Vehicle to grid: driver plug-in patterns, their impact on the cost and carbon of charging, and implications for system flexibility

Vehicle-to-grid (V2G) from electric vehicles (EVs) represents an opportunity to provide transitioning electricity systems with battery storage as they face increasing shares of variable renewable generation. However, whilst the availability of V2G as dispatchable storage depends on the travel and charging habits of drivers, there is scarce experience of managing portfolios of EVs in this way. This paper investigates the impact of plug-in frequency - given real-life travel data - on the potential of V2G to reduce i) consumer bills and ii) carbon emissions of charging. In doing so, we investigate the extent to which consumers are incentivised to participate in V2G, how this might change based on different charging behaviours, and what the implications are for V2G as a storage asset. Two models of plug-in behaviour are input into a time-coupled optimisation that schedules EV (dis)charging to minimise the net cost of an EV's required energy gain within network constraints, simulating how V2G could be dispatched by a 'load controller' in a liberalised electricity market. The cost minimisation is based on the Octopus Agile V2G tariff in January 2021, which is matched to GB grid carbon intensity data from National Grid ESO for the same period. It was found that, on the basis of the time range studied, V2G can reduce the average price paid for EV-charging electricity by 28-67% versus a flat tariff - with the lower end of that range representing a case where consumers only plug in when they 'need' to, and the higher end representing the case where consumers plug in whenever their cars are at home. It was also found that due to the weak positive correlation between price and carbon during the time range studied, optimising for price also resulted in slight reductions in carbon intensity of the EV-charging electricity by 5-6% compared to uncontrolled charging, with the range representing the same cases as before. Taking into account a review of battery degradation costs from V2G, using an EV's battery in this manner only makes financial sense to the owner if they maximise their plug-in frequency; this, alongside the increased savings, should provide an incentive to owners to plug in as much as possible - thereby maximising storage resource for a low carbon electricity system. (c) 2022 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).