Research On Capacity Allocation And Optimal Operation Of Hydropower Complementary Clean Energy Systems

To cope with the challenge of climate change and the crisis of energy shortages,the global power supply gradually tends to clean and renewable energy,such as hydro,solar/photovoltaic(PV),and wind power.However,due to the natural characteristics of randomness,volatility,and unpredictability,a single solar or wind energy cannot guarantee the reliability of power supply,and a large amount of power curtailments will occur.In view of the advantages of rapid start-stop units,fast output adjustment,and strong peak-shaving capability of hydropower,multi-energy complementary systems composed of hydro,PV,and wind power are gradually being favored.Capacity allocation and optimal operation are always two key problems faced by multi-energy complementary systems.Therefore,how to determine the capacity allocation scheme and optimal operation strategy of a hydro-PV-wind multi-energy complementary system is of great significance to the development of a large-scale hydro-PV-wind complementary system and the establishment of a long-term mechanism for clean energy consumption.Thus,this paper takes the multi-energy complementary system in the upper reaches of the Yellow River in Qinghai Province as an example to carry out research on the capacity allocation and optimial operation of hydropower complementary clean energy systems from aspects: capacity allocation and optimial operation.The main research contents and achievements of this article are as follows:First,a method for the PV capacity configuration of the cascade hydro-PV complementary system in river basin is proposed.By analyzing the typical daily load characteristics of the power grid,the multi-segment line generalization method that uses time parameters and characteristic parameters to describe the electricity delivery demand is improved;then,comprehensively considering the runoff characteristics,electricity delivery demand,reservoir regulation characteristics,and hydraulic-water connection,etc.,a mathematical model for PV capacity configuration of the cascade hydro-PV complementary system in river basin is constructed;finally,based on historical mean daily runoff characteristics,a complementary guarantee rate(CGR)index for quantifying and evaluating the complementary PV capability of cascade hydropower stations is proposed.The method is applied to the Banduo-Yangqu cascade hydro-PV complementary system in the upper reaches of the Yellow River,and the study shows that with the increase of PV installed capacity,the mean daily runoff bandwidth and CGR gradually decrease.For the run-off hydropower,the hydro-PV complementary system should adopt the three-segment line complementary operation mode according to the PV output characteristics;for the daily regulating hydropower,the hydro-PV complementary system can adopt the three-and five-segment line complementary operation modes according to the actual load demand.Under the three-segment line complementary operation mode,it is recommended that the complementary PV capacities of the Banduo,Yangqu,and Banduo-Yangqu cascade hydropower stations are 138.3,578.9,and 593.8 MW,respectively,while under the five-segment line complementary operation mode,it is recommended that the complementary PV capacities of Yangqu and Banduo-Yangqu cascade hydropower stations are 627.3 and 681.3 MW,respectively.In addition,the complementary PV capacity of a run-off hydropower station is mainly subject to the upstream inflow and reservoir storage capacity,while the complementary PV capacity of the daily regulated hydropower stations is mainly subject to the upstream inflow and hydropower installed capacity.The CGR is improved through upstream reservoir regulation,increasing hydropower installed capacity,and increasing reservoir storage capacity,and the corresponding average increaments are 0.128,0.081,and 0.061 respectively.Therefore,the above three measures should be reasonably selected during the planning-construction and actual operation of cascade hydro-PV complementary systems to improve hydro-PV complementary performance.Second,a research framework for the short-term optimal operation of the cascade hydro-PV complementary system in river basin is proposed.Based on the power grid typical daily load characteristics and PV output characteristics,a method using the daily average net load and fluctuation coefficient to describe the net load characterization of the cascade hydro-PV complementary system is improved;then,comprehensively considering the system load characteristics,PV output characteristics,runoff characteristics,reservoir regulation characteristics,and hydraulic-water connection,etc.,a mathematical model of the short-term optimal operation of the cascade hydro-PV complementary system in river basin is constructed;finally,based on the net load fluctuation coefficient,a coordinated peak-shaving strategy for cascade hydropower stations is proposed.This framework is applyied to the Banduo-Yangqu cascade hydro-PV complementary system in the upper reaches of the Yellow River,and the study shows that there is an obvious competitive relationship between the cascade hydropower stations daily power generation and the residual load fluctuation.In addition,the daily regulating hydropower station is mainly responsible for the peak-shaving task of the cascade hydro-PV complementary system,and the system base load task is jointly undertaken by the runoff and the daily regulating hydropower stations.The cascade hydro-PV complementary system should determine the role of the cascade hydro-PV complementary system in the power grid(single-peak,double-peak load)based on the average daily runoff and PV output characteristics(weather type).On sunny,cloudy,and dusty days,when the average daily runoff is less than 30% of the rated flow of the hydropower station,the cascade hydro-PV complementary system should bear the single-peak load,otherwise,the cascade hydro-PV complementary system should bear the double-peak load;on rain and snow days,the cascade hydro-PV complementary system should bear the double-peak load under different daily average runoffs.After the relative positions of Banduo-Yangqu cascade hydropower stations are interchanged,the base-load output,peak-load output,and daily operation mode of each hydropower station in the cascade hydro-PV complementary system change,and the standard deviation of residual load increases by 4.1%(sunny day)and 29.8%(rainy day)on averagethe.Therefore,it is necessary to comprehensively consider the relative position of the cascade hydropower station,reservoir storage capacity,PV output characteristics,daily runoff characteristics,and daily load demand characteristics to formulate the short-term optimal operation strategy of the cascade hydro-PV complementary system in river basin.Third,a method for the large-scale hydro-PV-wind complementary system capacity configuration and economic evaluation is presented.First of all,comprehensively considering the method for the PV capacity configuration of the cascade hydro-PV complementary system in river basin,hydropower theory complementary PV-wind capability,PV-wind output characteristics,feed-in tariff,social discount rate,component costs,and land lease costs,etc.,a large-scale hydro-PV-wind complementary system capacity configuration and economic evaluation model with the goal of maximizing the life-cycle net present value of the PV power plants and wind farms is constructed;then,the method for determining the typical daily output of PV power plants and wind farms is proposed;finally,a mathematical model for determining the optimal capacity proportions of PV power plants and wind farms is proposed.Applying this method to the large-scale hydro-PV-wind complementary system in the upper reaches of the Yellow River in Qinghai Province,the study shows that the large-scale hydro-PV-wind complementary systems corresponding to the cascade hydropower stations in the upper reaches of the Yellow River in Qinghai Province are all economically feasible,and the actual optimal total installed capacities of PV and wind for the cascade hydropower stations(from Longyangxia to Dahejia)are 603.9,1946.5,91.4,938.7,70.5,156.3,751.5,133.2,129.2,525.1,and 30.9 MW,respectively.Compared with the independent hydropower operation,the average annual water abandonment amount,water abandonment rate,and transmission line utilization hours of the cascade hydropower stations in the upper Yellow River increase after the hydro-PV-wind complementary operation,and the water abandonment mainly occurs in the flood season.Through the joint regulation of Longyangxia-Liujiaxia cascade reservoirs,the water abandonment of hydropower stations can be reduced(the water abandonment rate is reduced to 0),the complementarity of hydro-PV-wind can be improved(the CGR is increased by0.35),and the average annual power generation of Longyangxia-Liujiaxia cascade hydropower stations has increased by 1.89%.In addition,the large-scale hydro-PV-wind complementary system capacity allocation and economic evaluation model in river basin is most sensitive to five parameters,namely,PV feed-in tariff,average annual utilization hours of PV,social discount rate,wind power feed-in tariff,and average annual utilization hours of wind power.