Estimating the seasonal variation in electricity demand of future electric vehicle fleets

Large-scale uptake of electric vehicles will contribute to emission reductions but may also challenge future highly-renewable electricity grids. Daily variation in charging demand can be synchronized with renewable supply and moved out of grid congestion periods using a range of storage and demand shifting technologies. However, seasonal variation in charging demand, which could add to increasingly-electrified building space-heating demand, is potentially much more difficult to resolve. We develop a statistical model of monthly vehicle energy intensity (Wh/km) based on a citizen-science sourced dataset of multi-year charging data from >1000 vehicles. The model depends on electric vehicle model type, heating and cooling degree day, and location, and can be used to predict seasonal variation in vehicle energy intensity in any climate zone given a distribution of vehicle models. We use the model to explore the seasonal variation in electricity demand from future large scale electric vehicle uptake in New Zealand. We find that electricity consumption for vehicle charging can vary seasonally by up to 16% in some regions and increase winter monthly consumption by up to 30%. These results have implications for future electricity infrastructure planning. The major uncertainties in these projections stem from the difficulty in estimating the energy intensity of the electric vehicle models that will make up the future fleet.