The WRI study looked at different stress factors that contribute to ageing of batteries and their overall impact on the automotive life of e-bus batteries.

New report shows ways to build an efficient e-bus ecosystem in India 

High upfront cost of e-buses, range issues, bottlenecks in the supply chain, and under-developed charging infrastructure stand in the way of large-scale adoption of e-buses across the world, report finds

Last December, during a side event at COP28 hosted at the Indian Pavilion, officials from the US and India shared plans for a joint finance mechanism to roll out 50,000 electric buses in India by 2027

The government is also working on a plan to set up a de-risking fund to boost electric bus mobility. The objective of the fund is to reduce risks for banks that finance the acquisition of electric buses by both public and private sectors.

The transport sector is one of the fastest-growing carbon emitters and a leading cause of air pollution in major cities and in need of interventions for decarbonisation. Therefore, like India, several countries across the world are accelerating e-bus adoption through enabling policies, tax incentives, and subvention. 

However, challenges such as upfront cost of e-buses being twice or thrice that of internal combustion engine (ICE) buses, range issues, bottlenecks in the supply chain, and under-developed charging infrastructure stand in the way of large-scale adoption of e-buses across the world. 

As the e-bus market develops across the world, a study by the World Resources Institute (WRI) looked at different stress factors that contribute to ageing of batteries and their overall impact on the automotive life of e-bus batteries. It also assessed how this battery degradation can affect the battery and e-bus performance in the near term, and the battery life and economic viability of the e-bus in the long term. 

High upfront costs, need for optimal battery usage

The study said that in e-buses, batteries account for 40–50% of the total upfront purchase cost and form the most critical component of the e-bus powertrain. The performance of e-buses also depends on the batteries, which degrade faster under non-optimal usage.

For example, the ideal lifespan of lithium-ion batteries (LIBs) in the e-bus application should be five to seven years. However, the batteries’ lifespan is affected tremendously by non-optimal conditions of temperature, state of charge (SoC), charging rate (C-rate), and depth of discharge (DoD).

Factors, such as driving behaviour, auxiliary consumption, road quality, passenger load, speed, topography, and climate, influence the energy consumption per kilometre, which in turn impacts the driving range per charge of the e-bus. 

The study found that while stakeholders are already planning to overcome bottlenecks associated with range and energy consumption, accelerated battery degradation will affect battery capacity, further reducing the driving range per charge of the e-bus. This would lead to frequent charging requirements to achieve the desired daily trip length. 

Battery ageing: The biggest challenge 

According to the study, the lifespan of e-bus batteries depends on calendar ageing and cyclic ageing. Calendar ageing occurs when a battery is at rest condition; this is when no current flows through the battery. Cycling ageing occurs when the battery is charged or discharged. While high ambient temperature (> 30°C) and high SoC (> 80 %) accelerate calendar ageing, the extreme operating temperature of the batteries, and high C-rates accelerate cyclic ageing.

The report found that a battery degrades the most during the initial years due to initial high calendar ageing, especially in regions that experience high-temperature extremes. Degradation rate due to cyclic ageing is affected by both high and low temperature extremes and is consistent throughout the battery lifespan. The capacity of the lithium iron phosphate (LFP) battery degrades to 80% (i.e., end of automotive life) in 4,000 cycles at 25°C and in 2,000 cycles at 45°C. Similarly, a lithium nickel manganese cobalt (NMC) battery completes its automotive life in 1,200 cycles at 34°C and in 500 cycles at 46°C.

Additionally, the report said, external factors like temperature, topography, and driving behaviour also affect the energy efficiency. Battery degradation leads to capacity fade, which reduces e-bus drive range by 26% over its automotive life. Capacity loss or capacity fading is a phenomenon observed in rechargeable battery usage where the amount of charge a battery can deliver at the rated voltage decreases with use. This in turn requires frequent charging to finish the desired trip, further increasing energy demand on a route. Increase in the charge time in a day will reduce the service time of e-buses, affecting the operational efficiency. This will lead to a requirement of a larger number of e-buses to reach the operational efficiency of diesel buses, unbalancing the replacement ratio at a city level. 

Planning recommendations

This analysis then shared a series of recommendations to adopt best practices, improve planning, and devise policy, which will be instrumental in improving battery lifespan in countries like India, which are planning for large-scale adoption of e-buses for public transport.

After the end of the automotive life of the battery, the battery should go for reuse and recycling to generate additional profits, reducing the total cost of ownership per km of e-buses, and ensuring the efficient utilisation of resources.

The report recommended that drivers must be trained for energy efficient driving. The training must include equipping the drivers with the basic knowledge of the technology, driver simulator training, and on-road training. This will reduce trip energy consumption and ensure good battery health in the e-bus application.

Moving on to technical recommendations, in tropical and subtropical regions, an efficient battery thermal management system (TMS) must be deployed to maintain the battery temperature under optimal range. Also, an advanced battery management system (BMS) must be installed for real-time monitoring of battery health and recording of data for detailed analysis.

Also, the report added, the e-bus must be equipped with an intelligent energy management system (IEMS) to monitor and regulate auxiliary energy demands, and an eco-driving assistance system (EDAS) to ensure energy-efficient driving.

The report said a policy and regulatory framework to facilitate an active collaboration among stakeholders for battery data collection, management, and sharing can help researchers, e-bus operators, and original equipment manufacturers (OEMs), analyse e-bus battery operational data, devise best operating practices, and come up with innovative solutions to minimise battery degradation under different operating conditions. 

It’s good to note that while real-world data on battery operation are fragmented in countries such as China, Europe, and the USA, which are leading in e-bus adoption, data is unavailable in India due to the nascent stage of the domestic ecosystem and inhibitions around sharing data.

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