A December report published by Natural Gas Vehicles for America reviewed data produced by the National Renewable Energy Laboratory and other sources to evaluate how buses powered by compressed natural gas compare to battery electric alternatives.
Contrary to many environmental groups’ calls for the mandatory adoption of so-called “zero emission” battery powered electric vehicles, the report found that investing in new, cleaner natural gas buses would achieve greater reductions in pollution and generate greater economic savings compared to more costly and unproven electric bus fleets.
FLAWED COST ARGUMENTS
Proponents of battery electric buses (BEBs) contend that, although they are much more expensive to purchase, they will be less expensive to operate and maintain over their lifetime.
They also point to declining battery costs to justify an assumption that BEBs will cost the same as, or even less than, natural gas or diesel buses within a few years.
However, such claims of lifetime cost savings are not supported by the data. BEBs are no less costly to own and operate than their CNG or diesel competitors.
As shown in Table 1, below, the total cost of ownership of a CNG-powered bus is found to be lower than either of the alternatives.
The numbers look even worse for BEBs if battery prices fail to drop as projected.
Demand for vehicle batteries is expected to skyrocket in the next few years as EV mandates around the world take effect, putting the supply chain for battery materials under extreme pressure. Limited supplies of critical raw materials are likely to drive battery prices up, rather than down, until fundamentally new designs are developed.
Finally, BEB advocates fail to account for major utility updates that will be needed to accommodate the surge in electricity transmission and storage.
There are also questions about the long-term reliability of BEBs under realistic public transport scenarios.
To date, BEBs have largely been operated on shorter, specially selected routes. Yet, even under these less-demanding conditions, BEBs have failed to demonstrate reliability or cost-effectiveness comparable to natural gas buses.
In one study, a test fleet of twelve BEBs could only achieve 63% average availability, falling well short of the 85% availability considered a minimum standard for bus fleets.
Longer and more demanding routes will either require additional batteries or a significant increasing in the number of on-route charging stations – both of which will contribute to additional infrastructure and maintenance costs.
When factoring in the need for additional buses, infrastructure upgrades, and potential route and service changes to accommodate BEB limitations, the cost of switching to a fully electric bus fleet could be staggering.
EMISSIONS REDUCTION POTENTIAL
Another misconception is that BEBs will entirely eliminate the emissions currently generated by a mostly diesel bus fleet.
Although BEBs are undoubtedly cleaner to operate than diesel buses, factoring in a typical mix of electricity generation sources paints a different picture. Many BEBs also include gas-fueled heaters to avoid drawing on the battery to warm the passenger cabin.
As shown in Table 2, below, CNG outperforms BEB alternatives in the reduction of both NOx and greenhouse gases (a combination of methane and CO2).
Based on existing studies and data, the NGVAmerica report finds it apparent that natural gas buses are more affordable, more reliable, and deliver greater environmental benefit than electric buses.
Switching from diesel to CNG buses at a nationwide level (approx. 50,000 buses) would save over $20 billion compared to replacing them with battery electric vehicles.
Fully accounting for all costs is critical when comparing the lifecycle cost of CNG and battery electric powered options, since federal and state financial support largely masks the true cost of ownership and operation.
Significant infrastructure upgrades would also be required to deploy a fully electric bus fleet, while many transit authorities have already invested in CNG infrastructure for other elements of their vehicle fleet.
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