Electric vehicles in the cold
Transportation sector consumes over 25% of all energy and more than 60% of oil. Cars make a major contribution to the global CO2 emissions. Electric mobility is a promising future sustainable transportation solution. The sensitivity of the battery performance to temperature is often overlooked in the related Electric Vehicle (EV) studies.
Researchers at the New Energy Technologies group at Aalto University have developed an improved lithium-ion battery model to better understand the temperature effects. The new battery model has been combined with a vehicle fleet model to analyze the related effects in large scale.
City of Helsinki with its local driving patterns was used as a test case. The simulated test fleet comprised 212 EVs with a 120 km nameplate range.
We found that in terms of e-mileage, the EV-range was maximized near +20°C as the vehicle's battery is subject to less secondary load from heating, ventilation, air conditioning, and active battery thermal management. The efficiency at temperature extremes (-10°C and +40°C) could be improved by 8-9% by pre-heating the cabin at low ambient temperature and pre-cooling it at high outdoor temperature ca 10 minutes before departure.
Low ambient temperature tends to decrease the battery charging speed due to higher internal resistance. The median of the EV fleet's self-weighted mean charging power decreased by 15% at -10°C outdoor temperature compared to reference outdoor temperature of +20°C. Battery heating during parking was found to significantly improve charging speed at low temperatures, even up to 30%. The findings are important to maximize the efficiency of an EV fleet and for time-constrained charging if vehicles need to queue for charging service.
Lindgren, J., Asghar, I., Lund, P. D., A hybrid lithium-ion battery model for system-level analyses. International Journal of Energy Research 2016, 40, 1576-1592
Lindgren, J., Lund, P. D., Effect of extreme temperatures on battery charging and performance of electric vehicles. Journal of Power Sources 2016, 328, 37-45.