Public Transportation Electrification with the Support of Mobile Energy Storage

Abstract

In recent decades, fossil fuels and carbon emissions reduction have become an increasingly popular global phenomenon; therefore, a number of governments worldwide have allocated substantial funds to transportation electrification projects. As a result of its significant positive environmental impact, the electrification of public transportation in particular is becoming increasingly popular. It is important to note, however, that this wide-scale electrification presents a number of challenges: numerous technical challenges arise due to the infancy of the technology, high capital costs associated with the infrastructure and assets involved pose a significant financial barrier, and last but not least, the additional load imposed by the new electric fleets on the electrical distribution system poses a significant electrical barrier. It is for this reason that this thesis is designed to address a series of questions posed by transit agencies as they strive to electrify their fleets and address the many barriers they face along the way.

In order to electrify the public transportation system, the first stage is to determine the appropriate sizing of the necessary assets. Consequently, the first objective of this thesis is the sizing of the fleet and chargers according to the charging technology selected by the transit agency. The developed methodology incorporates detailed route assignment, energy consumption modeling, and charging requirements for electric fleets. The formulation reflects the real-world selection and procurement process, which accounts for the interactions between transit agencies and technology manufacturers or suppliers. After determining which assets are required, a transit agency must determine when they should be purchased. This is addressed by the second objective of this thesis which is the development of a comprehensive fleet transition plan. As key stakeholders in transportation electrification, the perspectives and interests of transit and distribution systems are intertwined and therefore must be accounted for in order to determine when and how to make optimal purchasing decisions. For this reason, the methodology developed has two stages an input stage and a transition stage, where the input stage entails the identification of the optimal depot location depending on the distribution system as well as the operation of the transit system. The results from the input stage are utilized in the next stage; the transition stage, which aims to minimize the net present value of the purchase decisions. Together, these produce an optimal transition plan, based on accurate input models. A transit system consisting of four short-distance routes is studied using two modes of charging: overnight and opportunity. The results demonstrate the effectiveness of the proposed approach in meeting electrification targets while adhering the budget constraints, respecting the limitations of the distribution system, and providing continuity of service to the transit agency through an adaptable and scalable formulation.

Once the transition plan is determined, the transit agencies are ready to electrify their fleets, but there remain a number of barriers preventing their widespread use: whether they are technical, financial, or electrical in nature. The third objective of this thesis is to present mobile energy storage (MES) as a fast, flexible, and holistic solution to the aforementioned barriers. As seen from the transit agency's perspective, a comprehensive optimal sizing, routing, and scheduling problem is developed, which aims to minimize purchase and operation costs simultaneously. The MES is operated to meet battery electric buses (BEBs) on their designated routes, thereby reducing or eliminating the need for on-route charging, or reducing the number of BEBs required to operate a route. The incorporation of MES results in substantial cost savings, as well as a variety of benefits, including reducing driving range anxiety among BEB operators, and reducing stress on the electrical grid as a result of the large sudden load imposed by on-route charging. Additionally, MES offers transit systems resiliency in case of accidents and emergencies, as well as the flexibility needed for the dynamic transportation sector. Hence, this thesis brings together two important players in the e-mobility field: electric buses and mobile energy storage.

In order for the transit system to be able to take full advantage of a powerful tool like MES, it is imperative to study how it can be utilized to its full potential. Due to the added complexity of the mobility factor, a study was designed and presented as the fourth objective to investigate privately-owned stationary energy storage and their interactions with potential customers. Upon completion, the findings of this study along with the previous studies are used to model revenue stream generation of the transit-owned MES. A profit maximization model based on optimization and a profit maximization model based on an integrated auction and optimization are developed to determine which external customers are served by the MES. The results of the final objective presented show the efficacy of the MES in serving its own internal system while utilizing the unused capacity to serve additional customers and generate profit.