A prediction method for the real-time remaining useful life of wind turbine bearings based on the Wiener process Renew. Energy (IF 4.357) Pub Date : 2018-04-12 Yaogang Hu, Hui Li, Pingping Shi, Zhaosen Chai, Kun Wang, Xiangjie Xie, Zhe Chen
A performance degradation model and a real-time remaining useful life (RUL) prediction method are proposed on the basis of temperature characteristic parameters to determine the RUL of wind turbine bearings. First, using the moving average method, the relative temperature data of wind turbine bearings are smoothed, and the temperature trend data are obtained on the basis of the uncertainty of wind speed and wind direction that causes the temperature of wind turbine bearings to vary widely. Second, given that the degradation speed of bearings changes with operational time and uncertain external factors, the performance degradation model is established with the Wiener process. The parameters of this model are obtained through the maximum likelihood estimation method. Third, according to the failure principle of the first temperature monitoring value beyond the first warning threshold, the RUL prediction model for wind turbine bearings is established on the basis of an inverse Gaussian distribution. Finally, the performance degradation process and real-time RUL prediction are demonstrated by predicting the RUL of a practical rear bearing of a wind turbine generator. The comparison of the predicted RUL and actual RUL shows that the proposed model and prediction method are correct and effective.
The future of wind energy in California: Future projections with the Variable-Resolution CESM Renew. Energy (IF 4.357) Pub Date : 2018-04-12 Meina Wang, Paul Ullrich, Dev Millstein
Shifting wind patterns are an expected consequence of global climate change, with direct implications for wind energy production. However, wind is notoriously difficult to predict, and significant uncertainty remains in our understanding of climate change impacts on existing wind generation capacity. In this study, historical and future wind climatology and associated capacity factors at five wind turbine sites in California are examined. Historical (1980–2000) and mid-century (2030–2050) simulations were produced using the Variable-Resolution Community Earth System Model (VR-CESM) to understand how these wind generation sites are expected to be impacted by climate change. A high-resolution statistically downscaled WRF product provided by DNV GL, reanalysis datasets MERRA-2, CFSR, NARR, and observational data were used for model validation and comparison. These projections suggest that wind power generation capacity throughout the state is expected to increase during the summer, and decrease during fall and winter, based on significant changes at several wind farm sites. This study improves the characterization of uncertainty around the magnitude and variability in space and time of California's wind resources in the near future, and also enhances our understanding of the physical mechanisms related to the trends in wind resource variability.
Impact fatigue damage of coated glass fibre reinforced polymer laminate Renew. Energy (IF 4.357) Pub Date : 2018-04-12 Anthony Fraisse, Jakob Ilsted Bech, Kaj Kvisgaard Borum, Vladimir Fedorov, Nicolai Frost-Jensen Johansen, Malcolm McGugan, Leon Mishnaevsky, Yukihiro Kusano
Impact fatigue caused by rain droplets, also called rain erosion, is a severe problem for wind turbine blades and aircraft. In this work, an assessment of impact fatigue on a glass fibre reinforced polymer laminate with a gelcoat is presented and the damage mechanisms are investigated. A single point impact fatigue tester is developed to generate impact fatigue damage and SN data. Rubber balls are repeatedly impacted on a single location of the coated laminate. Each impact induces transient stresses in the coated laminate. After repeated impacts, these stresses generate cracks, leading to the removal of the coating and damage to the laminate. High-resolution digital imaging is used to determine the incubation time until the onset of coating damage, and generate an SN curve. An acoustic emission sensor placed at the back of the laminate monitors changes in acoustic response as damage develops in the coated laminate. The subsurface cracks are studied and mapped by 3D X-ray computed tomography. A finite element method model of the impact shows the impact stresses in the coating and the laminate. The stresses seen in the model are compared to cracks found by 3D tomography. The damage is also evaluated by ultrasonic scanning.
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 4.357) 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.
Marine Current Power with Cross-stream Active Mooring: Part II Renew. Energy (IF 4.357) Pub Date : 2018-04-12 Che-Chih Tsao, Le Han, Wen-Ting Jiang, Chun-Chen Lee, Jia-Shi Lee, An-Hsuan Feng, Chieh Hsieh
This is the second of three papers that propose and study a new concept of mooring turbine generators with the aim of resolving key difficulties in realizing ocean current power generation. The concept of Cross-stream Active Mooring (CSAM) features a hydro sail system that allows deployment of generator turbines, from anchoring points on shore or on shallow seafloors, across current stream to access current core flowing over deep seas or over seabed not suitable for anchoring construction. The CSAM can increase system power capacity by changing horizontal positions of generator turbines to track meandering current core, and can also change system depth to avoid storms. New anchoring designs of improved efficiency and implementation methods for resolving seafloor geological issues in the Kuroshio off southeast Taiwan are also included. This second paper discusses conceptual design and construction of the tethers, mooring implementations and reduction of flow drag, mooring of power cable and design of linear array and 2D formation. Model tests were conducted to demonstrate and observe the feasibility of the basic concept and its stability. Formation stability under the influences of waves and other possible perturbations was analyzed and discussed.
Advances in switchable and highly insulating autonomous (self-powered) glazing systems for adaptive low energy buildings Renew. Energy (IF 4.357) Pub Date : 2018-04-12 Aritra Ghosh, Brian Norton
Building energy reduction requires highly advanced low heat loss, heat gain and comfortable daylight allowing glazing. Presently available glazing systems are classified mainly in two categories, controlling solar heat gain and controlling low heat loss. Low heat loss through glazing systems can be achieved by (i) suppression of convection in the air between the outer panes by use of multiple glass panes or aerogels, (ii) having an inert gas or vacuum between the panes to reduce or eliminate respectively convective heat transfer. In all these systems, low emissivity coatings are also required to reduce the radiative heat transfer. Low heat glazing allows large areas of a building façade to be glazed without large attendant heat losses. However, they require the addition of an ability to switch from transparent to opaque to avoid excessive solar heat gain and to control glare. Electrically actuated electrochromic, liquid crystal and suspended particle device glazing systems and non-electrically-actuated thermochromic, thermotropic, and gasochromic glazing systems offer control of solar heat gain control and daylight. Recent relevant developments are reviewed with the contemporary status of each technology provided.
Assessing the IEC simplified fatigue load equations for small wind turbine blades: How simple is too simple? Renew. Energy (IF 4.357) Pub Date : 2018-04-12 S.P. Evans, D.R. Bradney, P.D. Clausen
It is well known that wind turbine blades are fatigue critical, with much literature and methodologies available for assessing fatigue loading of large wind turbine blades. Little research effort has been directed at assessing the fatigue life of small wind turbines which operate at higher rotational speeds and are subject to highly unsteady aerodynamic loading. In this paper the simplified load model proposed in IEC 61400.2 is used to determine the fatigue life of a small 5 kW wind turbine blade. This estimated life is compared to that determined from both measured operational data and aeroelastic simulations. Fatigue life was estimated by the standard at 0.09 years, compared to 9.18 years from field measurements and 3.26 years found via aeroelastic simulations. All methods fell below the 20 year design life, with the standard over-conservative by a factor of 102 and 36 for measurements and simulations respectively. To the best of the authors' knowledge these three fatigue methods specified in the standard have not been quantitatively compared and assessed for small wind turbines. Results are of importance to small wind turbine developers as they seek best practice for determining blade fatigue life. Shortcomings of the IEC methodology are detailed and discussed.
The Betz limit applied to Airborne Wind Energy Renew. Energy (IF 4.357) Pub Date : 2018-04-11 Marcelo De Lellis, Romeu Reginatto, Ramiro Saraiva, Alexandre Trofino
In this paper we revisit the modeling framework used to derive the Betz limit of power extraction from the wind based on linear momentum theory. One of our contributions is to suggest that the Betz limit of 16/27≈59% 16 / 27 ≈ 59 % should in fact hold true for any device that harvests power through drag or torque in a horizontal-axis rotational motion perpendicular to the wind field, which is not only the case of conventional wind turbines but also of Loyd's drag power Airborne Wind Energy (AWE) systems. Another contribution is to show that Loyd's lift power AWE devices during the reel-out phase can harvest up to 4/27≈15% 4 / 27 ≈ 15 % of usable power available in the wind, i.e. exactly 1/4 1 / 4 of the theoretical limit of the horizontal-axis turbines and AWE drag power systems with ideal airfoils. Moreover, in order to operate at such limit, AWE lift power systems must also extract from the wind an amount of drag power that is equal to the reel-out power. These claims are supported by physical principles and mathematical formulations.
Performance of building integrated photovoltaic thermal system with PV module installed at optimum tilt angle and influenced by shadow Renew. Energy (IF 4.357) Pub Date : 2018-04-11 S. Yadav, S.K. Panda, M. Tripathy
Building integrated photovoltaic (BIPV) thermal system is an efficient system for urban applications to convert a building to net zero energy buildings by utilizing solar insolation. In this study, HDKR/S (Hay, Davies, Klucher, Reindl/shadow) model is developed which is a modified HDKR model where influence of shadow is incorporated in the mathematical model. Four discrete rectangular buildings situated in four directions (North, South, East and West) around a BIPV thermal system are considered for creating adverse effect of shadow. Variation of width (B), storey height (H) and horizontal distance (D) of these surrounded buildings are taken into account for evaluating optimum tilt angle, insolation and performance of BIPV thermal system by introducing corresponding shadow effects. The performance of the system is adversely affected because of the presence of surrounded building located at close proximity i.e., due to higher influence of shading and sky view blocking effects.
Factors influencing solar drying performance of the red algae Gracilaria chilensis Renew. Energy (IF 4.357) Pub Date : 2018-04-11 Rodrigo Poblete, Ernesto Cortes, Juan Macchiavello, José Bakit
The aim of this study was to establish the optimal conditions of distinct factors affecting the performance of a closed solar dryer in drying Gracilaria chilensis, a commercially important red algae. The evaluated factors were algae arrangement (vertical versus horizontal), baffle existence (present versus absent), and air fan use (on versus off). Process productivity was maximized when the algae were arranged horizontally, a baffle was present, and the air fan was turned on. Of these, air fan use was the most important determinant of process performance. This optimized solar dryer system was then compared against the productivity of an open-air system. The solar dryer achieved a greater degree of moisture evaporation than open-air drying (86.1% versus 67.6%, respectively). This result is directly associated with the recorded peaks in air temperature (41.3 °C in the solar dryer versus 21.7 °C outside of the solar dryer). The specific energy consumption required for the optimized solar dryer process was 1.64 kWh/kg, as due to the energy requirements of the air fan and recirculation pump. Solar drying is very effective in drying G. chilensis when parameters are optimized.
Non-parametric models for joint probabilistic distributions of wind speed and direction data Renew. Energy (IF 4.357) Pub Date : 2018-04-11 Qinkai Han, Zhuolin Hao, Tao Hu, Fulei Chu
Two non-parametric models, namely the non-parametric kernel density (NP-KD) and non-parametric JW (NP-JW) models, are proposed for joint probabilistic modeling of wind speed and direction distributions. In the NP-KD model, a novel bivariate kernel density function, which could consider the characteristics of both wind direction (angular) and speed (linear) data, is firstly constructed and the optimal bandwidth is selected globally through two cross-validation (CV) methods. In the NP-JW model, the univariate Gaussian and von Mises kernel density functions are, respectively, utilized to fit the wind speed and direction data. The estimated wind speed and direction distributions are used to form the joint distribution according to the JW model. Several classical parametric models, including the AG, Weibull, Rayleigh, JW-TNW and JW-FMN models, are also introduced in order for comparisons with the proposed non-parametric models. By conducting various tests on the real hourly wind speed and direction data, the goodness of fit of both parametric and non-parametric models is compared and evaluated in detail. It is shown that the non-parametric models (NP-KD, NP-JW) generally outperform the parametric models (AG,Weibull, Rayleigh,JW-TNW,JW-FMN) and have more robust performance in fitting the joint speed and direction distributions. Among the two non-parametric models, the NP-KD model has better performance in fitting joint distribution, while the NP-JW model has higher accuracy in fitting the marginal speed (or direction) distributions.
Graphene supported magnetically separable solid acid catalyst for the single step conversion of waste cooking oil to biodiesel Renew. Energy (IF 4.357) Pub Date : 2018-04-10 Reena D'Souza, Tripti Vats, Amit Chattree, Prem Felix Siril
Conversion of vegetable oils to biodiesel typically involves the use of highly corrosive acids or bases as catalysts. Solid catalysts can be used to avoid the use of corrosive mineral acids/bases and they have the possibility of reuse. Development of a highly active solid acid based on graphene oxide that can be recovered using magnetic seperation and reactivated by simple washing is reported here. High catalytic activity of the iron oxide supported on sulphonated graphene oxide (GO-Fe2O3 SO3H) was established for the esterification of oleic acid as well as single step biodiesel production from waste cooking oil (WCO) using ethanol. Catalytic activity of GO-Fe2O3 SO3H was higher than GO, GO-SO3H as well as GO-Fe2O3. Thorough characterization of the prepared catalysts was done using a number of spectroscopic, thermal and microscopic techniques. Complete conversion of oleic acid to its ethyl ester could be done in 4 h, at 100 °C using 5 (% by wt.) of the catalyst. Moreover, single step conversion of WCO to biodiesel could be achieved at 90 °C in 6 h using 5 wt % of the catalyst. The catalyst was reclaimed by magnetic separation and reused upto 7 cycles without any significant loss of activity.
Chamber pressure skewness corrections using a passive relief valve system at the Pico oscillating water column wave energy plant Renew. Energy (IF 4.357) Pub Date : 2018-04-10 Kieran Monk, Victor Winands, Miguel Lopes
Power production levels at the Pico plant fall significantly short of pre-project estimates. Poor turbine performance compared to expectations from scale model testing accounts for much of this shortfall. Unanticipated chamber pressure skewness is also found to contribute to the deficit. This skewness manifests from wave shoaling because of the shallow chamber water depth from boulder collection and is worsened by intermittent chamber pressure losses caused by chamber wall defects. A passive non-return by-pass relief valve system for partially counteracting chamber pressure skewness is investigated. This functions by venting more of the unconvertible pneumatic over-power during the more intense but shorter duration exhalation half-wave cycles. At the same time, it retains more of the convertible pneumatic under-power in the weaker but longer duration inhalation half-wave cycles. This method reduces the degree of pressure skewness, which improves the system performance in higher energy excitation conditions. The passive relief valve specifications are optimised with a time-domain wave to wire model which is also used to project the expected plant performance enhancement in a range of wave conditions. Simulation results are compared to limited field tests results using a simple prototype passive valve system and good agreement is found.
In situ, one-step and co-electrodeposition of graphene supported dendritic and spherical nano-palladium-silver bimetallic catalyst on carbon cloth for electrooxidation of methanol in alkaline media Renew. Energy (IF 4.357) Pub Date : 2018-04-10 Caesar Ghiabi, Ali Ghaffarinejad, Hojjat Kazemi, Razieh Salahandish
In this paper, we report the preparation of graphene supported nano-palladium-silver on carbon cloth (G-PdAg/CC) electrode for electrocatalytic oxidation of methanol in alkaline medium and its performance is compared with graphene supported nano-palladium and silver on CC (G-Pd/CC and G-Ag/CC respectively) electrodes. The G-PdAg composite is prepared for the first time via a completely electrochemical, fast, green and one-step procedure leading to the formation of both dendritic and spherical graphene supported PdAg bimetallic catalysts on a commercially applicable CC electrode. Field emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and atomic absorption spectrometry (AAS) are used for physical and elemental characterization of the modified electrodes. Electrochemical characterizations are performed using cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy (EIS). The results are indicative of outstanding properties in terms of catalytic activity, stability and resistance toward poisoning reaction intermediates for electrooxidation of methanol in alkaline medium. All results reveal that this electrode is a favorable candidate for alkaline direct methanol fuel cell.
Full scale behavior of a small size vertical axis wind turbine Renew. Energy (IF 4.357) Pub Date : 2018-04-10 Luisa Pagnini, Giuseppe Piccardo, Maria Pia Repetto
This paper shows the on-going experimental campaign carried out over a small size vertical axis wind turbine in the facility of the Savona Harbor. Investigations mainly concern two issues: power production assessment and full-scale structural behavior. The first one highlights the importance of a deep knowledge of the local orography and of the wind characteristics (e.g., turbulence intensity); in the absence of reliable wind data it is impossible to properly estimate the performance of the system. The latter allows to identify the possible critical aspects of the structural system (e.g., in terms of resonance conditions) and to investigate the actual dynamic behavior (e.g., in terms of dissipative capacity), necessary for assessing the useful life. The paper points out how these two issues are closely related. Results obtained can provide indications suitable for improving future installations.
Conversion Efficiency Gain for Concentrated Triple-Junction Solar Cell System through Thermal Management Renew. Energy (IF 4.357) Pub Date : 2018-04-09 Dianhong Li, Yimin Xuan, Ershuai Yin, Qiang Li
The application of the thermoelectric (TE) modules can provide extra power in PV cell systems, but the increased thermal resistance leads to an increase in the temperature of the PV cells. In this paper, the phase change materials (PCMs) attached to the back side of the PV cell is used to control the temperature of the PV cells. The PCMs transfers the heat absorbed from the PV cell to the TE modules. A comprehensive experimental study is carried out to investigate the performance of the photovoltaic-thermoelectric hybrid system with PCMs. The outdoor tests are performed to reveal the influence of the cooling methods, the sunlight intensity, and the uniformity of the concentrated light spot on the conversion efficiency of the system. The results indicate that the conversion efficiency of the PV-TE hybrid system with PCMs is 0.56 % more than solo PV cell system due to a decrease of the PV cell temperature and the efficiency contribution of the TE modules. This work investigates the factors that affect the full spectrum utilization of solar energy in PV cell systems.
Effect of the diffuser efficiency on wind turbine performance Renew. Energy (IF 4.357) Pub Date : 2018-04-09 Jerson R.P. Vaz, David H. Wood
A diffuser surrounding a rotor is able to increase the power coefficient of a wind turbine above the Betz-Joukowsky limit (16/27), and so has attracted great attention for many years. This work presents a novel analysis of the performance of diffuser-augmented wind turbines (DAWTs) taking into account the influence of the diffuser efficiency and thrust, in which a new formulation for the far-wake velocity is proposed. The mathematical model extends Blade Element Theory to include the diffuser efficiency in the axial velocity formulation, which in turn, modifies the thrust and power. Additionally, a correction for high rotor thrust is presented, where a quadratic equation is used to incorporate the losses within the diffuser that are associated with the efficiency being less than 100%. An algorithm to assess DAWT performance was developed and implemented. The new model was validated by comparison with experimental data match and shows good agreement when a diffuser efficiency of 80% is assumed. The impact of the diffuser is assessed by the augmentation factor, the ratio of turbine efficiency to the Betz-Joukowsky limit. It is shown, for example, that the augmentation factor exceeds unity only for efficiency greater than 74% when the diffuser thrust is 0.2 of the total thrust and ratio of the rotor area to diffuser exit area is 0.54.
Added-mass effects on a horizontal-axis tidal turbine using FAST v8 Renew. Energy (IF 4.357) Pub Date : 2018-04-09 Robynne E. Murray, Robert Thresher, Jason Jonkman
Added mass on tidal turbine blades has the potential to alter the blade dynamic response, such as natural frequencies and vibration amplitudes, as a response to blade acceleration. Currently, most aeroelastic design tools do not consider such effects as they are complex and expensive to model, and they are not an intrinsic part of most blade-element momentum theory codes, which are commonly used in the tidal energy industry. This article outlines the addition of added-mass effects to the National Renewable Energy Laboratory's design tool FAST v8. A verification is presented for a spring-mass system with an initial displacement, and a case study is performed for the Reference Model 1 20-m-diameter tidal turbine. For the 20-m-diameter turbine, it was shown that the natural frequency of vibration is reduced by 65% when added mass is considered. Further, the thrust loads are increased by 2.5% when the blades are excited by a 5% step increase in inflow velocity when added mass is considered. This decrease can have a significant impact on the overall turbine design, as it is important to design the blades with a natural frequency so that they are not excited by the rotor speed and its harmonics, wherein aerodynamic excitation can lead to fatigue damage. However, it was shown that when turbulent inflow with an intensity of 20% was modeled, there was almost no impact on the loads and blade displacement with added-mass effects except for a small difference in the fatigue response of the blade to turbulent load fluctuations.
Model and simulation of a packed resin column for biodiesel purification Renew. Energy (IF 4.357) Pub Date : 2018-04-09 Nilva R. Uliana, Louise A. Kuhl, Marintho B. Quadri, J. Vladimir Oliveira
This study aims to develop a multiphysics model using the finite element method for the simulation of a packed column. This column was filled with ion exchange resins SP112H and GF101, performing purification for the dry washing process mainly to reduce the free fatty acid content (FFA), monoacylglycerol (MAG), diacylglycerol (DAG), and triacylglycerol (TAG) biodiesel samples. Results obtained from simulations were compared to the experimental results for acidity, MAG, DAG and TAG. It was found that the simulation results represented with reasonable agreement the experimental.
Enhanced lipid production and nutrient utilization of food waste hydrolysate by mixed culture of oleaginous yeast Rhodosporidium toruloides and oleaginous microalgae Chlorella vulgaris Renew. Energy (IF 4.357) Pub Date : 2018-04-09 Yu Zeng, Tonghui Xie, Panyu Li, Banggao Jian, Xiang Li, Yi Xie, Yongkui Zhang
Using food waste hydrolysate as medium for culturing oleaginous microorganism is a dual-purpose strategy for relieving environmental burdens both in food waste disposal and energy crisis. The pure culture of one oleaginous microorganism when single waste as culture media has shortages such as high operation cost, low lipid production and low substrate utilization. Mix-culture of yeast and microalgae in this work enhanced this process result in better waste treatment, higher lipid production and shorter cultivation time. Compare to pure culture of Rhodosporidium toruloides, the nitrogen utilization rate, reducing sugar utilization rate and lipid production increased by 23%, 17 and 12%, respectively, and the cultivation time shorten by 40%, in mix-culture of Rhodosporidium toruloides and Chlorella vulgaris. The results showed that the mix-culture of yeast and microalgae using food waste hydrolysate as culture medium would be a good strategy for both waste disposal and biofuel production.
Hydraulic performance evaluation of a micro-turbine with counter rotating runners by experimental investigation and numerical simulation Renew. Energy (IF 4.357) Pub Date : 2018-04-09 E. Vagnoni, L. Andolfatto, S. Richard, C. Münch-Alligné, F. Avellan
The development of energy recovery systems on existing water utility networks is a new challenge for increasing the sustainability of electricity generation mix. The concept of the new micro-turbine with counter rotating runners braces this goal by allowing the recovery of the energy which is spoiled in pressure reducing valves in many water supply networks. The hydraulic performances of the micro-turbine are evaluated through an analysis on the angular momentum balance applied to the investigated cross-sections of the machine. For this analysis, an experimental campaign involving 2D Laser Doppler Velocimetry (LDV) is performed to measure the velocity field of the flow at the inlet and outlet sections of the machine. Since the optical access to perform LDV measurements is blocked close to the hub of the runners, a further analysis on the mass balance and numerical simulations are performed to complete the velocity profiles and to evaluate the machine performance. The combination of numerical and experimental methods grants a full study on the operating condition of the micro-turbine and strengthens the results achieved. The results back up the best operating condition of the machine for different discharges and support further improvements of the runner blades shape.
Development of biomass fast proximate analysis by thermogravimetric scale Renew. Energy (IF 4.357) Pub Date : 2018-04-09 B. Velázquez- Martí, J. Gaibor-Chávez, I.Z. Niño-Ruiz, E. Cortés-Rojas
EN norms set the methods for determining the ash and volatile content in biomass. These establish the use of a muffle to heat the samples at temperatures of 550ºC and 900ºC respectively, with a minimum analysis time of 4h as standard method. The objective of this work was to reduce significantly the analysis times, making very short heating periods using a thermogravimetric scale (TGA), and to apply an equation to the residual weight to obtain the weight of ash, volatiles and fixed carbon in biomass samples. We analyzed the factors: the temperature ramp, atmosphere and airflow in the determination. In this work new validated methods were developed with an analysis time of 10-20 min.
Enhancement of biogas production from cattle manure pretreated and/or co-digested at pilot-plant scale. Characterization by SEM Renew. Energy (IF 4.357) Pub Date : 2018-04-07 P. Ormaechea, L. Castrillón, B. Suárez-Peña, L. Megido, Y. Fernández-Nava, L. Negral, E. Marañón, J. Rodríguez-Iglesias
The aim of this study was to evaluate the enhancement of biogas production from cattle manure (CM) at pilot-plant scale using: a) ultrasound pretreatment (US) (520 kJ/kg Total Solids (TS); 409.59 kJ), b) co-digestion with crude glycerine (Gly) from the biodiesel industry (6% w/w), and c) US pretreatment (520 kJ/kg TS; 340.84 kJ), applied to the aforementioned mixture of both substrates prior to anaerobic co-digestion. The reactor used for this purpose was an Induced Bed Reactor (IBR), with a useful volume of 1250 L. Methane production from CM was enhanced by the application of low-energy ultrasound pretreatment (520 kJ/kg TS) (from 0.29 to 0.46 m3 CH4/kg Volatile Solids (VSadded)), and by co-digestion with Gly (from 0.29 to 0.44 m3 CH4/kg VSadded). The best results were obtained when the mixture of CM + Gly was pretreated by US (up to 0.59 m3 CH4/kg VSadded). Observation by Scanning Electron Microscopy (SEM) of the microstructural changes the CM underwent after pretreatment and/or co-digestion with crude glycerine enabled the discussion and justification of the results obtained in the present study.
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 4.357) 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.
Improved near surface wind speed predictions using Gaussian process regression combined with numerical weather predictions and observed meteorological data. Renew. Energy (IF 4.357) Pub Date : 2018-04-07 Victoria Hoolohan, Alison S. Tomlin, Timothy Cockerill
This study presents a hybrid numerical weather prediction model (NWP) and a Gaussian process regression (GPR) model for near surface wind speed prediction up to 72 hours ahead using data partitioned on atmospheric stability class to improve model performance. NWP wind speed data from the UK meteorological office was corrected using a GPR model, where the data was subdivided using the atmospheric stability class calculated using the Pasquill-Gifford-Turner method based on observations at the time of prediction. The method was validated using data from 15 UK MIDAS (Met office Integrated Data Archive System) sites with a 9 month training and 3 month test period. Results are also shown for hub height wind speed prediction at one turbine. Additionally, power output is predicted for this turbine by translating hub height wind speed to power using a turbine power curve. While various forecasting methods exist, limited methods consider the impact of atmospheric stability on prediction accuracy. Therefore the method presented in this study gives a new way to improve wind speed predictions. Outputs show the GPR model improves forecast accuracy over the original NWP data, and consideration of atmospheric stability further reduces prediction errors. Comparing predicted power output to measured output reveals power predictions are also enhanced, demonstrating the potential of this novel wind speed prediction technique.
Effects of Jatropha oil blending with C-heavy oil on soot emissions and heat absorption balance characteristics for boiler combustion Renew. Energy (IF 4.357) Pub Date : 2018-04-06 Nozomu Hashimoto, Hiroyuki Nishida, Msayoshi Kimoto, Kazuki Tainaka, Atsushi Ikeda, Satoshi Umemoto
This study investigated the effect of crude Jatropha oil (CJO) blending with C-heavy oil on the combustion characteristics of oil-fired boilers. Combustion experiments were conducted using a 550 kW liquid fuel combustion test facility equipped with a steam-atomizing burner. The results indicated that the flame radiation intensity is decreased by the CJO blending with C-heavy oil. Consequently, the heat absorption of the sections near the burner decreases. Due to the lower nitrogen and sulfur contents in CJO, the NOx and SO2 emissions are decreased by the CJO blending with C-heavy oil. It was also found that both the particulate matter concentration and the particle size in the exhaust gas are decreased by the CJO blending. This is attributed by the low carbon residue content of CJO. The results of this study imply that when CJO is introduced into oil-fired thermal power stations, considerable attention should be paid to changes in the heat absorption balance and the possibility of a decrease in the particle collection efficiency of the electrostatic precipitator.
Integer programming to optimize Micro-Hydro Power Plants for generic river profiles Renew. Energy (IF 4.357) Pub Date : 2018-04-06 A. Tapia, P. Millán, F. Gómez-Estern
This paper addresses the problem of designing an optimal micro-hydro power installation in rivers with generic profiles, when micro-hydro schemes are studied. This is geared towards the application of Micro-Hydro Power Plants to supply marginal isolated areas using small Pelton wheels, where both technology and resources are limited. For this purpose, a model of a Pelton micro-hydro plant is first developed. Subsequently, a discretization of the river profile is made, on the basis of which a set of integer variables are proposed, being the model transformed then into an integer optimization problem. Finally, the effectiveness of the proposed method is showed through a specific design problem. The application of the developed method is especially interesting when designing micro-hydro plants to provide electricity to isolated populations, where both technology and resources are limited.
Numerical simulation of solar chimney power plant adopting the fan model Renew. Energy (IF 4.357) Pub Date : 2018-04-05 Rayan Rabehi, Abla Chaker, Tingzhen Ming, Tingrui Gong
Numerical simulations and design of solar chimney power plant adopting the fan model was presented in this study. A mathematical model describing fluid flow and heat transfer has been set up for the three regions of solar chimney power plant: collector, chimney and turbine. The Spanish prototype was chosen as an example for numerical simulation that incorporates turbine model, simulation during turbine operation and no load conditions were compared. For this purpose a simulation of 3D solar chimney power plant system with the standard k-ε turbulence model was developed, using CFD Ansys Fluent. Furthermore the effect of turbine operation and the influences of pressure drop across the turbine and solar radiation were investigated and the results revealed that the variation of solar radiation has an evident effect on the flow and heat transfer characteristics. Meanwhile the influence of turbine pressure drop on the collector efficiency was slight, while has a considerable effect on the power output.
Analysis of Extremely Modulated Faulty Wind Turbine Data Using Spectral Kurtosis and Signal Intensity Estimator Renew. Energy (IF 4.357) Pub Date : 2018-04-05 Mohamed Elforjani, Eric Bechhoefer
The use of signal processing for condition monitoring of wind turbines data has been on-going since several decades. Failure in the analysis of high modulated data may make the machine break. An example of this is the reported real case of bearing failure on a Repower wind turbine, which could not be detected by currently applied methods. The machine had to be out of service immediately after a faulty bearing outer race was visually ascertained. Vibration dataset from this faulty machine was provided to facilitate research into wind turbines analysis and with the hope that the authors of this work can improve upon the existing techniques. In the response to this challenge, the authors of this paper proposed Spectral Kurtosis (SK) and Signal Intensity Estimator (SIE) as proven time-frequency fault indicators to tackle the question of data with different modulation rates. Extensive signal processing using time domain and time-frequency domain analysis was undertaken. It was concluded that SIE is well established mature approach and it provides a more reliable estimate of wind turbine conditions than conventional techniques such as SK, leading to better discrimination between “good” and “bad” machines.
Gaussian Process Regression based Inertia Emulation and Reserve Estimation for Grid Interfaced Photovoltaic System Renew. Energy (IF 4.357) Pub Date : 2018-04-05 S. Kanwal, B. Khan, S.M. Ali, C.A. Mehmood
Accurate power reserve estimation for a Photovoltaic Generator (PVG) is of paramount importance to combat frequency changes in a smart grid. Standalone PVG lacks inertia, or an internal power reserve due to power electronic converter grid-interface. Operating a PVG at deloaded percentage of its maximum power capacity mimics an internal power reserve, simulating the Automatic Generation Control (AGC) feature of synchronous machines. Thus, a deloaded PVG releases or absorbs the reserve according to the frequency variations for the grid stability. Moreover, an efficient switching between various reserves during grid operation is required. The common reserve estimation technique is to apply PVG manufacturer’s specification based deterministic approach. In this work, we compare the deterministic modeling results with a statistical learning model of Gaussian Process Regression (GPR). The GPR model is trained by dataset of PVG maximum power values evaluated by load line analysis in a simulation, according to the irradiance and historical temperature of Abbottabad, Pakistan. The trained model performance is compared with the deterministic model in a simulation, where the PVG is saturated to turn on a synchronous generator. Time difference of turning on the backup generator between GPR model and deterministic modeling validates the importance of accurate reserve estimation.
Experimental study and Life Cycle Assessment (LCA) of Hybrid Photovoltaic/Thermal (PV/T) solar systems for domestic applications Renew. Energy (IF 4.357) Pub Date : 2018-04-05 Manolis Souliotis, Nektarios Arnaoutakis, Giorgos Panaras, Angeliki Kavga, Spiros Papaefthimiou
The paper presents the study of a Hybrid Photovoltaic/Thermal solar water system installed on the roof of buildings. The conducted analysis focuses on a detailed experimental investigation of both the electrical and thermal behavior, and in addition on the holistic environmental analysis during the complete life cycle of the system. The photovoltaic module, used for electricity production, is connected with a heat recovery unit with circulating fluid flow for cooling, while the extracted heat can be used for domestic hot water provision. The aim of this study is to analyze the energy and environmental performance of arrangements based on natural and forced circulation, and to draw general conclusions for the viability of such systems. The environmental performance of the studied devices was evaluated through a detailed Life Cycle Assessment. The energy analysis proves that hybrid systems are more efficient compared to conventional solar thermal and photovoltaic appliances, while they are less environmentally friendly mainly during their production and installation phases.
A numerical study of NOx and soot emissions in methane/n-heptane triple flames Renew. Energy (IF 4.357) Pub Date : 2018-04-05 Prithviraj Sabnis, Suresh K. Aggarwal
There is significant interest worldwide in using cleaner/renewable fuels, such as syngas and biogas, in transportation and power generation systems. We report herein a computational study to investigate NOx and soot emissions in n-heptane/methane triple flames in an opposed-jet configuration. The objective is to evaluate various fuel injection scenarios in a dual-fuel engine using a simple configuration to emulate important aspects of diesel combustion. Simulations are performed by combining a detailed fuel and NOx chemistry model with a soot model. Three blending strategies are examined. For each strategy, NOx, PAH and soot emissions, and thermal efficiency are characterized by varying the energy content between the two fuels, while keeping the total energy input rate fixed. As methane in the blend is increased, the benzene emission index and soot emission decrease with all three strategies, but the reduction is more pronounced with strategies 2 and 3. In addition, it leads to higher efficiency with strategies 2 and 3, but lower efficiency with strategy 1. Thus strategy #1 yields higher NOx, PAH and soot emissions, and lower efficiency compared to other two strategies, and is not recommended.
Numerical Investigation of in-Cylinder Air Flow Characteristic Improvement For Emulsified Biofuel (EB) Application Renew. Energy (IF 4.357) Pub Date : 2018-04-04 M.F. Hamid, M.Y. Idroas, S. Sa’ad, A.J. Saiful Bahri, C.M. Sharzali, M.K. Abdullah, Z.A. Zainal
Emulsified biofuel (EB) has a relatively higher viscosity compared to conventional diesel; which affects the spray injection and restricts the maximum evaporation. The modification is necessary to standard engines in order to realize its application. This paper presents the effects of three dissimilar designs of piston-bowl geometry in the compression ignition (CI) engine to in-cylinder airflow characteristics improvement of the EB during injection. The three piston bowl geometry designs; open cylinder bowl (OCB), shallow depth re-entrance combustion chamber (SCC) and omega combustion chamber (OCC). ANSYS FLUENT 15 is utilized to run a three dimensional (3D) cold flow internal combustion (IC) engine simulation. The main parameters of this investigation; swirl, tumble and cross tumble ratios, as well as turbulence kinetic energy (TKE), with respect to crank angle. It shows that the SCC piston bowl design is the best due to significant effect on swirl, tumble, cross tumble ratios and TKE in the injection fuel region. It breaks up the length penetration of injection to mix with the surrounding air and capable to organize the distribution of the heavier molecules of the EB during the compression stage.
The effect of Research and Development incentive on wind power investment, a system dynamics approach Renew. Energy (IF 4.357) Pub Date : 2018-04-04 M. Esmaieli, M. Ahmadian
Due to high and unstable fossil fuel prices, air pollution arising from conventional power plants, and the need for higher levels of energy security, the necessity of using renewable energy, especially wind power have increased. But barriers such as high investment cost and uncertainty in generation, limit the participation of investors in this respect. Therefore, different incentives have been considered to speed up the development of renewable energy units. Most of these incentives focus on compensating the high investment cost and uncertainty in the future revenue of these units. On the other hand, this paper proposes a new approach based on supporting research and development activities to reduce the investment cost of wind units. Accordingly, a fixed amount is paid to the wind units proportional to their installed capacity but they should spend this fixed amount on research and development activities. These activities lead to lower construction costs due to technology maturity. In order to study the performance of the proposed incentive, the long-term behavior of electricity market was simulated by a dynamic model followed by a sensitivity analysis to investigate the effect of different factors. The results indicated the effectiveness of the proposed incentive compared to other known incentives.
Effectiveness of optimized control strategy and different hub height turbines on a real wind farm optimization Renew. Energy (IF 4.357) Pub Date : 2018-04-04 Longyan Wang, Michael E. Cholette, Yunkai Zhou, Jianping Yuan, Andy C.C. Tan, Yuantong Gu
In this paper, a real wind farm layout optimization is carried out by applying the novel optimized wind farm control strategy (coordinating wind turbine operations by setting different axial induction values) and multiple wind turbine hub height selections. The unrestricted coordinate method (using Cartesian coordinates to determine wind turbine positions) is applied to study the effectiveness of different wind farm control strategies and wind turbine hub heights on the wind farm optimization. Means of handling the irregular boundary constraints and calculating the wind speed over non-flat terrain at different heights are proposed for the real wind farm. The results show that the optimized control strategy can always yield better results than the self-optimum control strategy, achieving a smaller cost of energy production and a larger wind farm efficiency. Quantitatively, the optimized control strategy yields approximately 9 kW more power per turbine than the self-optimum control strategy and reduces the cost of energy by 0.08 million dollars per megawatt with 39 wind turbines installed. The application of different hub height turbines facilitates to place wind turbines more flexibly achieving better optimization results than that with constant hub height turbines.
Quasi-Steady State Moving Boundary Reduced Order Model of Two-Phase Flow for ORC Refrigerant in Solar-Thermal Heat Exchanger Renew. Energy (IF 4.357) Pub Date : 2018-04-03 Rudrodip Majumdar, Suneet Singh, Sandip K. Saha
Span80/Tween80 stabilized bio-oil-in-diesel microemulsion: formation and combustion Renew. Energy (IF 4.357) Pub Date : 2018-04-03 Jie Liang, Yingying Qian, Xingzhong Yuan, Lijian Leng, Guangming Zeng, Longbo Jiang, Jianguang Shao, Yuan Luo, Xiaowei Ding, Zhaoxue Yang, Xuemei Li
A detailed experimental study was conducted to investigate the production and fuel properties of bio-oil-in-diesel microemulsion (BDM) and its emission characteristics. Bio-oil was produced from liquefaction of methanol, castor oil and sewage sludge. Hydrophilic surfactant (Span 80) and hydrophobic surfactant (Tween 80) of different mixing ratio and different co-surfactant (alcohols) were tested to form BDM with higher bio-oil solubility and better stability. The best mixed ratio was proved to be 7/3 (Span 80/ Tween 80) with 2% n- hexanol. The principle of “likes dissolve likes” was set as a guiding mechanism on bio-oil solubilization process. The emulsified fuel stabilized by mixed surfactant and co-surfactant, in comparison with other hybrid fuels and diesel, was tested in a single cylinder, four-stroke, water cooling, direct injection, diesel engine to study the emission characteristics. The results show that, compared with diesel, BDM performed well in brake specific fuel consumption (BSFC) and brake thermal efficiency (BTE) while reduced CO, CO2 and NOX emissions by 21.4%-66.7%, 7.1%-27.3% and 1.5%-14.7%, respectively. This was the first time of using surfactant compound to form bio-oil microemulsion, which provides a possibility for practical application of microemulsion fuels and further benefiting SS utilization.
A spatiotemporal universal model for the prediction of the global solar radiation based on Fourier series and the site altitude Renew. Energy (IF 4.357) Pub Date : 2018-04-03 E. Kaplani, S. Kaplanis, S. Mondal
This paper presents the development, testing and validation of a novel generic type universal model consisting of a set of sine and cosine harmonics in the temporal and spatial domain suitably parameterized for the prediction of the mean expected global solar radiation H(n,φ) on the horizontal for a day, n, at any latitude φ. Its prediction power is further enhanced with the introduction of a correction term for the site altitude taking into account the φ dependent atmospheric height. Solar radiation data from 53 stations around the earth were obtained from GEBA database to train the model. H(n,φ) is expressed by a Fourier series of compact form with the zero frequency component dependent on φ providing the main spatial dependence and two n dependent harmonics in the form of cosine functions giving the time dependence. The φ dependent model parameters follow symmetry rules and are expressed by Fourier series up to the 3rd order harmonic. The 3D spatiotemporal profile of the model is in agreement to the extraterrestrial one. The model was validated using GEBA data from additional 28 sites and compared with NASA, PVGIS and SoDa data, showing the robustness, reliability and prediction accuracy of the proposed model.
Second generation biofuels production from waste cooking oil via pyrolysis process Renew. Energy (IF 4.357) Pub Date : 2018-04-03 Aïda Ben Hassen Trabelsi, Kaouther Zaafouri, Withek Baghdadi, Slim Naoui, Aymen Ouerghi
The thermal cracking of waste cooking oil (WCO) via pyrolysis was performed using a laboratory scale fixed-bed reactor. The effects of the final pyrolysis temperature (from 550 to 800 °C) and the heating rate (5°C/min, 15°C/min, 20°C/min, 25°C/min) on pyrolysis products distribution has been investigated and a maximum bio-oil yield of 80 wt% has been obtained at 800 °C and 15°C/min. The bio-oil fuel properties shows that this pyrolytic oil has high caloric value (HHV around 8843 Kg/Kcal) promoting its use as a liquid fuel but some other properties (high acidity index around 126.8 mg KOH/ g sample and high viscosity about 8.95 cSt) need to be upgraded. The GC/MS characterization of the bio-oil highlights its high molecular complexity allowing it to be used as source of chemical products and of active molecules. The syngas heating value (reaching 8 MJ/Kg) is suitable for its application as source of energy for the pyrolysis reactor. The remaining biochar is suitable for application as fertilizer since it is rich of iron and organic carbon. The stochiometric model of WCO pyrolysis has been established basing on the pyrolysis products yields, the CHNS-O composition of raw material and remaining biochar, and the syngas chemical composition.
Performance and stability of semitransparent OPVs for building integration: A benchmarking analysis Renew. Energy (IF 4.357) 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.
The adoption of building-integrated photovoltaics: barriers and facilitators Renew. Energy (IF 4.357) Pub Date : 2018-04-03 Hans Christoph Curtius
Widespread deployment of building-integrated photovoltaics (BIPV) could potentially lead to a multiplication of the area available for harvesting solar energy in densely populated countries. Despite its advantages to contribute to meeting renewable energy targets and substitute conventional building materials, the diffusion of BIPV has so far remained well below expectations. This paper investigates barriers to and facilitators of adoption based on 43 qualitative interviews with stakeholders across the BIPV value chain. It conceptualizes a framework that classifies the determinants of the adoption processes of renewable energy technologies and of BIPV in particular. Product-specific, stakeholder-specific and institutional barriers are identified. Central product-specific barriers include high initial costs and high complexity. The main stakeholder-specific barriers are low awareness of BIPV, and the reluctance of many architects to adopt BIPV. Institutional barriers refer to political risks. The paper derives recommendations for policy makers and marketers. Successful BIPV policies should create clear incentives for BIPV adopters, either in the form of financial support or inclusion of BIPV in building codes or labels. As for marketing, BIPV suppliers should develop targeted communication strategies towards building owners and architects and offer turn-key solar roofs in order to overcome concerns about the complexity of BIPV.
The Role of Hydropower Installations for Sustainable Energy Development in Turkey and the World Renew. Energy (IF 4.357) Pub Date : 2018-04-02 Mehmet Bilgili, Harun Bilirgen, Arif Ozbek, Firat Ekinci, Tugçe Demirdelen
Hydropower has the largest share among renewable energy sources in the world, supplying more than 16.6% of total global electricity to over 160 countries around the world. Global hydropower capacity increased to approximately 1,096 GW with the addition of 25 GW of new hydropower capacity in 2016. With a 216 TWh per year generation capacity, Turkey’s hydropower potential is the largest in Europe. The increased rate of installed capacity in Turkey was ranked 7th in the world in 2016 with an annual installed hydroelectric capacity of 0.8 GW. The main objective of this paper is to review the developments of hydropower installations around the world and in Turkey with an emphasis on the potential of small scale hydropower systems such as waterwheels in utilizing low head water flow for household electricity usage. In the first part of this study, the growth of worldwide hydropower capacity is reviewed and the countries with the largest installed and new built hydropower capacities are reported. In the second part of this study, the current status of Turkey’s hydropower plants is discussed in detail with respect to annual regional rainfall, gross water mass flow and potential of Turkey’s major water basins to demonstrate the potential energy output that can be harnessed from small-scale systems implemented in low-head water sources. In addition, the most recent information on Turkey’s electricity generation and consumption rates are reported.
Development of a propeller-type hollow micro-hydraulic turbine with excellent performance in passing foreign matter Renew. Energy (IF 4.357) Pub Date : 2018-04-02 Tomomi Uchiyama, Satoshi Honda, Tomohiro Degawa
This study develops a micro-hydraulic turbine with excellent performance in the passage of foreign matter included in the water flow. The runner has four blades, with a circular hollow around the rotating axis to pass foreign matter through the runner. The ratio of the hollow diameter D2 D 2 to the runner outer diameter D1 D 1 , D2/D1 D 2 / D 1 , is defined as the hollow ratio ε. Laboratory experiments are conducted by introducing polyester fibers into the water flow as foreign matter. The turbine efficiency η decreases with increasing ε under the fiber-free condition. For the runner having no hollow (ε = 0), η decreases drastically with increasing the mass of the introduced fibers. This is due to the blockage of the runner by the fibers. But η for the runners provided with the hollow decreases less. This demonstrates that the hollow makes the fibers pass successfully through the runner. Additional experiments are conducted using the runner with ε = 0.25. The blade leading edges near the central axis are rounded with radius R . When R/D1 R / D 1 = 0.1875, the decrease in η due to the fibers is extremely small. The rounded leading edges successfully prevent the runner from catching the fibers, demonstrating that they effectively heighten the passage performance of foreign matter through the runner.
Variability of wind turbine noise over a diurnal cycle Renew. Energy (IF 4.357) Pub Date : 2018-04-02 Emre Barlas, Ka Ling Wu, Wei Jun Zhu, Fernando Porté-Agel, Wen Zhong Shen
The diurnal variation of atmospheric conditions over land has a significant effect on the wind and temperature distributions which greatly influence the generation and propagation of wind turbine aerodynamic sound. In this paper, a fully consistent unsteady approach is used to study wind turbine noise such that large eddy simulation with a rotational actuator disk wind turbine model is used to model the wind and temperature around a mega-watt scale wind turbine over a diurnal cycle, and time dependent flow and temperature fields are used as input to the coupled wind turbine noise generation-propagation model. Computations are carried out for four different 10 min datasets selected at certain periods of a day for a same hub height wind speed. It is observed that the time dependent as well as the time averaged sound pressure levels in near field do not show large variations during the day. However, as we move away from the turbine, the propagation effects take over and downwind of the turbine the night time levels exceed the day time levels (at 3600 m the averaged difference reaches 6.5 dBA).
Contributions of ultrasonic wave, metal ions, and oxidation on the depolymerization of cellulose and its kinetics Renew. Energy (IF 4.357) Pub Date : 2018-03-30 Hengxiang Li, Kang Zhang, Xiaohua Zhang, Qing Cao, Li’e Jin
Short-term extreme response and fatigue damage of an integrated offshore renewable energy system Renew. Energy (IF 4.357) Pub Date : 2018-03-30 Liang Li, Zhengshun Cheng, Zhiming Yuan, Yan Gao
This study addresses short-term extreme response and fatigue damage of an integrated wind, wave and tidal energy system. The integrated concept is based on the combination of a spar type floating wind turbine, a wave energy converter and two tidal turbines. Aero-hydro-mooring coupled analysis is performed in time-domain to capture the dynamic response of the combined concept in a set of environmental conditions. The mean up-crossing rate method is used to evaluate the extreme response, which takes advantage of an extrapolation method to reduce the simulation sample size. The cumulative fatigue damage is computed based on the S-N method. Simulation results show that the tower base fore-aft bending moment is improved, in terms of extreme value and fatigue damage. Nevertheless, the tension force of a mooring line is worsened. The mooring line bears increased maximum tension due to the tidal turbine thrust force and it is subjected to higher fatigue damage load as well.
Modelling the hydrodynamic and morphological impacts of a tidal stream development in Ramsey Sound Renew. Energy (IF 4.357) Pub Date : 2018-03-30 David Haverson, John Bacon, Helen C.M. Smith, Vengatesan Venugopal, Qing Xiao
A number of sites around the UK are being considered for development of tidal stream energy, one of which is Ramsey Sound off the coast of Pembrokeshire, South Wales. The Sound was used to test the prototype of the Delta Stream by Tidal Energy Ltd. After initial testing, a 10 MW tidal array was proposed at St David’s Head. To investigate any possible environmental impacts of the array due to energy extraction, a case study of the Pembrokeshire coast was performed using a high-resolution depth averaged hydrodynamic model, Telemac2D, to investigate changes to hydrodynamics and morphodynamics. Results show that the proposed array of nine tidal energy converters will cause alterations to eddy propagation leading to changes in the velocity field up to 24km from the tidal array. Changes in morphodynamics are predicted through alterations to the bed shear stress. Changes to the mean and maximum bed shear stress, over a 30-day period, are found to be more localised and extend 12km from the array. These changes indicate that the proposed tidal array will lead to localised sediment accumulation and will act as a barrier to sediment transport, with potential consequences for the benthic ecology of the region.
Effect of percussion vibration on solidification of supercooled salt hydrate PCM in thermal storage unit Renew. Energy (IF 4.357) Pub Date : 2018-03-30 Guobing Zhou, Maochuan Zhu, Yutong Xiang
Experiments are performed on the effect of percussion vibration on triggering solidification of supercooled sodium acetate (CH3COONa) salt solution in the rounded - rectangular thermal storage unit. To provide quantitative analysis, the steel ball freely falling down to the surface of PCM (phase change material) unit is applied for percussion vibration with parameters of percussion number and crystallization induction time. Factors such as the steel ball diameter and falling height, as well as the percussion position on the PCM unit are examined about their effects on the crystallization induction. The results show that it is favorable to activate solidification of supercooled sodium acetate solution with larger percussion momentum (larger ball diameter and higher falling height), percussion near the cover lid and edges of unit. A term named percussion effectiveness is also introduced for evaluation of percussion effect on solidification activation. The results in this paper are useful for seasonal thermal storage of solar energy within supercooled inorganic PCMs and control of discharging the stored energy for space heating.
Investigating co-firing characteristics of coal and masson pine Renew. Energy (IF 4.357) Pub Date : 2018-03-30 Wanhe Hu, Fang Liang, Hongzhong Xiang, Jian Zhang, Xiaomeng Yang, Tao Zhang, Bingbing Mi, Zhijia Liu
Co-firing characteristics of masson pine and coal was determined using thermogravimetric analysis at different heat rates in an air atmosphere. The kinetic parameters were calculated using Kissinger-Akahira-Sunose and Coats-Redfern method. Pollutant emission and ash characteristics were also investigated. Results showed that all samples had two separated combustion zones during co-firing process except for coal, corresponding to volatile and char combustion. CO2 had the highest releases and SO2 had the lowest release. The chemical compositions and thermodynamic properties of blend ash were similar with coal ash. The optimum blend ratio was 20% masson pine and 80% coal because it had the similar kinetic parameters and ash characteristics with coal. Furthermore, it also had a lower pollutant emission. The results from this research will be helpful to develop masson pine as fuel products in China.
An analysis of harmonic heating in smart buildings and distribution network implications with increasing non-linear (domestic) load and embedded generation Renew. Energy (IF 4.357) Pub Date : 2018-03-30 Chittesh Veni Chandran, Keith Sunderland, Malabika Basu
Harmonic distortion is generally not taken into account within domestic installations and the associated wiring systems, as its potential is considered sufficiently small to be neglected. Standards to limit harmonic manifestations in the low voltage (LV) network are available, but these can be breached as a consequence of advancements in power electronics in some modern household devices contributing higher levels of harmonic distortion than permitted.While these devices individually might not be considered serious in terms of system level harmonic distortion manifestations, electrical equipment failures and insulation failures - increasingly being derived from harmonic cable heating - suggest a different story. A 10% increase in THD in a circuit will result in an increase of 10% in cable heat. Recently, attempts have been made to offer harmonic derating factors for building electrical circuit design in BS7671, but this approach currently prioritizes large power devices. This article explores the need for harmonic considerations during the design stage of electrical services engineering projects. Best practice suggestions, in the context of the dissemination of heat caused by harmonics related to household load deployments/configurations, are also provided based on the analysis conducted with real household data. This is further extended to a practical distribution network where the effect of harmonic heating at the network level is explored. The results suggest that the harmonics in the distribution network can amass to cause a cumulative effect on the network. Furthermore, it can be observed from the results that in a distribution network containing (domestic) solar photo voltaic (PV) systems, the harmonic heating issue can be reduced. This benefit is not without consequence however, as increasing PV penetration does not reduce the harmonic content of the overall system and therefore presents a further concern that may need to be addressed in due time.
CO2 –Water Mixture Reinjection into Two-Phase Liquid Dominated Geothermal Reservoirs Renew. Energy (IF 4.357) Pub Date : 2018-03-30 Eylem Kaya, Victor Callos, Warren Mannington
Geothermal energy resources are considered to be one of the main contributors to clean, renewable and low-risk energy production. However geothermal power production may result in some greenhouse gas (GHG) emissions. Injection of GHGs into geothermal reservoirs can be used to reduce these emissions, providing reservoir pressure support and possibly improve reservoir permeability. To understand the migration and behavior of injected gases in the reservoir and to forecast gas breakthrough, simulation studies are required. This work investigates the possible impacts of infield reinjection of CO2 in two-phase liquid-dominated geothermal reservoirs using an earlier 3D numerical model of the Wairakei-Tauhara system as a representative case study. Wairakei-Tauhara is an interesting case study as it has been operated with no reinjection for most of its lifetime. The work investigated the impact of various scenarios of separated geothermal water and CO2 reinjection on reservoir sustainability. The breakthrough of CO2 was also monitored since it can result in higher gas production and lower power generation. The modelling results showed that the injection of CO2-water mixture helps to maintain the reservoir’s pressure, but, at the same time, it may suppress natural recharge and boiling, which results in reduction of the enthalpy of the produced fluid.
Mechanism of High Amplitude Low Frequency Fluctuations in a Pump-Turbine in Pump Mode Renew. Energy (IF 4.357) Pub Date : 2018-03-29 Deyou Li, Hongjie Wang, Yonglin Qin, Zhenggui Li, Xianzhu Wei, Daqing Qin
Pumped storage technology has become the most important energy storage technology in industry today. The instabilities of pump-turbines as key parts of pumped storage power plants have become critical issues in development of pump storage technology. High-amplitude pressure fluctuations are one of such instabilities. In this study, unsteady numerical simulations were carried out in the pump mode of a pump-turbine at using the shear stress transport (SST) k-ω turbulence model. Performance characteristics agree well with experimental data. Unsteady characteristics of typical operating points were obtained. The results show that there are high-amplitude pressure fluctuations at the partial operating points. The frequency characteristics and the propagation law of an at-large partial operating point (0.74QBEP) were determined using time and frequency domain analysis methods (bispectrum, coherence) in combination with the flow field. The analysis results reveal that high-amplitude pressure fluctuations at point 0.74QBEP result from the rotation of Dean Vortices in the draft tube. Due to the rotation of the Dean Vortices, the blocking intensity of the two regions in the guide vane and the stay vane passages are periodically changed at a frequency 0.58fn, which results in a shock phenomenon in the guide/stay vanes.
An hourly simulation method for the energy performance of an office building served by a ground-coupled heat pump system Renew. Energy (IF 4.357) Pub Date : 2018-03-29 Linfeng Zhang, Gongsheng Huang, Quan Zhang, Jinggang Wang
Ground heat exchangers are key component of ground-coupled heat pump systems, and their thermal response is therefore very important for ground-coupled heat pump system design and operation. This paper proposes a new hourly simulation method, and uses it to study the performance improvement potential for the ground-coupled heat pump system. First, with an effective U-pipe shank spacing determined by the calculated and measured borehole thermal resistance, a reasonable and accurate fluid temperature prediction method is developed, and the hourly energy performance simulation method is also proposed accordingly with the Fast Fourier Transform superposition algorithm. This hourly simulation method is validated using experimental data collected from a well-designed ground-coupled heat pump experiment platform, which shows that the maximum absolute error for the predicted fluid temperature is smaller than 1.04 °C. Second, using the proposed hourly simulation method, a framework for the energy performance simulation of an office building served by the ground-coupled heat pump system is developed. Impact factors on ground-coupled heat pump system performance are systematically analyzed using this simulation method, and the results show that performance can be improved with shorter operation schedules and lower heat fluxes.
Treatment of slaughterhouse blood waste using pilot scale two-stage anaerobic digesters for biogas production Renew. Energy (IF 4.357) Pub Date : 2018-03-29 Shunli Wang, Gary L. Hawkins, Brian H. Kiepper, Keshav C. Das
Anaerobic digestion (AD) is an attractive technology for treatment of slaughterhouse blood waste for energy recovery to offset energy used in the slaughterhouse. However, no studies have been conducted at the pilot or full scales using such waste streams as the primary substrate. In this study, three 197-L pilot scale two-stage AD systems, with or without bamboo biocarriers, treating poultry blood waste were evaluated at two organic loading rates (OLRs) (low = 0.4 and high = 0.7 g COD L−1 day−1) under mesophilic condition (26 ± 2 °C) for 260 days. Biocarriers were added to immobilize the microflora and increase cell residence time in the digesters. Results show that the system with biocarriers had methane yield of 192 mL g−1 CODadded and COD removal of 32.4% at the high OLR, and methane yield of 384 mL g−1 CODadded and COD removal of 68.5% at the low OLR, which were significantly higher than those of the system without biocarriers (used as control). Methanobrevibacter and Methanobacterium beijingense were the dominant archaea in the system using biocarriers. It is estimated that 39.7–41.4 kJ can be recovered from the treatment of blood waste from each kg of slaughtered livestock weight using the two-stage AD system.
Graphite/diamond ethylene glycol-nanofluids for solar energy applications Renew. Energy (IF 4.357) Pub Date : 2018-03-29 E. Sani, N. Papi, L. Mercatelli, G. Żyła
The rapid development of thermodynamic solar systems requires increasingly efficient absorption materials. This work reports on the investigation of light-intensity dependent optical properties of graphite/nanodiamond suspensions in ethylene glycol, in the perspective to evaluate their potential for direct absorption solar collectors and solar vapor generation. The study was carried out two sample types, differing in the ash content (0.3% and 5.9% wt in the powder), and at three concentrations each (0.0025%, 0.0050%, 0.0100% wt in the fluid). A high sunlight extinction was found, with full absorption in 15 mm and 30 mm path lengths for the 0.0100% and 0.0050% wt concentrations, respectively. This makes investigated nanofluids appealing as volumetric direct solar absorbers in solar collectors. Moreover, by characterizing optical properties at high incident intensities, we proved the creation of vapor bubbles in the base fluid via optical limiting effects active at least from ultraviolet to near infrared wavelengths. This result propose graphite/nanodiamond-based suspensions for sunlight-induced vapor generation application as well.
A novel polysulfone-based ternary nanocomposite membrane consisting of metal-organic framework and silica nanoparticles: as proton exchange membrane for polymer electrolyte fuel cells Renew. Energy (IF 4.357) Pub Date : 2018-03-29 Leila Ahmadian-Alam, Hossein Mahdavi
Optimization of a building integrated solar thermal system with seasonal storage using TRNSYS Renew. Energy (IF 4.357) Pub Date : 2018-03-28 Christodoulos N. Antoniadis, Georgios Martinopoulos
In the current work a building integrated solar thermal system with seasonal storage is optimized with the use of TRNSYS modeling software in order to evaluate different integration options of the solar collector array. The model calculates the space heating needs during the heating period as well as the annual domestic hot-water needs of a typical single-family detached home in the city of Thessaloniki, Greece that has been built according to the latest building code. The contribution of the solar system and the thermal load covered by the auxiliary conventional system are determined, for both space heating and domestic hot water, considering the respective simulation periods. The relative solar fractions as well as the combined annual solar fraction are also calculated. A parametric analysis on the impact of various solar collector areas and types, building integration type, as well as the volume of the seasonal storage tank is also presented in order to optimize system design and obtain a seasonal combined solar fraction of at least 39%.
Biogas: developments and perspectives in Europe Renew. Energy (IF 4.357) Pub Date : 2018-03-28 Nicolae Scarlat, Jean-François Dallemand, Fernando Fahl
This paper presents an overview of the development and perspectives of biogas in and its use for electricity, heat and in transport in the European Union (EU) and its Member States. Biogas production has increased in the EU, encouraged by the renewable energy policies, in addition to economic, environmental and climate benefits, to reach 18 billion m3 methane (654 PJ) in 2015, representing half of the global biogas production. The EU is the world leader in biogas electricity production, with more than 10 GW installed and a number of 17,400 biogas plants, in comparison to the global biogas capacity of 15 GW in 2015. In the EU, biogas delivered 127 TJ of heat and 61 TWh of electricity in 2015; about 50% of total biogas consumption in Europe was destined to heat generation. Europe is the world’s leading producer of biomethane for the use as a vehicle fuel or for injection into the natural gas grid, with 459 plants in 2015 producing 1.2 billion m3 and 340 plants feeding into the gas grid, with a capacity of 1.5 million m3. About 697 biomethane filling stations ensured the use 160 million m3 of biomethane as a transport fuel in 2015.
Downscaling solar irradiance using DEM-based model in young volcanic islands with rugged topography. Renew. Energy (IF 4.357) Pub Date : 2018-03-27 Miloud Bessafi, Vishwamitra Oree, Abdel Khoodaruth, Guillaume Jumaux, François Bonnardot, Patrick Jeanty, Mathieu Delsault, Jean-Pierre Chabriat, Muhammad Dauhoo
Many small island developing states are adopting solar photovoltaic technologies as a solution to curtail their overreliance on fossil fuels. Some of these islands are young and of volcanic origin, characterised by intricate topographic heterogeneity. Since they are mostly small, flat land is scarce and valuable. As a result, solar photovoltaic projects are usually developed at sites with complex terrain where frequent changes in elevation, slope and shadows cast by topographic features can significantly attenuate the amount of solar irradiance received. The existence of strong local solar radiation gradients on such islands implies that any solar resource assessment must be performed at a small enough spatial and temporal resolution in order to provide a reliable basis for investment decisions. Ground-based measurements of solar irradiance are accurate but are widely dispersed geographically. Although satellite-derived solar resource data have better spatial and temporal resolution than those recorded by radiometric stations, they are less accurate. Moreover, their spatial resolution is still too large with respect to the small size of the islands. In this work, a downscaling methodology is used to derive monthly and annual average global solar irradiance maps at a resolution of 250m x 250m using satellite hourly datasets, spanning over the period 1999 to 2015 and having a spatial resolution of 0.05° x 0.05°. The combined effects of horizon blocking and sky obstruction resulting from heterogeneous topography are considered by applying a binary blocking factor and sky view factor respectively. The downscaled maps are then refined by convolving them with ground-based measurements through a kriging procedure. The methodology is validated using leave-one-out kriging procedure and illustrated successfully with the case of Reunion Island, where strong local gradients of solar irradiance were easily distinguished in regions marked by uneven topographic features.
A novel method to optimize electricity generation from wind energy Renew. Energy (IF 4.357) Pub Date : 2018-03-27 E.E. Vogel, G. Saravia, S. Kobe, R. Schumann, R. Schuster
We present and discuss a new technique based on information theory to detect in advance favorable periods of wind activity (positive ramps) for electricity generation. In addition this technique could also help in the analysis of plant operation and management protocols design. Real data from wind power plants in Germany is used; this information is freely available in the internet with reliable registers every 15 min. A simple protocol to mix such wind energy production with electricity coming from conventional sources is proposed as a way to test the proposed algorithm. The eight-year period 2010–2017 is analyzed looking for different behaviors in wind activity. The first five years (2010–2014) are employed to calibrate the method, while the remaining three years (2015–2017) are used to test previous calibration without any further variation in the tuning possibilities described below. Thus, the proposed protocol is tried on under different seasonal wind conditions. Both the algorithm and the general protocol could be adjusted to optimize performances according to regional conditions. In addition, this algorithm can also be used in retrospective studies to adjust productivity to operational conditions.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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