V2G in fleet charging scheduling and value creation

Abstract

There is a trade-off for electric bus depots between ensuring a reliable daily schedule and minimizing energy cost under time-varying electricity prices. This thesis explores such trade-off through a simulated case study of an electric bus depot with 20 electric buses running on three real routes in the city of Lappeenranta in Finland, with spot prices from the Nord pool, and energy consumption dependent on temperature. A comparison of three depot scheduling approaches with the same bus routes is given: a price-aware depot with charging scheduling, a bidirectional depot with 200 kW V2G charger cabinets, and a bidirectional depot with larger 300 kW V2G charger cabinets. All three approaches must follow the same operational constraint, that each bus must leave with a full charge. Chargers have dynamic charging enabled with charging limits set by the buses and chargers.

Findings indicate that the smart scheduling contribution alone is the biggest marginal gain, which translates to 47% annual energy cost savings from approximately 70 000 € to 37 000 € with no significant new hardware investment. V2G is an additional positive contribution that is significantly reliant on profit margins and idle periods. Using the 200 kW cabinets, the depot supplied around 500 MWh annually with an annual profit of 2000 €, yielding an 11.87- year payback period for the incremental CAPEX of 24 000 €. Raising the power of the cabinets to 300 kW boosted supplied energy to approximately 600 MWh with a better payback of 8.75 years for the incremental CAPEX of 36 000 €. However, adding a further premium of 20 000€ for each cabinet upgrade, pushes the payback to about 33 years. It is clear from the analysis that scheduling is a low-cost, high-impact solution, whereas V2G economics are more dependent on compensation schemes than just export capability.