In this article, we’ll explain the concept of stranded energy in EV batteries, its significance, and the safety considerations surrounding it.
What is stranded energy for electric vehicles?
After extensive research, we came across an interesting article that explains and clarifies the concept of stranded energy. Indeed, in this scientific paper, stranded energy is simply described as the energy stored in the battery of an EV after an accident.
When you consider combustion-engine vehicles involved in an accident, there might still be gas left in the tank. For first responders, it is very important to understand whether the remaining gas poses a risk or not. When it comes to EVs, one might wonder: “How can I determine the energy left in the EV’s battery?”. This is a nuanced topic for EVs.
Stranded energy: fuel in a tank vs. juice in a battery
Imagine driving a gasoline-powered car. As you drive, you watch the fuel gauge to ensure you don’t run out of gas. This gauge tells you how much potential energy (in the form of fuel) remains. Once the gauge hits “empty,” it’s time to refuel. For EVs, the analogy is more complex because of battery characteristics.
In electric vehicles, stranded energy refers to the residual energy in the battery even after it’s shown as ’empty’ or ‘depleted’. Just as a combustion car’s tank isn’t truly empty when the gauge nears empty, an EV’s battery often has energy left when it displays zero. This design helps safeguard the battery, extending its life.
The challenge of measuring stranded energy in EVs
The stranded energy amount varies based on the EV model and the battery’s capacity. Battery chemistry complexities and state-of-charge determination algorithms make it difficult to quantify stranded energy accurately. For example, cold weather affects battery performance and usable energy. As batteries age, their capacity and stranded energy ratio may change. Hence, EV drivers should consider external factors and battery health, not just the indicated range.
Moreover, accidents can impact the battery directly. There could be damaged battery cells or an internal short circuit. First responders, in most cases firefighters, need to understand the risks they face.
In a publication, the U.S. Department of Transportation suggests a standard vehicle diagnostic protocol. This could provide insights not only into the State of Charge but also into the state of each battery cell. Such insights are invaluable when making decisions about storing vehicles after an accident.
Safety concerns: stranded energy’s implications for first responders
Stranded energy ensures battery longevity, but poses safety concerns, particularly for first responders at accident sites. EV batteries store significant energy. And even if “depleted,” the stranded energy can be hazardous.
If a compromised battery short-circuits or is penetrated, the residual energy can lead to fires or explosions. First responders who are unfamiliar with EVs might assume an “empty” battery is safe, risking their safety. For this reason, It’s essential for emergency responders to receive training on handling EVs and understanding the potential risks of stranded energy. The U.S. Fire Department has even provided training and a standardized guide for Electric Vehicles and Lithium-ion Batteries.
Storing EVs post-accident: A crucial safety consideration
Post-accident, damaged vehicles often need storage for insurance assessment, repairs, or legal reasons. With EVs, the primary concern revolves around the battery and its residual stranded energy. Unlike fuel-driven cars, where fuel can be drained, fully discharging an EV battery isn’t straightforward.
Why extra care is needed
EV batteries consist of cells packed closely together. If any cells get damaged in an accident and come into contact with oxygen or moisture, they might ignite. A compromised battery might not exhibit immediate signs of danger; it can take hours or days for a damaged cell to heat up and ignite, emphasizing the importance of post-accident storage.
Guidelines for storing damaged EVs
- Isolation: Damaged EVs should ideally be kept separate from other vehicles or structures to prevent potential fire spread.
- Weather Protection: Protect any exposed battery components from rain or moisture to avoid short circuits and fire risks.
- Space and Ventilation: Store EVs in well-ventilated areas to dispel any hazardous battery gases.
- Monitoring: monitor the vehicle for the first 48 hours post-accident, using regular checks or cameras.
- Firefighting Equipment: Keep appropriate firefighting equipment on hand. For lithium battery fires, a Class D fire extinguisher is recommended.
- Seek Expertise: If the battery area is severely damaged, consult the vehicle manufacturer or a specialist for specific guidance.
Our personal takeaways
If we ever get into an accident with an EV, we will make sure, that an expert checks the car and its battery for potential damages.
If everything is cleared, we will still leave the car outside of the garage for some days, to make sure, that there are no damages overlooked.
Both regular EV drivers and emergency workers should know about stranded energy. It helps protect the battery, but it’s also important to understand its risks. As more people drive EVs, everyone needs to learn about this battery behavior.