A recent blog post from Electric Era, an EV charging company focused on battery storage charging stations in the western US, revealed a notable development in California.
The state’s Energy Commission has decided to shift away from traditional metrics like stall uptime or station uptime, which measure the overall availability of a charger. Instead, they will adopt the “successful charge attempt rate” (SCAR).
Defining and Setting Goals for SCAR
The Commission defines SCAR as the percentage of charging attempts that last for at least five minutes. They have set an ambitious goal of 90%, meaning that 90% of all charging attempts at regulated chargers must initiate and sustain a charge for five minutes or more.
This minimum SCAR requirement applies to each individual charging port rather than the entire charging site. In simpler terms, every single stall at each charging station needs to successfully start and maintain a charge for at least five minutes in 90% of attempts.
Assessing the Effectiveness of SCAR
To determine whether SCAR is truly the most effective measure of charging station reliability, it’s crucial to examine the alternative metrics and their pros and cons.
Alternative Reliability Metrics
One widely used method for measuring reliability is the PlugShare approach, which simply indicates whether a charge was successful or not. This method can be misleading, as a station with many non-functional stalls could still receive a perfect score if even one charge is successful.
While this approach allows charging providers to maintain high scores through redundancy, it leaves users in the dark about issues like non-functional stalls, slow charging speeds, and other frustrating experiences.
Uptime, another metric, can also be misleading. A station could have a seemingly impressive 97% uptime (required by NEVI) but still be down for almost 22 hours per month. This equates to nearly 11 days of downtime annually, which is far from ideal.
Furthermore, the method of measuring uptime raises questions. Is it calculated for the entire network, the entire site, or each individual stall? Each approach has its own potential drawbacks, such as averaging uptime across an entire network potentially masking numerous faulty chargers.
Limitations of Previous Proposals
The author previously proposed a more intricate system for assessing station reliability, involving multiple data points like up/down status, real-time availability, past uptime, and user ratings. However, this approach proved to be too complex for users seeking a quick and easy way to assess charging station reliability.
Advantages of SCAR
In comparison to other systems, SCAR stands out due to its simplicity, its ability to measure every charging attempt, and its application at the individual stall level. Since it’s measured by an agency overseeing the network and funding, SCAR can help identify problems and trigger further investigation, ultimately leading to informed decisions regarding government funding allocation.
Drawbacks of SCAR
However, SCAR might not be the most effective metric for user-facing ratings. While knowing how often a station successfully charges on the first attempt is valuable, it doesn’t reveal other potential issues. For instance, a station with a high SCAR might still deliver slow charging speeds or have other problems.
Additionally, SCAR might be less accurate in cases where users avoid attempting to use broken chargers. It’s common for EV drivers to signal faulty stalls by hanging the cables over the top of the station. If people don’t attempt to charge, there are no failed sessions to lower the score, potentially masking the problem.
The Right Tool for the Right Job
SCAR proves to be a valuable tool for government regulators and grant providers. It establishes a minimum performance standard, with a 90% SCAR indicating that a plug should result in a charge 90% of the time. Networks failing to meet this standard at the stall, station, or network level might not be eligible for further grant funding.
For users, a multi-faceted approach remains necessary. Objective data like charging success rates are essential, but a star rating system alongside raw numbers can offer insights into user satisfaction. This allows drivers to quickly gauge the overall experience at a station and delve into reviews for more specific feedback.
In conclusion, while SCAR is an excellent quantitative measure for establishing regulations, it needs to be supplemented with tools that capture driver satisfaction. Ultimately, the goal is to ensure happy EV drivers, which requires a comprehensive approach to evaluating charging station reliability.