Exploring the profitability of using electric bus fleets for transport and power grid services

Electric buses (E-buses) are increasingly replacing internal combustion powered bus fleets. They can further function as distributed energy storage units. We investigate the feasibility of the novel "Bus-to-Grid" (B2G) or "E-Buses as Power Storage" (EBaPS) concept, which allows battery E-buses to provide transportation as well as power-grid services. By aggregating the electrified bus fleets into Virtual Power Plants and discharging the energy to the grid, a bus operator can provide grid services and open up a secondary revenue source in addition to fareboxes. We discuss two con-tracts the bus operator can arrange with the grid. The first one is "Sale by Market Price (SbMP)", presuming that the buses can discharge and sell the energy at real-time market prices. The second one is "Frequency Control Reserve (FCR)", in which the buses discharge on immediate requests of the grid. We formulate the two contracts and their associated fleet allocation problems as two non-linear optimization problems maximizing the operator's profit. Optimal bus charging, dis-charging, and dispatching plans are solved on an aggregate level for strategic planning, allowing scalability to large fleet sizes. The profitability of the contracts is illustrated based on the schedule and demand of a real bus line and observed time-of-day dependent price variations of the energy market.