Impact of Minimum Energy Requirement on Electric Vehicle Charging Costs on Spot Markets

Simultaneous charging of electric vehicles (EVs) increases the peak demand and might lead to higher electricity prices. This could increase EV charging costs and make EVs unattractive. Smart charging utilizes the flexibility provided by EVs and adapts charging behavior in response to the electricity market price signals. However, some studies indicate users' reluctance to participate in smart charging programs, as they perceive the risk of their vehicle not being charged sufficiently at required times. As a countermeasure, several researchers use the concept of minimum state of charge (SOCmin). It is the percentage of the battery up to which the EV is charged uncontrollably at full power right after it is connected to the charger. Depending on the users' SOCminrequirement, there might be an impact on EV flexibility and subsequently on EV charging costs. We developed a novel flexibility algorithm which quantifies EV flexibility in terms of both energy and power as a function of time. To calculate the EV charging costs, we developed a two-stage scenario-based stochastic optimization model. Optimization utilizes flexibility input and minimizes charging costs while participating in both day-ahead and intraday markets. We found that in most cases where EVs provide some flexibility, there was no significant increase in charging costs. However, we observed a 50% increase in costs when EVs do not provide flexibility. Therefore, EVs possess high flexibility potential. This flexibility can be provided almost without any loss of user comfort for high monetary gains.