar dryers enhanced both the drying rate and the overall quality of the final product. In the designed solar dryer, over three days of consecutive drying (30 hours of drying), the moisture content of tomato wedges was reduced from 19 to less than 1 kg [H2O] kg-1 [dry matter]. The closed-mode dryer configuration, which recirculates the drying air, showed a considerable increase in the drying rate and weigh loss over the traditional sun dryers and open-mode dryer systems. Among all mathematical models, a non-linear quadratic model (Wang and Singh model) has shown a better fit to the experimental drying data compared to the other models.
Experimental and modeling study of tomato pomace waste drying in a new solar greenhouse: Evaluation of new drying models Renew. Energy (IF 4.9) Pub Date : 2018-10-06 Ouassila Badaoui, Salah Hanini, Ahmed Djebli, Haddad Brahim, Amina Benhamou
Algeria industry fruit processing generates a huge amount of waste which causes a serious environmental problem. Thereby, the use of solar drying as a clean energy process seems to be a promising solution. This will enhance the value of fruit waste by reusing it in a dry form,and will also contribute to the protection of the environment. For this prupose, an innovative greenhouse solar dryer has been designed at the Solar Equipment Development Unit in Bou Ismail. An experimental study of solar drying kinetics of industrial tomato pomace was conducted to test the performance of the new solar dryer as a waste processing dryer. The drying temperature of the tomato waste, using this type of dryer, varies between 40 and 58 °C. The duration of the drying operation for a final product is only five hours. Five new universal and dimensionless models and five different drying models chosen from the literature were evaluated in order to select the model that better fits the experimental data generated during the drying process. Among the different models tested, it emerged that the new model2 was the most suitable to describe the drying process of tomato waste. Also, the diffusion coefficient and the activate energy were studied and determined. The effective diffusivity varies between 3.2E-9 and 4.7E-10 m2/s with activation energy is 75.6 kJ/mol.
The study of producing “drop-in” fuels from agricultural waste through fast pyrolysis and catalytic hydro-processing Renew. Energy (IF 4.9) Pub Date : 2018-10-06 Wei-Cheng Wang, An-Cheng Lee
For converting biomass into renewable fuel, fast pyrolysis and further upgrading processes have been a promising pathway for years. Catalytic deoxygenation of the oxygenate compounds in the pyrolytic bio-oil significantly improves the quality of bio-oil and increases the possibilities of directly using that as transportation fuel. In this study, two types of experiment, fluidized bed fast pyrolysis of Miscanthus and hydro-processing of the produced bio-oil, were conducted in sequence. The Miscanthus biomass was first pyrolyzed to produce the bio-oil in a fluidized bed and the oil product was then hydro-processed into upgraded fuel in a fixed bed reactor over Pd/C catalyst with various operating conditions including reaction temperature, reaction pressure, liquid hourly space velocity (LHSV), and H2-to-oil ratio. The chemical compositions, FTIR spectra and physical/chemical properties of the two products were demonstrated and compared. The degree of deoxygenation (DOD) was additionally presented with varying experimental conditions, showing that the maximum DOD of 95% was obtained.
A versatile one-dimensional numerical model for packed-bed heat storage systems Renew. Energy (IF 4.9) Pub Date : 2018-10-06 Thibaut Esence, Arnaud Bruch, Jean-François Fourmigué, Benoit Stutz
Thanks to their versatility and their relatively low cost, packed-bed sensible heat storage systems are promising for various applications like in central solar power plants, adiabatic compressed energy storage and pumped thermal energy storage. A versatile one-dimensional numerical model able to describe many packed-bed configurations is developed and presented. This model is able to treat liquid or gaseous heat transfer fluids. The packed bed can include a mixture of large and small solid particles such as rocks and sand, commonly encountered in the literature due to the advantages it procures. The model is compared and validated with specific experimental data and results from the literature covering wide ranges of configurations and operating conditions: several heat transfer fluids (molten salts, thermal oil, air), solid materials (rocks, sand, ceramics), fluid velocities, temperature levels and packed bed configurations are successfully tested. This shows the versatility of the developed model. The influence of the fluid velocity on heat losses, thermal diffusion and fluid/solid heat exchange are analysed. It enables to determine the optimal velocity which maximizes the performance of the storage system.
Investigation on the effects of gasoline reactivity controlled compression ignition application in a diesel generator in high loads using safflower biodiesel blends Renew. Energy (IF 4.9) Pub Date : 2018-10-06 Mehmet Zerrakki Işik, Hüseyin Aydin
In this study, the effects of Reactivity Controlled Compression Ignition (RCCI) application on engine combustion, performance and emissions in a diesel generator were investigated. In the experiments, safflower oil derived biodiesel and diesel mixtures were used as the high reactivity fuel (primary fuel) and gasoline as the low reactivity fuel. The RCCI application was provided by the connection of a secondary fuel injection system with the intake manifold. The gasoline RCCI application rate was 30% and 50% of the total mass fuel consumption of the engine and was pre-mixed as port fuel injection (PFI). Tests were performed at a constant engine load (10.8 kW) and engine speed of 1500 rpm. The purpose of using diesel and biodiesel mixtures is to increase the reactivity of the primary fuel that facilitates the start of the combustion. The combustion, performance and emissions, which are the most important parameters of the engine operation, have been thoroughly investigated and the results were presented. In RCCI application, in peak values of pressure, velocity of heat release, average gas temperature partial increases were determined. When the ratio of gasoline PFI was increased, the NOx emissions significantly decreased and the engine efficiency was also increased, while the CO and HC emissions were slightly increased.
High Efficiency Sub-critical Carbon Dioxide Supplementary Heat Pump for Low Temperature Climates (Energy and Exergy Analysis) Renew. Energy (IF 4.9) Pub Date : 2018-10-06 M. Purjam, K. Goudarzi
Nowadays heat pumps are crucial elements of air conditioning systems and still gaining popularity, but they suffer from limitations in very cold climates such as low coefficient of performance (COP) and air leaking. Recently-developed trans-critical CO2 heat pumps are proper replacements for their (H)CFC counterparts, especially in environmental concerns, but they have not answered the temperature limitations yet. The temporal solution is to bridge the temperature gap between low temperature ambient air (lower than -15°C) and normal operating temperature of heat pump (about 0°C) by intermediate systems such as supplementary heaters or geothermal sources. The main idea of this study is to define a highly-efficient heat pump instead of intermediate systems. Consequently, instead of a heat pump with auxiliary heater, there is a cascade of heat pumps which operates properly in very cold climates. In this regard, two sub-critical CO2 heat pumps were studied. One uses expansion valves and another utilizes expanders. COPs more than 3.7 were obtained in -40°C. Using the first and second laws of thermodynamics, analyses on the performance characteristics of the cycles were carried out. Also, a parametric study was conducted to optimize the performance of each cycle under various operating conditions. The results show that these cycles perform properly in both energy and exergy points of view and expander increases COP and reduces lost exergy. Inter-stage pressure and performance of internal heat exchanger were studied and optimal values were extracted. Lastly, a thermo-economic comparison between the purposed cycles and conventional fossil fuel heating systems were done. The findings show that this sub-critical CO2 heat pump can make a conventional heat pump to remain functional at low temperatures without any significant fall in COP.
Variable speed wind turbine control scheme using a robust wind torque estimation Renew. Energy (IF 4.9) Pub Date : 2018-10-04 Oscar Barambones, Jose A. Cortajarena, Isidro Calvo, Jose M. Gonzalez de Durana, Patxi Alkorta, A. Karami-Mollaee
This work proposes a robust controller for a variable speed wind turbine system with a doubly feed induction generator. The controller aims at tracking the optimal speed of the wind turbine so that extracts the maximum power from the wind. Also, a robust aerodynamic torque observer is proposed in order to avoid the use of wind speed sensors. This torque observer allows to estimate the aerodynamic torque to be used by the controller in order to calculate the value of the optimal reference speed for the wind turbine. The vector control theory is applied in the present approach, and thereby the stator flux-oriented control is used for controlling the speed of the wind turbine generator. The proposed robust control law is based on sliding mode control theory, which has proved to provide good performance under system uncertainties.The stability of the proposed controller under disturbances and parameter uncertainties has been analyzed using the Lyapunov stability theory. Finally, real time experimental results show that, on the one hand, the proposed controller provides high-performance dynamic characteristics, and on the other hand, this scheme is robust with respect to the uncertainties that usually appear in this kind of systems.
Energy Efficient Design of High Depth Raceway Pond using Computational Fluid Dynamics Renew. Energy (IF 4.9) Pub Date : 2018-10-05 S.S. Sawant, S.N. Gosavi, H.P. Khadamkar, C.S. Mathpati, Reena Pandit, A.M. Lali
Open Raceway Ponds (RWP) are at present the most used large-scale reactors for microalgae culture. RWPs are extensively applied technology for algae mass cultivation although the scientific design of these ponds remains a major hurdle in this field. An erroneous design result in the presence of dead zones where the fluid flow is sluggish and non-uniform velocity throughout the pond actualized negative impact on algae growth, further these designs are energy inefficient. A dominant component of energy loss is the energy required to circulate the fluid around the raceway, particularly at the 180° bends. This paper investigates effects of various ratio of channel length to width (L/W) and position of side entry axial flow impeller (distance from the bottom of the tank) on the hydrodynamics in RWP. To curtail the dead zone, power consumption, shear stress and enhance surface renewal, the different designs of RWPs with flow deflectors and different types of central baffles were investigated by using Computational Fluid Dynamics (CFD). The CFD model was validated through Particle Image Velocimetry (PIV) tests. A feasible move headed for energy optimization and thus reduction in operational cost can be established through a better understanding of the mixing phenomena by CFD simulations.
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