When reviewing electric vehicles (EVs), automobile journalists usually cite a long list of superlatives — they’re quick, quiet, reliable and economical, and their ranges keep increasing while charge times keep getting faster.
But oftentimes, there’s a caveat: The charging networks in some U.S. cities and highway corridors aren’t always reliable, journalists report. Even when drivers can find an available EV charging station, it’s sometimes broken, too slow, or drivers find it difficult to start or end a charging session.
Usually, these journalists’ accounts are anecdotal. And anecdotally, EV researchers say charging networks are getting better.
“As an EV driver, things have improved a ton, even in the last year,” said Casey Quinn, senior electric vehicle charging infrastructure reliability engineer at the Idaho National Laboratory. “I’ve never been in a situation where I needed a charge, and I couldn’t charge. I’ve encountered some annoyances, but I’ve never been stranded.”
But anecdotal evidence can’t reflect the real world as well as hard data, and until recently, the industry lacked common standards to measure the charging experience.
Now, Quinn and his colleagues in the Joint Office of Energy and Transportation-sponsored ChargeX Consortium have released a set of detailed recommendations — the Implementation Guide of Customer-Focused Key Performance Indicators for Electric Vehicle Charging — that the EV industry can implement immediately to gauge a driver’s experience at public charging stations.
The recommendations follow the summer 2024 release of a set of foundational guidelines designed to help the industry measure a driver’s experience finding a charger, accessing a charger, and starting and completing a charge.
Those earlier guidelines included both interim and ideal metrics based on feedback from dozens of industry stakeholders. The ideal metrics provide a more comprehensive measure of the charging experience, but the industry must add or modify existing business practices, technologies and standards to calculate and implement them. Ideal metrics could be implemented in the future. Researchers designed the interim metrics so industry could implement them immediately.
The most recent report does a deep dive into the interim recommendation.
“The implementation guide provides a common framework for different charging operators to have that discussion,” said Paden Rumsey, transportation modeling and machine learning engineer at the Idaho National Laboratory. “If everybody defines the same problem differently, you don’t have a common starting place. Codifying the language around some of these problems is a big step forward. It’s a common language that we can start speaking together.”
The guide suggests leveraging existing data to calculate four interim metrics:
1) Charge start success — Can the driver arrange payment with the charging station, plug the charger into the EV and begin sending electricity to the battery?
2) Charge ending success — Does the session end when the battery is full or the driver ends the session on purpose, or does it end prematurely?
3) Session success — This is a useful metric for industry that includes data from charge start success and charge ending success.
4) The time it takes from starting a session to beginning a charge.
These metrics can tell industry important things about charging session success, like whether charging networks are having issues before charging happens or if the problem is with ending the session.
Answering these questions is complex.
Issues before charging can be related to any number of factors. For example, some charging stations can automatically access payment information when the vehicle is plugged in, while others require payment authorization first. A third method requires an app on a phone. An EV driver may have trouble getting the payment authorized or may not have the correct app for the charging network.
Ending charging sessions can also be complicated. Some sessions that end early result from an issue with either the vehicle, the charger or the communication between the two. “DC fast charging profiles are complex, vary from vehicle to vehicle and are dependent on a number of environmental factors,” Quinn said. “These complex charging profiles require constant communication between the vehicle and the charger, which can break down and cause a session to end early, for example.”
The interim metrics are a stopgap until industry can develop and implement the ideal metrics after modifying existing business practices, technologies and standards. The metric development has recently been handed from the ChargeX Consortium to SAE International to ensure this work transitions over to industry, Quinn said. SAE International is an advanced mobility company that participates in the ChargeX Consortium.
The hope is that these standardized metrics will provide industry practitioners with the quantitative data they need to identify problems and improve performance. They could also help industry improve relationships between charging networks, car makers and equipment manufacturers – and especially between charging networks and drivers.
Or the recommendations could provide industry with a way to counter bad media by providing numbers that show driver experiences are getting better.
“We’re saying, ‘Here’s something you can use today to measure charging success,’” Quinn said.
NEWS MEDIA CONTACTS:
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About ChargeX Consortium
The ChargeX Consortium, funded by the Joint Office of Energy and Transportation, is a collaborative effort between Argonne National Laboratory, the Idaho National Laboratory, National Renewable Energy Laboratory, electric vehicle charging industry experts, consumer advocates and other stakeholders. Its mission is to work together to measure and significantly improve public charging reliability and usability by June 2025. For more information, visit chargex.inl.gov.