This study focuses on how the amount of time that electric vehicle (EVs) are plugged into chargers impacts the potential benefits of managed charging. The study considers multiple objectives for managed charging and assesses the impacts on the cost of charging, the stress on the distribution network and the potential to align charging with renewable energy generation. 

Key findings

• Vehicles being plugged in 25% of the day (6 hours), or 42 hours a week, is sufficient to realise most of the benefits of managed charging.  
• A modest plug-in-fraction of 25%:
  – reduces charging costs from $1.28 to $0.72 per day in the absence of vehicle-to-grid, 
  – enables vehicle-to-grid to greatly reduces costs further to $0.24 per day (plugged in at all times), 
  – provides sufficient flexibility to ensure EV charging occurs at times of low zone substation load, facilitating a near optimal hosting capacity. 
• The ACT contracted solar and wind farms provides a reliable output to power EV charging at any time. When EVs are plugged in most of the time charging can occur when renewable generation exceeds 2000MW. 
• The nighttime offers more opportunities to charge at simultaneously low prices and network demand.  
• The financial value of vehicle-to-grid is similar when vehicles are plugged in during the daytime or overnight, but the grid impacts are far better overnight. 

The central policy implication of these findings is that encouraging EV drivers to plug their vehicles in as frequently as possible should be the primary behavioural message. Plugging in around 25% of the time – 6hrs a day or most of the weekend – appears to be a good target. Encouraging charging overnight is a secondary priority. Options should be explored for making managed charging the default behaviour of EVs, while discouraging, restricting, or prohibiting unmanaged Level 2 charging. Unmanaged Level 1 charging places five times less stress on the network. Managed charging could be implemented via auto manufacturers, who have stable communication with their vehicles, irrespective of where they are and what charger/socket they’re connected to.