A novel hierarchical contribution factor based model for distribution use-of-system charges Appl. Energy (IF 7.182) Pub Date : 2017-09-21 A. Sharma, R. Bhakar, H.P. Tiwari, R. Li, F. Li
Due to the limited visibility at low voltage (LV) networks, existing Distribution Use-of-System (DUoS) charging methodologies assume that all the network users use the network in proportion to their peak flows. This naive supposition fails to reflect the contribution of network users to network peak flows, which actually is the driver for network reinforcement. This can send an inadvertent signal to customers, leading to aggravated network pressure. This paper for the first time, brings the new dimension into the design of DUoS charging methodology by considering the true contribution of customer class’s load on network peak flows. It proposes a novel Hierarchical Contribution Factor based Model (HCM), recognizing the contributions of differing customer classes to the network reinforcement of upstream asset. Such contribution will be further propagated to network assets at higher voltage level, forming a Hierarchical CF model and reflecting the true individual class contribution to the whole-system reinforcement. Benefit of the proposed model on investment deferral is assessed by determining annuitized present value (PV) of future investments, and consequences are assessed on a 22-bus practical Indian reference network. The approach helps customers as a class to reduce their network usage charges by minimizing their energy usage contribution during distribution network peaks, eventually reducing distribution network investment and energy transfer costs.
Nano-enhanced Phase Change Material for thermal management of BICPV Appl. Energy (IF 7.182) Pub Date : 2017-09-21 S. Sharma, L. Micheli, W. Chang, A.A. Tahir, K.S. Reddy, T.K. Mallick
Building-Integrated Concentrated Photovoltaics (BICPV) is based on Photovoltaic (PV) technology which experience a loss in their electrical efficiency with an increase in temperature that may also lead to their permanent degradation over time. With a global PV installed capacity of 303 GW, a nominal 10 °C decrease in their average temperature could theoretically lead to 15 GW increase in electricity production worldwide. Currently, there is a gap in the research knowledge concerning the effectiveness of the available passive thermal regulation techniques for BICPV, both individually and working in tandem. This paper presents a novel combined passive cooling solution for BICPV incorporating micro-fins, Phase Change Material (PCM) and Nanomaterial Enhanced PCM (n-PCM). This work was undertaken with the aim to assess the unreported to date benefits of introducing these solutions into BICPV systems and to quantify their individual as well as combined effectiveness. The thermal performance of an un-finned metallic plate was first compared to a micro-finned plate under naturally convective conditions and then compared with applied PCM and n-PCM. A designed and fabricated, scaled-down thermal system was attached to the electrical heaters to mimic the temperature profile of the BICPV. The results showed that the average temperature in the centre of the system was reduced by 10.7 °C using micro-fins with PCM and 12.5 °C using micro-fins with n-PCM as compared to using the micro-fins only. Similarly, the effect of using PCM and n-PCM with the un-finned surface demonstrated a temperature reduction of 9.6 °C and 11.2 °C respectively as compared to the case of natural convection. Further, the innovative 3-D printed PCM containment, with no joined or screwed parts, showed significant improvements in leakage control. The important thermophysical properties of the PCM and the n-PCM were analysed and compared using a Differential Scanning Calorimeter. This research can contribute to bridging the existing gaps in research and development of thermal regulation of BICPV and it is envisaged that the realised incremental improvement can be a potential solution to (a) their performance improvement and (b) longer life, thereby contributing to the environmental benefits.
Cost comparison of printed circuit heat exchanger to low cost periodic flow regenerator for use as recuperator in a s-CO2 Brayton cycle Appl. Energy (IF 7.182) Pub Date : 2017-09-21 Jacob F. Hinze, Gregory F. Nellis, Mark H. Anderson
Supercritical Carbon Dioxide (sCO2) power cycles have the potential to deliver high efficiency at low cost. However, in order for an sCO2 cycle to reach high efficiency, highly effective recuperators are needed. These recuperative heat exchangers must transfer heat at a rate that is substantially larger than the heat transfer to the cycle itself and can therefore represent a significant portion of the power block costs. Regenerators are proposed as a cost saving alternative to high cost printed circuit recuperators for this application. A regenerator is an indirect heat exchanger which periodically stores and releases heat to the working fluid. The simple design of a regenerator can be made more inexpensively compared to current options.The objective of this paper is a detailed evaluation of regenerators as a competing technology for recuperators within an sCO2 Brayton cycle. The level of the analysis presented here is sufficient to identify issues with the regenerator system in order to direct future work and also to clarify the potential advantage of pursuing this technology. A reduced order model of a regenerator is implemented into a cycle model of an sCO2 Brayton cycle. An economic analysis investigates the cost savings that is possible by switching from recuperative heat exchangers to switched-bed regenerators. The cost of the regenerators was estimated using the amount of material required if the pressure vessel is sized using ASME Boiler Pressure Vessel Code (BPVC) requirements. The cost of the associated valves is found to be substantial for the regenerator system and is estimated in collaboration with an industrial valve supplier. The result of this analysis suggests that a 21.2% reduction in the contribution to the Levelized Cost of Electricity (LCoE) from the power block can be realized by switching to a regenerator-based system.
Economic feasibility of calcium looping under uncertainty Appl. Energy (IF 7.182) Pub Date : 2017-09-21 Dawid P. Hanak, Vasilije Manovic
An emerging calcium looping process has been shown to be a promising alternative to solvent scrubbing, which is regarded as the most mature CO2 capture technology. Its retrofits to coal-fired power plants have the potential to reduce both energy and economic penalties associated with the mature CO2 capture technologies. However, these conclusions have been made based on the deterministic outputs of the economic models that have not considered uncertainties in the model inputs. Therefore, this study incorporates a stochastic approach into the economic analysis of the retrofit of such emerging CO2 capture technology to the coal-fired power plant. The stochastic analysis revealed that levelised cost of electricity (LCOE) and specific total capital requirement were highly affected by the uncertainty in the input variables to the process and economic models. The most probable values for these key economic performance indicators were shown to fall between 75 and 115 €/MWelh, and 2100 and 2300 €/kWel,gross, respectively. Interestingly, the most probable LCOE values for the coal-fired power plant will fall between 50 and 150 €/MWelh. This indicated that the calcium looping retrofit scenario can become economically favoured, mainly due to the high economic penalties incurred by unabated coal-fired power plant associated with carbon tax. Importantly, the outputs of the stochastic economic assessment aligned well with the deterministic results reported in the literature. As the latter were generated using different sets of assumptions regarding the process and economic models, the stochastic approach to the economic assessment can minimise the impact of the model assumptions on estimates of the key economic parameters. Moreover, by indicating the probability of particular outputs, as well as ranking the model input variables according to their influence on the key economic performance, such analysis would allow making more insightful decisions regarding further funding and development of the calcium looping process. Finally, use of the stochastic approach in the economic feasibility assessment enables a more profound and reliable comparison of the different calcium looping retrofit configurations, as well as benchmarking different CO2 capture technologies.
Development of an optimization algorithm for the energy management of an industrial Smart User Appl. Energy (IF 7.182) Pub Date : 2017-09-21 Lorenzo Ferrari, Fabio Esposito, Michele Becciani, Giovanni Ferrara, Sandro Magnani, Mirko Andreini, Alessandro Bellissima, Matteo Cantù, Giacomo Petretto, Massimo Pentolini
The growth of world energy demand combined with global warming and climate change is one of the most urgent global challenges and induced policy measures to foster the use of renewable energy sources. In order to cope with the intrinsic variability of solar and wind, active management of distribution networks and customers is required, if the creation of the so called Smart Grid is desired.This paper focuses on the strategies to enable prosumers (i.e. customers able to self-generate all or part of their energy needs) to optimally manage their generation and loads in order to minimize their energy bill and, at the same time, support the distribution grid stability by responding flexibly to its requirements in terms of active load management. In this study an industrial prosumer equipped with solar and wind generation as well as with a co-generation unit with absorption chiller and heat/cold storage was considered. The work presents an optimization algorithm that was developed and applied to this Smart User to manage operations of the CHP in order to optimize the power generation and the usage depending on internal and external inputs as loads, weather forecast and price from the electricity and natural gas market. The proposed algorithm was tested with real experimental inputs of different typical days and its performance was compared with three common scenarios, i.e. traditional supply, electric load following and thermal load following operation of the CHP. Results compare the different control strategies of the CHP (i.e. thermal and electric load following) and shows economic advantages allowed by means of the optimization algorithm, which appears to be an effective instrument to prepare prosumers to the smart grid of the future.
Multi-objective operation optimization of an electrical distribution network with soft open point Appl. Energy (IF 7.182) Pub Date : 2017-09-20 Qi Qi, Jianzhong Wu, Chao Long
With the increasing amount of distributed generation (DG) integrated into electrical distribution networks, various operational problems, such as excessive power losses, over-voltage and thermal overloading issues become gradually remarkable. Innovative approaches for power flow and voltage controls are required to ensure the power quality, as well as to accommodate large DG penetrations. Using power electronic devices is one of the approaches. In this paper, a multi-objective optimization framework was proposed to improve the operation of a distribution network with distributed generation and a soft open point (SOP). An SOP is a distribution-level power electronic device with the capability of real-time and accurate active and reactive power flow control. A novel optimization method that integrates a Multi-Objective Particle Swarm Optimization (MOPSO) algorithm and a local search technique – the Taxi-cab method, was proposed to determine the optimal set-points of the SOP, where power loss reduction, feeder load balancing and voltage profile improvement were taken as objectives. The local search technique is integrated to fine tune the non-dominated solutions obtained by the global search technique, overcoming the drawback of MOPSO in local optima trapping. Therefore, the search capability of the integrated method is enhanced compared to the conventional MOPSO algorithm. The proposed methodology was applied to a 69-bus distribution network. Results demonstrated that the integrated method effectively solves the multi-objective optimization problem, and obtains better and more diverse solutions than the conventional MOPSO method. With the DG penetration increasing from 0 to 200%, on average, an SOP reduces power losses by 58.4%, reduces the load balance index by 68.3% and reduces the voltage profile index by 62.1%, all compared to the case without an SOP. Comparisons between SOP and network reconfiguration showed the outperformance of SOP in operation optimization.
Research and application of a combined model based on frequent pattern growth algorithm and multi-objective optimization for solar radiation forecasting Appl. Energy (IF 7.182) Pub Date : 2017-09-20 Jiani Heng, Jianzhou Wang, Liye Xiao, Haiyan Lu
Solar radiation forecasting plays a significant role in precisely designing solar energy systems and in the efficient management of solar energy plants. Most research only focuses on accuracy improvements; however, for an effective forecasting model, considering only accuracy or stability is inadequate. To solve this problem, a combined model based on nondominated sorting-based multiobjective bat algorithm (NSMOBA) is developed for the optimization of weight coefficients of each model to achieve high accuracy and stability results simultaneously. In addition, a statistical method and data mining-based approach are used to determine the input variables for constructing the combined model. Monthly average solar radiation and meteorological variables from six datasets in the U.S. collected for case studies were used to assess the comprehensive performance (both in accuracy and stability) of the proposed combined model. The simulation in four experiments demonstrated the following: (a) the proposed combined model is suitable for providing accurate and stable solar radiation forecasting; (b) the combined model exhibits a more competitive forecasting performance than the individual models by using the advantage of each model; (c) the NSMOBA is an efficient algorithm for providing accurate forecasting results and improving the stability where the single bat algorithm is insufficient.
Coupled thermal and optical analysis of a planar waveguide concentrator-receiver Appl. Energy (IF 7.182) Pub Date : 2017-09-20 K. Nithyanandam, J. Deshpande, R. Pitchumani
Harvesting solar energy using optical concentrators such as parabolic troughs or heliostats involve active tracking that requires costly drives and sizable support structures. This study explores the use of optical waveguides based on total internal reflection for concentrating sunlight onto thermal receivers, with the goal of minimizing or eliminating moving parts, tracking structures and cost. To this end, the paper presents an analytical closed-form solution for the coupled optical and thermal transport of solar irradiation through an ideal planar waveguide concentrator integrated with linear receiver at both ends. The effects of various design and operating parameters are systematically investigated on the system performance, which is quantified in terms of net thermal power delivered, aperture area required and collection efficiency. Design envelopes that identify feasible waveguide configurations based on thermal stress, maximum continuous operation temperature and structural constraints are illustrated. The study provides an upper bound for the maximum performance achievable with planar waveguide concentrator-receiver configuration that can be used as a benchmark to compare different practical designs. Further, a cost analysis is presented to determine the preferred design configurations that minimize the cost per unit area of the planar waveguide concentrator coupled to the receiver. Considering applications to thermal desalination and concentrated solar thermal power generation, optimal design configuration of waveguide concentrator-receiver system is identified that results in the least levelized cost of power (LCOP). Sensitivity analysis of the total cost per unit area and LCOP to waveguide material parameters and cost is used to derive improvements needed to meet the U.S. Department of Energy (DOE) SunShot’s solar field cost target of $75/m2.
More than half reduction in price per watt of thermoelectric device without increasing the thermoelectric figure of merit of materials Appl. Energy (IF 7.182) Pub Date : 2017-09-20 Junphil Hwang, Hoon Kim, Dimuthu Wijethunge, Nagaraj Nandihalli, Yoomin Eom, Hwanjoo Park, Jungwon Kim, Woochul Kim
In a power generation system, the price per watt ($/W) is an important parameter to be considered for checking the feasibility for practical implementation. In this paper, we experimentally demonstrate that $/W of a thermoelectric device can be reduced to around 60%. The conventional approach to reducing $/W in thermoelectrics is to enhance the thermoelectric figure of merit (zT) of the thermoelectric materials used, which can increase the power output (W). We propose that $/W can be reduced by lowering the material consumption ($) with a slight sacrifice in power output by changing the device architecture. A simple calculation suggests that zT ∼ 6 is needed for such a reduction in $/W based on the conventional approach. This method can be accompanied by a search for high-zT material so that further reduction in $/W can be achieved with efficient thermoelectric materials.
CO2 separation from offshore natural gas in quiescent and flowing states using 13X zeolite Appl. Energy (IF 7.182) Pub Date : 2017-09-20 S.J. Chen, Z.C. Tao, Y. Fu, M. Zhu, W.L. Li, X.D. Li
To improve the efficiency of offshore natural gas exploitation, CO2 separation from offshore natural gas in quiescent and flowing states using 13X zeolite was studied systematically by examining the voidage, adsorption time, inlet velocity, adsorber diameter, temperature, and pressure. An adsorption purification model was established and validated based on the experimental data. In quiescent adsorption, the contact area between 13X zeolite and the gas mixture is the most important factor for evaluating the adsorption purification efficiency, and higher voidages in the range of 0.25–0.50 were favorable for gas adsorption. However, in addition to the contact area, the contact time is an important factor for flowing adsorption. The purification efficiency of flowing adsorption is highest at a voidage of 0.35. At this voidage, the pressure drop in the adsorber was 70 Pa. The stabilization time for adsorption equilibrium decreased with increasing inlet velocity. As the adsorption time increased, the adsorption heat at different axial lengths of the adsorber tended to reach a constant value, while a symmetric adsorption heat curve was observed at different radial lengths. Toward the reduction of the energy consumption in the adsorption process, the optimum adsorber lengths for different diameters, temperatures, and pressures were determined. Adsorption purification was enhanced with increasing temperature. Further, it could also be improved by an appropriate pressure. Optimization of the adsorber structure parameters and regulation of the state parameters during the adsorption process are important for reducing energy consumption and improving the purification efficiency. The findings of this study serve as a guide for setting the purification parameters for CO2 separation from offshore natural gas in engineering applications.
An enhanced SOCP-based method for feeder load balancing using the multi-terminal soft open point in active distribution networks Appl. Energy (IF 7.182) Pub Date : 2017-09-20 Haoran Ji, Chengshan Wang, Peng Li, Jinli Zhao, Guanyu Song, Fei Ding, Jianzhong Wu
The integration of distributed generators (DGs) exacerbates the feeder power flow fluctuation and load unbalanced condition in active distribution networks (ADNs). The unbalanced feeder load causes inefficient use of network assets and network congestion during system operation. The flexible interconnection based on the multi-terminal soft open point (SOP) significantly benefits the operation of ADNs. The multi-terminal SOP, which is a controllable power electronic device installed to replace the normally open point, provides accurate active and reactive power flow control to enable the flexible connection of feeders. An enhanced SOCP-based method for feeder load balancing using the multi-terminal SOP is proposed in this paper. By regulating the operation of the multi-terminal SOP, the proposed method can mitigate the unbalanced condition of feeder load and simultaneously reduce the power losses of ADNs. Then, the original non-convex model is converted into a second-order cone programming (SOCP) model using convex relaxation. To tighten the SOCP relaxation and improve the computation efficiency, an enhanced SOCP-based approach is developed to solve the proposed model. Finally, case studies are performed on the modified IEEE 33-node system to verify the effectiveness and efficiency of the proposed method.
Towards the Power Synergy Hub (PSHub): Coordinating the energy dispatch of super grid by modified Benders decomposition Appl. Energy (IF 7.182) Pub Date : 2017-09-20 Zhao Yuan, Sonja Wogrin, Mohammad Reza Hesamzadeh
The challenge of operating ultra-large-scale power system or super grid is addressed in this paper. We set up the concept of power synergy hub (PSHub) serving as the operation hub coordinating the energy dispatch of multiple nations or regions across the continent to achieve global optimal targets. An efficient mechanism based on the modified Benders decomposition (BD) is proposed to coordinate the operations of national or regional power networks. The key contribution is that we take the total power outputs of regional power networks as the complicating variables to formulate the master problem and subproblems in the modified BD. Instead of using DC optimal power flow model (DC OPF), we propose to use convex AC optimal power flow model based on second-order cone programming (SOC-ACOPF) to operate the super grid. A comprehensive investigation proves that the SOC-ACOPF outperforms DC OPF in terms of accuracy. Numerical evaluations also show that our SOC-ACOPF model has stronger convergence capability and computational efficiency over other considered SOC-ACOPF models. The convergence of the modified BD is guaranteed by the convexity of SOC-ACOPF. A parallel computation framework in GAMS is proposed to assist real-time operation of the super grid. Compared with operating super grid in a centralized way, the modified BD approach shows stronger convergence capability, computational efficiency and robustness.
Numerical analysis of seawater desalination based on a solar chimney power plant Appl. Energy (IF 7.182) Pub Date : 2017-09-20 Tingzhen Ming, Tingrui Gong, Renaud K. de Richter, Cunjin Cai, S.A. Sherif
In this paper, the desalination performance of a plant variant with the same size as the Manzanares pilot model was numerically investigated. A three-dimensional compressible flow and heat transfer model has been developed, describing the air cooling process along the chimney and the associated condensation. In this plant variant, instead of installing the turbine, water droplets were sprayed for evaporation at the bottom of the chimney, and thus airflow was subjected to humidification. Results show that with increased mass fraction of water in the air, the influence of the microclimate on the local environment will also increase. The evaporation of the droplets improves the relative humidity of the air within the chimney, and the condensation level can thus be greatly reduced. Moreover, the freshwater output increases with increasing amount of water sprayed, which is beneficial for the improvement of the desalination efficiency of the system.
Probabilistic assessment of aquatic species risk from thermoelectric power plant effluent: Incorporating biology into the energy-water nexus Appl. Energy (IF 7.182) Pub Date : 2017-09-20 Lauren H. Logan, Ashlynn S. Stillwell
As global populations grow, demand for generation of affordable and efficient electricity will likely increase, requiring tradeoffs between power generation and ecosystems sustainability, including water quality and species habitat. Once-through thermoelectric power plants, representing 30% of the electricity generation in the United States, withdraw and discharge large quantities of water for cooling purposes. This process can cause thermal pollution in waterways, adversely affecting aquatic communities. Incorporating biology into the energy-water nexus can aid decision-makers in identifying tradeoffs and more effectively assessing and managing aquatic ecosystems. To quantify thermal pollution and the risk posed to aquatic species, we created an adaptable, novel methodology that utilizes plume mixing and probability distribution analyses on temperature and flow data for both a power plant’s discharge and the adjoining river. To assess risk, we developed a probability risk space that quantifies the probability of exceeding a given temperature. The Shawnee Fossil Plant on the Ohio River was selected to demonstrate the methodology, and three fish species with associated upper thermal avoidance limits were selected for comparison. Our results highlight that both the lateral and longitudinal location from the point of effluent mixing within the river affects the probability of thermal risk to aquatic species. A high degree of risk within a plume can reduce to a smaller total risk within the context of a large river cross-section. Our results emphasize the need for individualized risk assessment for Clean Water Act §316(a) requirements for power plant effluent temperature limits and National Pollutant Discharge Elimination System permits. These findings are applicable in policy-making, environmental mitigation, and power plant operations management.
An innovative multi-objective optimization approach for long-term energy planning Appl. Energy (IF 7.182) Pub Date : 2017-09-19 Md Shahriar Mahbub, Diego Viesi, Sara Cattani, Luigi Crema
Designing future energy scenarios is an important topic to energy planners. As designing future optimized scenarios is a multi-objective optimization problem; therefore, it is required to identify trade-off scenarios (Pareto-front) in order to optimize conflicting objectives. In this study, three Pareto-fronts are identified for designing future scenarios for Val di Non (VdN) for three different time horizons. As the community has to reach different emission targets in different time horizons, it is require to select the optimized scenarios that fulfill the targets. In this regards, we propose a new approach for selecting scenarios based on maximizing decision space diversity in order to provide a diverse set of scenarios to the decision makers. The technique is tested on optimized scenarios of VdN and three sets containing 10 diverse scenarios for different time horizons are selected. Moreover, a smooth transition (in terms of decision variables) is desirable when having a transition from a scenario from one time horizon to a consecutive time horizon. A novel method is proposed to choose scenarios from the sets for a smooth transition based on minimizing distances among the scenarios. The approach is applied on VdN where transient scenarios are identified among different possible optimized scenarios.
Printed, metallic thermoelectric generators integrated with pipe insulation for powering wireless sensors Appl. Energy (IF 7.182) Pub Date : 2017-09-19 Brian Iezzi, Krishnamraju Ankireddy, Jack Twiddy, Mark D. Losego, Jesse S. Jur
The Internet of Things (IoT), coupled with advanced analytics, is poised to revolutionize manufacturing maintenance and efficiency. However, a practical route to powering these many IoT devices remains unclear. In this work, flexible thermoelectric generators (TEGs) are fabricated from low cost, screen printed silver and nickel inks before being integrated into a novel form factor device based on commercial steam pipe insulation. Through optimization of internal resistances and total device design, this 420-junction TEG device produces 308 µW of power at a temperature difference of 127 K. This is sufficient to power a temperature sensing circuit with wireless communication capabilities. In this report we demonstrate that, after an initial 4 h of charging, this TEG can power a standard RFduino microcontroller for 10 min while sending temperature readings every 30 s via Bluetooth Low Energy (BLE) to a cell phone. Additional optimization and scaling could further increase system efficiency and provide a viable route to powering an industrial wireless sensing network (WSN).
Lithium as energy carrier: CFD simulations of LI combustion in a 100 MW slag tap furnace Appl. Energy (IF 7.182) Pub Date : 2017-09-19 Pascal Maas, Martin Schiemann, Viktor Scherer, Peter Fischer, Dan Taroata, Günther Schmid
Thermal transfer performance of a spherical encapsulated PEG 6000-based composite for thermal energy storage Appl. Energy (IF 7.182) Pub Date : 2017-09-19 E.M. Anghel, P.M. Pavel, M. Constantinescu, S. Petrescu, I. Atkinson, E. Buixaderas
Using 3DVAR data assimilation to measure offshore wind energy potential at different turbine heights in the West Mediterranean Appl. Energy (IF 7.182) Pub Date : 2017-09-19 Alain Ulazia, Jon Sáenz, Gabriel Ibarra-Berastegui, Santos J. González-Rojí, Sheila Carreno-Madinabeitia
In this article, offshore wind energy potential is measured around the Iberian Mediterranean coast and the Balearic Islands using the WRF meteorological model without 3DVAR data assimilation (the N simulation) and with 3DVAR data assimilation (the D simulation). Both simulations have been checked against the observations of six buoys and a spatially distributed analysis of wind based on satellite data (second version of Cross-Calibrated Multi-Platform, CCMPv2), and compared with ERA-Interim (ERAI). Three statistical indicators have been used: Pearson’s correlation, root mean square error and the ratio of standard deviations. The simulation with data assimilation provides the best fit, and it is as good as ERAI, in many cases at a 95% confidence level. Although ERAI is the best model, in the spatially distributed evaluation versus CCMPv2 the D simulation has more consistent indicators than ERAI near the buoys. Additionally, our simulation’s spatial resolution is five times higher than ERAI. Finally, regarding the estimation of wind energy potential, we have represented the annual and seasonal capacity factor maps over the study area, and our results have identified two areas of high potential to the north of Menorca and at Cabo Begur, where the wind energy potential has been estimated for three turbines at different heights according to the simulation with data assimilation.
Semi-physical models to assess the influence of CI engine calibration parameters on NOx and soot emissions Appl. Energy (IF 7.182) Pub Date : 2017-09-19 Xavier Tauzia, Alain Maiboom, Hassan Karaky
The progressive reduction of authorized emission levels in automotive Diesel engine standards has motivated the development of numerous technologies (exhaust gas recirculation (EGR), high pressure injection systems, sophisticated boosting systems, after-treatment devices, etc.) which, in turn, drastically increases the complexity of engine calibration. In this context the development of reliable simulation tools can help reduce the cost and time required for calibration. After a short introduction analysing the main currently existing models for evaluating engine emissions, this paper presents a novel 0D semi-physical model to assess engine-out NOx and soot emissions. The combustion process is modelled via Barba’s approach, while a thermodynamic two-zone calculation is used to evaluate adiabatic flame temperature. Emissions are modelled with semi-physical sub-models. This rather original approach does not evaluate emission on a crank-angle basis but only at exhaust valve opening (EVO), thus saving calculation time. The main physical parameters influencing pollutant formation are evaluated by the high-frequency 0D model and used as inputs for pollutant sub-models. NOx evaluation relies on a cartography linking NOx to O2 concentration and maximum values of in-cylinder bulk temperature and adiabatic flame temperature. Soot evaluation relies on a global equation, linking soot concentration to the main factors influencing formation and oxidation processes, in particular O2 concentration, in-cylinder pressure, temperatures and durations of some specific phases of the heat release rate (HRR), as well as turbulence intensity. The calibration of the models is thus quite easy and is described in the paper. The results of the models are then compared with measurements (different from those used for model calibration). NOx predictions are within ±20% of measured values for 95% of the tested operating points, with a R2 of 0.99, while for soot prediction a R2 coefficient of 0.93 is obtained and 96% of the tested points are within ±0.005 mg/cycle. Moreover, engine parameters sweeps (at constant engine speed and load) involving EGR rate, boost pressure, injection pressure and timing are performed for five operating points. The agreement with experiments is good on both qualitative and quantitative points of view, as long as a conventional combustion mode is achieved. Although simple and fast, these models are not only able to interpolate between the training points but also to extrapolate with a reasonable accuracy when the engine calibration parameters are changed. This latter property is rarely demonstrated in existing models.
A two-level multi-objective optimization for simultaneous design and scheduling of a district energy system Appl. Energy (IF 7.182) Pub Date : 2017-09-18 Mohammad Sameti, Fariborz Haghighat
Optimal planning of microgrid power and operating reserve capacity ☆ Appl. Energy (IF 7.182) Pub Date : 2017-09-18 Mike Quashie, Chris Marnay, François Bouffard, Géza Joós
This paper proposes a bi–level formulation for a coupled microgrid power and reserve capacity planning problem, cast within the jurisdiction of a distribution system operator(DSO). The upper level problem of the proposed bi–level model represents a microgrid planner whose goal is to minimize its planning and operational cost, while the lower level problem represents a DSO whose primary duty is to ensure reliable power supply. The microgrid planner, pursues its interest by co–optimizing the design configuration and power output of individual distributed energy resources (DERs), while the DSO maximizes the capacity of flexible reserve resources. The proposed model is recast as a mathematical program with equilibrium constraints (MPEC) wherein the decision variables of the two problems are independently controlled. Application of the proposed approach to the energy infrastructure of a Canadian utility network is discussed. Results obtained through its application are compared to an alternative multi–objective planning model and the improved benefits are assigned to the corresponding stakeholders.
Dynamics of China’s carbon prices in the pilot trading phase Appl. Energy (IF 7.182) Pub Date : 2017-09-18 John Hua Fan, Neda Todorova
This paper is the first to investigate empirically the link between carbon prices and macro risks in China’s cap-and-trade pilot scheme. Using data from four pilot markets in Beijing, Guangdong, Hubei, and Shenzhen from 2014 to 2016, we demonstrate that the carbon price in Hubei is weakly linked to international prices of natural gas. Our results also indicate that energy, utilities, industrial and materials sector indices are positively related to the allowance prices in Shenzhen and Guangdong, suggesting that higher emitters in the region may have factored the carbon price into their production mix. We find no statistically significant relationship in the Beijing pilot. Overall, the findings suggest that China’s carbon market is currently in an early stage of development, as the carbon price fundamentals are weak and the markets are comparatively less efficient than the European trading scheme in an informational sense. The findings of the paper have policy implications for the upcoming integration of regional markets into the national carbon market.
A computationally efficient pseudo-3D model for the numerical analysis of borehole heat exchangers Appl. Energy (IF 7.182) Pub Date : 2017-09-18 Giuseppe Brunetti, Hirotaka Saito, Takeshi Saito, Jiří Šimůnek
Ground-Source Heat Pump (GSHP) systems represent one of the most efficient renewable energy technologies. Their efficiency is highly influenced by the thermal properties of the ground, which are often measured in-situ using the Thermal Response Tests (TRTs). While three-dimensional mechanistic models offer significant advantages over analytical solutions for the numerical interpretation of TRTs, their computational cost represents a limiting factor. Moreover, most of the existing models do not include a comprehensive description of hydrological processes, which have proven to strongly influence the behavior of GSHP. Thus, in this study, we propose a computationally efficient pseudo-3D model for the numerical analysis and interpretation of TRTs. The numerical approach combines a one-dimensional description of the heat transport in the buried tubes of the exchanger with a two-dimensional description of the heat transfer and water flow in the surrounding subsurface soil, thus reducing the dimensionality of the problem and the computational cost. The modeling framework includes the widely used hydrological model, HYDRUS, which can simulate the movement of water, heat, and multiple solutes in variably-saturated porous media. First, the proposed model is validated against experimental data collected at two different experimental sites in Japan, with satisfactory results. Then, it is combined with the Morris method to carry out a sensitivity analysis of thermal properties. Finally, the model is exploited to investigate the influence of groundwater and lithologic heterogeneities on the thermal behavior of the GSHP.
A data-driven methodology to support pump performance analysis and energy efficiency optimization in Waste Water Treatment Plants Appl. Energy (IF 7.182) Pub Date : 2017-09-18 Dario Torregrossa, Joachim Hansen, Francesc Hernández-Sancho, Alex Cornelissen, Georges Schutz, Ulrich Leopold
Studies and publications from the past ten years demonstrate that generally the energy efficiency of Waste Water Treatment Plants (WWTPs) is unsatisfactory. In this domain, efficient pump energy management can generate economic and environmental benefits. Although the availability of on-line sensors can provide high-frequency information about pump systems, at best, energy assessment is carried out a few times a year using aggregated data. Consequently, pump inefficiencies are normally detected late and the comprehension of pump system dynamics is often not satisfactory. In this paper, a data-driven methodology to support the daily energy decision-making is presented. This innovative approach, based on fuzzy logic, supports plant managers with detailed information about pump performance, and provides case-based suggestions to reduce the pump system energy consumption and extend pump life spans. A case study, performed on a WWTP in Germany, shows that it is possible to identify energy inefficiencies and case-based solutions to reduce the pump energy consumption by 18.5%.
Numerical modeling study of a man-made low-permeability barrier for the compressed air energy storage in high-permeability aquifers Appl. Energy (IF 7.182) Pub Date : 2017-09-18 Yi Li, Lehua Pan, Keni Zhang, Litang Hu, Jinsheng Wang, Chaobin Guo
Compressed air energy storage (CAES) is a grid-scale energy storage technology for intermittent energy, as proven by the decades-long successful operation of two existing compressed air energy storage in cavern (CAESC) power plants. Because of the limited availability of salt domes appropriate for CAESC, the more widely available aquifers (compressed air energy storage in aquifers, CAESA) have recently attracted considerable attention as candidates for CAES. An ideal aquifer for CAESA is highly permeable around the well to facilitate easy injection and withdrawal of air, but the high-permeability region is surrounded by low-permeability zones to minimize the loss of injected air and decrease in energy efficiency. However, such ideal geological structures are not always available in nature. Therefore, the potential of creating man-made low-permeability barrier in high-permeability aquifers is very interesting. In this paper, we investigate the feasibility of man-made low-permeability barriers in high-permeability aquifers using the numerical simulator TOUGH2/Gel to calculate the three-component flow (including a miscible gelling liquid). The simulation results show that an expected low-permeability barrier can be created by injecting grout with certain properties, and the altered aquifer performs well for CAESA. Additional sensitivity studies are also performed to reveal the effects of the various factors on the success of the low-permeability barrier creation, including the critical solidification concentration, the scale factor of the time dependence of the grout viscosity, the relative density of the grout, and the volume of the follow-up water injection. The results indicate that, in a horizontal aquifer, low critical solidification concentrations, and small scale factors are generally preferred and the density of grout should be close to that of the in situ water. For the given volume of the injected grout, there is an optimal follow-up water injection that will create the largest storage space without damaging the barrier. These results may help to extend the candidate sites for CAESA and the prospect of large scale energy storage.
Quantification of heat losses through building envelope thermal bridges influenced by wind velocity using the outdoor infrared thermography technique Appl. Energy (IF 7.182) Pub Date : 2017-09-18 Małgorzata O'Grady, Agnieszka A. Lechowska, Annette M. Harte
Improving the thermal performance of the existing building stock is essential to significantly reduce the overall energy consumption in the building sector. A key objective is the retrofitting of the existing building envelope. A necessary first step in the building envelope optimization process is the assessment of its actual thermal performance. This assessment should be repeated after retrofitting to clearly define the improvements that were made and the heat loss reduction that was achieved. In this study, an efficient, non-destructive, in-situ measurement method, based on an outdoor infrared thermographic survey, is developed to determine the thermal bridging performance. As wind velocity significantly influences the heat losses through the building envelope, this study includes quantification of the wind velocity impact on the Ψ-value. This was assessed by undertaking ITT of the same thermal bridge at various wind velocities, in a controlled environment, in a hot box device. The results showed that the Ψ-value is highly dependent on wind velocity so that measurement of the Ψ-value taken at different wind conditions cannot be directly compared. An adjustment procedure is proposed that can be used to convert the Ψ-value measured at any wind velocity to a standard value corresponding to a velocity of 4 m/s. From a practical point of view, this adjustment procedure makes the methodology widely applicable.
Challenges and uncertainties of ex ante techno-economic analysis of low TRL CO2 capture technology: Lessons from a case study of an NGCC with exhaust gas recycle and electric swing adsorption Appl. Energy (IF 7.182) Pub Date : 2017-09-18 Mijndert van der Spek, Andrea Ramirez, André Faaij
this work addresses the methodological challenges of undertaking techno-economic assessments of very early stage (technology readiness level 3–4) CO2 capture technologies. It draws lessons from a case study on CO2 capture from a natural gas combined cycle with exhaust gas recycle and electric swing adsorption technology. The paper shows that also for very early stage technologies it is possible to conduct techno-economic studies that give a sound first indication of feasibility, providing certain conditions are met. These conditions include the availability of initial estimates for the energy use of the capture technology, either from bench scale measurements, or from rigorous process models, and the possibility to draw up a generic (high level) equipment list. The paper shows that for meaningful comparison with incumbent technologies, the performance of very early stage technologies needs to be projected to a future, commercial state. To this end, the state of the art methods have to be adapted to control for the development and improvements that these technologies will undergo during the R&D cycle. We call this a hybrid approach. The paper also shows that CO2 capture technologies always need to be assessed in sympathy with the CO2 source (e.g. power plant) and compression plant, because otherwise unreliable conclusions could be drawn on their feasibility. For the case study, it is concluded that electric swing adsorption is unlikely to become economically competitive with current technologies, even in a highly optimised future state, where 50% of the regeneration duty is provided by LP steam and 50% by electricity: the net efficiency of an NGCC with EGR and optimised ESA (49.3%LHV; min–max 45.8–50.4%LHV) is lower than that of an NGCC with EGR and standard MEA (50.4%LHV). Also, investment and operational costs are higher than MEA, which together with ESA’s lower efficiency leads to an unfavourable levelised cost of electricity: 103 €/MWh (min–max 93.89–117.31 €/MWh) for NGCC with ESA, versus 91 €/MWh for NGCC with MEA.
Uncertainties in corn stover feedstock supply logistics cost and life-cycle greenhouse gas emissions for butanol production Appl. Energy (IF 7.182) Pub Date : 2017-09-18 Nawa Raj Baral, Carlos Quiroz-Arita, Thomas H. Bradley
The success and sustainable operation of a commercial cellulosic biorefinery are highly dependent on price, quality, and availability of feedstocks. Currently, corn stover is a primary feedstock choice for cellulosic ethanol production and the same feedstock can be used for butanol production, which is a potential alternative biofuel. However, butanol production requires different levels of feedstock and logistical resources when compared to ethanol due to about 20% lower theoretical yield. A thorough analysis of cost, life-cycle energy use and life-cycle greenhouse gas emissions associated with a feedstock supply logistics system for butanol production is yet to be done. Additionally, quality standards for corn stover feedstock are yet to be determined, which could determine cost of the feedstock for commercial applications. Thus, this study aimed to fulfill these research gaps using techno-economic analysis and life-cycle assessment methodologies. Variability in logistical resources and other input parameters gathered from recent literature were used for analyses in this study. Average corn stover supply logistics cost ($/metric ton(t), dry), life-cycle energy use (MJ/t, dry) and life-cycle greenhouse gas emissions (kg CO2e/t, dry) were 86.9, 1073.7 and 83.8, which could increase at 95% certainty to 159–504, 1672–3817 and 138–271, respectively, depending on the types of probability distributions of the input parameters. However, the mode value of logistics cost ($/t, dry), life-cycle energy use (MJ/t, dry) and life-cycle greenhouse gas emissions (kg CO2e/t, dry) of 80–120, 913–1231 and 79–120, respectively, closely represents the results of the static model. The average estimated feedstock cost for butanol production was about 1.3 times and the minimum 95% certainty value is about 2 times more than the targeted feedstock cost ($/metric ton, dry) of 66.4, excluding preprocessing. Overall, the location of the biorefinery, quality of corn stover, sustainable agricultural practices, and optimum utilization of transportation resources were key factors that enable a sustainable feedstock supply logistics system.
Effect of land use change for bioenergy production on feedstock cost and water quality Appl. Energy (IF 7.182) Pub Date : 2017-09-18 Jia Zhong, T. Edward Yu, Christopher D. Clark, Burton C. English, James A. Larson, Chu-Lin Cheng
The effects of flow-field orientation on water management in PEM fuel cells with serpentine channels Appl. Energy (IF 7.182) Pub Date : 2017-09-18 Moosa Ashrafi, Mehrzad Shams
A numerical scheme for the effect of flow-field orientation on water management in PEM fuel cell is developed. Since there are limitations on the location of proton exchange membrane fuel cell such as portable applications, different configurations are used for proper water management. Therefore, the best configuration must be chosen for the most efficient and stable operation of the fuel cells. In this research, a 3D numerical model is proposed based on the VOF method in order to simulate the effects of gravity on the gas–liquid two-phase flow in a full-scale single-serpentine flow-field. This model, which is validated by the experimental results, considers the microstructure of the gas diffusion layer by two square pores in every cross section along the channels. The simulations are done for the vertical and horizontal fuel cells. The effects of water coverage ratios and flow regimes on pressure drop and the resulting parasitic power loss are investigated for different configurations. In the vertical orientation, the channels are placed horizontally or vertically in each configuration. The results reveal that in the vertical cells, when the channels are located horizontally and the inlet manifold is embedded on the upper side of the flow-field, the pressure drop is the lowest. The reason is that the film flow is formed in the channels and the gravity assists in the water removal. However, when both the cell and channels are vertical and the cathode inlet manifold is placed on the bottom of the flow-field, the pressure drop and the resulting parasitic power is the highest. This is due to the gravity is against the water purging from the elbows leading to formation of long plugs along the channels. The present numerical model can be used for simulation of two-phase flow in channels of the serpentine flow-field at any cell orientation angle by changing the gravity direction in the model.
Effects of oxygen carrier mole fraction, velocity distribution on conversion performance using an experimentally validated mathematical model of a CLC fuel reactor Appl. Energy (IF 7.182) Pub Date : 2017-09-18 R. Ben-Mansour, H. Li, M.A. Habib
Due to the severity of the worldwide climate change problem and the ocean acidification problem, chemical looping combustion (CLC) technology is studied worldwide by researchers in order to meet the urgency of carbon emission reduction after its concept has been put forward. An experimentally validated computer model has been implemented in Ansys-Fluent code with the most appropriate kinetic model implemented in User Define Functions. The validated model has been used to carry out a numerical study on a model fuel reactor using CaSO4 as oxygen carrier and H2 as fuel; is conducted in the present work. Effects of mole fraction of CaS, operating temperature, superficial feeding velocity magnitude of fuel and the diameter of oxygen carrier particles were discussed. The results indicate that the superficial feeding velocity of gaseous fuel has significant effects on the flow condition with fuel reactor and conversion performance, while operating temperature mainly affects the fuel conversion. The effects of particle diameter on flow condition within FR are obvious but insignificant on conversion performance of fuel. The mole fraction of CaS has the least effect among these three parameters. Several velocity distributions are also studied. The rectangle-trianble distributor results in better bubbles distributions, but the gain of higher fuel conversion rate is insignificant due to the low chemical activity of OC used in this study.
Influence of the vertical wind and wind direction on the power output of a small vertical-axis wind turbine installed on the rooftop of a building Appl. Energy (IF 7.182) Pub Date : 2017-09-18 Kung-Yen Lee, Shao-Hua Tsao, Chieh-Wen Tzeng, Huei-Jeng Lin
The goal of this study is to investigate the performance of a small vertical-axis wind turbine at an environment with the turbulence intensity more than 30%, particularly on the influence of the vertical wind, the vertical angle, the wind with the unknown direction, the horizontal wind speed, and the turbulence intensity on the power output, which are seldom reported before. The results show that more than 90% of the power is generated when the vertical angle is less than or equal to 45°. The vertical wind speed has the obvious influence on the power when the horizontal wind speed is between 5 m/s and 8 m/s. The percentage of the power generated by the wind with the unknown direction decreases from 31.1% to 8.4% as the horizontal wind speed increases from 4 m/s to 9 m/s. The efficiency is over 40% only when the horizontal wind speed is over 8 m/s. The higher turbulence intensity increases the power at the lower wind speed, but decreases the power at the higher wind speed. Furthermore, the results can be used as a reference for the improvement of aerodynamic characteristics, efficiency, CFD simulation and the location selection of a vertical-axis wind turbine.
Dynamic modeling and control analysis of a methanol autothermal reforming and PEM fuel cell power system Appl. Energy (IF 7.182) Pub Date : 2017-09-18 Dimitris Ipsakis, Martha Ouzounidou, Simira Papadopoulou, Panos Seferlis, Spyros Voutetakis
In the present study, a rigorous dynamic and control-oriented model is developed towards accurately describing the autonomous operation of a methanol reforming-fuel cell power system (up to 5 kWel). The system consists of an autothermal steam reformer that provides hydrogen to a polymer electrolyte membrane (PEM) fuel cell. A purification stage (preferential oxidation reactor) intercedes between the steam reformer and the fuel cell and maintains CO levels below 10–50 ppm, while a heat-exchanging network (comprising of two coolers and a burner) is employed towards managing a well-balanced autothermal operation. The proposed dynamic model is developed on the basis of describing accurately the evolving chemical and electrochemical interactions between the subsystems and utilizes a group of partial/ordinary differential equation (reactors and heat exchangers) along with a set of non-linear equations (reaction kinetics and current-voltage dependence). Based on the system main operating features, a control structure through the implementation of PI controllers is proposed for the control of (a) the reformer feed and exit temperature through methanol burning and steam reformer feed flowrate manipulation respectively, (b) CO concentration through O2/CO feed ratio manipulation, (c) power production (specified by the fuel cell operation current) through methanol reformer feed and (d) subsystem exit temperatures through coolant flowrate manipulation. An overall simulation case study reveals the proper selection of system manipulated and controlled variables towards achieving the applied operating set-points, where it is shown that the system sustains a flexible operation, along with fast start-up and dynamic transients.
Electrical power generation under policy constrained water-energy nexus Appl. Energy (IF 7.182) Pub Date : 2017-09-18 Blaže Gjorgiev, Giovanni Sansavini
Water-energy nexus refers to the interdependence between water resources and energy conversion, and it encompasses the multiple phases of electric power generation and water processing and distribution. Current policies for the utilization of freshwater resources in electric power generation regulate the thermal discharges and their effect on the aquatic life. Water withdrawals and consumption polices are mainly prescribed at the regional level instead. This paper focuses on the effects of water policy constraints on electric power generation in changing climate conditions. A river basin is simulated, which hosts two hydraulically linked power generating stations, namely an upstream hydropower plant with reservoir and a downstream thermal power plant. Two alternative cooling designs are tested for the thermal power plant, i.e. once-through and wet tower cooling. Severe drought conditions leading to small river flows and high water temperatures are analyzed, and the limitations to the energy conversion at the thermal plant stemming from the water policies are quantified. The results show that some small flexibility in the water policy constraints during extreme droughts can secure a significant amount of energy to the power system, which would have been curtailed otherwise. Remarkably, the relaxation of 1.5 °C in the water policy constraints prevents the curtailment of 42% of the generation capacity of a 1000 MWe thermal plant during the analyzed 24 h drought scenario. In general, the type and the required amount of constraint relaxation depend on the environmental conditions and are to be judged case-by-case. Furthermore, the smart scheduling of water resources grants a 7% increase of the energy converted during droughts in the hydraulically linked hydro and thermal power plants. Finally, the analysis shows that once-through cooling systems are extremely sensitive to changes in water flow and temperature opening space for less sensitive technologies, i.e. wet cooling towers.
Simultaneous production of CH4-rich syngas and high-quality tar from lignite by the coupling of noncatalytic/catalytic pyrolysis and gasification in a pressurized integrated fluidized bed Appl. Energy (IF 7.182) Pub Date : 2017-09-18 Zhaohui Chen, Shiqiu Gao, Guangwen Xu
An integrated fluidized bed (IFB) reactor with a two-stage configuration has been developed to process small-size coal particles for the simultaneous production of CH4-rich syngas and high-quality tar, in which coal pyrolysis occurred in an upper transport bed (TB) within an atmosphere mixing steam and syngas generated by steam-oxygen gasification of coal or char in a lower fluidized bed (FB). The coupling effect was investigated by combining non-catalytic/catalytic pyrolysis and gasification in a pressurized IFB. Having TB pyrolysis obviously raised CH4 yield (also its content in producer gas) and tar yield. The respective contributions to CH4 formation from the TB pyrolysis and FB gasification were mainly relevant to operating pressure and Ca(OH)2 catalyst. Raising pressure facilitated CH4 formation. When lignite was treated without catalyst, the contribution from TB pyrolysis was greater than that from FB gasification as hydropyrolysis was intensified by pressure in H2-rich gas atmosphere from the FB gasifier. Adding catalyst into lignite reversed their contributions. The FB catalytic gasification formed more CH4 because Ca(OH)2 functioned well as a catalyst for CH4 formation in pressurized gasification. With elevated pressure or/and the addition of Ca(OH)2, pyrolysis tar yield decreased in different degrees but its quality was improved. With the combination effect of pressure and Ca(OH)2, producer gas from the tested IFB reactor was highly rich in CH4 to reach 10.8 vol%, with as well a high H2/CO ratio of 2.3 that is suitable for making SNG. The obtained tar had its light tar content as high as 95 wt%.
Thermionic energy conversion for concentrating solar power Appl. Energy (IF 7.182) Pub Date : 2017-09-15 Gang Xiao, Guanghua Zheng, Min Qiu, Qiang Li, Dongsheng Li, Mingjiang Ni
Concentrating solar power (CSP) is a mainstream of solar energy utilization, and thermionic emission is a potential way to convert concentrated solar radiation into power with a theoretical efficiency of 50–70%, surpassing both Shockley-Queisser limit and photo-thermal limit. This literature attempts to provide a comprehensive understanding of and an insight into solar thermionic energy conversion. The fundamentals of electron emission from electrodes and electron transport in vacuum gap are presented, as well as the state of the art of solar thermionic energy conversion technologies, including heat-induced thermionics and photon-enhanced thermionics. The former is driven by thermal energy, whereas the latter takes advantage of both quantum photon energy and thermal energy. Burgeoning research indicates that photon-enhanced thermionic conversion is a promising technology for concentrating solar power due to the high efficiency and simple operating mode. Now, it is important to develop novel materials and coating technologies to facilitate electron emission and reduce space charge effect in interelectrode vacuum. Structural design of thermionic converters and top–bottom configuration of solar-electricity systems are suggested for practical applications.
Leading-edge serrations for performance improvement on a vertical-axis wind turbine at low tip-speed-ratios Appl. Energy (IF 7.182) Pub Date : 2017-09-15 Zhenyu Wang, Mei Zhuang
Synergistic engine-fuel technologies for light-duty vehicles: Fuel economy and Greenhouse Gas Emissions Appl. Energy (IF 7.182) Pub Date : 2017-09-15 Kai Morganti, Marwan Al-Abdullah, Abdullah Alzubail, Gautam Kalghatgi, Yoann Viollet, Robert Head, Ahmad Khan, Amir Abdul-Manan
Advanced engine technologies will play a central role in achieving future greenhouse gas (GHG) emissions targets for light-duty vehicles. However, these technologies will place greater emphasis on optimizing the engine and fuel as a synergistic system, since many technologies will require higher octane gasolines to realize their full social and environmental benefits. The most extreme example of a synergistic engine-fuel system is the Octane-on-Demand concept. This technology platform makes use of an oil-derived fuel at low and intermediate loads where the octane requirement of the engine is comparatively low, while a second high octane fuel is introduced at higher loads to suppress knock. This paper presents the first comprehensive study of vehicle fuel economy and well-to-wheel GHG emissions for the Octane-on-Demand concept with respect to a regular grade E10 gasoline (RON 93) and a high octane E30 gasoline (RON 101). Experimental fuel consumption maps are first used to evaluate the drive cycle fuel economy and GHG emissions for a light-duty vehicle equipped with two alternative powertrains. The upstream GHG emissions arising from the production of the fuels are then quantified, with consequent uncertainties assessed using Monte Carlo analysis based on probability distribution functions for critical input parameters. The results demonstrate that the Octane-on-Demand concept used in conjunction with either methanol or ethanol generally provides comparable well-to-wheel GHG emissions to the high octane E30 gasoline, with up to a 10% improvement in the vehicle fuel economy. The use of a non-traditional engine calibration strategy that maximizes the trade-off between thermal efficiency and fuel energy density also enables the amount of high octane fuel required to suppress knock to be reduced significantly. This increases the distance that the vehicle can be driven before the secondary tank requires refueling by a considerable margin, but comes at the expense of marginally higher well-to-wheel GHG emissions than could otherwise be achieved. These findings are shown to be largely insensitive to uncertainties in the upstream fuel production GHG emissions, with the exception of the land use change (LUC) for bioethanol. Overall, this study has implications for the design of engine-fuel systems for future light-duty vehicles.
Free piston expander-linear generator used for organic Rankine cycle waste heat recovery system Appl. Energy (IF 7.182) Pub Date : 2017-09-15 Xiaochen Hou, Hongguang Zhang, Fei Yu, Hongda Liu, Fubin Yang, Yonghong Xu, Yaming Tian, Gaosheng Li
This study presents an experimental investigation of a free piston expander-linear generator (FPE-LG) used for organic Rankine cycle (ORC) waste heat recovery system. A FPE-LG test rig using compressed air as working fluid is established. The motion characteristics, dynamic characteristics and the indicated efficiency of FPE-LG are analyzed. The motion characteristics and power output performance for different valve timings are studied. The degree of symmetry is defined to evaluate the asymmetry motion characteristics of the free piston assembly. The coefficient of cycle-to-cycle variation (COV) is presented to evaluate the cycle-to-cycle variation characteristics of the FPE-LG. Experimental results show that the free piston assembly displacement profile is similar to a sinusoidal wave and the free piston assembly can operate at high and relatively constant speed at the middle portion of the stroke. The maximum power output of 19 W can be achieved when the intake pressure is 2.0 bar and the operation frequency is 2.5 Hz. The valve timing and intake pressure demonstrate a significant influence on the asymmetric motion and the power output performance of the FPE-LG. The indicated efficiency of the FPE (left cylinder) decreases with the increase in the intake pressure. The maximum indicated efficiency reaches 92.8% when the intake pressure is 1.4 bar and the operation frequency is 2.0 Hz. The indicated efficiency firstly increases and then decreases with the increase in the operation frequency. The COV of the FPE-LG decreases with increasing the intake pressure. The motion stability of FPE-LG improves with the increase in the intake pressure. Valve timing and valve train should be optimized in the near future.
A boundary layer scaling technique for estimating near-surface wind energy using numerical weather prediction and wind map data Appl. Energy (IF 7.182) Pub Date : 2017-09-15 D.J. Allen, A.S. Tomlin, C.S.E. Bale, A. Skea, S. Vosper, M.L. Gallani
A boundary layer scaling (BLS) method for predicting long-term average near-surface wind speeds and power densities was developed in this work. The method was based on the scaling of reference climatological data either from long-term average wind maps or from hourly wind speeds obtained from high-resolution Numerical Weather Prediction (NWP) models, with case study applications from Great Britain. It incorporated a more detailed parameterisation of surface aerodynamics than previous studies and the predicted wind speeds and power densities were validated against observational wind speeds from 124 sites across Great Britain. The BLS model could offer long-term average wind speed predictions using wind map data derived from long-term observational data, with a mean percentage error of 1.5% which provided an improvement on the commonly used NOABL (Numerical Objective Analysis of Boundary Layer) wind map. The boundary layer scaling of NWP data was not, however, able to improve upon the use of raw NWP data for near surface wind speed predictions. However, the use of NWP data scaled by the BLS model could offer improved power density predictions compared to the use of the reference data sets. Using a vertical scaling of the shape factor of a Weibull distribution fitted to the BLS NWP data, power density predictions with a 1% mean percentage error were achieved. This provided a significant improvement on the use of a fixed shape factor which must be utilised when only long-term average wind speeds are available from reference wind maps. The work therefore highlights the advantages that use of a BLS model for wind speed and NWP data for power density predictions can offer for small to medium scale wind energy resource assessments, potentially facilitating more robust annual energy production and financial assessments of prospective small and medium scale wind turbine installations.
Performance investigation on polymeric electrolyte membrane-based electrochemical air dehumidification system Appl. Energy (IF 7.182) Pub Date : 2017-09-15 Ronghui Qi, Dujuan Li, Li-Zhi Zhang
Indoor thermal comfort assessment using different constructive solutions incorporating PCM Appl. Energy (IF 7.182) Pub Date : 2017-09-14 António Figueiredo, Romeu Vicente, José Lapa, Claudino Cardoso, Fernanda Rodrigues, Jérôme Kämpf
Sustainable energy and thermal retrofit design of buildings or districts has a strong global impact in the viewpoint of economies and energy-efficiency perspectives. Several aspects such as architectonic design, building materials, construction technology, mechanical systems and outdoor climate determines the thermal behaviour of buildings and their ability to provide indoor thermal comfort to occupants. The use of geothermal energy and phase change materials (PCMs) in the construction systems are an opportunity that may attenuate indoor air temperature fluctuation as well as overheating risk. This paper presents the results of a study on indoor thermal comfort and energy efficiency regarding the PCM’s positive role when applied to new constructive solutions, inside a building with a geothermal system linked to the air conditioning system. The PCM study was based on real and simulated investigations in two rooms of a new university department at the Aveiro campus. Higrothermal monitoring (indoor air temperature) of two rooms in which one of them has PCM panels incorporated into gypsum board partition wall and into a suspended ceiling. The scope was driven to investigate the potential of these solutions for overheating mitigation. The numerical study was conducted by using an evolutionary algorithm coupled with the software EnergyPlus® used in simulations. In the scope of this optimization process, constructive solutions with the incorporation of different types of PCM with different melting temperatures and enthalpy, and different flow rates of natural ventilation were combined to investigate the potential and the payback time of these novel solutions.The results for the room measurements show that the indoor thermal comfort of the rooms, present long periods of discomfort namely in overheating. However, it was proved that the PCM application in one of the rooms lead to an overheating reduction of 7.23% representing a PCM efficiency of 35.49%. After the optimization process an overheating reduction of about 34% was attained by the use of PCM in one of the rooms. Regarding the economic analysis of the use of the PCM for cooling demand reduction, a payback time of 18 years was attained.
Modeling a new energy harvesting pavement system with experimental verification Appl. Energy (IF 7.182) Pub Date : 2017-09-14 Lukai Guo, Qing Lu
A novel design of an energy harvesting pavement system (EHPS) is introduced in this paper. The basic concept behind this design is to transform asphalt layers into a piezoelectric energy harvester to collect dissipated vehicle kinetic energy in a large-scale system. This EHPS design consists of two conductive asphalt layers and one piezoelectric material layer. To verify the feasibility of the design, this ongoing study theoretically analyzed the EHPS via a three-degree-of-freedom electromechanical model and practically tested a prototype in the laboratory. As a result, voltage outputs measured in the laboratory from the prototype design matched those estimated from the electromechanical model. Through testing the effects of several components in the EHPS on electricity generation, this study confirms that using more flexible conductive asphalt mixtures and arranging more piezoelectric elements with a higher piezoelectric stress constant can increase electrical outputs from the EHPS. Regarding specific external vibration conditions, a high frequency of external vibration can lead to a dramatic effect of each piezoelectric element’s capacitance on increasing electrical outputs, but also can reduce the benefit from adding more piezoelectric elements to produce higher electrical outputs. After optimizing this EHPS prototype by adding more piezoelectric elements with higher piezoelectric stress constant and improving the flexibility of conductive asphalt mixtures, the maximum electric power from the proposed EHPS can be increased from approximately 1.2 mW to 300 mW under a high frequency (30 Hz) external vibration. The levelized cost of electricity of this EHPS can be $19.15/kWh on a high-volume roadway within a 15-year service life.
Factors affecting methane loss from a water scrubbing based biogas upgrading system Appl. Energy (IF 7.182) Pub Date : 2017-09-14 Rimika Kapoor, P.M.V. Subbarao, Virendra Kumar Vijay, Goldy Shah, Shivali Sahota, Dhruv Singh, Mahesh Verma
Biogas upgrading is a vital step to produce high quality fuel called biomethane with above 90% methane (CH4). Among the various technologies available for biomethane production, water scrubbing is the most extensively implemented technology around the world. However, during the process of biogas upgrading, a some amount of CH4 is separated as CH4 loss through the water flowing out of the water scrubbing column. In this paper, various factors affecting CH4 loss from water scrubbing method are analysed. Some factors such as pressure, water flow rate and CH4 concentration in input gas are dependent upon the solubility and partial pressures of the gases are generally known. Apart from these factors CH4 losses due to bubble entrainment due to high pressure difference between water scrubbing column and desorption tank and gas short circuiting of the gas through the bottom section of the column due to no water sealing and water level maintencence also contribute to CH4 losses. Therefore, CH4 losses during the water scrubbing process due to these factors have been experimentally studied in this paper. A pilot scale water scrubbing system for biogas upgradation was used for the study. It was observed that CH4 % (v/v) in the upgraded biogas and CH4 loss % from the desorbed gas increased with the increase in pressure and increase in the concentration of CH4 in the input gas. Increase in water flow rates caused removal of larger quantities of water containing more absorbed CH4 and CO2 from the scrubbing column, thereby increasing CH4 loss of the system. Highest CH4 loss % of 9.9% (±0.1%), was obtained with raw biogas sample when water was desorbed at atmospheric pressures in the desorption tank, i.e. when pressure difference between the water scrubbing column and desorption tank was highest. A pressure vessel was installed in between scrubbing column and desorption tank to reduce the pressure difference for water leaving the column by varying the pressure in the pressure vessel from 1 to 9 bar. With the increase in pressure in the pressure vessel, the pressure difference for water decreased which led to a saving in overall CH4 loss of the system. Water sealing and water level maintenance in the bottom section of the column also affected CH4 losses of the system. All the factors discussed in the article contribute to the CH4 losses from the scrubbing column and cannot be solely credited to a single factor.
Offshore wind farm repowering optimization Appl. Energy (IF 7.182) Pub Date : 2017-09-14 Peng Hou, Peter Enevoldsen, Weihao Hu, Cong Chen, Zhe Chen
Decommissioning is usually the last stage of the offshore wind farm life cycle. Due to the challenges of the decommissioning process, such as the impact on the marine environment, severe weather conditions, vessel limitations and lack of operational experience, the decommissioning strategy should be planned to avoid complications, which ultimately can cause radical changes to the levelized cost of energy (LCoE) and the wind farm owner’s business case. Instead of dismantling, repowering may be a sustainable alternative solution to extend the lifetime of a wind farm. In this paper, the research is focused on optimization of offshore wind farm repowering, which is one option for the wind farm owner at end of life for the offshore wind farm. The LCoE is used as the evaluation index to identify whether it is economical to invest in such a way. In an optimized repowering strategy, different types of wind turbines are selected to replace the original wind turbines to reconstruct the wind farm, which is demonstrated to be better than the refurbishment approach which replaces the old wind turbines with the same type. The simulations performed in this research reveal that the reconstructed wind farm, which consists of multiple types of wind turbine, has a smaller LCoE (10.43%) than the refurbishment approach, which shows the superiority of the proposed method. This research contributes an optimization tool to the wind industry, which consequently drives down the cost of energy produced by offshore wind turbines.
A comparison of radial-flow and axial-flow packed beds for thermal energy storage ☆ Appl. Energy (IF 7.182) Pub Date : 2017-09-14 J.D. McTigue, A.J. White
Packed-bed thermal reservoirs are an integral component in a number of electrical energy storage technologies. The present paper concentrates on packed beds where the heat transfer fluid travels along the radial co-ordinate. The governing energy equations and various mechanisms that cause exergetic losses are discussed. The radial-flow packed bed is compared to a dimensionally similar axial-flow packed bed. This approach provides a fair assessment of the underlying behaviour of the two designs. Multi-objective optimisation allows a wide range of design variables to be considered, and is employed to compare optimal radial-flow and axial-flow stores. Axial-flow stores that have been segmented into layers are also considered. The results indicate that radial-flow stores have a comparable thermodynamic performance, but that the additional volume required for by-pass flows leads to higher capital costs.
Comparative study of the transient natural convection in an underground water pit thermal storage Appl. Energy (IF 7.182) Pub Date : 2017-09-14 Chun Chang, Zhiyong Wu, Helena Navarro, Chuan Li, Guanghui Leng, Xiaoxia Li, Ming Yang, Zhifeng Wang, Yulong Ding
Quantitative analysis on the impact of nuclear energy supply disruption on electricity supply security Appl. Energy (IF 7.182) Pub Date : 2017-09-13 Shoki Kosai, Hironobu Unesaki
Improvement of power supply security is of paramount importance to sustain human activities. Technical and engineering failures of power grid system have been analyzed to evaluate power system reliability hitherto. However, after Fukushima nuclear accident, the sudden electricity supply disruption particularly associated with nuclear energy utilization brings upon a new risk of electricity supply security arising from societal issues, or nuclear vulnerability. As such, a methodology of quantifying nuclear vulnerability is firstly established under varying both the magnitude and time instant of sudden stoppage of nuclear power operation. Through the nuclear vulnerability analysis, a new electricity supply security index dedicated for nuclear power utilization, named System Interruption Nuclear Vulnerability Index (SINVI) is developed. SINVI could be used to predict the risk of electricity supply disruption arising from the sudden stoppage of nuclear power operation corresponding to the different capacity combination of various energy sources. Finally, the widely proposed dimensions of energy security for undisturbed electricity supply – diversification and redundancy – are incorporated with nuclear vulnerability to design the more secured power system taking into account the risk of nuclear energy utilization. The established algorithm can be readily implemented in any other electricity grid network including nuclear power technology.
Flame height of axisymmetric gaseous fuel jets restricted by parallel sidewalls: Experiments and theoretical analysis Appl. Energy (IF 7.182) Pub Date : 2017-09-13 Qiang Wang, Fei Tang, Zheng Zhou, Huan Liu, Adriana Palacios
This study reports experimental results and correlations for axisymmetric gaseous fuel jets restricted by parallel sidewalls at various separation distances. Although many investigations have been conducted to elucidate the flame height evolution of diffusion flames in an unrestricted environment; the restriction effect of sidewalls on diffusion flames, which occasionally occurs in accidental leakages of city natural gas pipelines, has received little attention. The underlying interaction dynamics of axisymmetric gaseous fuel jets with two parallel sidewalls at various separation distances has not been fully elucidated. In this work, a series of experiments on this issue were carried out with 3-, 6- and 10-mm nozzles. The sidewall separation distances were varied from 10 to 50 cm with a corresponding free condition. A series of new results and their interpretation are presented in this work. The results show that the flame height changes little when the sidewall separation distance reduces from +∞ to a critical value (Scri). Further reductions on the sidewall separation distance from Scri disturbed the evolution process of uprising vortexes and hindered air entrainment, leading to significant changes to the jet-flame shape by enlarging the flame height. The maximum flame heights had a linear relation with the critical separation distance of the sidewalls at the critical conditions, being consistent with the scaling analysis of the flow field. The dimensionless critical separation distance was found to be well correlated with the dimensionless heat release rate, Q ̇ D ∗ , with a 2/5 power law. A global model, characterizing the variation of the flame height with the dimensionless heat release rate, was proposed, showing good agreement with the experimental results. The results and the expressions obtained in this study contribute to a better understanding of jet fires, allowing a better prediction of flame height, relevant to the design of gas fuel storage systems and transportation systems in the city.
Evaluation and comparison of product yields and bio-methane potential in sewage digestate following hydrothermal treatment Appl. Energy (IF 7.182) Pub Date : 2017-09-13 C. Aragón-Briceño, A.B. Ross, M.A. Camargo-Valero
In recent years, sewage sludge management has been considered one of the biggest concerns in the wastewater industry for the environmental impacts linked to its high content of pollutants. Hydrothermal Treatments are a good option for converting wet biomass such as sewage sludge into high-value products. The digestate following anaerobic treatment of sewage sludge has high organic matter content despite initial conversion into biogas and is normally spread on land or composted; however, this does not fully harness its full potential. In fact, the digestate is a potential feedstock for hydrothermal processing and this route may produce higher value products. In this study, the potential of hydrothermal processing as a novel alternative to treat the digestate has been be evaluated. The effect of temperatures is evaluated with respect to product yields, biomethane potential and solubilisation of organic carbon. Three different temperatures were evaluated: 160, 220 and 250 °C at 30 min reaction time. The hydrochar yields obtained were 73.42% at 220 °C, 68.79% at 250 °C and 56.75% at 160 °C treatment. The solubilisation of carbon was increased from 4.62% in the raw feedstock to 31.68%, 32.56% and 30.48% after thermal treatments at 160, 220 and 250 °C, respectively. The thermal treatment enhanced the potential methane production in all products up to 58% for both, the whole fraction (hydrochar + processed water) and processed waters. The Boyle’s and Buswell’s equation were used to calculate theoretical methane yields for all hydrothermal products. Theoretical methane yields were compare with experimental data from biomethane potential (BMP) tests and it was found that the Boyle’s equation had closer agreement to BMP values.
Evaluation and comparison of an adaptive method technique for improved performance of linear Fresnel secondary designs Appl. Energy (IF 7.182) Pub Date : 2017-09-13 Madeline Hack, Guangdong Zhu, Tim Wendelin
As a line-focus concentrating solar power (CSP) technology, linear Fresnel collectors have the potential to become a low-cost solution for electricity production and a variety of thermal energy applications. However, this technology often suffers from relatively low performance. A secondary reflector is a key component used to improve optical performance of a linear Fresnel collector. The shape of a secondary reflector is particularly critical in determining solar power captured by the absorber tube(s), and thus, the collector’s optical performance. However, to the authors’ knowledge, no well-established process existed to derive the optimal secondary shape prior to the development of a new adaptive method to optimize the secondary reflector shape. The new adaptive method does not assume any pre-defined analytical form; rather, it constitutes an optimum shape through an adaptive process by maximizing the energy collection onto the absorber tube. In this paper, the adaptive method is compared with popular secondary-reflector designs with respect to a collector’s optical performance under various scenarios. For the first time, a comprehensive, in-depth comparison was conducted on all popular secondary designs for CSP applications. It is shown that the adaptive design exhibits the best optical performance.
Non-intrusive load monitoring by using active and reactive power in additive Factorial Hidden Markov Models Appl. Energy (IF 7.182) Pub Date : 2017-09-13 Roberto Bonfigli, Emanuele Principi, Marco Fagiani, Marco Severini, Stefano Squartini, Francesco Piazza
Non-intrusive load monitoring (NILM) is the task of determining the appliances individual contributions to the aggregate power consumption by using a set of electrical parameters measured at a single metering point. NILM allows to provide detailed consumption information to the users, that induces them to modify their habits towards a wiser use of the electrical energy. This paper proposes a NILM algorithm based on the joint use of active and reactive power in the Additive Factorial Hidden Markov Models framework. In particular, in the proposed approach, the appliance model is represented by a bivariate Hidden Markov Model whose emitted symbols are the joint active-reactive power signals. The disaggregation is performed by means of an alternative formulation of the Additive Factorial Approximate Maximum a Posteriori (AFAMAP) algorithm for dealing with the bivariate HMM models. The proposed solution has been compared to the original AFAMAP algorithm based on the active power only and to the seminal approach proposed by Hart (1992), based on finite state machine appliance models and which employs both the active and reactive power. Hart’s algorithm has been improved for handling the occurrence of multiple solutions by means of a Maximum A Posteriori technique (MAP). The experiments have been conducted on the AMPds dataset in noised and denoised conditions and the performance evaluated by using the F1 F 1 -Measure and the normalized disaggregation metrics. In terms of F1 F 1 -Measure, the results showed that the proposed approach outperforms AFAMAP, Hart’s algorithm, and Hart’s with MAP respectively by +14.9% + 14.9 % , +21.8% + 21.8 % , and +2.5% + 2.5 % in the 6 appliances denoised case study. In the 6 appliances noised case study, the relative performance improvement is +25.5% + 25.5 % , +51.1% + 51.1 % , and +6.7% + 6.7 % .
Tolerance analysis of electrified vehicles on the motor demagnetization fault: From an energy perspective Appl. Energy (IF 7.182) Pub Date : 2017-09-12 Hongwen He, Nana Zhou, Jinquan Guo, Zheng Zhang, Bing Lu, Chao Sun
Due to possible overheat, abrasion or mechanical vibrations, demagnetization fault is inevitable in permanent magnet synchronous motors (PMSMs), which could greatly decrease the motor’s efficiency and hence an electrified vehicle’s performance. This paper, from an energy efficiency point of view, proposes to analyze the tolerance ability of different electrified vehicles on motor demagnetization faults, via PMSM flux density degradation modeling, efficiency estimation and dynamic programming (DP) based powertrain energy management. The relationship between different demagnetization levels and resultant motor efficiencies is obtained, and analyzed according to the motor operation area. Demagnetized PMSM is adopted in a pure electric vehicle (PEV), a hybrid electric vehicle (HEV) and a plug-in hybrid electric vehicle (PHEV) for energy efficiency analysis. Tolerance analysis indicates that the powertrain efficiency decrease caused by motor demagnetization is more severe under urban driving conditions, especially with PEV and PHEV configurations compared with HEV. A demagnetization threshold investigation is also given in this paper.
Multi-objective optimization design and performance evaluation for plug-in hybrid electric vehicle powertrains Appl. Energy (IF 7.182) Pub Date : 2017-09-12 Xingyu Zhou, Datong Qin, Jianjun Hu
This study provides an optimal selection methodology for plug-in hybrid electric vehicle (PHEV) powertrain configuration by means of optimization and comprehensive evaluation of powertrain design schemes. The challenge of this study is to reveal each powertrain configuration performance potential in different situations of object trade-off and solve the control-physical integrated optimization problem of the PHEV powertrain design. To determine performance potential, a configuration-sizing-control strategy integrated multi-objective powertrain optimization design is proposed and applied to series, parallel pre-transmission (P2), output power-split, and multi-mode power-split powertrain configurations. Firstly, considering simultaneous optimization of fuel economy, electric energy consumption, and acceleration capacity, the parameters of the powertrain components and vehicle performance of each configuration are optimized based on global optimal control in different situations of object trade-off. Then, the Pareto optimal selection of powertrain configuration and its corresponding optimal component parameters are obtained by performance comparison and non-domination sorting. The results suggest that the P2 configuration and its optimal sizing can be selected when the goal is to optimize acceleration capacity, the multi-mode power-split configuration and its optimal sizing can be selected when the goal is to optimize electric energy efficiency, and the output power-split configuration and its optimal sizing can be selected when the fuel economy needs to be optimized.
A multi-scale framework for simultaneous optimization of the design and operating strategy of residential CHP systems Appl. Energy (IF 7.182) Pub Date : 2017-09-12 Abigail Ondeck, Thomas F. Edgar, Michael Baldea
The expected increase in energy demand in the United States has led to the pursuit of more efficient methods to generate thermal and electrical energy for the residential sector. One possible approach that could both increase generation efficiency and reduce CO2 emissions is Combined Heat and Power (CHP). CHP plants, powered by natural gas, can act as an integrated residential utility supplier by producing the thermal and electrical energy needed to meet the heating, cooling, and electricity demands of a (future) residential neighborhood. However, a CHP plant operating in island (i.e., grid-disconnected) mode must be optimally sized to maximize efficiency and to lower the capital and marginal costs. In this paper, we describe a novel simultaneous optimization of design and operating strategies for a CHP plant as a utility producer for a residential neighborhood. The plant, operating in island mode, integrates distributed residential photovoltaic solar power generation, and is optimized to meet a time-dependent energy demand profile characteristic of residential energy use. To accurately capture the variability (hourly and seasonal) and uncertainty in residential energy demand and rooftop photovoltaic generation, a vast amount of energy data were incorporated in the problem formulation. The multi-scale optimization problem was solved using a temporal Lagrangean decomposition method, generating the design of a CHP plant that can efficiently meet all residential utility demands, taking into consideration the long-term (design) and short-term (operational) costs.
Designing efficient distribution network charges in the context of active customers Appl. Energy (IF 7.182) Pub Date : 2017-09-11 Ibtihal Abdelmotteleb, Tomás Gómez, José Pablo Chaves Ávila, Javier Reneses
The transformation of electricity network users from passive to active agents, as a result of decreasing costs of distributed energy resources, requires several adaptions, one of which is revising the distribution network charges. Often current network charge designs do not ensure network cost recovery and lack to incentivize efficient network investments and usage. New network charge methodologies are required to guide and incentivize customers in an efficient way while maximizing system economic efficiency. This paper proposes an efficient methodology that ensures network cost recovery while promoting efficient usage of the network as well as efficient network investments. The proposed network charge design consisting of two components: a peak coincidence network charge (PCNC) and fixed charge. The PCNC is a forward-looking charge as it considers the cost of future network reinforcements required and assigned to customers during peak hours of the network utilization. Fixed charges allocate the residual of the network costs following Ramsey-pricing principles. This paper compares the outcome from economic optimum customers’ response to four different network charges: (i) volumetric charges (ii) fixed charges (iii) peak demand charge (iv) PCNC plus fixed charges. Two case studies for two different load profiles are simulated using linear programming to minimize their total costs within each charges design, considering the possibility of buying electricity from the grid and investing on onsite generation or curtail load. Finally, the paper highlights through the case studies how customer’s response is highly influenced by different network charge designs, and compares the consequences of these responses in terms of network cost recovery and total system costs. The paper concludes with practical issues that need to be considered for the implementation of the proposed network charges design.
Evaluation of energy efficient hybrid hollow plaster panel using phase change material/xGnP composites Appl. Energy (IF 7.182) Pub Date : 2017-09-09 Seunghwan Wi, Su-Gwang Jeong, Seong Jin Chang, Jongki Lee, Sumin Kim
Performance assessment of a hybrid SOFC/MGT cogeneration power plant fed by syngas from a biomass down-draft gasifier Appl. Energy (IF 7.182) Pub Date : 2017-09-09 Alessandra Perna, Mariagiovanna Minutillo, Elio Jannelli, Viviana Cigolotti, Suk Woo Nam, Kyung Joong Yoon
Hybrid systems combine two or more power generating devices and make use of the synergism to generate maximum power and offer very high efficiencies.The aim of this work is to investigate the performance achievable from a small-scale hybrid power plant based on the integration between a micro gas turbine (MGT) and a solid oxide fuel cell (SOFC) fed by the syngas generated by a biomass downdraft gasifier (BG). The thermal energy needed to reach the turbine inlet temperature is supplied by the exhausts coming from a catalytic burner in which the SOFC anode and cathode off-gases are burnt.The hybrid BG-SOFC/MGT plant, based on a simplified configuration and realized considering components commercially available, is designed for optimizing not only the electric power generation, but also the thermal power production, in accordance with the promotion of decentralized CHP plants.The performance assessment has been carried out by means of a numerical model, based on thermodynamic/thermochemical approaches and realized by integrating the models of each plant section, developed by using the Aspen Plus software package. The models validation, performed by using experimental data, demonstrates that the results produced are close to those obtained from each unit, so that the overall integrated model can provide a sufficiently accurate prediction of the expected actual hybrid power plant.The effects of some operating parameters on cogeneration performances, such as the MGT pressure ratio and the S/C (steam to carbon) in the SOFC unit, have been evaluated and analyzed.Results show that the best performances are achieved by assuming the MGT pressure ratio equal to 4.5 and the S/C equal to 0. In this case the electric power is 262 kW (SOFC supplies 180 kW), the thermal power is 405 kW and the electric (AC) and cogeneration efficiencies are 35% and 88%, respectively.
Demand forecast of PV integrated bioclimatic buildings using ensemble framework Appl. Energy (IF 7.182) Pub Date : 2017-09-09 Muhammad Qamar Raza, Mithulananthan Nadarajah, Chandima Ekanayake
Buildings are one of the major sources of electricity and greenhouse gas emission (GHG) in urban areas all around the world. Since a large integration of solar energy is observed in the form of rooftop photovoltaic (PV) units, electricity use of buildings is highly uncertain due to intermittent nature of solar output power. This leads to poor energy management for both network operators and building owners. In addition, uncertain metrological conditions, diversity and complexity of buildings are big hurdles to accurate prediction of the demand. To improve accuracy of load demand forecast of PV integrated smart building, a hybrid ensemble framework is proposed in this paper. This is based on a combination of five different predictors named as backpropagation neural network (BPNN), Elman neural network (EN), Autoregressive Integrated Moving Average (ARIMA), feed forward neural network (FNN), radial basis function (RBF) and their wavelet transform (WT) models. WT is applied to historical load data to remove the spikes and fluctuations. FNN and RBF network were trained with particle swarm optimization (PSO) for higher forecast accuracy. The output of each predictor in the ensemble network is combined using Bayesian model averaging (BMA). The proposed framework is tested using real data of two practical PV integrated smart buildings in a big university environment. The results indicate that the proposed framework show improvement in average forecast normalized root mean square error (nRMSE) around 17% and 20% in seasonal daily and seasonal weekly case studies, respectively. In addition, proposed framework also produces lowest of nRMSE about 3.88% in seasonal monthly forecast of smart buildings with rooftop PV as compared to benchmark model. The proposed forecast framework provides consistent forecast results for global change institute (GCI) and advance engineering building (AEB) during seasonal daily and weekly comparison.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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