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Title: Study on renewable energy systems with different energy storage solutions for power supply in remote areas
Authors: Ma, Tao
Advisors: Yang, Hongxing (BSE)
Lu, Lin (BSE)
Keywords: Renewable energy sources
Energy storage
Issue Date: 2015
Publisher: The Hong Kong Polytechnic University
Abstract: At present, more than 1.3 billion inhabitants worldwide still lack access to grid electricity. Most of the people live in remote areas, such as islands, mountain areas and isolated villages, all some distance from the utility grid. Grid extension to such remote communities is both uneconomical and technically difficult owing to dispersed population or rugged terrain. As a result, their electrical demand is normally met by use of diesel power or there is no power supply at all. Fortunately, such areas, although remote, are usually rich in renewable energy (RE) resources, thus making it worthwhile to explore such local RE resources with the objective of producing much needed electricity. In recent years, the unpredictability of diesel costs, falling RE generation costs as well as technological improvements have encouraged a wider adoption of renewable energies in such areas. Stand-alone renewable energy power generation systems have been the target of substantial research over the past decades. However, the focus on comprehensive renewable energy power supply solutions for remote areas, together with the identification of effective and low-cost technologies is limited. In addition, one significant technical challenge for those stand-alone RE systems, such as solar and wind energy, is the fluctuation of their output. This feature prevents the RE from being fully reliable for remote areas. In this context, the development of some effective energy storage solutions, to keep energy in excess for use in time of need, is an essential requirement. Currently battery must be a front-runner for use in remote RE systems. However, it has well known limitations, such as high cost, short lifespan, possibility of environmental damage and explosion, and difficulties for maintenance in isolated areas. Pumped hydro storage (PHS), usually used for conventional power plants, shows a great potential to replace batteries in standalone application, but to date few studies have reported the micro PHS for remote RE systems. The aim of this thesis is to study the options of power supply and energy storage for remote areas. One remote inhabited island 20 km off the coast of Hong Kong is taken to act as a test site for the proposed RE systems and storage technologies. To achieve the objectives of the study, a detailed study of different energy technologies for remote electrification was conducted, including system development, mathematical modeling, simulation, optimization, techno-economic evaluation, and sensitivity analysis. Different energy storage technologies, i.e. batteries, PHS, super-capacitors and their hybrids, are investigated via theoretical analysis, numerical simulation and experimental validation. The operational performance of a real PV-battery system on this example island was evaluated. Firstly, the RE potential and load demand of the selected island were assessed. Mathematical models for each RE technology were developed, and system evaluation criteria discussed. In particular, a novel simulation model for PV devices, offering a good compromise between accuracy and simplicity, was developed in Matlab to fit the I-V curves and predict PV power output. The model was solved using an integrated analytical and numerical method, then validated through field measurements in a real grid-connected and a standalone PV system.
A detailed study on the use of a traditional energy storage technology, battery, to support a remote area power generation system has been conducted. System configurations of possible combinations of solar energy, wind energy, diesel generator and battery bank were developed. Hourly simulations for a wide variety of configurations were performed to achieve an optimal one based on techno-economic analysis. Two representative systems, the 100% RE and hybrid RE-diesel, were selected for deeper analysis. Emphasis was also placed on examinations of the effects of the PV, wind turbine, diesel generator, and battery bank capacity on the system{174}s reliability and economic performance. The results demonstrated that the island could be powered by a 100% RE system, although it is possible that the energy cost provision will be quite high. The addition of a back-up diesel generator would make the hybrid system, i.e. solar-wind-diesel-battery, a more economically viable option. The problems which were observed concerning batteries limit a wider and future application of the battery-based RE systems. Thus as an alternative, a small PHS unit was proposed to support the remote area RE power supply systems at a few hundred kW scale. Of interest is the development in this study of a novel operating principle and design process for PHS-based RE systems. With the simulation program developed in this study, the system was simulated for a whole year. The genetic algorithm, along with the Pareto optimality concept, was then employed for system optimization, i.e. to identify the maximization of power supply reliability and minimization of system cost. The optimized system configuration under zero loss of power supply probability (LPSP) was then investigated. In addition, the system performance of hybrid solar-wind, solar-alone and wind-alone systems with pumped storage under LPSPs from 0 to 5% were compared. Sensitivity analysis on several key parameters was also performed to examine their effects on system performance. This study proposed a new concept of energy storage to compensate the intermittent nature of renewable energy applications. Even though the overall efficiency of the micro-scaled pumped storage system is not high, a sustainable and environmentally friendly power supply solution is able to be provided, indicating that the pumped storage is one future ideal partner for remote area RE power supply systems. Further investigation of the battery-based and PHS-based RE system indicates that the use of more than one storage technology will give a better performance as regards complementing fluctuating RE outputs and dynamic power demands. Therefore, a new hybrid energy storage system (HESS), which combines battery for long-term energy management and supercapacitor for fast dynamic power regulation, was proposed. The mathematical models of the passive connected HESS were developed, and then implemented in Matlab/Simulink for numerical simulations. An electric inductance was further introduced to improve the performance of the HESS. In addition, an experimental test bench was developed to validate simulation results. It was demonstrated that the HESS can stabilize energy provision, not only for intermittent RE, but also for other fluctuating load applications. Finally, the benefit of another kind HESS, a combination of pumped storage and battery energy storage system, was analyzed and the system was experimentally studied, as an illustration of the operation states of such hybrid energy storage technology. The operating data of a 19.8kWp solar PV-battery system on the island was collected and evaluated for the following aspects: the PV array, inverters, the battery bank and overall system. This evaluation enables a detailed understanding of the operating performance of the existing PV system from the technical point of view. It also provides useful reference data for further system extension. A comprehensive study of stand-alone RE power supply system using different energy storage solutions for remote areas with useful research outputs has been outlined above. The results provide researchers, engineers and policy makers with choices regarding the use of local RE resource, which could be aligned with the characteristics of individual remote area of interest. It is believed that the findings have provided a good reference for the selection of suitable RE and energy storage technologies, and the methodology presented can also be viewed as a starting point for planning and designing RE systems for remote communities around the world.
Description: PolyU Library Call No.: [THS] LG51 .H577P BSE 2015 Ma
xxxi, 302 leaves :illustrations (some color) ;30 cm
Rights: All rights reserved.
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