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Über dieses Buch

This book offers methods to improve energy access and support social and economic development through the appropriate and reliable design of isolated wind energy systems. The findings reported on wind based isolated power generation show that the proper match of turbine diameter and generator rating is vital, and is governed by the site wind resource and the load profile to be served. The methodology for sizing and selecting appropriate system parameters, taking into account the resource uncertainty, is demonstrated throughout the chapters of this monograph.
Readers will discover information on the methodologies for modelling, design and optimization of the systems in terms of safety, functionality, longevity, and practicality. Details are provided on the design space of wind-battery systems, multiple wind generator systems, and wind-PV-battery hybrids to cover all the bases of isolated wind energy systems. This monograph aims to serve as a guide to system developers, manufacturers, and financing institutions on the design aspects of isolated wind energy systems.



Chapter 1. Introduction to Isolated Energy Systems

The opening of the transmission and distribution grid to independent power producers offering cheaper, efficient, smaller-scale plants is a paradigm shift from the era of larger centralized power schemes. This transformation is being witnessed by most developed and developing nations of the world. This chapter begins with a brief description of the world energy scenario, thereby emphasizing the need for isolated systems. In the present circumstances, where environmental vulnerability of energy systems is a sensitive issue, the relevance of isolated power systems is obvious. The potential of off-grid systems over the world, as well as in India, and the challenges to be addressed are derived from a detailed account of country-specific energy scenarios.
Anindita Roy, Santanu Bandyopadhyay

Chapter 2. Wind Energy Systems

This chapter provides a historical account of wind power development and its varied applications. Given that centralized electrification embodies huge investments which many developing and underdeveloped countries cannot afford, the pivotal role of wind power as a major source of electricity in off-grid locations is outlined. These applications include but are not restricted to rural electrification, island power systems, replacement of diesel-powered generation in telecommunication towers and agricultural pumps, street lighting and home lighting systems. The two major configurations of wind turbines, viz. vertical and horizontal axis type, are elucidated along with their operational characteristics. Further, the design parameters of wind machines which characterize its performance and play a role in the energy generation and system sizing are discussed.
Anindita Roy, Santanu Bandyopadhyay

Chapter 3. Modelling of Isolated Systems

A detailed overview of the necessity and classification of off-grid power systems along with its component subsystems is presented in this chapter. Different interconnection schemes and their relative merits are then discussed. The fundamental issues underlying the design of an isolated power system are the match between the load and resource and the size of the storage system. Parameters affecting the sizing of the storage and the entire isolated system have been discoursed. In order to understand the trade-offs in the design, it is necessary to formulate the problem in terms of a mathematical model. The mathematical model of the wind turbine consisting of the blades, transmission and electrical generator, the model of the photovoltaic system, the inverter and battery bank are discussed. Models of the photovoltaic array and diesel generator system are also presented. These subsystem models are linked together to form the entire system model through an energy balance on the system. Through time series simulation of the system energy balance along with different design constraints, a set of feasible design options, known as the design space, can be identified. Such a plot of various feasible design options enables identification of the limits of wind turbine rated power and the battery size for a given demand and resource characteristics within which a feasible design is guaranteed. Contemporary software tools used accomplishing similar tasks are also discussed.
Anindita Roy, Santanu Bandyopadhyay

Chapter 4. Design and Optimization of Wind-Battery Systems

This chapter gives a detailed account of the sizing and optimization of an isolated wind-battery system. A procedure is proposed which simulates the minimum battery capacity given the resource and load profiles and generator rating-turbine diameter combination along with other system level constraints. Varying the turbine diameter-generator rating combinations enables to generate a set of feasible design options, known as the design space. The design space of a wind-battery system is identified on a rotor diameter vs. rated power diagram. This forms the core philosophy for sizing the system. The optimum configuration of the stand-alone system is identified on the basis of the minimum cost of energy. Similar results can also be obtained by applying principles of pinch analysis originally designed for optimizing heat exchanger networks. Multiple case studies are included to demonstrate the procedure. It is demonstrated that there are maximum and minimum limits associated with each design variable abiding by which it is possible to supply the demand.
Anindita Roy, Santanu Bandyopadhyay

Chapter 5. Probabilistic Modelling and Optimization

As wind speed fluctuations manifest in energy fluctuations, the instantaneous uncertainty of wind speed availability is a bottleneck for successful implementation of wind-based power generation technology. Although being a proven technology, this crucial issue has affected the market growth of wind power technology in the isolated hybrid mode. In this chapter, a methodology which accounts for the stochastic nature of wind is developed using chance-constrained programming integrated into a time step simulation process is introduced. This enables the formulation of a deterministic equivalent energy balance through which the design space for a pre-specified reliability requirement can be generated. Thus, the design space is expressed as a function of the targeted reliability, thereby enabling a tailor-made design specific to a given reliability requirement. A major outcome of the treatment is in showing that the cut-in wind speed of the turbine plays a critical role in delivering desired power supply reliability. Through illustrative examples, it is also demonstrated that wind-battery systems cannot be designed to provide power supply reliability beyond a maximum value.
Anindita Roy, Santanu Bandyopadhyay

Chapter 6. Non-convexity in the Design Space of Wind-Battery Systems

Wind-battery system design problems typically embody a non-linear generator characteristic. If the co-relation between the load and generation profiles is poor, the solution set is likely to be non-convex. That is, for a certain rotor blade diameter and generator rating combinations within the feasible design region, no solution exists. Reasons for such non-convexities are identified and parameterized with an illustrative example. It is found that the likelihood of a non-convex solution set is profound when the power supply reliability is high and the ratio of standard deviation to mean wind speed at the site is within a certain range (0.3–0.6 in this case). Design space methodology helps to predict the occurrence of a non-convex solution set and can aid the planner/decision-maker in selecting a global optimal solution in the light of non-convexity. When the design space is non-convex, arbitrary oversizing of design variables may lead to non-compliance with overall reliability requirement.
Anindita Roy, Santanu Bandyopadhyay

Chapter 7. Multiple Wind Generator Systems

Systems consisting of multiple wind generators along with a battery bank are a sustainable alternative for supplying the energy requirements of remote locations not connected to the national grid. This chapter presents a methodology for sizing and optimizing wind-battery systems employing multiple wind turbines. Uncertainty in wind resource availability is taken into account by formulating the problem as a chance constraint. Based on a time step simulation, subject to different technical and physical design constraints, the entire solution space in terms of the system design variables, viz. generator rating, rotor diameter and battery bank size for a specified number of wind turbines and reliability requirement, is generated. The domain containing all feasible solutions is the design space, and it is a function of system reliability requirement and the number of wind turbines. From the design space of multiple wind turbine-battery systems, it is shown that with an increase in the number of wind generators, the rotor diameter, generator rating of individual turbines, as well as battery bank size, can be minimized along with a benefit in the overall cost of energy (US$/kWh). Additionally, by increasing the number of wind generators, it is possible to comply with a stringent power supply reliability target which would otherwise not be possible.
Anindita Roy, Santanu Bandyopadhyay

Chapter 8. Design and Optimization of Wind-PV-Battery Hybrid System

The complementarity in the nature of wind speed and solar radiation makes the wind-photovoltaic hybrid combination a preferred option in comparison to wind-battery systems. Such a combination can serve to reduce the storage capacity and increase the system availability. The design and optimization of such systems need incorporation of both wind and solar resource availability at the location. The system design variables are the wind turbine rating, blade diameter, photovoltaic array rating and the battery bank capacity. A method to optimally size and to evaluate the cost of energy produced by a wind-photovoltaic-battery system is demonstrated with an illustrative example. It is shown that inclusion of a photovoltaic generator serves to reduce the minimum wind turbine diameter requirement from about 14–60% and the wind generator rating from 20% to 70% in relation to a wind-battery system. The proposed method based on the design space approach can be used to determine the conditions for which hybridization of the system is cost effective.
Anindita Roy, Santanu Bandyopadhyay

Chapter 9. Conclusion

The penetration of distributed generation is poised to grow substantially in the future, especially in developing countries. To promote generation of electricity using renewable resources, a system level approach to the problem needs to be developed. Moreover, the developed approach should imbibe features of simplicity, generality and flexibility as well. A simple and generalized methodology for sizing the components of an isolated wind-based system has been proposed through this book. The depiction of the solution set termed as ‘design space’ brings out the clarity of consequences when a particular solution point is selected in comparison to any other. It can aid the planner/decision-maker in selecting a global optimal solution in the light of various constraints.
Anindita Roy, Santanu Bandyopadhyay


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