Research On Solar Organic Rankine Cycle Optimizing Design Based On The Time-varying Solar Radiation

Solar energy,as a low energy density of the heat source,is susceptible to geographical latitude,cloud,day and night alternation,climatic conditions and other factors.This brings a huge challenge to the energy efficiency optimization and stability design of solar organic Rankine cycle(SORC).In response to this challenge,a dynamic model of SORC system is developed;based on this model,the influence of different solar radiation fluctuation characteristics on the output of SORC system is analyzed;after that,a construction method of typical solar radiation condition(TSRY)based on historical data is proposed;Finally,based on TSRY and the above dynamic model,multi-objective genetic algorithm is used to optimize the design of SORC.The main contents of the article are as follows:The dynamic model of SORC system including solar collector,thermal energy storage,heat exchanger,expander and pump is developed.The comparison between the model and the experimental results shows that the average relative error of instantaneous output power is 0.93%.It is shown that the accuracy of the model can meet requirement of the optimization of SORC system.Based on this model,the influence of solar fluctuation characteristics(including period,offset,amplitude),volume of thermal energy storage(TES)and evaporation temperature on the stability and the total efficiency of the system are analyzed.Fluctuation Suppression Ratio,which represents the degree of inhibition of the dynamic impact by TES,is proposed.The analysis shows that there are specific characteristics of solar radiation fluctuations that cause a given SORC system to resonate,leading to an increase in the output fluctuations of the system.The resonance area,which should be avoided,is mainly related to the period of solar radiation fluctuation and the volume of TES.TSRY are constructed based on historical solar radiation.Using a set of features,which describing the characteristics of solar radiation fluctuation,k-means is used to cluster the historical daily radiations,and four typical daily radiations can be obtained to represent the certain region.Then the discrete-time Markov chain is used to model the transition between four typical daily radiations.Finally,TSRY was constructed based on this above.The result shows that the average errors for the four sites of TSRY are less than 10%.This indicates that TSRY can characterize the variation of daily radiation based on the historical daily radiations.In the dynamic SORC system with TSRY,NGSA-II algorithm was used to optimize the design parameters with multi-objectives by the goal of total output power and fluctuation of output power.The 17 groups of Pareto frontiers were obtained.Annual Net Profit(ANP)is as an economical indicator of the SORC.The result shows that there is a minimum SORC size that can be profitable for a given region.Only systems larger than this size can profit.In the DRA region,only SORC systems with a solar collector area of more than 165m~2 can make a profit.