| With a series of problems brought about by the energy crisis and climate change,developing cleaner energy is an inevitable choice for energy structure transformation and sustainable development.Solar energy is one of the most abundant and widely available renewable energy sources,but its intermittency and instability have hindered large-scale industrial applications.Integrating thermal energy storage system has been proved to be an effective way to improve energy efficiency and stabilize the system operation.In this thesis,in order to seek feasible solutions of the problems existing in the application of two-tank molten salt energy storage system in the concentrated solar power(CSP)plants,energy storage systems using concrete and phase change materials as the energy storage medium were proposed.The thermal performance of different energy storage systems was analyzed.Meanwhile,the economic feasibility of different thermal energy storage(TES)systems was evaluated by developing a techno-economic model.Furthermore,the probability distributions of levelized cost of electricity(LCOE)for different energy storage systems were obtained based on the Monte Carlo(MC)approach considering the parameter uncertainty.The main contents and results of this thesis are as follows:(1)The concrete-based energy storage system used the form of embedded tubes to enhance heat transfer,and the packed bed energy storage system used encapsulated phase change materials to improve energy storage density.Based on the heat transfer characteristics of the concrete energy storage system and the single-tank packed bed energy storage system,the transient heat transfer mathematical models of the energy storage process were constructed respectively.By comparing with experimental data,the validity of the model was verified and the heat storage mechanisms of different energy storage systems were revealed.(2)The thermal performance of the concrete based TES system was analyzed by simulating the heat transfer process of the TES system.A mathematical model between the influencing factors and thermal performance indicators was established.The validity of the model and the significant factors affecting the thermal performance of the system were identified based on analysis of variance(ANOVA).Among the single factors,the flow velocity was the most important factor affecting the charging time and charging efficiency,and the inlet temperature had a large impact on the energy storage.In addition to single factors,the interactions between different factors also had a significant impact on thermal performance.Among the interactions,the interaction of inlet temperature and flow velocity had a great influence on the charging time,and the interaction of the number of fins and tubes had a great influence on the energy storage and charging efficiency.The optimal combination of parameters for the overall thermal performance of the system was obtained by the multi-objective optimization.(3)The mathematical model of the packed bed TES system was established based on the theory of local non-thermal equilibrium of porous media and the theory of phase change heat transfer.The temperature distributions during the charging and discharging process of the energy storage system were observed.The influence of key parameters on the thermal performance of different energy storage systems(single-layer latent heat,three-layer latent heat and combined sensible-latent heat)was analyzed.Both the increase of flow velocity and the higher operating temperature range could improve the charging rate,but had little effect on the charging efficiency.In the combined sensible-latent heat packed bed TES system,as the increase of concrete volume fraction,the energy storage decreased and the charging rate increased.But it had little effect on charging efficiency.(4)According to the cost components of the TES system,their investment cost as well as unit energy storage cost were calculated.Compared with the traditional two-tank molten salt energy storage system,the use of both the concrete energy storage system and the packed bed energy storage systems could reduce the unit energy storage cost.For the phase change packed bed energy storage system,except for the PCM-H system where the unit energy storage cost was most sensitive to the impact of phase change material price,the encapsulation cost had the greatest impact on the unit energy storage cost in other phase change energy storage systems.The use of combined sensible-latent heat packed bed energy storage system could reduce the encapsulation cost of phase change materials and reduce the energy storage cost with less impact on the energy storage.The 50%concrete volume ratio was an optimal alternative.(5)Based on the analytical framework of the combination of MC simulation techniques and economic indicators,a data-intensive techno-economic model was developed to evaluate the economic feasibility of different energy storage systems,taking into account the uncertainties of input variables.The uncertainty analysis method could be used to distinguish the stochasticity of parameters through sensitivity analysis,and the probabilistic estimation was performed by LCOE-MC analysis.Under the consideration of environmental and social benefits as well as parameter uncertainties,the LCOE of the C-PCM2 system was lower than that of other energy storage systems,which provided a useful model for determining the investment decision of selecting an energy storage system. |
