Special Issue "Renewable Energy"

Guest Editor
Prof. Dr. Tomonobu Senjyu
Department of Electrical and Electronics Engineering, Faculty of Engineering, University of the Ryukyus, 1 Senbaru Nihihara-cho, Okinawa 903-0213, Japan
Website: http://pesc.eee.u-ryukyu.ac.jp
E-Mail: b985542@tec.u-ryukyu.ac.jp
Phone: +81 98 895 8686
Fax: +81 895 8686
Interests: power electronics; electronic machine; power systems; intelligent control; renewable energy; system optimization

Dear Colleagues,

Renewable energy is a promising energy source in order not to have emission of carbon dioxide at the time of power generation. Although renewable energy is mainly exploited photovoltaic energy or wind energy, however it changes by climate conditions, stabilization of electric power is needed. The smart grid attracts attention as research on stabilization and effective use of renewable energy in recent years, and research on a smart grid is advanced in the world. As core technology of smart grid, power electronics, optimization technology, demand response, smart meter, large storage battery, cooperative control, etc. are needed, and it is technology indispensable to large-scale introduction of renewable energy. In this special issue, the contribution of the paper about the circumference technology for large-scale introduction of renewable energy is expected broadly.

Prof. Dr. Tomonobu Senjyu
Guest Editor

Submission

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• photovoltaic generation
• wind-turbine generation
• smart grid
• demand response
• battery
• unit commitment
• optimal operation
• coordinated control
• distributed generators

Type of Paper: Article
Title: Hydrolyzation and Ethanol Production from Waste Potato Mash by Using Saccharomyces Cerevisiae
Authors: Gulten Izmirlioglu and Ali Demirci
Affiliation: Department of Agricultural and Biological Engineering, The Huck Institutes of Life Sciences, Pennsylvania State University, University Park, PA 16802, USA; E-Mail: axd29@engr.psu.edu
Abstract: Ethanol is one of the renewable sources with high efficiency and low environmental impact. It is commonly produced by microbial fermentation. Various raw materials have been used during fermentation as carbon sources for ethanol production. However, the cost for raw materials can be costly. In this study, waste potato mash was chosen as a carbon source, because it is relatively cheaper compared to other feedstock considered food sources. However, a pretreatment process is needed through process; specifically liquefaction and saccharification processes to convert starch of potato to fermentable sugars before ethanol fermentation. In this study, hydrolysis of waste potato mash was optimized. In order to obtain a maximum glucose conversions, relationship among parameters of the liquefaction and saccharification process were investigated by response surface method. The optimum combination of temperature, dose of enzyme (α-amylase), and amount of waste potato mash was 95°C, 1 ml of enzyme (18.8 mg protein/ml), and 4.04 g dry-weight/100 ml DI water, with a 68.86% loss in dry weight for liquefaction. For saccharification, temperature, dose of enzyme, and saccharification time were optimized and optimum condition was determined as 60°C-72 h-0.8 ml (300 Unit/ml) of amyloglucosidase combination, yielded 34.9 g/L glucose. After optimization of hydrolysis of the waste potato mash effects of pH and inoculum size were evaluated to obtain maximum ethanol. Results showed that pH of 5.5 and 3% inolculum size were determined as optimum pH, and inoculum size, respectively for maximum ethanol concentration and production rate. The maximum ethanol production rate was obtained at optimum conditions as 30.99 g/L ethanol. Since yeast extract is not the most economical nitrogen source, four animal-based substitutes (poultry meal, hull and fines mix, feather meal, and meat and bone meal) were evaluated to determine an economical alternative nitrogen source to yeast extract. Poultry meal and feather meal were able to produce 35 g/L and 32.9 g/L ethanol, respectively, which are compatible with yeast extract (30.8 g/L). In conclusion, waste potato mash was found as a promising carbon source for ethanol fermentation with alternate nitrogen sources.
Keywords: enzyme hydrolysis; biofuel; bioethanol; Saccharomyces cerevisiae; fermentation; waste potato mash

Type of Paper: Article
Title: Feasibility Study of Energy Storage Systems in Wind/Diesel Applications Using the HOMER Model
Author: Andrew Stiel and Maria Skyllas-Kazacos
Affiliation: School of Chemical Sciences and Engineering, University of New South Wales, Sydney, NSW, 2052, Australia; E-Mail: m.kazacos@unsw.edu.au
Abstract: With an increased focus on solutions to the ensuing ‘climate crisis’, the need for energy storage systems is becoming increasingly important as a means to increase the penetration of renewable technologies such as wind energy. The Vanadium Redox Battery is one such energy storage system showing considerable potential owing to its flexibility in power output and capacity, high efficiency and long operating life. This study models the use of the Vanadium Redox Battery as an integration technology in realistic large-scale remote wind/diesel power systems using the HOMER Micropower Optimization Model computer program developed by the US National Renewable Energy Laboratory. Results from this modelling demonstrate the significant financial and environmental benefits to be gained in installing energy storage in a wind farm. The storage system considered here was a Vanadium Redox Battery.

Type of Paper: Article
Title: Comparison of Net Energy Metrics for Solar Photovoltaics (PV), Concentrating Solar Power (CSP) and Wind Power
Author: Michael Dale et al.
Affiliation: Global Climate and Energy Project (GCEP), Stanford University, Palo Alto, CA 94305, USA; E-Mail: mikdale@stanford.edu
Abstract: The energy and material resource use efficiency of energy extraction and processing pathways strongly affects the overall affordability and environmental impacts of energy supply. These whole-system efficiencies, which have been the focus of net energy analysis (NEA) studies, are difficult to compute due to the complexity of energy supply chains. Therefore, they have received much less attention than device efficiencies. Life cycle assessments (LCAs) also consider energy flows in estimating environmental impacts such as greenhouse gas emissions. Despite sharing net energy metrics as a research outcome, the two fields have heretofore existed almost entirely separately. Because LCAs are more commonly available than NEAs, to develop better understanding of these whole-system efficiencies, results from a comprehensive LCA harmonization project will be adapted for use in NEA research. The analysis will compare results between LCA and NEA studies for solar PV, concentrating solar power (CSP) and wind power. These energy flows will then be used to generate NEA metrics for renewable energy harvesting, including energy return on investment (EROI), net energy return (NER),gross energy return (GER), and other NEA metrics.

Type of Paper: Article
Title: Plants and Algae Species: A Promising Renewable Energy Production Source
Authors: V. Kumar and S. Mohan Jain
Affiliation: Department of Agricultural Sciences, PL-27, University of Helsinki 00014, Helsinki, Finland; E-Mail: mohan.jain@helsinki.fi
Abstract: Rapid increase in fossil energy consumption has raised price rise and environmental issues. Attempts are being made to reduce carbon dioxide emission from fossil fuels. Biomass is recognized as an important source for renewable energy production, known for emitting low quantity carbon dioxide and methane. Moreover, carbon dioxide is utilized in algae cultivation for Biofuel production. Plants have become a major source for biofuel production, e.g., sugarcane. By using biotechnology and mutagenesis, better plants and algae would be developed for enhancing biofuel production. Different processes of biofuel production from various energy crops and Algae will be discussed, especially bio-ethanol and bio-diesel.

Type of Paper: Article
Title: New Fuzzy Logic Based Controller of Permanent Magnet Wind Generator to Enhance Dynamic Stability of Wind Farm
Authors: Marwan Rosyadi ¹, S. M. Muyeen ², Rion Takahashi ¹ and Junji Tamura ¹
Affiliations: ¹ Kitami Institute of Technology, Kitami, Japan; E-Mails: marwanrosyadi@yahoo.co.id; tamuraj@mail.kitami-it.ac.jp)
² Petroleum Institute, Abu Dhabi, UAE
Abstract: In this paper, new fuzzy logic based controller of variable speed permanent magnet wind generator connected to a grid system through LC-filter is proposed. A new current control method of grid side AC/DC/AC converter is developed with integrating the fuzzy controller, in which both active and reactive power delivered to a power grid system are controlled effectively. The fuzzy logic controller is designed to adjust the gain parameters of the PI controllers for any operating conditions for the dynamic stability to be enhanced. A simple method based on frequency response of bode diagram is proposed in design of the fuzzy logic controller. To evaluate the controller system capabilities, simulation analyses are performed on small wind farm model system including induction wind generator connected to an infinite bus. The simulations have been performed using PSCAD/EMTDC. Simulation results show that the proposed control scheme is more effective to enhance the stability of wind farms during temporary and permanent network disturbances and randomly fluctuating wind speed compared with that with conventional PI controller.

Type of Paper: Review
Title: Asynchronous Wind Turbine Models in the Load Flow Analysis
Authors: Andrés Feijóo, José Luis Pazos and Daniel Villanueva
Affiliation: Departamento de Enxeñería Eléctrica, Universidade de Vigo, Vigo, Galicia, Spain; E-Mails: afeijoo@uvigo.es (A.F.); pazos@uvigo.es (J.L.P.); dvillanueva@uvigo.es (D.V.)
Abstract: Asynchronous wind turbines have been among the most used type of converters in wind energy plants. Conventional asynchronous wind turbines were installed during the first years of wind energy research and, nowadays and in the future, doubly-fed induction wind turbines and other types are also in use. So, the massive presence of such machines in electrical networks means it is important to develop dynamic and steady-state models to describe their behaviour. This paper presents a review of steady-state models of asynchronous wind turbines for the load flow analysis that have been presented in recent years. A large number of conventional asynchronous wind turbines can still be found in electrical systems in many different countries the world over. This fact constitutes a reason for us not to overlook them when studying the operation of such systems. In addition, there has been some discussion about these models over the last years. Furthermore, doubly-fed induction wind turbines will be more important and abundant in future years, which has also led us to include them in the study. Also, some reflexions will be presented about the inverse relationship between the complexity of the machines and the complexity of steady-state models for representing them.

Type of paper: Review
Title: Enhanced Sunlight Harvesting in Photovoltaic Devices
Authors: Pieter Stroeve
Affiliation: Chemical Engineering and Materials Science, University of California Davis 1 Shields Ave., Davis, CA 95616, USA; E-Mail: pstroeve@ucdavis.edu
Abstract: Conversion of sunlight into electricity using photovoltaic (PV) devices is considered by many to be the most feasible strategy to fulfill world energy consumption in the future. During the past decade an increasing number of photovoltaic power plants have been erected to provide clean electricity at a scale approaching that of fossil fuel power plants. However, solar generated electricity currently has a higher cost-per-watt than fossil fuels, which limits its widespread acceptance as a power source. One avenue to reducing PV's overall cost-per-watt is by increasing the absorption of sunlight into the active semiconducting PV materials. Methods to increase the absorption of light in PV devices have been widely studied; in this article, we present an overview of various methods to improve sunlight absorption and we discuss their advantages and limitations.
Keywords: solar cell; photovoltaic; surface plasmon; light capture; scattering structure; absorption enhancement

Type of Paper: Article
Title: What Role Can Wind Play to Meet the UK and Scotland Renewable and Climate Policies?
Author: Gabrial Anandarajah Affiliation: UCL Energy Institute, University College London, Central House, 14 Upper Woburn Place, London, WC1H 0NN, UK; E-Mail: g.anandarajah@ucl.ac.uk
Abstract: The UK government has set targets both for reducing carbon emissions and for deploying renewables to address climate change mitigation and promote renewable energy. Scotland, a constituent nation of the UK, has also set its own targets for climate change mitigation and renewable electricity. This paper analyses what role wind can play to meet renewable and climate policies of the UK and Scotland using a newly developed two-region UK MARKAL energy system model, where Scotland (SCT) and rest of the UK (RUK) are the two regions. The two region model well suits for this analysis as the climate and renewable policies of Scotland and the UK can be incorporated in the model. The paper also analyses the implications of larger penetration of winds in the power generation capacity mix at the UK level.