Exergetic and thermo-ecological assessment of heat pump supported by electricity from renewable sources Renew. Energy (IF 4.9) Pub Date : 2018-07-19 Wojciech Stanek, Tomasz Simla, Wiesław Gazda
Heat pumps (HP) represent an attractive option as a heat source, since they utilise “free” ambient heat. However, as they need to be driven by electric energy, their ecological efficiency depends not only on their performance, but also on the energy mix used for electricity generation. Effectiveness of HP can be improved by applying renewable energy sources (RES) providing electricity to drive the system. In order to properly assess such a system, it should be evaluated within a global balance boundary reaching the level of primary resources. The authors propose the use of thermo-ecological cost (TEC) indices for exergo-ecological assessment. TEC is defined as cumulative consumption of non-renewable exergy connected with the fabrication of a particular product. TEC also includes additional consumption of non-renewable natural resources which results from the necessity of compensating environmental losses caused by rejection of harmful substances to the environment. Within the paper, a HP system has been analysed from the ecological point of view. The system consists of a heat pump driven by electricity, and photovoltaic panels or wind turbines as a basic source of electricity. The balance of electricity demand for HP is complemented by electricity from grid. To evaluate this system, real environmental data on solar radiation, wind and ambient temperature deciding on heat demand have been taken into account. The authors present the ecological benefits resulting from supporting heat pumps by electricity generated in RES. It has been demonstrated by comparing results obtained within local and global balance boundaries, that the second approach should be consequently applied when systems based on a mix of renewable and non-renewable energy are analysed, since the first approach may lead to misleading conclusions.
Co-gasification of coal and biomass blends using dolomite and olivine as catalysts Renew. Energy (IF 4.9) Pub Date : 2018-07-19 Xinyue Ma, Xue Zhao, Jiyou Gu, Junyou Shi
Natural catalysts (dolomite and olivine) not only reduce the tar content, they also have a high potential to enhance hydrogen production during gasification process. In this study, a bubbling fluidized bed (BFB) was used to evaluate the effect of the operating parameters on co-gasification of pine sawdust and brown coal namely gasification temperature (Tg) in the range of 700–1000 ◦C, fuel particle size (dp) in the range of 2.0–3.5 mm, steam/fuel ratio (S/F) in the range of 0.5-0.8, equivalence ratio (ER) in the range of 0.1–0.4, biomass ratio (BR) in the range of 0.0-100 %, and catalyst loading in the range of 3.0 -12.0 wt%. With increase in catalyst loading from 3.0 to 12.0 (wt %), the hydrogen yield was increased from 52.9 to 55.5 (g/kg-fuel) for dolomite and from 47.5 to 52.1 (g/kg-fuel) for olivine, while the tar yield sharply decreased from 5.4 to 0.4 (g/Nm3) and from 7.0 to 0.8 (g/Nm3), respectively. Fuel particle size showed a negligible influence on the upgrading of hydrogen production and tar yield.
Elemental, Morphological and Thermal Analysis of Mixed Microalgae Species from Drain Water Renew. Energy (IF 4.9) Pub Date : 2018-07-19 Nazia Hossain, Juliana Zaini, T.M.I. Mahlia, Abul K. Azad
In this study, Stigonematales sp. microalgae were collected from drain water and characterized for its’ morphological edifice, elemental composition, thermal condition and energy generation capacity by using scanning electron microscopy, energy dispersive X-ray, thermogravimetric analyzer and bomb calorimeter, respectively. Scanning electron micrographs revealed the top view of microalgae and ash pellet with carbon coated specimens at low voltage (5.0kV) through the secondary electron image detector. Elemental analysis revealed all the major and minor constituents of this microalgae species and its’ ash in terms of dry weight (%) and atomic weight (%). Thermogravimetric analysis was conducted at heating rate, 10°C/min and this experimental results determined moisture content, volatile matter, ash content and fixed carbon of the sample with 4.5%, 35%, 39.5% and 21%, respectively. Microalgae powder blended with bituminous coal by 75%, 50% and 25% measured calorific value 14.07MJ/kg, 19.88MJ/kg and 26.42MJ/kg, respectively. Microalgae (75%) -coal (25%) blend showed excellent amount of energy content, 24.59MJ/kg. Microalgae blended with coal unveiled an outstanding outcome with elevation of the volatile matter and drop of the ash content. Optimization of microalgae-coal blend in large-scale application can initiate bright future in renewable energy exploration.
A shrinking core model for Nannochloropsis salina oil extraction using subcritical water Renew. Energy (IF 4.9) Pub Date : 2018-07-19 Mohammad H. Eikani, Nahid Khandan, Elnaz Feyzi, Iman M. Ebrahimi
In this study, subcritical water extraction (SCWE) was used for dynamic extraction of crude oil of Nannochloropsis salina. The effect of three parameters including water temperature, flow rate and sample loading on the extraction efficiency was investigated and the whole process was simulated by using a two-phase mathematical model. Water temperature, flow rate and sample loading were varied from 150 to 200 ºC, from 1 to 4 mL/min and from 1 to 4 g, respectively. The best operating conditions were selected to be 175 ºC, 4 mL/min and 1 g and at those conditions, the fatty acids profile was compared with the Folch method. Because of the nature of the biomass and small particle sizes of the cells, a mathematical model based on the shrinking core model (SCM) was developed to evaluate the behavior of the extraction process. Kinetic parameters of the model incl. external film mass transfer coefficient (kf), solute-solvent binary diffusion coefficient (D12), axial dispersion coefficient (Dax) and effective diffusivity (De) in solid particle were determined. The later one was selected as the tuning parameter of the model and the others were attained from available correlations. The model predictions were in good agreement with experimental data.
The effects of unsteady wind on the performances of a newly developed cross-axis wind turbine: A wind tunnel study Renew. Energy (IF 4.9) Pub Date : 2018-07-19 Wei-Cheng Wang, Jheng-Jie Wang, Wen Tong Chong
For the purpose of meeting the wind field in urban area, the performances of a newly invented cross-axis wind turbine (CAWT), which consists of the advantages of horizontal and vertical axis wind turbines (HAWTs and VAWTs), was examined in a calibrated open-circuit low speed wind tunnel. Firstly, to ensure the quality of the wind tunnel, the evaluations in accordance with the flow uniformity, turbulent intensity and pressure gradient along the test section were conducted within the wind tunnel, based on the IEC61400-12 standard. Furthermore, the CAWT was tested with and without the artificial turbulence generator for examining the static and dynamic performances within the steady/unsteady wind conditions at various Reynolds numbers, and the blockage inside the wind tunnel was additionally taken into account. The results showed that both the static and dynamic performances were improved with the addition of turbulence generator. Moreover, the payback period of the CAWT was calculated associated with its power performance.
Using Renewables Coupled with Thermal Energy Storage to Reduce Natural Gas Consumption in Higher Temperature Commercial/Industrial Applications Renew. Energy (IF 4.9) Pub Date : 2018-07-19 Rhys Jacob, Martin Belusko, Ming Liu, Wasim Saman, Frank Bruno
In the current study the feasibility of using solar-based renewables coupled with thermal energy storage (TES) to displace gas for heating was explored. To assess the feasibility, a numerical model of an air-based encapsulated phase change (EPCM) storage system was developed, validated, optimised, and economically costed. The optimised air-based EPCM system utilised a high and low melting temperature phase change material (PCM) with a sensible storage filler. It was found that a capsule radius of 10 mm and PCM volume of 13 % resulted in the lowest cost of discharged thermal energy of $25.55/kWh when storage effectiveness and pumping power was considered. This system was then coupled to solar data for Adelaide, South Australia, to simulate the performance of a 1 MWt heat load over a year. By solving an hourly system generation and demand profile, it was found that a concentrated solar thermal (CST) and photovoltaic (PV) system coupled with TES was able to economically reduce gas consumption by 45-65 % when the price of gas was $30/GJ. By employing near-term cost estimates for CST and PV systems coupled with TES, it was found that gas consumption could be reduced by similar amounts with a gas price of $20/GJ.
Equilibrium FCC catalysts to improve liquid products from biomass pyrolysis Renew. Energy (IF 4.9) Pub Date : 2018-07-19 Melisa Bertero, Juan Rafael García, Marisa Falco, Ulises Sedran
A commercial equilibrium FCC catalyst of the octane-barrel type was subjected to lixiviation treatments with both acidic (HNO3) and basic (NaOH) solutions in order to modify its textural and acidic properties. The alkaline lixiviation doubled the mesopore volume in the commercial catalyst, while the acidic treatment increased the concentration of crystalline component in the catalyst. The catalytic performances of the parent and modified catalysts in the immediate conversion of vapors from pine sawdust fast pyrolysis were evaluated in a fixed bed reactor at 550 ºC using mass catalyst to bio-oil ratios from 3 to 8. The modified catalysts both produced more hydrocarbons and less coke than the parent commercial catalyst. In turn, comparing the modified samples, the one subjected to alkali treatment was more effective in deoxygenating the pyrolysis vapors, resulting in higher hydrocarbon yields (up to 13.2 %) and lower coke yields than the acid modified catalyst, a fact assigned to the higher mesoporosity which improves the diffusion transport of bulky coke precursor molecules. The acid modified catalyst allowed a higher extension of the reaction pathway, the selectivity to aromatic hydrocarbon products being much higher (up to 95.5 % of hydrocarbons in the gasoline boiling range).
Al- Abdaliya Integrated Solar Combined Cycle Power Plant: Case Study of Kuwait, Part I Renew. Energy (IF 4.9) Pub Date : 2018-07-18 Anwar O. Binamer
Kuwait is planning to develop a solar project using a 60 MWe parabolic trough collector in Al- Abdaliya. This will be part of a 280 MWe Integrated Solar Combined Cycle (ISCC) System, which will be the first of its kind and size in Kuwait. The objective of this paper is to develop a mathematical model of a typical ISCC system using Engineering Equations Solver (EES), to evaluate the performance of such commercial ISCC power plants. A sensitivity analysis has been carried out to investigate the effect of selected parameters on the performance of the planned ISCC power plant. Results show that the efficiency of Abdaliya ISCC power plant could reach more than 66% which is 20 to 100% higher than that of the current conventional power plants in Kuwait. The plant output power is also a strong function of solar heat input, it could reach 290 MWe at solar heat input of 75 GJ/s. The annual fuel saving and emissions reduction are more pronounced in case of adding thermal energy storage than that of increasing its solar fraction from 0.2 to 0.3. The expected annual benefits could support the decision-makers to accelerate the adoption of ISCC power plants in Kuwait.
Performance improvement and development of correlation for friction factor and heat transfer using computational fluid dynamics for ribbed triangular duct solar air heater Renew. Energy (IF 4.9) Pub Date : 2018-07-18 Rajneesh Kumar, Anoop Kumar, Varun Goel
Solar air heater (SAH) is a device used to convert sun radiations into heating applications. To improve its performance, the heat absorbing side of SAH is modified with the ribs called roughness. The flow characteristics and augmentation of heat due to square shaped ribs in SAH having triangular cross-sectional passage has been simulated using computational fluid dynamic (CFD) technique. The CFD simulations consisted of design and modeling of SAH. Two different roughness parameters has been considered in the analysis i.e. relative roughness pitch (P/e) and relative roughness height (e/D) and their value ranges from 5 to 13 (in four sets) and 0.013 to 0.05 (in four sets), respectively for Reynolds number varies from 3900-17900. Better augmentation of heat has been seen in SAH by providing ribs on the absorber plate. The highest improvement in heat transfer is seen of the order of 97% in P/e value of 10 and e/D value of 0.05 at Re of 17900. The thermohydraulic performance parameter (TPP) is also calculated and have highest value of 1.97 for P/e value of 10 and e/D value of 0.05 at Re of 17900. Correlation has been developed for both friction factor and Nusselt number based on observed results.
Optimization of the performance of the SnTe uni-leg thermoelectric module via metallized layers Renew. Energy (IF 4.9) Pub Date : 2018-07-18 Xue Wang, Hongchao Wang, Wenbin Su, Jinze Zhai, Teng Wang, Tingting Chen, Fahad Mehmood, Chunlei Wang
We attempt to develop an optimized metallized layer and evaluate the performance for a SnTe uni-leg thermoelectric module by finite-element simulation. The maximum conversion efficiencies of 3.0% and 0.7% have been achieved under ideal and rough contacted thermoelectric modules at ΔT = 600 K. The Ag metal is found to be the optimized metallized layer. The module with metallized Ag layer shows the lowest contact resistance and the best performance. The efficiency reaches about 60% of ideal contacted module. Following that, the pressure forced on module and the surface roughness between the electrode, metallized layer and thermoelectric material have been simulated. With the increase of surface roughness slope, the contact and inner resistances of the thermoelectric module are decreased, and the voltage, maximum output power and efficiency are increased. When the average surface roughness slope is over 0.8, the efficiency reaches 90% of the ideal contacted module. The contact and inner resistances obviously decrease with increasing pressure, while the voltage, maximum output power and efficiency are enhanced. The greater than 90% efficiency of an ideal contacted module is achieved when the pressure is beyond 100 kPa. These simulated results will be beneficial for the fabrication of SnTe-based thermoelectric modules.
Costs and benefits of renewable energy development in China's power industry Renew. Energy (IF 4.9) Pub Date : 2018-07-18 Yuanyuan Liang, Biying Yu, Lu Wang
China's power sector has become the largest contributor to China's carbon emissions because of its coal-dominated power structure. Replacing fossil fuels with renewable energy is an effective way to reduce carbon emissions and, therefore, a series of targets for renewable electricity generation have been put forward in national plans. However, how these targets will be reached is unclear. This paper uses a Long-range Energy Alternative Planning system (LEAP) model to explore the optimum development path of China's power sector from 2015 to 2050, taking into consideration the impacts of the renewable energy targets. Three scenarios are designed to examine the costs and benefits of developing renewable energy and improving the technologies for renewable power generation, comprising a base scenario, a renewable energy policy scenario and a technological progress scenario. The results show that the power generation cost would increase by at least 2.31 trillion RMB and that CO2 emissions would be reduced by 35.8 billion tonnes during 2015–2050 if power generation follows current planning. Furthermore, every 1% increase in the capacity factors of renewable electricity would on average result in the cumulative CO2 emissions decreased by 979 million tonnes and average CO2 abatement cost decreased by 5.56 RMB/tCO2 during 2015–2050. Based on this study, several policy implications are proposed for the development of power sector in China. Firstly, government may reconsider the current planning for gas-fired power and nuclear power to reach low-carbon electricity generation. Secondly, adjusting the carbon price can offset the additional cost of renewable electricity generation. Thirdly, promoting advanced technologies to match renewable electricity generation can obtain greater economic and environmental benefits. Finally, from the perspective of development potential, reducing the costs of solar power would be the emphasis at this stage.
Biodiesel production from Calophyllum inophyllum oil a potential non-edible feedstock: An overview Renew. Energy (IF 4.9) Pub Date : 2018-07-18 A. Arumugam, V. Ponnusami
Utilizing renewable feedstock for the production of alternate fuels is a challenging task. The need for finding a new fuel is gaining importance owing to rapid depletion of fossil-fuel resources and fluctuating crude oil price. Alternate fuel must also be environmental friendly, cheap, technically acceptable and abundant. Biodiesel, eco-friendly alternative liquid fuel, are fatty acid alkyl esters produced by chemical or lipase-catalyzed transesterification of fats or oils. It has both economic and environmental benefits in addition to its renewable origin. Feedstocks such as animal fats and vegetable oils play a vital role in biodiesel production. The demand for biodiesel production from non-comestible oil is growing steadily as there are restrictions on the conversion of edible oils into fuels. Hence, researchers are looking for promising newer sources of non-comestible oil which can sustain biodiesel production and use. These attributes have contributed to growing interest on biodiesel production from Calophyllum inophyllum oil. This study focuses on a promising newer source of non-comestible oil which can sustain biodiesel growth. Various technological options available for the conversion of C. inophyllum oil into biodiesel, their strengths and weaknesses are highlighted. Also, engine performance of the C. inophyllym biodiesel blends is also reviewed.
Transient heat transfer performance of a vertical double U-tube borehole heat exchanger under different operation conditions Renew. Energy (IF 4.9) Pub Date : 2018-07-18 Li Zhu, Sarula Chen, Yang Yang, Yong Sun
The transient thermal performance of a vertical double U-tube borehole heat exchanger (BHE) was numerically studied by validated heat transfer model. Further, the influence of several operation parameters, including inlet velocity, temperature and operation interval, on radial/axial soil temperature distribution were investigated. The simulation result showed that the increased amplitude of the BHE’s heat transfer rate was similar when charging temperature was increased under the same velocity conditions. Meanwhile, the difference of the heat transfer rate between 0.1 and 0.3 m/s was greater than that of the 0.3 and 0.5 m/s when the inlet temperature kept constant. The charging temperature had a more vital influence than the flow velocity on soil temperature lifting, and the flow velocity around 0.3 m/s was recommended under the conditions in this work. Moreover, the heat charging time had a more obvious effect on the heat transfer sensitive zone in the radial direction than the other two parameters. Finally, the choice of charging temperature, appropriate interval, space and depth of borehole were discussed. This study could contribute to the comprehensive understanding of the dynamic thermal behaviour and operation parameter optimization of BHE and its further application in the field of borehole thermal energy storage.
Using high-frequency SCADA data for wind turbine performance monitoring: A sensitivity study Renew. Energy (IF 4.9) Pub Date : 2018-07-19 Elena Gonzalez, Bruce Stephen, David Infield, Julio J. Melero
Intensive condition monitoring of wind generation plant through analysis of routinely collected SCADA data is seen as a viable means of forestalling costly plant failure and optimising maintenance through identification of failure at the earliest possible stage. The challenge to operators is in identifying the signatures of failure within data streams and disambiguating these from other operational factors. The well understood power curve representation of turbine performance offers an intuitive and quantitative means of identifying abnormal operation, but only if noise and artefacts of operating regime change can be excluded. In this paper, a methodology for wind turbine performance monitoring based on the use of high-frequency SCADA data is employed featuring state-of-the-art multivariate non-parametric methods for power curve modelling. The model selection considerations for these are examined together with their sensitivity to several factors, including site specific conditions, seasonality effects, input relevance and data sampling rate. The results, based on operational data from four wind farms, are discussed in a practical context with the use of high frequency data demonstrated to be beneficial for performance monitoring purposes whereas further attention is required in the area of expressing model uncertainty.
Estimates of clear-sky solar irradiances over Nigeria Renew. Energy (IF 4.9) Pub Date : 2018-07-19 T.A. Otunla
This study attempts to circumvent the problem of paucity of input data required in climatology mapping of clear-sky solar irradiance in Nigeria by computing beam normal (Ebn) and diffuse (Ed) irradiances using a high performance broadband radiative model in the country climate zones. Air temperature, relative humidity and global datasets of ozone thickness and angstrom turbidity were used as input parameters. The biases in the Ebn estimates with NASA datasets across Nigeria (11–25%) are of similar magnitudes with NASA observations with ground measurements. The estimates show persistent negative biases that increased from tropical savannah to semi-arid climate zones (−8 to −24%). The bias in the Ed estimates is only of similar magnitude with NASA in semi-arid climate zone (10%). The Ed estimates show persistent negative biases that increase from semi-arid to tropical savannah across Nigeria (−7 to −54%). Also, the estimates in each climate zone correspond to the expected climatology of water vapour, aerosol turbidity and absolute optical mass. Lastly, the response of Ebn to water vapour absorption and aerosol extinction signals is mostly active in monsoon zone while the response to the signals by Ed are active in all the zones.
Design methodology of hybrid turbine towards better extraction of wind energy Renew. Energy (IF 4.9) Pub Date : 2018-07-19 Joe Jacob, Dhiman Chatterjee
Hybrid vertical axis turbines that combine Savonius and Darrieus turbines on a single shaft have been proposed as a way of combining the excellent starting torque of Savonius turbine with the high operational efficiency of the Darrieus turbine. Although hybrid turbines with improved starting characteristics have been demonstrated in literature, the performance of these turbines at higher tip speed ratios have been poor. In this work systematic study of stand-alone Savonius and Darrieus turbines have been carried out using experimental and numerical techniques as a precursor to study their roles in hybrid configuration. The radius ratio of the two turbines, when combined in the form of a hybrid turbine, is identified as an important parameter the dictates the performance of hybrid turbines. An expression for an optimal radius ratio is derived and a methodology for designing hybrid turbines is proposed. The efficiency in energy conversion by hybrid turbine can be expressed in terms of a parameter called effectiveness given by the ratio of power produced by the hybrid turbine to the sum of the power produced by individual Darrieus and Savonius turbines. This idea has been verified through experiments and numerical simulations.
Numerical investigation of modeling frameworks and geometric approximations on NREL 5 MW wind turbine Renew. Energy (IF 4.9) Pub Date : 2018-07-19 M. Salman Siddiqui, Adil Rasheed, Mandar Tabib, Trond Kvamsdal
The key to the better design of an industrial scale wind turbine is to understand the influence of blade geometry and its dynamics on the complicated flow-structures. An industrial-scale wind turbine can be numerically represented using various approaches (from simpler 2 D steady flow to complex 3 D with moving mesh, with and without the inclusion of hubs) that can alter the results substantially. At the same time, to standardize and test methodologies, the reference industrial-scale NREL 5 MW wind turbine is gaining popularity. The wind energy community will learn through an improved understanding of the aerodynamics of this NREL 5 MW reference mega-watt size wind turbine by taking into consideration the various levels of geometric approximations. Hence, in this work the NREL 5 MW reference wind turbine is used for both: (a) understanding the associated flow-complexities due to various geometric approximation, and (b) comparison and validation of the performance of different numerical approaches for flow-simulation. The various geometric approximations considered here are related to simulating the influence of the shape of turbines structure (blade, an inclusion of hub, tower) and motions of blades. It involves (a) influence of 2D, 2.5D and 3D turbine blade geometry to highlight the impact of section bluntness, (b) influence of steady frozen rotor and rotating rotor simulations and (c) influence of inclusion of hub through a full-scale geometry of the complete reference turbine. Furthermore, the key features of the flow dynamics of a rotor and full machine are identified and parametric studies are conducted to evaluate overall performance prediction under variable Tip Speed Ratios (TSR = 6, 6.5, 7, 7.5, 8, 8.5, 9) and variable level of geometric and flow modeling approximations.
Efficient workflow for simulation of multifractured enhanced geothermal systems (EGS) Renew. Energy (IF 4.9) Pub Date : 2018-07-19 Pranay Asai, Palash Panja, John McLennan, Joseph Moore
The increasing demand for clean energy with minimum environmental impact motivates development of geothermal energy. Simulating a geothermal reservoir is complex and time consuming, mainly because of the systems spatial and temporal non-isothermal nature and the enormous size of the domain/reservoir. Simulations become even more complex when representing Enhanced Geothermal Systems (EGS), where wells in a hot, low permeability reservoir are interconnected by hydraulic fracturing to provide pathways for injection of cold water, in situ heating, and consequent production of hot water. In this study, various issues related to simulation of enhanced geothermal systems are investigated and practical solutions are proposed. A comprehensive study was conducted to show the effect of different grid systems on predictions of the transient temperature of the produced water. It is shown that the performance of an EGS is affected by the transmissivity (product of permeability and width of the fracture) of the fracture more so than by the values of permeability and width of the fracture considered individually. A simplified model (downscaled model) reduces the simulation times significantly (by 1.5–14.5 times) without compromising the accuracy of the results. In the proposed model, only two simulations - capturing small portions of the top and bottom of a reservoir with two active hydraulic fractures is used to evaluate performance of the entire reservoir. The proposed model is proved to be robust when exposed to different scenarios created by varying the inclination of the wells with respect to horizontal, spacing of the hydraulic factures, and spacing between the injection and producing wells. Value of R2 close to unity (0.96–1.0) and smaller value of MAPE (Mean Absolute Percentage Error), less than 3% in comparison to the entire reservoir simulations, indicate the utility of proposed model.
A mechanism investigation of synergy behaviour variations during blended char co-gasification of biomass and different rank coals Renew. Energy (IF 4.9) Pub Date : 2018-07-18 Juntao Wei, Yan Gong, Qinghua Guo, Xueli Chen, Lu Ding, Guangsuo Yu
Co-gasification reactivity of rice straw and bituminous coal/anthracite blended chars under CO2 atmosphere was evaluated using thermogravimetric analysis, and the influences of coal type and gasification temperature on synergy behaviour variations on co-gasification reactivity as carbon conversions increased were quantitatively studied. Furthermore, active AAEM transformation characteristics at different co-gasification conversions were quantitatively analyzed for revealing co-gasification synergy mechanism. The results demonstrate that as conversions increased, synergy behaviour on co-gasification reactivity of rice straw-bituminous coal blends was shown as the weakened inhibition effect firstly and then the enhanced synergistic effect. Moreover, the inhibition effect on co-gasification reactivity of rice straw-bituminous coal blends was sustained up to higher conversion with the increment of gasification temperature. Differing from rice straw-bituminous coal blends, synergistic effect on co-gasification reactivity of rice straw-anthracite blends was obviously enhanced at early stage of co-gasification and started to slowly weaken after reaching the most significant synergistic effect at middle stage of co-gasification. Additionally, it was revealed that synergy behaviour variations on co-gasification reactivity of rice straw-bituminous coal blends were mainly attributed to the combination effects of active K and Ca transformation during co-gasification, while those of rice straw-anthracite blends indicated a good correlation with active K transformation during co-gasification.
Competitive Advantage in the Renewable Energy Industry: Evidence from a Gravity Model Renew. Energy (IF 4.9) Pub Date : 2018-07-17 Onno Kuik, Frédéric Branger, Philippe Quirion
Pioneering domestic environmental regulation may foster the creation of new eco-industries. These industries could benefit from a competitive advantage in the global market place. This article examines empirical evidence of the impact of domestic renewable energy policies on the export performance of renewable energy products (wind and solar PV). We use a gravity model of international trade with a balanced dataset of 49 (for wind) and 40 (for PV) countries covering the period 1995-2013. The stringency of renewable energy policies is proxied by installed capacities. Our econometric model shows evidence of competitive advantage positively correlated with domestic renewable energy policies, sustained in the wind industry but brief in the solar PV industry. We suggest that the reason for the dynamic difference lies in the underlying technologies involved in the two industries.
Saturation characteristics for stability of hydro-turbine governing system with surge tank Renew. Energy (IF 4.9) Pub Date : 2018-07-17 Zhiyuan Peng, Wencheng Guo
This paper aims to study the saturation characteristics for stability of hydro-turbine governing system with surge tank. Firstly, the mathematical model of hydro-turbine governing system under load disturbance is established, and the equivalent independent stability discriminants are presented. Then, the saturation characteristics for stability are analyzed. Using analytical stability discriminants and stable domain, the generation mechanism of saturation characteristics is revealed, and a distinguishing method of critical saturation state is proposed. Finally, the concept of saturation sectional area of surge tank is proposed. The distribution and partition for stability states is illustrated, and a combined tuning method of sectional area of surge tank and governor parameter is proposed. The results indicate that, for hydro-turbine governing system with surge tank, the fourth-order discriminant boundary is always the critical boundary of stable domain. The second-order and third-order discriminant boundaries determine the stable domain under saturation state. The equality for fourth-order discriminant has two real solutions when the system is saturated. The saturation sectional area of surge tank is the sectional area that makes the system reach critical saturation state. Domain C of the distribution and partition figure for stability states is the most favorable domain for the system stability.
Modeling residential adoption of solar energy in the Arabian Gulf Region Renew. Energy (IF 4.9) Pub Date : 2018-07-17 Nassma Mohandes, Antonio Sanfilippo, Marwa Al Fakhri
We present an agent-based model for residential model adoption of solar photovoltaic (PV) systems in the state of Qatar as a case study for the Arabian Gulf Region. Agents in the model are defined as households. The objective of the model is to evaluate PV adoption across households under diverse regulatory and incentive scenarios determined by home ownership status, the falling cost of PV, the reduction of electricity subsidies, the introduction of a carbon tax, and the diffusion of renewable energy innovation. Our study suggests that Qatar's residential PV adoption is strongly promoted by the falling cost of PV and can be further facilitated through the reduction of electricity subsidies and the extension of the electricity tariff to Qatari households, which are currently exempt. The introduction of a carbon tax can also play a role in accelerating residential PV adoption, if above $8 per metric ton of carbon dioxide equivalent. The ensuing PV adoption rates would help facilitate the national targets of 2% electricity production from solar energy by 2020 and 20% by 2030.
Investigation on effect of indoor air distribution strategy on solar air-conditioning systems Renew. Energy (IF 4.9) Pub Date : 2018-07-17 K.F. Fong, C.K. Lee, Z. Lin
Stratum ventilation (SV), a new indoor air distribution strategy, has been promoted for applications in different building premises in recent years. Compared to the conventional mixing ventilation (MV), the prominent advantage of SV is that indoor thermal comfort can be satisfied with a relatively high supply air temperature, hence less energy consumption in refrigeration. In solar air-conditioning, the energy performance can also be facilitated by high-temperature cooling. As such, the potential of SV to be involved in solar air-conditioning was evaluated. In this study, the solar air-conditioning systems included solar absorption cooling system (SAbCS), solar adsorption cooling system (SAdCS), solar desiccant cooling system (SDCS), hybrid solar absorption-desiccant cooling system (HSAbDCS) and hybrid solar adsorption-desiccant cooling system (HSAdDCS). Their performances using SV and MV were determined through year-round dynamic simulation. Compared to the counterpart using MV, SAbCS, SAdCS, SDCS, HSAbDCS and HSAdDCS associated with SV could have 35%, 54%, 59%, 29% and 44% saving in the annual primary energy consumption for building in subtropical climate respectively. Benchmarked with the conventional air-conditioning system, they could have primary energy saving up to 30%. Consequently, solar air-conditioning and SV can have synergetic merit in building application in hot and humid city.
Multi-unit renewables auctions for small markets designing the Danish multi-technology auction scheme Renew. Energy (IF 4.9) Pub Date : 2018-07-17 Marijke Welisch
This paper investigates different criteria for the design of multi-unit renewable energy (RES) auctions in small markets. The multi-technology RES auctions which are to be implemented in Denmark in 2018 serve as an exemplary case for the assessment. Focus of the analysis is how setting the auction schedule and the auctioned volume per round impacts the auction outcomes, accounting for the particular challenges of small markets. Agent-based modelling of the Danish auctions scheme demonstrates that the Danish RES market provides sufficient competition to auction higher volumes and follow more ambitious expansion goals. Furthermore, with a fixed budget, it is more effective in terms of deployment achieved, to hold fewer auctions with a larger volume. A flexibility mechanism that allows up to 50% of the auction volume to be shifted between auction rounds to accommodate potential large-scale marginal bidders, proves to be a useful tool to increase deployment rates, without negatively affecting bid prices. Furthermore it was shown that at current cost levels, only onshore bidders would be awarded in the envisaged multi-technology scheme. Also, large-scale and multi-project bidders are likely to be most cost competitive - indicating that further measures to maintain diversity could be useful.
What affects the development of renewable energy power generation projects in China: ISM analysis Renew. Energy (IF 4.9) Pub Date : 2018-07-17 Zhen-Yu Zhao, Yu-Long Chen, Heng Li
Developing renewable energy power generation projects (REPGPs) is significant to promote energy and environment sustainability. This study explores the inter-relationship amongst representative factors (RFs) affecting the development of REPGPs in China. Through literature survey, 43 factors affecting the development of REPGPs are identified. A questionnaire survey, targeting practitioners involved in the renewable energy (RE) industry is conducted for the relative importance of these factors. The survey data were processed by principal component analysis, and as a result, 16 RFs are obtained. Interpretive Structural Modeling (ISM) is adopted to establish a hierarchy structure to illustrate the intricate interrelationships among the RFs. They are classified into four clusters, i.e. autonomous factors, dependent factors, linkage factors, and driving factors by applying the Matrice d’Impacts croises-multipication appliqué a classement (MICMAC) technique to demonstrate their driving force and dependence power for REPGPs. Distribution of the RFs in the ISM and the driving force and dependence power diagram found that economy and urbanization development, incentive policy system, and government policy implementation are three most important factors. The results help both project developers and policy makers to understand the impact of forces on the development of REPGPs, resulting in better investment decisions and more targeted policies.
Bio-crude oil production from a new genotype of Miscanthus sacchariflorus Geodae-Uksae 1 Renew. Energy (IF 4.9) Pub Date : 2018-07-17 Sang Kyu Choi, Yeon Seok Choi, So Young Han, Seock Joon Kim, Tawsif Rahman, Yeon Woo Jeong, Quynh Van Nguyen, Young Rok Cha
A new genotype of Miscanthus sacchariflorus Geodae-Uksae 1, which was recently collected from damp land in South Korea, was pyrolyzed in a bubbling fluidized bed reactor for bio-crude oil production. Comparing to woody biomass this has a remarkably economic advantage of very low water content, because it is collected after naturally dried in autumn. This biomass was ground and sieved to acquire the fine size less than 1 mm and fed into the reactor with feeding rate of 200 g/hr continuously. Four reactor temperatures, 400, 450, 500, and 550 °C were set to investigate the optimal temperature for highest bio-crude oil yield and quality. Proximate and ultimate analyses were done for both biomass and bio-crude oil to scrutinize the property change during the fast pyrolysis. Experimental results showed that the maximum bio-crude oil yield was obtained to be 51.88 wt% at the pyrolysis temperature of 500 °C. The maximum higher heating value (HHV) of bio-crude oil was determined to be 15.88 MJ/kg at 400 °C, which was similar to the original biomass. At the pyrolysis temperature of 400 °C, the moisture content of bio-crude oil was 19.46 wt% which was increased by 8.61 wt% than the original biomass. Overall fuel properties of miscanthus sacchariflorus Gedae-Uksae 1 was thought to be similar to the general woody bio-crude oil.
Effect of waves on the leading-edge undulated tidal turbines Renew. Energy (IF 4.9) Pub Date : 2018-07-17 Weichao Shi, Mehmet Atlar, Rosemary Norman, Sandy Day, Batuhan Aktas
This paper presents an investigation on the efficiency performance of the leading-edge undulated tidal turbine blades under the effect of waves. This biomimetic blade application is inspired by humpback whale flippers which provide these mammals with an exceptional manoeuvring ability that is mainly accredited to the beneficial of their leading-edge tubercles. The paper first presents the design, optimisation and experimental validation of these turbine models. With the aim of further validating the efficiency performance in a different testing environment as well as exploring the combined effect of the tidal current and wave interaction, a test campaign in a towing tank facility was conducted. Both regular and irregular wave conditions were considered combining with varying towing speeds to simulate the tidal current effect. The test results revealed that the leading-edge undulated turbine has a stable hydrodynamic performance over a combined range of current speeds and waves indicating that the overall performance was not affected considerably by the combined effects as opposed to the performance solely due to steady tidal current.
The effect of electricity markets, and renewable electricity penetration, on the levelised cost of energy of an advanced electro-fuel system incorporating carbon capture and utilisation Renew. Energy (IF 4.9) Pub Date : 2018-07-17 Shane McDonagh, David M. Wall, Paul Deane, Jerry D. Murphy
Power-to-Gas (P2G) is a technology that converts electricity to gas and is termed gaseous fuel from non-biological origin. It has been mooted as a means of utilising low-cost or otherwise curtailed electricity to produce an advanced transport fuel, whilst facilitating intermittent renewable electricity through grid balancing measures and decentralised storage of electricity. This paper investigates the interaction of a 10MWe P2G facility with an island electricity grid with limited interconnection, through modelling electricity purchase. Three models are tested; 2016 at 25% renewable electricity penetration and 2030 at both 40% and 60% penetration levels. The relationships between electricity bid price, average cost of electricity and run hours were established whilst the levelised cost of energy (LCOE) was evaluated for the gaseous fuel produced. Bidding for electricity above the average marginal cost of generation in the system (€35-50/MWeh) was found to minimise the LCOE in all three scenarios. The frequency of low-cost and high-costs hours, analogous to balancing issues, increased with increasing shares of variable renewable electricity generation. However, basing P2G systems on low-cost (less than €10/MWeh) hours alone (999 hours in 2030 at 60% renewable penetration) is not the path to financial optimisation; it is preferential to increase the run hours to a level that amortises the capital expenditure.
Dynamic response analysis of Darrieus wind turbine geared transmission system with unsteady wind inflow Renew. Energy (IF 4.9) Pub Date : 2018-07-17 Imen Bel Mabrouk, Abdelkhalak El Hami
Most of the wind turbines analysis studies have been conducted under steady and uniform wind conditions. The unsteady flow past rotating rotor blades is, however, one of the most challenging applications for a numerical simulation. This is attributed to the existing aerodynamic complexities under such conditions. In this paper, a numerical approach to investigate the global dynamic behaviour of a Darrieus turbine under unsteady and non-uniform flow conditions is proposed. The dynamic response of Darrieus wind turbine geared system operating in fluctuating inflow present a more significant challenge for this approach. In this work, unsteady Computational Fluid Dynamic simulation is used to investigate the aerodynamic performance. Using the validated numerical model, unsteady wind inflow performance that affects the aerodynamic performance and the bevel gear dynamic response is conducted. The present results show that the dynamic behaviour of the Darrieus turbine geared system is strongly affected by the fluctuating inlet velocity. As such, a change in the inlet velocity results in the entire response changing in both the aerodynamic performance and the dynamic vibration of the studied wind turbine. The study results will hopefully be of importance to wind industries that require designs of VAWTs operating in unsteady winds condition.
Bill Saving Analysis of Rooftop PV Customers and Policy Implications for Thailand Renew. Energy (IF 4.9) Pub Date : 2018-07-17 Aksornchan Chaianong, Sopitsuda Tongsopit, Athikom Bangviwat, Christoph Menke
Since a new policy supporting rooftop photovoltaics (PV) will be launched in Thailand, this study investigates the economics of utility customers’ investments in rooftop PV (values of bill savings) for four customer groups (residential scale, small general service, medium general service and large general service) across electricity tariffs, PV-to-load ratios and compensation schemes (net metering and net billing). The values of the bill savings of all groups are higher under the conditions of higher buyback rates/credit, lower PV-to-load ratios, and higher retail rates. Under the current retail rate design, the values of the bill savings of residential and small general service groups are slightly higher than those of medium and large general service groups, since there are demand charges for the latter two groups that cannot be completely avoided using rooftop PV. Load shapes do not significantly impact the values of the bill savings for all customer groups. Additionally, net metering causes a smaller variation in bill savings as compared to net billing, implying more flexibility for the customers to size their PV systems over a broader range. In contrast, net billing would encourage customers to limit their PV sizes, thereby mitigating the concerns of the utilities.
Decentralized solar rooftop photovoltaic in India: On the path of sustainable energy security Renew. Energy (IF 4.9) Pub Date : 2018-07-17 Pushpendra Kumar Singh Rathore, Durg Singh Chauhan, Rudra Pratap Singh
In India, utility-scale power plants face problems like, availability of larger land, Transmission & Distribution losses (T&D), Aggregate Technical & Commercial losses (AT&C) and availability of the grid because of which around 240 million of people do not have access to electricity. Increasing installed capacity of fossil-based power plants to meet the power requirement will increase the greenhouse gas emissions, our dependency on fossil fuels, adverse environmental and social impacts. Decentralized solar rooftop PV system, because of its proven technology and environmental benefits, will overcome these factors in a sustainable way. The growth and development of solar rooftop PV, as per the current status, are of substandard level despite the fact that the Government of India has set a target of installing 40 GW of decentralized solar rooftop PV up-to 2022. Therefore, this paper highlights the solar power policies adopted for the decentralized solar rooftop PV segment along with various business models adopted and current status in India. The author has also analyzed various factors which motivate the end consumer to invest in solar rooftop PV. At the end, the author has summarized some key barriers to the growth and development of the solar rooftop PV segment in India.
Comparative analysis of liquid versus vapor-feed passive direct methanol fuel cells Renew. Energy (IF 4.9) Pub Date : 2018-07-17 Mohammad Ali Abdelkareem, Anis Allagui, Enas Taha Sayed, M. El Haj Assad, Zafar Said, Khaled Elsaid
Passive direct methanol fuel cells (pDMFCs) have several advantages such as high theoretical energy density, quick refueling and environmentally safe. However, methanol crossover (MCO) is one of the major challenges to the commercialization of pDMFCs. Significant progress has been achieved over the last few years in controlling MCO through different approaches, such as applying porous plate, pervaporative membranes, and so forth. These methods are mainly based on supplying methanol to the anode surface in vapor phase. Thus, two types of pDMFCs are available: low methanol concentration (liquid-feed pDMFC) and high methanol concentration (vapor-feed pDMFC). The methanol and water transports are different in these two types of cells. Moreover, under low operating temperature and at high methanol concentration (i.e., above 50 mol%) in the vapor-feed pDMFC, the possibility for chemical intermediate to form increases. Such intermediates not only decrease the efficiency of the cell but are also harmful for the health and the environment. The aim of this review is to highlight and clarify the differences between liquid and vapor-feed pDMFCs. Moreover, the mechanism of intermediates formation in vapor-feed pDMFC and the different approaches to controlling it are presented. Finally, we present recommendations for designing safe and high performance pDMFCs.
A comprehensive exergy analysis of a prototype Peltier air-cooler; experimental investigation Renew. Energy (IF 4.9) Pub Date : 2018-07-17 Hamed Sadighi Dizaji, Samad Jafarmadar, Shahram Khalilarya, Samira Pourhedayat
Thermoelectric coolers have been abundantly investigated from the viewpoint of the first law of thermodynamic. However, extremely few exergy analysis have been probed for thermoelectric air-coolers. Because of the importance of exergy consideration in each thermodynamic process, this paper experimentally focuses on the effect of various parameters on exergy destruction and the second law performance through a thermoelectric air cooler. The effects of flow and thermodynamic parameters including air flow rate, incoming air temperature, water flow rate, incoming water temperature, DC voltage/ampere etc. on exergetic characteristics are clarified in this study. Interesting meaningful curve behavior was observed for exergetic performance of thermoelectric cooler. Indeed, curve behavior of exergetic performance is descending-ascending and therefore a critical value of DC voltage was found in which the amount of second law performance has a minimum/maximum value. Increment of air flow rate improved the exergetic performance of Peltier-air cooler. Besides, higher air inlet temperature reduced exergy destruction of thermoelectric module (TEM) which means that Peltier air cooler is appropriate for regions with warmer weather in comparison with moderate climates.
Analysis of Direct Interconnection Technique for Offshore Airborne Wind Energy Systems under Normal and Fault Conditions Renew. Energy (IF 4.9) Pub Date : 2018-07-17 Mahdi Ebrahimi Salari, Joseph Coleman, Daniel Toal
Direct interconnection is a novel technique for interconnecting offshore airborne wind energy (AWE) generators which facilitates the removal of power converters from the offshore generation site. In this technique, unlike the conventional approach, all generators are interconnected directly and after dispatching the generated power to shore, a back to back converter or several paralleled back to back converters change the generated power to grid-compliant power. Considering that the high expenses of offshore operations for back to back converter repair and maintenance and the higher accessibility of shore-side back to back converters, this technique can improve the reliability and economy of the energy generation system. This research aims to implement and study the practicality and reliability of the direct interconnection approach for offshore non-reversing pumping mode airborne wind energy generator systems. The interaction of direct interconnected AWEs in normal and fault conditions is investigated, and synchronisation, frequency control and load sharing control of the AWE farm are examined and discussed.
A New Distributed Energy System Configuration for Cooling Dominated Districts and The Performance Assessment Based on Real Site Measurements Renew. Energy (IF 4.9) Pub Date : 2018-07-17 Jing Kang, Shengwei Wang, Chengchu Yan
In this paper, a new configuration of distributed energy system (DES), which integrates a district cooling system, is proposed as a new energy-efficient technology to be used in cooling dominated districts. An optimal design approach is developed for DES design and operation scheduling by using the real site measurements of energy demands. A case study on the DES in a high density district, i.e., a university campus in Hong Kong, is performed. The energy and economic performance of the DES, the matching performance of on-site generations and the efficiency of electric chillers are analyzed and compared with that of the centralized energy system (CES). It can be found that the proposed DES is a cost-effective and energy-efficient technology for the regions concerned. The DES contributes to substantial primary energy saving of 9.6% and a significant reduction in the operating cost of 44%. The distributed generations in the DES can match electricity demand very well around the year while the absorption chillers can match cooling demand well in transition months. Compared with the CES, the DES allows electric chillers of larger capacities to be used and to operate at higher part load ratios, resulting in higher energy efficiency in operation.
Performance and stability of semitransparent OPVs for building integration: A benchmarking analysis Renew. Energy (IF 4.9) Pub Date : 2018-04-03 D. Chemisana, A. Moreno, M. Polo, C. Aranda, A. Riverola, E. Ortega, Chr. Lamnatou, A. Domènech, G. Blanco, A. Cot
Semitransparent (ST) organic photovoltaics (OPVs) are demonstrating great potential for building integration applications, especially in windows. For that purpose, ST-OPVs should achieve adequate transparency and performance stability. In this regard, the present research deals with the experimental performance of three different building-integrated ST-OPV technologies (technology A: developed in the frame of the present study; technologies B and C: commercial modules). More specifically, spectral transmittance and electrical measurements have been conducted in order to determine the characteristics of the modules for building integration and electricity generation purposes. Results regarding the transmittance reveal that technology A outperforms technologies B and C. The stability analysis of the modules verifies that module C is the most stable one with almost no decrease (3.6%) in the power conversion efficiency (PCE). Furthermore, the PCE of technology B is slightly higher than in the case of technology C, which experiences a PCE degradation of about 10–15% over the whole time period. Finally, technology A presents a 20% reduction in PCE at around 500 h.
Experimental performance characterisation of a Hybrid Photovoltaic/Solar Thermal Façade module compared to a flat Integrated Collector Storage Solar Water Heater module Renew. Energy (IF 4.9) Pub Date : 2018-04-07 M. Smyth, A. Pugsley, G. Hanna, A. Zacharopoulos, J. Mondol, A. Besheer, A. Savvides
A modular Hybrid Photovoltaic/Solar Thermal (HyPV/T) Façade technology that utilizes Integrated Collector Storage (ICS) solar technology, providing cost effective solar PV and thermal energy collection for direct use in the building, whilst providing significant thermal insulation has been developed and evaluated experimentally at Ulster University. The HyPV/T system, based upon a patented ICS solar thermal diode concept and shaped into a flat modular profile incorporating PV cells/module can provide space heating, domestic water heating and power generation. The complete system is designed to be compatible with traditional façade structures and fenestration framing arrangements, facilitating direct integration into new and retrofit building applications.The experimental performance of HyPV/T unit has been determined and compared with a flat Integrated Collector Storage Solar Water Heater (ICSSWH) under constant indoor solar simulated conditions. The daily thermal collection efficiencies for the ‘traditional’ flat ICSSWH units performed better than the unglazed HyPV/T, by 5–10%. However, when the additional electrical power produced by the HyPV/T is included, the overall system collection efficiencies are more equal. The heat retention performance shows that's the unglazed (bare) ICS unit had a retention efficiency of 8.3% whilst the ICS unit with a single transparent cover was 23.6% and double glazed unit was 28%. The HyPV/T heat retention efficiencies were approximately 65% over the same cool-down period.
Environmental and cost life cycle analysis of the impact of using solar systems in energy renovation of Southern European single-family buildings Renew. Energy (IF 4.9) Pub Date : 2018-04-12 Ricardo Mateus, Sandra Monteiro Silva, Manuela Guedes de Almeida
Nowadays, in the European Union (EU) the construction rate of new buildings is very low and therefore achieving the EU targets regarding the energy efficiency of the building sector is only possible through the reduction of the energy needs of the existing building stock. A building design based on passive measures is a priority to reduce operational energy consumption but it is not enough to achieve the nearly Zero Energy Building (nZEB) level. Consequently, the design must also consider active systems with high efficiency and the use of renewable energy sources to partially/totally replace the use of non-renewable energy. At this level, solar thermal and photovoltaic panels play an important role, mainly in countries with high levels of solar radiation, as in the Southern European countries. Nevertheless, there are still some barriers to overcome for the broader dissemination of the implementation of these systems. One of the most important is that building owners are not fully aware of the life cycle benefits that these systems have at environmental and economic levels. The best way to raise awareness to these benefits is through the analysis of case studies, highlighting the short or mid-term benefits resulting from the integration of these active solutions. Thus, this paper is aimed at analysing the environmental and life cycle costs of different energy renovation scenarios, assessing the contribution of the solar systems to achieve three levels of energy performance. The study is focused on the energy renovation of a detached single-family house considering the climatic conditions of Porto, Portugal. From the results, it is possible to conclude that, on an annual basis, and for the Portuguese climate, it is possible to overcome, many of the energy needs for acclimatization and preparation of domestic hot water with the integration of these systems. The study also shows attractive economic and carbon payback times resulting from their use.
Description and performance analysis of a flexible photovoltaic/thermal (PV/T) solar system Renew. Energy (IF 4.9) Pub Date : 2018-04-25 Antonio Gagliano, Giuseppe M. Tina, Francesco Nocera, Alfio Dario Grasso, Stefano Aneli
The main objectives of the present paper are to describe a pilot cogenerative PV/T plant and discuss its preliminary electrical and thermal experimental data. The PV/T plant is installed in the campus of the University of Catania, (Catania, Italy) on the eastern coast of Sicily, right in the centre of the Mediterranean area. The operative conditions of the experimental PV/T plant can be modified to implement parallel and series electrical and hydronic connections to the PV/T modules. The electrical and thermal load supplied by the PV/T plant can also be managed in order to simulate different energy demand scenarios. This study reports the main thermal and electrical operating parameters of the PV/T plant on the basis of experimental measurements, with the PV/T modules connected in series. A good level of correspondence was found between the measurements and the simulations obtained from a model of the system, particularly as regards electrical features.
Transient thermal prediction methodology for parabolic trough solar collector tube using artificial neural network Renew. Energy (IF 4.9) Pub Date : 2018-07-11 Shye Yunn Heng, Yutaka Asako, Tohru Suwa, Ken Nagasaka
The solar radiation fluctuation occurs at practically anywhere on the earth. When a solar thermal power generation system is designed for the areas with considerable solar radiation fluctuation, the collector tube exit temperature becomes more difficult to predict and requires significant calculation time. This paper presents a fast and accurate transient thermal prediction method to predict the parabolic trough collector tube exit temperature. In this work, an artificial neural network (ANN) is combined with the principle of superposition. ANN is used to predict the exit temperature rise caused by a single heat flux pulse in the first step of the proposed methodology, while superposition is used to predict the from multiple heat flux pulses in the second step. Limited cases of conjugate heat transfer analytical results by the finite element method (FEM) are used to train the ANN. The one-day exit fluid temperature from 7 a.m. to 6 p.m. is predicted within 1 min of computational time with mean absolute deviation less than 2 K. The exit fluid temperature of the collector tube for one year operation can be predicted in less than 6 h. Because fluid velocity is included in the input parameters, the proposed methodology is especially useful for flow control simulations where a constant exit temperature is targeted. Through this, the optimum performance of collector tube under multiple radiation conditions can be assessed during an early design phase of parabolic solar trough systems. The predicted results can be used for initial system planning, heat balance analysis, and system design. Since the method shows good prediction capability under the fluctuating solar radiation as well as the stable solar radiation, it is applicable to be used for designing the parabolic trough technology at any weather conditions in the world.
An experimental and modeling approach for ethanol production by Kluyveromyces marxianus in stirred tank bioreactor using vacuum extraction as a strategy to overcome product inhibition Renew. Energy (IF 4.9) Pub Date : 2018-07-11 Bruna Tavares, Maria das Graças de Almeida Felipe, Júlio César dos Santos, Félix Monteiro Pereira, Simone Damasceno Gomes, Luciane Sene
Vacuum ethanol removal effect on the fermentative performance of Kluyveromyces marxianus was assessed. Yeast was cultured in bench bioreactor at initial glucose concentration of 90 g.L-1 in two sequential batches of 36 hours, with a vacuum ethanol removal step and glucose feed before the second batch. Ethanol concentration after the first batch was 34.13 g.L-1 (YP/S 0.38 g.g-1; QP 0.94 g.L-1.h-1), and 40.90 g.L-1 (YP/S 0.18 g.g-1; QP 0.43 g.L-1.h-1) after the second batch. Ethanol production in a control assay without vacuum extraction only happened in the first batch (36.37 g.L-1; YP/S 0.4 g.g-1; QP 1.01 g.L-1h-1). The phenomenological modeling showed product inhibition and the importance of product removal to process improvement, although the yeast had needed an adaptation period to recover its fermentative metabolism after the stress caused by vacuum.
Optimization of a stand-alone photovoltaic–wind–diesel–battery system with multi-layered demand scheduling Renew. Energy (IF 4.9) Pub Date : 2018-07-11 Tu Tu, Gobinath P. Rajarathnam, Anthony M. Vassallo
Operational and financial optimization of a renewable energy-based stand-alone electricity micro-grid is described. Due to the large problem size in time-series models, we construct the model using mixed integer linear programming (MILP). As the constraints required in this model generally have modest complexity, we were able to perform piece-wise linearization on any non-linear variable relationship. Additionally, controls have also be applied on the demand side. Here, a two stage MILP model has been developed to minimize the overall levelized electricity cost for a micro-grid containing a photovoltaic power source, wind turbine, diesel generator, and an energy storage system. The model aimed to converge on a balance of decision accuracy and computational efficiency. Model outputs were capable of defining both the optimal system sizing and scheduling for each system component, with additional demand management control levers on the loss of power supply probability and load deferring allowance. We believe that this model is one of the first to explore the possibilities of the influences of potential demand management strategies in overall system cost reduction, while presenting a relatively efficient first-pass component sizing for stand-alone micro-grids.
Effect of calcination temperature on the association between free NiO species and catalytic activity of Ni−Ce0.6Zr0.4O2 deoxygenation catalysts for biodiesel production Renew. Energy (IF 4.9) Pub Date : 2018-07-11 Kyung-Won Jeon, Jae-Oh Shim, Won-Jun Jang, Da-We Lee, Hyun-Suk Na, Hak-Min Kim, Yeol-Lim Lee, Seong-Yeun Yoo, Hyun-Seog Roh, Byong-Hun Jeon, Jong Wook Bae, Chang Hyun Ko
In this study, a series of Ni−Ce0.6Zr0.4O2 catalysts, which were synthesized by co-precipitation followed by calcination at different temperatures, were applied for the deoxygenation of oleic acid. The physicochemical properties of the catalysts were characterized by N2 adsorption-desorption, X-ray diffraction (XRD), H2 chemisorption, H2 temperature-programmed reduction (H2-TPR), NH3 temperature-programmed desorption (NH3-TPD), and X-ray photoelectron spectroscopy (XPS). The Ni−Ce0.6Zr0.4O2 catalyst calcined at 300 oC exhibited the highest conversion for oleic acid as well as selectivity for diesel-range compounds. It is predominantly related to the highest amount of free NiO species. In addition, the acidity of the catalyst significantly affected the selectivity and distribution of products.
Analysis and Optimization of a Dual Mass-Spring-Damper (DMSD) Wave-Energy Convertor with Variable Resonance Capability Renew. Energy (IF 4.9) Pub Date : 2018-07-11 Zhongfei Chen, Liang Zhang, Ronald W. Yeung
To adapt to an ocean environment of changing wave period, a novel point-absorber concept is proposed: a fully-enclosed Dual Mass-Spring-Damper (DMSD) floater system that has an internal mass and spring so that its resonance frequency can be varied by changing the movable internal mass and spring. In a waterproof floater, this one-degree-of-freedom heaving energy converter can float or be submerged to evade excessive storm load. Optimization of the internal mass, spring and damping system in the frequency domain is first developed to demonstrate that favorable capture width is achievable for a range of incident-wave frequency. Next, power and motion response of this system in an ISSC wave spectrum are studied in time domain. With constant damping for power-takeoff, the DMSD system is found to have noticeably lower capture width in irregular waves than that in regular waves at a frequency that is the same as the peak wave frequency of the spectrum. Since excessive relative motion can occur in irregular-wave excitation, end-stops, modeled by a stiff spring and strong damper, are applied in the time-domain simulation. When properly designed, degradation of only 1∼2% in the capture width in the irregular-wave environment is found when end-stops are applied.
Fabrication of noble-metal-free CdS nanorods-carbon layer-cobalt phosphide multiple heterojunctions for efficient and robust photocatalyst hydrogen evolution under visible light irradiation Renew. Energy (IF 4.9) Pub Date : 2018-07-11 Peifang Wang, Tengfei Wu, Yanhui Ao, Chao Wang
Photocatalytic water splitting has aroused great interest as a clean and renewable energy conversion process. In this study, we prepared a novel noble-metal-free multiple heterojunction photocatalyst (CdS@C-CoP) composed of CdS nanorods, conducting carbon layer and CoP nanoparticles cocatalyst for the first time. The obtained CdS@C-CoP composites exhibited excellent performance and stability under visible light irradiation when it was used as photocatalysts for hydrogen evolution. For the optimum CdS@C-CoP sample, an average hydrogen evolution rate reached up to 10089 μmol g−1 h−1, nearly 6 fold as high as that of pure CdS. The enhanced photocatalytic hydrogen production rate can be ascribed to the synergistic effect between conductive carbon layer and surface cocatalyst CoP, which resulted in efficient separation of photoexcited charge carriers and abundant active sites for hydrogen reduction. This work presented a novel way to design composite photocatalyst with efficient hydrogen generation properties through combining two kinds of surface modification methods: thin carbon layer coating and surface cocatalysts loading.
Techno-Economic Analysis of a Megawatt-Scale Thermoplastic Resin Wind Turbine Blade Renew. Energy (IF 4.9) Pub Date : 2018-07-11 Robynne E. Murray, Scott Jenne, David Snowberg, Derek Berry, Dylan Cousins
Two-part, in-situ reactive thermoplastic resin systems for composite wind turbine blades have the potential to lower the blade cost by decreasing cycle times, capital costs of both tooling and equipment, and energy consumption during manufacturing, and enabling recycling at the end of the blade life. This paper describes a techno-economic model used to estimate the cost of a thermoplastic wind turbine blade relative to a baseline thermoset epoxy blade. It was shown that a 61.5-m thermoplastic blade costs 4.7% less than an equivalent epoxy blade. Even though the thermoplastic resin is currently more expensive than epoxy, this cost reduction is primarily driven by the decreased capital costs, faster cycle times, and reduced energy requirements and labor costs. Although thermoplastic technology for resin infusion of wind turbine blades is relatively new, these results suggest that it is economically and technically feasible and warrants further research.
Optimization of esterification reaction over niobium phosphate in a packed bed tubular reactor Renew. Energy (IF 4.9) Pub Date : 2018-07-11 L.L. Rade, C.O.T. Lemos, M.A.S. Barrozo, R.M. Ribas, R.S. Monteiro, C.E. Hori
The aim of this work was to investigate the effect of the calcination temperature on the textural properties, structure and acidity of niobium phosphate and the relationship between those properties and the catalytic activity for the continuous esterification reaction using oleic acid and ethanol. For this purpose, samples of niobium phosphate were prepared by calcination at 300, 350, 400, 450 500 and 600 °C. Despite the good thermal stability presented by niobium phosphate, best results were achieved for samples pretreated at 300 °C, which presented higher acidity, surface area and catalytic activity. For this sample, the experimental conditions of temperature (from 220 to 290 °C), amount of catalyst (from 0 to 0.8 g) and ethanol:oleic acid molar ratio (from 2:1 to 14:1) were studied using design of experiments (DOE) and optimized with canonical analysis. The esterification reaction of oleic acid led to yields of esters up to 70% and conversion up to 90% at optimized conditions.
Investigation of the thermoelectric potential for heating, cooling and ventilation in buildings: Characterization options and applications Renew. Energy (IF 4.9) Pub Date : 2018-07-11 Amaia Zuazua-Ros, César Martín-Gómez, Elia Ibañez-Puy, Marina Vidaurre-Arbizu, Yaniv Gelbstein
Researchers have spent decades exploring strategies for reducing energy consumption in buildings worldwide, proposing passive solutions and optimizing active systems. However, no breakthrough technology has been developed. The use of thermoelectricity in buildings for heating, cooling and ventilation has been proposed as an alternative solution to many systems anchored in our day-to-day. This paper seeks to classify, analyze and summarize the possibilities of the thermoelectric technology integration in buildings. The results obtained from the search were divided into two main groups: systems that are integrated in the building envelope and non-integrated systems that operate independently. Among the analyzed parameters, on the one hand the characteristics of the prototypes' components needed for the construction were described. On the other, the thermoelectric specific parameters required for optimization under the operating scenarios' conditions were studied. The results of most of the studies showed that even though the technology can provide the comfort conditions, still the performance of these systems is not competitive compared to conventional vapor compression systems. However, the advantages of thermoelectricity such us the non-use of refrigerants or the high durability, makes this technology an alternative solution to consider, of which interest is growing in line with recent studies.
Hydraulic and Biological Characterization of a Large Kaplan Turbine Renew. Energy (IF 4.9) Pub Date : 2018-07-11 J.J. Martinez, Z.D. Deng, P.S. Titzler, J.P. Duncan, J. Lu, R.P. Mueller, C. Tian, B.A. Trumbo, M.L. Ahmann, J.F. Renholds
One of the most cost-effective and environmentally sound methods of developing hydropower is through the uprating of hydroelectric turbines. In many countries hydroelectric dams have turbines that are approaching their expected service life, with plans underway to install replacement turbines that are expected to improve fish passage survival. To validate these improvements, there is a need to develop a baseline hydraulic characterization of existing Kaplan turbines. An autonomous sensor device known as the Sensor Fish was deployed at Ice Harbor Dam to characterize the hydraulics under different operating conditions. Nadir pressures varied by operating condition, with values decreasing with operating power (144 to 106 kPaA). Pressure changes during turbine passage varied by operating condition, with values increasing with operating power (311 to 344 kPa). There were slightly more significant events (acceleration ≥95G) in the stay vane/wicket gate region than the runner region. Rotational velocity data were similar between operating conditions. Sensor Fish data amassed during field studies in similar turbines were used for comparison. This study offers critical insights into the biological performance of large Kaplan turbines and provides vital information that can be used to make informed decisions that lead to additional design or operational improvements.
Esterification of Palm Fatty Acid Distillate (PFAD) to Biodiesel using Bi-functional Catalyst Synthesized from Waste Angel Wing Shell (Cyrtopleura costata) Renew. Energy (IF 4.9) Pub Date : 2018-07-11 Osman Nur Syazwani, Umer Rashid, Mohd Sufri Mastuli, Yun Hin Taufiq-Yap
In this work, a green solid acid catalyst derived from the waste material of the angel wing shell (AWS) was synthesized using a two-step method: calcination followed by sulfonation. The calcined angel wing shell (CAWS) was supported with varied concentrations of sulphuric acid to obtain an optimum high acidity level of the catalyst. The CaO-based calcined angel wing shell sulphated (CAWS-(x)SO4) catalysts, where x= sulphuric acid concentration, were analysed using X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy, temperature programmed desorption of carbon dioxide and ammonia, BET surface area, and scanning electron microscope. The specific surface area, pore volume, and pore diameter of the CAWS was increased significantly after being sulphated at the optimum sulphuric acid concentration; whereas, the CAWS-(7) SO4 showed the highest total amount of acidity (4726 µmol/g). The optimal FAME conversion (98%) from the PFAD was acquired at the reaction temperature of 80 °C, 15:1 MeOH:PFAD molar ratio and 5 wt.% catalyst loading for a 3 h reaction time. The CAWS-(7)SO4 catalyst was reused two times with a high FAME yield without further treatment under optimized reaction conditions. The use of the AWS for the synthesis of catalysts has enormous potential for biodiesel production from high FFA oils due to its lower production cost, abundant availability and high catalytic activity.
Process modeling and simulation for butanol removing from fermentation broth by extraction with biodiesel Renew. Energy (IF 4.9) Pub Date : 2018-07-11 A.M. Dumitrescu, I. Banu, G. Bumbac
The present paper evaluates the feasibility of a process flowsheet for butanol bioproduction, as pure compound or as a blend with the biodiesel used as the liquid-liquid extraction (LLEx) solvent. In order to evidence this aspect, a modeling and simulation study was performed using Aspen Hysys commercial simulator. Process simulation results evidenced specific (per ton of butanol separated) power consumption of 22.5 kW/t and hot and cold utility specific consumptions were in power equivalences of 3.4 MW and 2.6 MW respectively. In order to achieve a feasible extraction process of biobutanol from the fermentative broth, a specific quantity of 1.125 t/t biodiesel (recovered as a blend) was required.
How business model innovation affects firm performance in the energy storage market Renew. Energy (IF 4.9) Pub Date : 2018-07-11 Martijn Hamelink, Raymond Opdenakker
There is a global goal to reduce carbon emissions and create a more sustainable world. Over the past decades, a growing share of renewable energy resources have been developed to reach this goal. Due to their intermittent nature, these resources make it more difficult for an electrical grid to remain stable as it is designed for slow-reacting, constant, and predictable power plants. This issue can be solved through energy storage for load balancing without using power plants for this operation, and with a reaction time that is much faster than conventional power plants. The implementation of energy storage seems inevitable for a more sustainable future. Still, this market has only slowly started to move in the right direction, with implementation on both large- and small-scale applications awaiting their first successes. An innovative business model may be key to this success. This study investigated how business model innovation affects firm performance in the energy storage market, by measuring firm performance on firms acting in the energy storage market. Four cases were investigated: two large-scale applications using grid-level solutions and two small-scale applications on the consumer level. Results show that business model innovation affects firm performance in the energy storage market. With current legislation limiting a true new value proposition, for large-scale applications, the business model innovation with an efficiency design theme results in higher environmental performance and, therefore, increased customer satisfaction. For small-scale applications, a business model innovation with a complementarities theme results in increased numbers of partnerships, customer segments, and channels, contributing to higher customer satisfaction through a more complete and innovative product-value proposition to the customer.
Utilization of residues from rice parboiling industries in southern Brazil for biogas and hydrogen-syngas generation: heat, electricity and energy planning Renew. Energy (IF 4.9) Pub Date : 2018-07-11 Willian Cézar Nadaleti
Brazil is one of the world's largest rice producers with trends for the growth of this sector. During the processing of the grain, high amounts of husk are generated, corresponding to 22% of its weight. On the other hand, in the process of parboiling, in turn, the final result is considerable volumes of effluent rich in organic matter. Thereby, this study demonstrates in an energetic, economic and environmental way the possibilities of using these residues for power generation in the southern Brazilian rice parboiling industries. Two scenarios are presented: the first, with the use of biogas and the second, with the use of hydrogen-rich syngas. A case study was made in one of these industries, where it was discussed in detail the energy potential coming from systems operating with a CHP genset, using hydrogen-rich syngas from the rice husks and the biogas from the anaerobic treatment of the effluents. The results have shown that it is possible to produce more than 2,17E+04 MWh of electricity just considering the use of the biogas generated. On the other hand, the use of syngas generates enough thermal energy to operate the entire industrial process, with a surplus of 53,3% in MWh/year.
Numerical Simulation of Heat Transfer Process of the Raised Floor Heating System Integrated with a Burning Cave Renew. Energy (IF 4.9) Pub Date : 2018-07-11 Xueyan Zhang, Xin Liu, Bin Chen, Joe R. Zhao, Yizhou Sang
In order to optimize structural design and balance heat distribution of the raised floor heating system heated by a burning cave, an unsteady heat transfer process of the raised floor was analyzed and discussed. An unsteady heat transfer model of the raised floor heating system was established to solve the problem of inner natural convection by air coupled with radiation and conduction heat transfer between two floor surfaces by computational fluid dynamics (CFD). Moreover, heating intensity, structural size and position of the heat source (burning cave) impact on the heat transfer performance and heating effect were discussed, which can provide a theoretical basis for parameter matching and structure optimizing. The results indicate that the best position of burning cave is under the center ground of a rural house, where the reasonable heat intensity of the burning cave is about 200 W/m2. The calculated temperatures and velocities are in reasonable agreement with measurements on the model house, which can provide a basic data support for the engineering practice of raised floor heating system.
Dynamic analysis of an offshore monopile foundation used as heat exchanger for energy extraction Renew. Energy (IF 4.9) Pub Date : 2018-07-11 Arundhuti Banerjee, Tanusree Chakraborty, Vasant Matsagar
In the present study, a novel concept of incorporating a heat exchanger system in an existing offshore wind turbine-monopile foundation and its effect on the stress-strain response of the structure is investigated. Thermo-mechanical analysis of the steel monopile with fluid carrying pipes was carried out using finite element method (FEM) considering heat transfer and structural analyses. The effect of offshore loading is taken into account using random wind and wave loading simulated using the Kaimal and the Pierson Moskowitz spectra, respectively. The combined effect of thermal as well as offshore loading on the monopile, resultant pore pressure development in soil due to the loads, the axial and radial stresses and strains in the structure and the shear stresses in soil were studied in detail. The strains and displacement of the structure are checked against the serviceability limits for the offshore wind turbine structure and it has been observed that the combination of offshore as well as thermal load on the monopile foundation along with the duration of the load, affects the stresses and strains in the structure significantly.
Enzymatic Hydrolysis at High Lignocellulosic Content: Optimization of The Mixing System Geometry and of A Fed-Batch Strategy To Increase Glucose Concentration Renew. Energy (IF 4.9) Pub Date : 2018-07-11 Federico Battista, Mélanie Gomez Almendros, Romain Rousset, Pierre-Antoine Bouillon
Working at high values of lignocellulosic Dry Matter (DM), as wheat straw, increases the reaction medium viscosity, making the mixing inefficient with the traditional agitators. Batch and fed-batch tests were conducted using different impellers: i) inclined blades, ii) marine impeller, iii) anchor, iv) paravisc and v) double helical impeller. Inclined blades appeared an inadequate device for batch and fed-batch tests. On contrary, double helical impellers and anchor gave optimal performances. An alternative to improve the reactor’s rheology is the modification of the feeding strategy. A particular fed-batch strategy allowed keeping low the reaction medium viscosity by a gradual increasing of the DM content in the reactor. In this way, three main benefits were achieved: i) a very good performances in terms of glucose concentration (85 g/L), ii) a strong reduction of the energetic consumption compared to batch test and iii) the adoption of a simple mixing devise.
Accounting for low solar resource days to size 100% solar microgrids power systems in Africa Renew. Energy (IF 4.9) Pub Date : 2018-07-11 N. Plain, B. Hingray, S. Mathy
In many regions worldwide, the electrification of rural areas is expected to be partly achieved through micro power grids. Compliance with the COP21 conference requires that such systems mainly build on renewable energy sources. To deliver a high power and quality service may be difficult to be achieved, especially when micro-grids are based on variable renewable sources. We here explore the multiscale temporal variability of the local solar resource in Africa and its implication for the development of 100% solar systems. Using high resolution satellite data of global horizontal irradiance (GHI) for a 21-year period (1995–2015), we characterize the seasonality and temporal variability of the local resource. We focus on its low percentile values which give a first guess on the size of the solar panels surface required for the micro-grid to achieve a given quality service. We assess the characteristics and especially persistence of the low resource situations, for which the local demand would not be satisfied. We finally assess how the ability of electricity consumers for some day-to-day flexibility (e.g. via the postponement of part of one day as demand to the next), would help to achieve the design level of service quality with a smaller microgrid system.
Tube-based Explicit Model Predictive Output-feedback Controller for Collective Pitching of Wind Turbines Renew. Energy (IF 4.9) Pub Date : 2018-07-12 Ahmed Lasheen, Mohamed S. Saad, Hassan M. Emara, Abdel Latif Elshafei
Collective pitch control is the main tool used to regulate the speed and power of wind turbines while operating above their rated wind speeds. The main challenges that face collective pitch control designs are the constraints on the control actions, the unmodeled uncertainties, and the unmeasured system states. A tube – based explicit model-predictive output-feedback controller is designed to control the collective pitch angle. The proposed controller is capable of handling the constraints challenge, reducing the on-line computational time and producing the optimal control sequence. Furthermore, the proposed controller is robust against the unmodeled uncertainties. The challenge of unmeasured system states is eliminated since this is an output feedback controller. The performance of the proposed controller is compared to the performance of a gain-scheduled PI controller which is commonly adopted in industry. Simulation results through application to a typical 5-MW offshore wind turbine are obtained. Further, experimental results with hardware in loop are obtained for a reduced scale wind turbine model to demonstrate the feasibility of the controller for real time applications. Simulation and experimental results show the superiority of the proposed controller over the gain-scheduled PI controller.
Urban wind conditions and small wind turbines in the built environment: A review Renew. Energy (IF 4.9) Pub Date : 2018-07-12 Anup KC, Jonathan Whale, Tania Urmee
Wind conditions in the built environment are complex in nature and characterized by lower wind speeds and higher turbulence due to the presence of obstructions. A growing body of literature and research/testing activities related to performance evaluation of small wind turbines (SWTs) in urban wind conditions have inferred that urban installed SWTs are subjected to higher level of turbulence and face dynamic loading that impedes their performance, and reduces fatigue life. This paper reviews the diverse studies conducted on the application of SWT technology in the built environment to understand the characteristics of inflowing wind, their performance and identify the gaps in the knowledge. This review paper also investigates the extent to which the international design standard for SWTs, IEC 41400-2, is valid for urban installations. The findings from this review show that the wind models incorporated in IEC 61400-2 is not suitable for installation of SWTs in the built environment. The authors recommend a thorough study through measured data and characterization of urban wind to make current standard inclusive of wind classes that characterize urban wind conditions. Thus, SWT design can be made more consistent with urban wind conditions and their performance and reliability can be assured.
CO2 emissions, economic growth, renewable and non-renewable energy production and foreign trade in China Renew. Energy (IF 4.9) Pub Date : 2018-07-12 Yulong Chen, Zheng Wang, Zhangqi Zhong
Based on the autoregressive distributed lag (ARDL) bounds testing approach and vector error correction model (VECM) Granger causality approach, this paper explores the relationships among per capita carbon dioxide (CO2) emissions, gross domestic product (GDP), renewable, non-renewable energy production and foreign trade for China covering the period 1980-2014. One finding is that there is a long-run relationship among those variables. Another important finding is that China does not have the Environmental Kuznets Curve (EKC) of CO2 emissions under the influence of economic growth, non-renewable energy production and foreign trade. However, after the addition of renewable energy production variable, it is found that the inverted U-shaped EKC hypothesis is supported in the long-run. Our long-run estimates show that increasing non-renewable energy and GDP increases CO2 emission, whereas renewable energy and foreign trade have a negatively impact on CO2 emissions. The short-run Granger causality tests show that there are bidirectional causality running from foreign trade, CO2 emission and non- renewable energy to renewable energy. Furthermore, the finding indicates that renewable energy consumption is a key solution in reducing CO2 emissions over time. Finally on the basis of this study, we put forward the corresponding countermeasures and suggestions on China's carbon emission reduction strategy.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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