| Wind energy plays a significant role in solving the fossil energy crisis,tackling the global climate change,promoting the transformation of the energy structure,increasing the diversification of energy sources,and meeting the growing energy demand.As one of the most important renewable energy sources,large scale wind power will be connected to power grids in future decades.However,due to the random and seasonal intermittency of wind power,the large-scale connection of wind farms challenges power grids from peak regulation and frequency adjustment.The open literature survey indicates that using a low-cost and large-capacity energy storage technology has great significance in enhancing the flexibility of electric power system,facilitating a high penetration of wind energy and solving the wind power rejection issues.The dissertation firstly reviews and summarizes the development and status of the wind power generation,wind energy storage technologies and high temperature molten salt thermal energy storage technologies.A preliminary design of a two-tank integrated wind power-high temperature molten salt thermal energy storage(WTES)system is presented for electricity supply,district heating and both electricity supply and district heating,respectively.The WTES system relates to kinds of disciplines,such as mechanics,hydromechanics,heat transfer,etc.Moreover,the integrated system contains a variety of components.Thus,the modeling of the considered WTES system is a highly complicated task.Detailed mathematical models of components are derived,according to the corresponding component physics and operation characteristics.The WTES system consist of a wind power system,a molten salt thermal energy storage system,a Rankine cycle system and a district heating system.A generic model library including all these sub-system modules is developed using a multi-programing language Modelica and Dymola software according to the mathematical models derived above.Then the test work of these modules is implemented and analyzed,which is believed to help lay the foundation for the later design and performance analysis.And the model of the WTES system is built by the integration of the developed modules.The transient performances of the models based on those three operation designs are studied and a parametric study on the system performances are also investigated.The studies verify the technical feasibility of the molten salt thermal energy storage system in increasing the utilization of wind energy.Economic evaluation is anohter part of the feasibility analysis.The method for the economic evaluation of the considered WTES system is given on the basis of the construction and operation experiences of the wind power plant and thermal energy storage system.Comprehensive economical assessments of the WTES system are carried out by using a variety of evaluation indexes including the levelized cost,the internal rate of return and the payback period.The results indicate that the WTES system can effectively enhance the utilization of wind energy.The economic analysis proves that the thermal energy storage is able to improve the economy of a wind power system when there is a large share of wind power rejection.Through a comparative study,it is found that the molten salt thermal energy storage system can inspire its potential with the application of distrct heating.Moreover,one can obtain an optimized design scheme of any wind-thermal energy storage integrated system using the generic model library and analytical method developed in the present work.In general,the economical and environmental high temperature molten salt thermal energy storage technology used by the WTES system is meaningful for increasing the flexibility of power system,improving the utilization of wind energy,and reducing the dependence on fossil energy.The high temperature molten salt thermal energy storage technology can be used as a solution to wind energy rejection,energy conservation and emission reduction which are public concerns all over the world. |
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