Back to school: when school buses become power assets
PUBLISHED
The morning routine of a school goer has not changed much in decades.
Wake up early, walk to the bus stop while the sun is just coming up or sometimes even before, and patiently wait and listen — the kids are playing with the neighbours and parents trading gossip. Finally, there is the sound of the bus coming down the block, and once it turns the corner someone always yells “the bus is coming!”. Everyone starts lining up. The bus comes rolling in, and if you happen to be at the back of the line, you might get a face full of exhaust fumes while waiting for the doors to open and everyone to load into their favourite seat.
The yellow fleet behind that memory is bigger than most people realize. Nearly 500,000 school buses operate in the United States – the largest public transit system in the country transporting nearly 20 million kids a day. It is currently undergoing a transformation as old vehicles age out and a new wave of electrified buses are replacing them.
But it is much more interesting than just a one to one replacement.
Historically, a bus runs a pre-planned morning route and repeats it in the afternoon. The bus depot holds all the vehicles during midday, overnight, and weekends for refueling and regular maintenance like brakes, oil changes, and fluids. It has been that way for as long as anyone can remember. So why change?
School buses are an ideal application for electric vehicles.
The route is predictable so there is no range anxiety. It is mostly low speed and stop-and-go driving. While diesel engines would wait and haul around, electric motors shine both in instant torque and regenerative braking. Between operational blocks, these electric buses return to their home base with predictable dwell times and dedicated charging infrastructure.
So, what does the normal daily schedule look like for an electric school bus?
While everyone is sleeping, electricity is cheap from base generation and low demand. These buses fill up the battery at a fuel cost per mile that is roughly 80% cheaper than diesel. When taxpayers are funding the operation, it is hard to find any complaints here. The bus then partially discharges during its morning routing and returns back to the yard where it can plug in and either recharge off low-cost solar power or participate in a number of virtual power plant (VPP) modes like frequency regulation, demand response, and spinning reserve.
In the afternoon, the buses run their second cycle, return to the plug again and now can provide energy arbitrage, discharging back into the grid and generating revenue at a much higher multiple of what it charged overnight. It is a simple logic of automating buy-low sell-high market dynamics. It then repeats the cycle over, day after day. On working days, the buses might arbitrage around 50 kWh of energy. On non-working days, when the buses are parked and available for longer, that figure could double to 100 kWh. Spread across the students who ride the bus, that represents roughly 1–2 kWh of energy per rider.
Each electric bus can therefore transport students during the day, and use its stored energy to help power their school between routes, and send electricity back to the grid in the evening, enough power needed to cook dinner for every rider’s family. Multiply that by dozens of buses, and one bus yard becomes a megawatt-scale power plant, repeating the cycle every day.
Notably, three new technologies enable the humble yellow bus to transform into a stationary storage asset.
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Battery chemistry and its cycle life
A decade ago, range, which was constrained by battery energy density, and cost were the limiting factor to solve for the primary drive cycle. Many of those systems could do the first job, but did not have the cycle life for the second job.
About 5 years ago, lithium iron phosphate (LFP) started arriving in the market with significantly higher cycle life, lower cost, and better safety than before. Now we have sodium ion chemistries pushing even lower cost, even stronger safety and even better cycle life. The trend is clear, these batteries will now outlast the vehicles if they are not given a job to do outside of normal driving.
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Vehicle-to-grid (V2G) charging standards
The industry started off on just charging the vehicles and over time has worked through the complexity of making that work both ways. ISO 15118-20 is now the baseline for interoperability between chargers and vehicles, ensuring communication and control can go both ways. Utility grids are highly regulated and with that it took time for the concept of virtual power plants (VPP) and a monetization schedule to be approved.
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Bidirectional power electronics and charging
Systems are easier to design and less complicated if you are only ever a load connected to the grid. The moment you are looking to push back against the grid as a generation source, now there are safety features like islanding protection and a long list of other regulatory standards to make sure nothing goes wrong. These are all solvable issues, however, they just take time and market maturity.
So, while just a small fraction of the US school bus fleet has been electrified to date, older buses continue to age out and it is clear that a positive shift is happening.
In the near future, some kid is going to be listening for a bus to come around a corner, pull their head up from a phone and find that the bus is already there waiting for them, minus the noise and the fumes.
The ADVANTICS Advantage
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ADVANTICS single pistol charge controller (SPCC) supports CCS/NACS/MCS protocols and with ISO 15118-20 implemented, V2G is also ready to go out of the box.
The electric vehicle charge controller (EVCC) allows electric vehicles to connect to standardized infrastructure to DC or AC charge using the CCS or NACS protocols. This device is also ISO 15118-20-ready to turn your vehicle into a mobile grid storage asset.
A megawatt charging standard (MCS) controller designed for heavy-duty transport like truck, bus, marine, and mining applications where the power levels are on a different scale. This MCS controller is also ISO 15118-20 compliant, enabling bidirectional power flow at even higher power levels.
Contact: contact@advantics.fr
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