Tradeoffs in School Bus Electrification

Decisions that become clear when planning and deploying electric buses.

Electrifying school buses in the US is in full swing in 2023 stimulated by the federal Clean School Bus Program, a 5-year / $5 billion fund, as well as policy commitments in several states to ban the purchase of fossil fuel burning school buses by 2027. States have also stepped forward with funding for electric school buses and charging systems (approximately $500 million to date) to complement electric utility funding for EV charging infrastructure (over $5 billion). While these programs are crucial to overcome cost barriers intrinsic to early market adoption of new technologies, successfully operating electric school buses on the road requires more than funding alone. By evaluating tradeoff decisions fleet operators can be confident that their procurement and operational plan will work as expected, and that initial pilot deployments accurately inform follow-on fleet transition phases.

What to buy and where to deploy

The initial question asked by school bus fleet operators is: How much does an electric bus cost compared to diesel and propane options? What do charging systems cost? And will grants cover the gap? Federal and state funding is well designed to address this gap but stops short of unpacking the rest of the cost equation – design, installation, and electric service. The next question is: Which vehicles need to be retired/replaced in the fleet and will electric buses run those routes? This is a typical vehicle replacement strategy, but when the characteristics of electric vehicles are taken into account, drive range and charge time, a replacement plan approach doesn’t guide fleet transition – right sizing batteries and charging system for cost efficiency. When considering both cost and deployment options simultaneously fleet operators will save significant money and guarantee operational reliability.


The piloting vs planning mindset

Piloting new technology is prudent. Consider also that a pilot deployment of electric buses will take three years from grant writing to operational data collection. Most fleets will need an overall transition plan by the end of 2027, a timeframe that is misaligned with a pilot-and-reflect approach. Planning for fleet transition on the other hand can incorporate the excepted outcomes of pilot deployments and provide a feedback loop to inform transition phases. Simply put, a plan provides guardrails about what to buy and where to deploy, including a no-regrets set of deployments alongside hard-to-electrify set of routes, both dependent on a cost-effective and operationally sufficient charging strategy. In the Insight Brief Five Key Questions to Answer When Converting Your Fleet to Electric we elaborate on the importance of modeling a fleet for the specific operating environment. The reason is that energy consumed, across seasons, dictates which routes are electrifiable, what size batteries are needed over the life of operations, the proper charging strategy, and related charger power ratings.  There are two approaches to answering these questions today: back-of-the-napkin calculations based on vehicle specifications provided by the manufacturer (e.g. average mileage), and modeled operations based on real-world data and the local operating environment. The case study referenced at the end of this article unpacks how planning clarifies key decisions about what to buy and where to deploy.

The influencers of transition planning

School bus fleet operators rely on their trusted partners for decision support about electrifying. School bus dealers, charging partners, district energy consultants, and electric utilities are all trusted partners and each has their domain of expertise. The traditional approach to oversize systems for reliability or plan beyond the sight of our headlights in the attempt to answer edge cases turns out to be disserving to the mission to deploy electric buses quickly and at scale. A fleet electrification plan illustrated in phases of deployments allows all parties to be on the same page about what is needed, and when. Budgets, electric load, charger installations, and bus deliveries. In considering phases several benefits are realized including faster service connections and lower costs of hardware. A right-sized fleet electrification plan reduces time to installation, saves up to 40% of operating expenses over 10 years, and importantly can save 60% in capital at each phase of fleet electrification!


A Reference Case Study

Case Study: Hazelwood School District Zero-Emission Fleet Transition Planning The Hazelwood School District (HSD) in St. Louis, Missouri, has been considering the possibility of transitioning its school bus fleet from diesel to zero-emission vehicles. The local utility and electricity provider, Ameren needed to understand the potential impacts on the distribution network and how to facilitate a faster transition toward zero-emission fleets. Through an EPRI innovation partnership, MGL modeled the fleet’s operations and ran charging scenarios to derive an optimized fleet and charging strategy.

How many routes are feasible with one charge, and what battery sizes are needed? Using EVopt MGL modeled the routes of 86 buses operating on a cold February day, which had an average of 36 miles and an on-road time of 2 hrs and 30 minutes, and extracted the energy needed by an electric school bus to cover such mileages under cold-weather conditions. EVopt calculated that 77% of the routes could be completed by vehicles with battery sizes ranging from 50 to 318 kWh, with most routes requiring a 250-kWh battery to be completed on one single charge. The remaining routes are not ‘feasible’ on one charge and those buses would need additional charging between the morning and afternoon runs (Figure 1). With this type of insight, a fleet can start by converting the easier routes first, using a fleet electrification assessment as a guide, and address challenging routes later.

Figure 1: Results of the battery sizing analysis for the Hazelwood bus fleet.

What are the infrastructure requirements and costs associated with different charging scenarios? EVopt compared three charging scenarios to determine the minimum power rating and number of chargers needed to keep the electric fleet operational while minimizing costs. Using 60kW charging ports would generate a peak power 4,320 kW and require a 6,000 kVa transformer under unmanaged conditions while leaving many hours unused for charging (Figure 2). Under managed charging conditions, the peak power decreases to 1,350 kW, and requires a much smaller transformer of 1,900 kVa. EVopt also showed that using 19.2 kW charger ports would be sufficient if the fleet can charge for longer hours during the day. The 19.2 kW approach would require a much smaller transformer as well, thus reducing the magnitude of infrastructure upgrades and the capital costs associated with purchasing cheaper chargers – amounting to total savings of $2.5M+ over time compared to the 60-kW charger scenario (Table 1).

Charger Rating Chargers Needed Peak Power Unmanaged Transformer Unmanaged Peak Power Managed Transformer Managed Charger and Infrastructure Costs
19.2 kW 78 1,420 kW 2,000 kVA 1,214 kW 1,700 kVA $6.75M
30 kW 78 2,220 kW 3,100 kVA 1,322 kW 1,850 kVA $7.81M
60 kW 78 4,320 kW 6,000 kVA 1,350 kW 1,900 kVA $9.38M

Table 1: Results of the charging scenario comparison analysis.   In addition, managed charging could reduce HSD’s electricity bill by $2,000/month (Figure 2).

Figure 2: Results of the load profile analysis for the 60-kW charger scenario.   With this insight, a fleet operator and the utility can compare the infrastructure needs associated with different charging scenarios, evaluate the costs of equipment and system upgrades and make informed decisions based on the most cost-effective and practical charging strategy.

What are the emission reductions associated with fleet transition? EVopt estimates annual greenhouse gas (GHG) emission reductions – expressed in CO2 equivalent, CO2e – to be around 4000 tons (Figure 3). This quantity represents a net reduction and incorporates the emissions eliminated from replacing diesel tailpipes with electric school buses, plus the emissions generated from the production of electricity used for charging the vehicles.  Figure 3: Results of the GHG emission reduction analysis.   With this insight, a fleet operator can immediately demonstrate the benefits of fleet electrification to its school board or to government agencies whose vehicle replacement funding programs are directly tied to the reduction of harmful emissions.

Figure 3: Results of the GHG emission reduction analysis. 

With this insight, a fleet operator can immediately demonstrate the benefits of fleet electrification to its school board or to government agencies whose vehicle replacement funding programs are directly tied to the reduction of harmful emissions. 

Dr. Paola Massoli is a seasoned fleet electrification consultant with a decade of expertise in clean transportation and climate emissions and servers as MGL’s senior project director.


TESTIMONIAL: Ameren MO Collaborating with MGL, EPRI, and the Hazelwood School District on this EVOPT pilot has provided Ameren with hands-on experience in understanding our customers’ general struggles and areas of focus in vehicle fleet management, as well as in analyzing the capital and O&M expenses and grid impacts associated with fleet electrification projects. As a result, Ameren is better equipped to discuss electrification strategies with customers and identify options for helping them manage risks, reduce costs, and maximize benefits.

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Fleet Electrification 101: Modeling & Cost Analysis

September 9, 2021  – All Day Virtual Event

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