Analysis of the influence of average outside temperature and initial state of charge on the charging power of EVs and the maximum flexibility ratio
Summary
Electric vehicles (EVs) have the possibility to reduce CO2 emissions compared to conventional combustion vehicles. The international energy agency (IEA) predicts that the amount of EVs worldwide will rise to 125 million in 2030. A consequence of an increasing EV fleet is an increasing electricity demand, which can lead to congestion problems on the local distribution grid. A solution for dealing with grid congestion is smart charging, which enables grid operators to spread the electricity demand over time. A necessary condition for smart charging is sufficient EV demand flexibility. The maximum available flexibility is defined as the difference between the connection period and the charging period. The charging period is influenced by the charging power, which depends on several external factors. The goal of this study is to investigate the influence of the initial state of charge and the average outside temperature on the charging power for different EVs. Subsequently, the obtained relationship will be used to determine the maximum available flexibility.
Detailed charging transactions were collected from 4 charging stations present at the parking area of ElaadNL. Before analysing the data, a differentiation was made between battery electric vehicles (BEVs) and plug-in hybrid electric vehicles (PHEVs). After this, a second grouping was made between the different BEV and PHEV models. A linear regression analysis was performed between the factors initial SOC and average outside temperature and the maximum, average and minimum charging power of multiple transactions.
A strong linear relationship between the average outside temperature and the average charging power was observed for one PHEV model. This PHEV model also showed a linear relationship between the initial SOC and the average charging power. The results from the linear regression analysis were used to predict the charging duration and calculate the maximum available flexibility ratio. The predicted flexibility ratios for PHEVs showed similarities with the real flexibility ratios. For BEVs, the predicted flexibility ratios were different from the real flexibility ratios.