System Sizing And Control Strategy Comparison Of Distributed Photovoltaic-Battery System

The depletion of fossil fuels and environmental problems accelerate the development of renewable energy.The security and electricity quality of grid require the distributed system with intermittent photovoltaic electricity to integrate with battery,hence,self-consumed distributed photovoltaic-battery system developed rapidly.Under the limitation of usable civil area and grid transmission,properly designing system capacity and improving control strategy of photovoltaic battery system is crucial.This thesis established a comprehensive system mathematical model and carried out a multi-aspect evaluation system considering both technical indicators(self-consumption rate,self-sufficiency rate)and economic indicators(net present value,levelized cost of electricity,payback period).The study indicates that high self-sufficiency rate leads to small photovoltaic capacity and large battery capacity,whereas high self-consumption indicates large photovoltaic capacity and small battery bank.Furthermore,the additional cost of extra battery bank and local subsidy have obvious impact on the payback period.A techno-economic sizing method for grid-connected photovoltaic battery system has been proposed based on the study on change rules of various evaluation indicators with different system sizes.The energy flow and cash flow of eight cases with different technical levels have been studied in detail.An experiment system has been set up,which verifies the relative system model,and system operation performance under different weather conditions has been compared.The result demonstrates that the daily self-sufficiency rates of a sunny/cloudy/rainy day are 83.82%,68.80% and25.74% respectively.The use rate of battery bank increases with the increase of solar radiation and the power grid will encounter greater strike with higher solar radiation.Based on the system capacity design of the experiment system,the improvement of energy control strategy,including the addition of energy transmission between the grid electricity at valley hours and the battery bank,the utilization of simple radiation prediction,have been proposed and compared.Result indicates that not discharging battery at valley hours is less profitable than charging the battery at valley hours and the transmission between battery bank and power grid sharply reduces the self-sufficiency rate and self-consumption rate by 18.58% and16.67% respectively.Besides,simple solar radiation prediction based on perfect solar radiation data performs better in technical aspect to a small extent,whereas performs worse economically.The grid transmission difference of various strategies peaks at 196 k Wh in April with high solar radiation and low household load demand especially for heat load.The sensitivity analyses of key factors including battery size,load demand,grid electricity price and battery price on technical and economic performance of different energy control systems have been conducted.The study shows that basic strategy with largest renewable consumption is most sensitive to variation of battery size and load demand,while strategy with the largest amount of consumed grid electricity at valley hours is least sensitive.This study established a mathematical model of grid-connected photovoltaic battery system of relatively high accuracy and verified the model based on experimental study.Also,a techno-economic sizing method has been proposed with the consideration of practical electricity tariffs and subsidies.Moreover,system performance under different energy control strategies have been analyzed and compared based on grid transmission with the battery bank and short-term weather prediction.As a result,this study can help promote development and application of distributed photovoltaic system and serves as the basic research on system sizing and energy control strategy improvement for distributed energy systems.