Documents published in Scipedia

• Evaluation of the economics of conversion to compressed natural gas for a municipal bus fleet

  L. Yang, W. Tyner, K. Sarica

  Energy Science & Engineering (2017).

  
  

  Abstract

  Domestic natural gas production has increased markedly in the United States, and now compressed natural gas (CNG) has the potential to become a cleaner and less expensive energy source than diesel fuel for use in the public transportation sector, especially for city bus fleets. This paper provides an economic analysis of possible CNG conversion for Lafayette, IN CityBus Corporation. It uses benefit–cost analysis to compare the total cost of three potential options for bus replacement: standard diesel, hybrid diesel-electric, and CNG. A spreadsheet model was used to estimate the total cost of these three fleet options over a 15-year project horizon. Results suggest that the CNG option has the lowest net present value (NPV) cost, and that cost savings would be larger if the corporation could obtain a grant for the CNG fueling station or if the project life span could expand to 20 years. From the environmental perspective, the CNG option would reduce greenhouse gas and particulate emissions particularly in comparison with the diesel option. Monte Carlo simulation was used to examine the inherent riskiness of the three fleet options. CNG is always lower cost than hybrid diesel-electric. Depending on assumptions regarding the underlying price distributions, the CNG option has a 51–100% chance of being lower cost than the standard diesel option.

  Abstract
  Domestic natural gas production has increased markedly in the United States, and now compressed natural gas (CNG) has the potential to become a cleaner and less expensive [...]

  • 0
  •  read

• A wavelet-nearest neighbor model for short-term load forecasting

  G. Sudheer, A. Suseelatha

  Energy Science & Engineering (2017).

  
  

  Abstract

  Load forecasts of short lead times ranging from an hour to a day ahead are essential for improving the economic efficiency and reliability of power systems. This paper proposes a hybrid model based on the wavelet transform (WT) and the weighted nearest neighbor (WNN) techniques to predict the day ahead electrical load. The WT is used to decompose the load series into deterministic series and fluctuation series that reflect the changing dynamics of data. The two subseries are then separately forecast using appropriately fitted WNN models. The final forecast is obtained by composing the predicted results of each subseries. The hourly electrical load of California and Spanish energy markets are taken as experimental data and the mean absolute percentage error (MAPE), Weekly MAPE (WMAPE) and Monthly MAPE (MMAPE) are computed to evaluate the forecasting performance of the next-day load forecasts. The forecasting efficiency of the proposed model is evaluated using db2, db4, db5 and bior 3.1 wavelets. The results demonstrate the forecasting accuracy of the proposed hybrid model.

  Abstract
  Load forecasts of short lead times ranging from an hour to a day ahead are essential for improving the economic efficiency and reliability of power systems. This paper proposes [...]

  • 0
  •  read

• An overview of proactive wind turbine control

  A. Stotsky, B. Egardt, O. Carlson

  Energy Science & Engineering (2017).

  
  

  Abstract

  Recent achievements in the proactive turbine control, based on the upwind speed measurements, are described in a unified framework (as an extension of the tutorial [1]), that in turn represents a systematic view of the control activity carried out within the Swedish Wind Power Technology Center (SWPTC). A new turbine control problem statement with constraints on blade loads is reviewed. This problem statement allows the design of a new class of simultaneous speed and pitch control strategies based on the preview measurements and look-ahead calculations. A generation of a piecewise constant desired pitch angle profile which is calculated using the turbine load prediction is reviewed in this article as one of the most promising approaches. This in turn allows the reduction of the pitch actuation and the design of the collective pitch control strategy with the maximum possible actuation rate. Two turbine speed control strategies based on one-mass and two-mass models of the drivetrain are also described in this article. The strategies are compared to the existing drivetrain controller. Moreover, postprocessing technique that can be used for estimation of the turbine parameters with improved performance is also discussed. Postprocessing-based estimation of the turbine inertia moment is given as an example. All the results are illustrated by simulations with a wind speed record from the Hönö turbine, located outside of Gothenburg, Sweden.

  Abstract
  Recent achievements in the proactive turbine control, based on the upwind speed measurements, are described in a unified framework (as an extension of the tutorial [1]), that [...]

  • 0
  •  read

• Blade root moment sensor failure detection based on multibeam LIDAR for fault-tolerant individual pitch control of wind turbines

  A. Stotsky

  Energy Science & Engineering (2017).

  
  

  Abstract

  Detection of blade root moment sensor failures is an important problem for fault-tolerant individual pitch control, which plays a key role in reduction of uneven blade loads of large wind turbines. A new method for detection of blade root moment sensor failures which is based on variations induced by a vertical wind shear is described in this paper. The detection is associated with monitoring of statistical properties of the difference between amplitudes of the first harmonic of the blade load, which is calculated in two different ways. The first method is based on processing of the load sensor signal, which contains a number of harmonics. The first harmonic is recovered via least squares estimation of the blade load signal with harmonic regressor and strictly diagonally dominant (SDD) information matrix. The second method is a model-based method of estimation of the first harmonic, which relies on the blade load model and upwind speed measurements provided by multibeam Light Detection and Ranging (LIDAR). This is a new application for future LIDAR-enabled wind turbine technologies. Moreover, adaptation of the load model in a uniform wind field is proposed. This adaptation improves accuracy of the load estimation and hence the performance of the blade load sensor failure detection method.

  Abstract
  Detection of blade root moment sensor failures is an important problem for fault-tolerant individual pitch control, which plays a key role in reduction of uneven blade loads [...]

  • 0
  •  read

• Investigating residual trapping in CO2 storage in saline aquifers – application of a 2D glass model, and image analysis

  M. Soroush, D. Wessel-Berg, O. Torsaeter, J. Kleppe

  Energy Science & Engineering (2017).

  
  

  Abstract

  Two-dimensional glass model experiments are used to investigate the residual trapping mechanism of CO2 stored in saline aquifers. For this purpose, two proxy fluids are chosen to simulate the CO2-brine behavior under reservoir conditions. The first set of experiments is carried out by flooding n-heptane in a mixture of glycerol and water inside a glass bead porous media. Fluids and porous materials are designed so that the dimensionless groups are in the range of real storage sites. Another set of proxy fluid consists of dodecane and a different mixture of glycerol and water, representing the second wettability condition for the system. The size of the glass beads chosen was fine (70–110 μm) in order to investigate residual trapping phenomena. For each set, after complete drainage process, an imbibition process is performed and in each time step, images are taken from the phenomena. The images are processed using a red, green, blue (RGB) color concept using a Matlab code that was developed for this study. By using this process, it is possible to measure the residual trapping of CO2 proxy fluid for each test and to determine the saturation profile in the model. Tests are carried out at various imbibition and drainage rates to study the effect of the rate on the results. Fine-scale numerical simulation models are constructed for comparison with experimental results. Good agreement is obtained between the simulation results and the image processing estimations, as well as the readings from the material balances during the experiments. This study could provide a framework for modeling different reservoir conditions for residual trapping mechanism and the impact of different parameters in future studies.

  Abstract
  Two-dimensional glass model experiments are used to investigate the residual trapping mechanism of CO2 stored in saline aquifers. For this purpose, two proxy fluids are chosen [...]

  • 0
  •  read

• Practical evaluation of organic polymer thermoelectrics by large-area R2R processing on flexible substrates

  R. Søndergaard, M. Hösel, N. Espinosa, M. Jørgensen, F. Krebs

  Energy Science & Engineering (2017).

  
  

  Abstract

  Here, we present a process based on roll-to-roll (R2R) technology which allows for very fast processing of polymer thermoelectric (TE) devices and we furthermore demonstrate a simplified but more efficient way of serially connecting these devices by means of R2R thin-film processing. The new device architecture makes it possible to use only one TE material (opposed to two materials which are employed in well-known Peltier elements), and a total of 18, 000 serially connected junctions were prepared by flexoprinting of silver electrodes and by rotary screen printing of poly(3, 4-ethylenedioxythiophene) (PEDOT):polystyrene sulfonate (PSS) as the TE material. Testing of devices revealed that the new architecture clearly showed to be functioning as expected, but also pointed toward challenges for thin-film TE development which is the influence of the substrate thickness on the thermal gradient over a device and the currently low performance available. A life-cycle assessment (LCA) was carried out in order to evaluate the sustainability of the new architecture and to estimate the requirements for development of a successful technology.

  Abstract
  Here, we present a process based on roll-to-roll (R2R) technology which allows for very fast processing of polymer thermoelectric (TE) devices and we furthermore demonstrate [...]

  • 0
  •  read

• Study of demagnetization risk for a 12 kW direct driven permanent magnet synchronous generator for wind power

  S. Sjökvist, S. Eriksson

  Energy Science & Engineering (2017).

  
  

  Abstract

  One of the main aspects when designing a permanent magnet (PM) generator is to choose suitable PMs, both in terms of achieving the required flux in the generator but also of withstanding high demagnetizing fields, that is, having sufficiently high coercivity. If the coercivity is too low, the magnets are at risk of demagnetizing, fully or partially, at the event of a short circuit and/or an increase in temperature. This study aims to determine the risk of demagnetization for a 12 kW direct driven permanent magnet synchronous generator. Furthermore, as the prices on PMs have increased drastically the last few years the possibility to use smaller and/or cheaper PMs of different grades has been investigated. A new proprietary finite element method (FEM) model has been developed, which is also presented. The study is based on simulations from this FEM model and is focused on NdFeB magnets. Results show that the reference magnet can withstand a two-phase short circuit at both the temperatures tested and in both geometries. The use of cheaper magnets, smaller air gap and in the event of a two-phase short circuit often results in partial irreversible demagnetization. However, magnets with lower coercivity are easier demagnetized.

  Abstract
  One of the main aspects when designing a permanent magnet (PM) generator is to choose suitable PMs, both in terms of achieving the required flux in the generator but also [...]

  • 0
  •  read

• Why the molten salt fast reactor (MSFR) is the “best” Gen IV reactor

  D. Siemer

  Energy Science & Engineering (2017).

  
  

  Abstract

  A simultaneously “nuclear”, permanent, and in-time solution to mankinds energy-related problems would require the relatively rapid manufacture of 10, 000–30, 000 genuinely sustainable, full-sized (~1 GWe) reactors. This “nuclear renaissance” would have to be implemented with breeder reactors because todays commercial nuclear fuel cycle is unsustainable and based upon a fuel (235U) that is intrinsically expensive and politically problematic. The purpose of this paper is to point out why a simple/cheap “minimal reprocessing” implementation of the European Unions (EUs) molten salt fast reactor (MSFR) concept represents the most promising way to implement that technical fix: Its primary drawback is that it would require virtually everyone currently involved with managing, researching, implementing, regulating, or “helping” the USAs nuclear power industry to embrace a massive paradigm shift.

  Abstract
  A simultaneously “nuclear”, permanent, and in-time solution to mankinds energy-related problems would require the relatively rapid manufacture of 10, 000–30, 000 genuinely [...]

  • 0
  •  read

• Conducting polymer-based flexible supercapacitor

  I. Shown, A. Ganguly, L. Chen, K. Chen

  Energy Science & Engineering (2017).

  
  

  Abstract

  Flexible supercapacitors, a state-of-the-art material, have emerged with the potential to enable major advances in for cutting-edge electronic applications. Flexible supercapacitors are governed by the fundamentals standard for the conventional capacitors but provide high flexibility, high charge storage and low resistance of electro active materials to achieve high capacitance performance. Conducting polymers (CPs) are among the most potential pseudocapacitor materials for the foundation of flexible supercapacitors, motivating the existing energy storage devices toward the future advanced flexible electronic applications due to their high redox active-specific capacitance and inherent elastic polymeric nature. This review focuses on different types of CPs-based supercapacitor, the relevant fabrication methods and designing concepts. It describes recent developments and remaining challenges in this field, and its impact on the future direction of flexible supercapacitor materials and relevant device fabrications.

  Abstract
  Flexible supercapacitors, a state-of-the-art material, have emerged with the potential to enable major advances in for cutting-edge electronic applications. Flexible supercapacitors [...]

  • 0
  •  read

• Pilot-scale processing with alkaline pulping and enzymatic saccharification for bioethanol production from rice straw

  M. Sekine, Y. Ogawa, N. Matsuoka, Y. Izumi

  Energy Science & Engineering (2017).

  
  

  Abstract

  We examined pilot-scale bioethanol production from rice straw using sodium carbonate pulping as the alkaline pulping method and enzymatic saccharification. The yield of prewashed rice straw after the crushing and prewashing stage decreased with an increase in the input in rice straw. The pulp yield after alkaline cooking was 66–68% at kappa number ranging from 32 to 36, which was comparatively higher than the laboratory-scale study. The yield of enzymatic saccharized glucose was decreased with the increase in washed pulp and its saccharification rate was approximately 20%. We successfully produced approximately 100 liters of 95% ethanol from 1000 Bone-Dry kg (BDkg) rice straw. The results of our pilot-scale study indicated that the relationship between resource input and product yield for each operation exhibited exponential or logarithmic curves, rather than linear decreases or increases, which could suggest a high-cost structure for bioethanol production when the resource input is larger. However, we established an optimum quantity of resource input, approximately 2000–3000 BDkg in our pilot-scale study, for higher efficiencies.

  Abstract
  We examined pilot-scale bioethanol production from rice straw using sodium carbonate pulping as the alkaline pulping method and enzymatic saccharification. The yield of prewashed [...]

  • 0
  •  read