Nearly 50,000 electric buses were sold worldwide in 2023, accounting for 3% of total bus sales and increasing the stock to 635,000.[1] It indicates quick acceptance. Yet, severe heat makes them struggle. Battery efficiency decreases as temperatures rise to limit vehicle range and dependability. Preventing overheating requires energy-intensive cooling systems, which drain batteries.
Electric coaches or e-coaches with longer routes have even greater issues due to their bigger batteries’ heat deterioration. So, operators adopting electric fleets in hot areas must address such constraints. Yutong stands out with practical solutions: it launched advanced technologies for coaches’ better performance under extreme heat.
Some Notable Challenges
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Safety
In electric coaches, thermal runaway is a safety challenge under extreme heat. It occurs when one cell in the battery pack fails and causes a chain reaction that raises the temperature and pressure in adjacent cells. It can trigger fires or explosions, risking the safety of passengers and infrastructure. Lithium-ion batteries in electric coaches might be prone due to their high energy density.
Manufacturers can implement thermal management systems, sometimes falling short in extreme climates. For example, inadequate cooling or a failure in the BMS could allow temperatures to rise unchecked for thermal runaway. Solid-state electrolytes and lithium-titanate may help soften this risk. However, large battery packs for electric coaches present engineering challenges.
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Range
The range of an electric coach is influenced by the energy consumption of its cooling system in high-temperature environments. When temperatures soar, the cooling system must work harder for optimal battery temperatures and passenger comfort. It draws more power from the battery. Thus, it lowers the available range for long-distance operations. For instance, the range of an EV shrinks by 31% at 38°C. [2]
Moreover, high ambient temperatures may accelerate the aging of the battery’s graphite electrodes and electrolytes, further affecting range. At high operating temperatures (35°C to 55°C), the degradation rate of the electrodes increases with temperature, and the battery resistance increases dramatically with the formation of SEI on the electrodes. [1]
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Performance
Extreme heat poses a threat to the performance of batteries in electric coaches. Higher temperatures accelerate the chemical reactions within the battery cells for increased degradation rates. It causes a loss of capacity, power, and life for the battery pack. E.g., lithium-ion batteries at temperatures above 55°C can increase the rate of capacity loss compared to standard operating conditions.
At high temperatures, the rate of electrochemical reactions within the battery is accelerated, which can lead to a reduction in battery efficiency. This reduction in efficiency not only affects the energy storage capacity, but may also lead to a drop in the battery voltage, which reduces the output power of the drive motor, which can weaken the ability of the bus to operate stably on uphill sections or under heavy loads.
Furthermore, frequent exposure to high temperatures can prompt dendrites and microscopic metal filaments that can cause short circuits and reduce battery life. Some electric coach manufacturers may use liquid cooling or refrigerants to combat these issues. Still, it adds complexity and cost to the vehicle and needs consideration during the design phase.
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Cooling
A comfortable interior temperature in an electric coach during extreme heat is a challenge. The HVAC (Heating, Ventilation, and Air Conditioning) system must balance passenger comfort with avoiding undue energy consumption, which can diminish the vehicle’s range. A powerful HVAC system is a complete bus comfort system that can heat and cool the electric bus, as well as provide improved interior air quality and humidity control. Traditional air conditioning systems, which use compressors and refrigerants, are energy-intensive and may not keep steady temperatures in larger coaches.
Some manufacturers might employ thermoelectric or adsorption cooling systems for better reliability and lower energy use. Progressive control algorithms may also help regulate operating HVAC systems in real-time based on passenger load, external temperature, and battery status. Yet, implementing them entails integration with the vehicle’s energy management strategy for passenger comfort without compromising the coach’s working capabilities.
Advanced Battery Technology of Yutong Electric Buses
Yutong coaches lead the field in safety, driving range, performance, and cooling through their battery technology, as demonstrated by:
- Safety: Yutong electric coaches utilize high-efficiency liquid thermal technology, eliminating high-voltage heating components in the batteries, thus avoiding safety risks associated with the failure of high-voltage heating parts. Additionally, a highly adaptable short-circuit protection device has been developed to meet overload protection across the full current range. Moreover, Yutong’s nitrogen protection system isolates oxygen, ensuring the battery’s integrity for 2 hours, even under extreme conditions at 1300°C to prevent fires.
- Range: The high energy density of Yutong electric coach battery packs increases volumetric energy by 38%, providing optimized space for low-floor buses. Coupled with coach design that extends battery life to up-to 1.5 million kilometers, the structure surpasses the new national vibration standards by five times.
- Performance: Yutong electric coaches adopt a new generation of high-energy-density cells, enhancing the specific energy and lifespan of the batteries, which helps maintain their performance under high-temperature conditions. At the same time, the “multi-in-one power domain controller” improves the safety of high-voltage electrical systems and supports system efficiency through the sharing of hardware circuits and the integration of software functions, contributing to the overall vehicle performance.
- Cooling: Yutong’s vehicle air conditioning, battery and electric drive thermal management systems are harmonized to distribute and efficiently recover heat from the entire vehicle as needed. Yutong vehicles utilize a dual-source heat pump system that effectively manages heat from the air conditioning, battery and electric drive, ensuring robust vehicle cooling performance that can be maintained at extreme temperatures up to 50°C.
Yutong’s Successful Operation Case in Qatar
Yutong deployed over 1,500 buses, including 888 battery electric coaches, in Qatar’s extremely high-temperature environment during the FIFA World Cup. The operation required planning and execution for peak performance. For example, Yutong set up a 126-person service team, trained 3,000 drivers, and conducted daily checks on all vehicles for 100% operational readiness. The electric coaches accounted for 25% of the operating fleet while transporting over 50,000 passengers daily.
Yutong maintained service by unceasingly monitoring vehicle data and fixing issues through a communication system, showcasing Yutong’s capabilities in adapting to and overcoming the demanding heat of the region. It encouraged Qatar’s green public transport transformation.
Conclusion
Yutong’s advantage is its full integration of novel technology for varied markets. Its electric coaches are reliable in high-temperature areas like Qatar, thanks to their high endurance mileage, adaptive optimization for local circumstances, and improved safety features. Offering vehicles and complete coach travel solutions with solid service networks and support, Yutong refines bus designs for comfort and durability. The way Yutong works has established them as a worldwide leader in new energy buses, promoting sustainability and creativity in public transport frameworks.
Reference
[1] Trends in heavy electric vehicles. Available at:
https://www.iea.org/reports/global-ev-outlook-2024/trends-in-heavy-electric-vehicles (August 27, 2024)
[2] Study: Summer & Hot Weather on Electric Car Range. Available at:
https://www.recurrentauto.com/research/what-a-c-does-to-your-range (August 27, 2024)