Impact of optimal charging of electric vehicles on future generation portfolios

Battery electric vehicles are considered by many to be part of a series of measures necessary to reduce global carbon dioxide emissions and dependence on fossil fuel resources. The extent to which this is possible depends on how successfully they can be implemented into the broader system. This paper considers the power systems impact of different vehicle charging regimes. A test system with a high proportion of variable renewables was considered. Charging profiles were developed for slow, fast and controlled optimal charging and optimal generation portfolios were developed using a least-cost optimisation algorithm. It was found that over-night charging at the slow rate resulted in a reduction in the average cost of electricity by between 4.2 and 6% compared to the base-case. For the high charging rate cases, the average cost of electricity rises by between 3 and 7%. When the charging is controlled centrally and optimised so as to increase the minimum system load maximally, it is found that the average cost of electricity is reduced by between 4.5 and 8.2%. None of the above cases resulted in significant changes in the average CO₂ emissions per unit electricity output. However, it was found that by increasing the minimum system load, optimal charging could facilitate additional inflexible generation such as variable renewables or nuclear fission plant. Where nuclear capacity is added to the generation portfolios based on optimal charging, average CO₂ emissions per unit of electricity are seen to fall between 22 and 41% for the cases studied, with the average cost of electricity reducing by between 9.5 and 21.5%.