Transportation is the largest contributor to greenhouse gas (GHG) emissions in the United States (US) among major economic sectors. That is due to the widespread reliance on petroleum-based vehicles that result in direct emissions. However, the U.S. transportation sector is undergoing a transition to zero-emissions vehicles with electric vehicles having the most promise of wide adoption. That is partly a result of financial and other incentives introduced by policymakers to nurture the growth of plug-in electric vehicles (PEV). There are also other trends such as the declining costs, PEV technology maturity, decarbonization of the electricity grid and increased charging opportunities that fuel this trend. By 2035 and beyond we can expect our passenger mobility and logistics services dependent on electric vehicles. In 2018 California established a target of five million zero emission vehicles (ZEVs) by 2030 and 250,000 public EV charging stations to be installed. In 2020 California established a goal for all in-State sale of passenger vehicles to be ZEVs by 2035. Studies have suggested that PEVs are being adopted not only by high income families, but they continue to be adopted by other income groups across various socio-demographic groups. Overall PEVs are seeing a growth in adoption fueling the need for other support services such as charging infrastructure.
Just as internal combustion vehicles (ICE) depend on refueling infrastructure, these new energy vehicles are going to be dependent charging solutions. Studies have indicated that the most important location for PEV charging is at home, followed by work, and then public locations. Studies have found that charging behavior can differ among PEV owners based on their travel patterns, preferences and access to infrastructure and that cost differences in charging options play an important role in the demand for different charging options/ locations. While studies suggest that PEV charging may not impact electricity grids in the short term, charging needs to be managed as PEV adoption increases long term. Studies have also identified that a high adoption scenario of 6 million electric vehicles in California will require upgrades to nearly 20% of all circuits in PG&E service territory, and less than one fourth of them have planned upgrades. More recent studies find the need to upgrade 50% of the feeders in California’s distribution grid by 2035, and 67% the feeders by 2045 costing between $6 to $20 billion.
A network of publicly available, reliable, convenient, and rapid recharging stations is necessary to facilitate long-distance BEV trips. Such a national network is beginning to take shape with infrastructure funding made available by the Infrastructure Investment and Jobs Act of 2021 (IIJA) and other State and local initiatives. While most Battery Electric Vehicles (BEVs) can meet the energy needs of typical vehicle use in the US with a night-time home charger, long-distance BEV trips require a higher amount of energy. While plug-in hybrid electric vehicles (PHEVs) can continue to operate without being solely dependent on charging, BEVs are reliant on recharging infrastructure after the battery is depleted. Public direct current (DC) Fast chargers can also support routine charging for BEV drivers who cannot charge at home and support irregular charging for drivers who miss charging and/or have unplanned trips.
In 2020, the UC Davis-ITS Electric Vehicle Research Center was tasked by the California Department of Transportation (Caltrans) to study the construction and operations of such a network of publicly available corridor DCFCs. The project consisted of 54 different DC Fast Charger installation projects in 36 different locations. These sites were selected under the Caltrans ZEV 30-30 project along priority highways, such as Interstate 5, State Route 99, and U.S. Highway 101. The objective of the “30-30” project was to “fill the gaps within California’s DC Fast Corridor Network along key routes of the State Highway System where sufficient commercial zero-emissions vehicle (ZEV) fueling opportunities do not currently exist”. Uniquely, these sites are at remote or underserved locations that other commercial networks likely did not consider to be economically viable in their business model but were found to be necessary to support long distance travel using BEVs. This was a great opportunity for us to study a futuristic network of corridor DCFC here in California. Even in 2020, this project had the makings of an infrastructure project that had the potential to be replicated nationally. The passage of the Infrastructure Investment and Jobs Act (IIJA) in 2021 has made the learning outcomes of this project even more relevant and timely. Therefore, the first chapter of my study focuses on the complex nature of the cost drivers of corridor DCFCs along major transportation corridors.
While the construction of these charging stations was successful, recent issues have arisen regarding the reliability of this infrastructure. A new study found that public open-access charging stations in the Greater Bay area are far less reliable than what station operating companies have reported. Out of a random survey of public, open access DC fast charging stations, only 72.5% were found to be functional. A survey conducted by the California Air Resources Board (CARB) found out that many drivers cite ‘charging station operability issues’ as a top barrier to using charging stations and many drivers contacted customers services because charging station unit was not working. One common measure used to understand charging station reliability is called “uptime”. This time-based metric is calculated as a percentage of time a charger is functional based on a 24-hour, 7-day week. Many authors and studies have questioned the validity of this time-based measurement This is because (1) there is no standard definition of “uptime”, (2) because many studies have findings that are at odds with 95-98% uptime reported by charging station operators, and (3) it is unclear who is responsible for maintaining and measuring the uptime of stations. The new California Assembly Bill 2061 passed in 2022 also aims to understand this issue by encouraging the development of additional reliability metrics. Whichever metric is used to measure this issue, unless resolved, low charger reliability has the potential to derail the State’s goals to achieving a cleaner passenger transportation system.Chapter 2 will focus on developing better metrics to understand charger reliability in the context of DCFCs and aim to first (1) measure the real-world operational reliability of corridor charging stations and secondly (2) understand the factors that determine better operational reliability of public fast charging stations. The Caltrans ZEV 30-30 project is a unique source of charging behavior data from charging stations. When chapter 2 aims to understand reliability of individual charging stations, Chapter 3 aims to explore the level of reliability that is desirable in the context of drivers who are taking trips.
The National Electric Vehicle Infrastructure (NEVI) Formula Program created as part of the IIJA aims to have public fast recharging stations at least every 50 miles along designated routes or alternative fuel corridors (AFCs) . While addressing “range anxiety” was a critical problem many years ago, “charge anxiety” appears to be becoming a predominant barrier for BEV adoption. It is characterized as the feeling of uncertainty about the ability to use chargers while on a trip, as opposed to locating a charging station. This fear derives from unreliable charging stations that may potentially have one or more reasons that can prevent a driver from successfully charging their BEVs.
Chapter 3 of my dissertation focuses on identifying critical corridor DC fast chargers in California’s network through a comprehensive modeling approach considering various attributes of the existing corridor charging network in the United States. The objective is to develop a tool to measure the relative importance of different chargers for the resiliency of the whole network to ensure efficient and uninterrupted travel for BEV highway users. The methodology involves data collection, geospatial analysis, demand modeling (approximation), and the development of mitigation strategies via different maintenance strategies. We believe that higher levels of reliability can be attained through increased maintenance and better equipment, but this may come at a higher cost. It's worth noting that not all charging stations need to meet the same standards of reliability and evaluating them based on the same criteria can divert resources away from where they are most needed. A charging station located in a remote area with few other options should prioritize achieving a higher level of reliability to ensure that drivers can complete their trips without issues.
