Flipping the Switch on Electric School Buses: Vehicle In Use Performance: Module 2 (Text Version)

This is a text version of the video for Flipping the Switch on Electric School Buses: Vehicle In Use Performance: Module 2.

Abby Brown: Welcome to Part 6 of the Flipping the Switch on Electric School Buses series where we will discuss electric school bus vehicle in-use performance.

Lauren Lynch: If you've been following along to the Flipping the Switch series, Electric School Bus Vehicle In-Use Performance, you'll already know that it consists of three modules. Module 1 provided information on how to track electric school bus performance and why it's important to do so. Module 2, which I am going to be talking about now, will discuss electric school bus energy use and fuel economy. And finally, Module 3, I will provide information on electric school bus range and reliability.

So let's go ahead and dive into Module 2 of Electric School Bus Vehicle In-Use Performance, Energy Use and Fuel Economy. So understanding energy use for an electric bus is different compared to conventional bus fuel economy and tracking that. So with conventional buses you generally use fuel records to calculate the miles per gallon. Right? And that also has additional data of date, miles traveled, total fuel consumed. Since battery electric buses are fueled with electricity the fuel economy is based on energy used, and that energy use is actually based on multiple factors and not just the fuel consumption.

So one of those is what you're paying for from the utility, and it's important to understand that the energy that you're paying for from the utility is not actually what the bus gets from the meter. There is a small loss in that process. Collecting the energy for a charge cycle is more challenging than tracking fuel logs, because you need several data streams to fully understand the energy use and overall efficiency of the battery electric bus.

So the common data streams that a charging cycle and the energy needed are based on multiple things including your utility bills and charging infrastructure, as well as data from the duty cycle on energy use and efficiency. So those utility bills provide total energy for charging during the billing period in a kilowatt hour, and it's important to have the charging system metered separately from the rest of the facility in order to break out that information and understand those costs.

Your charging data, which is normally the daily energy put into each bus, and that may require daily logs from individual chargers, which can be labor intensive and is subject to human error. So it's nice if you again can work with your charging provider and be able to download and log those data.

And then a third is energy use from telematics. So similar to data from the charging infrastructure, but this telematics data is specific to the BEB and provides an accurate measure of energy used by that specific bus. So these data could also be available from the OEM, as I mentioned in our last module, or you can work with a third-party supplier to provide some after market data loggers and install them in the bus for tracking.

So let's talk about converting that energy use into a fuel economy. So battery electric bus efficiency is typically represented as a kilowatt hour per mile. To compare this energy use to conventional buses we need to convert to miles per diesel gallon equivalent assuming that your baseline technology is diesel. If it's another fuel you'll just have that fuel gallon equivalent. So for this example we'll be focusing on diesel.

And the conversion factor for diesel gallon equivalent to one kilowatt hour is 37.64. Therefore, to convert energy use from kilowatt hour you first convert it to the diesel gallon equivalent using that conversation factor, and then you divide it by the miles traveled within that diesel gallon equivalent energy to understand what the energy use would be in miles per diesel gallon equivalent. So again, this is taking your energy and converting it into a diesel gallon equivalent assuming a diesel bus is your baseline technology for comparison.

Now there is also another factor whenever you're converting your BEB efficiency, and that is the amount of electricity, because the amount of electricity that you pay from the utility is not actually what the bus gets from the meter, because there is a small loss in the conversion process. So what we've seen in battery electric bus transit studies is that there is typically a 10 to 13% loss in energy from what is supplied by the utility and what is actually available for use in the bus. So just another conversion factor or impact to efficiency to keep in mind.

Another important factor to keep in mind is how the cost of electricity impacts the total cost of ownership. So as electricity prices vary – keep in mind that's also seasonally as well as throughout different parts of the day – it's really important to track those changes and understand those costs, because even if the battery electric bus even has better fuel economy than the baseline technology the fuel economy savings of the battery electric bus can be offset by the cost of energy.

So thus increasing the total cost of ownership due to higher fuel costs for more fuel efficient technology. This graph here represents how electricity prices can fluctuate, so it's important to consider the average price of electricity and compare it to the average energy costs of the baseline technology to ensure that it is in fact the best fit for the fleet, as well as being mindful of ways to reduce the total cost of ownership of different technologies.

Because the energy used by a battery electric bus is based on several factors for a single charge cycle, so again you want to be mindful and track all of those that impacts the battery electric bus energy use. It can't be determined just by the energy purchase alone because there is a loss in what you pay for from the utility and what is actually available for use in your battery electric bus. It's helpful to convert your energy use to a baseline technology to track or understand what that fuel economy comparison looks like, and those conversion factors will vary and be dependent on that fuel.

And then again be mindful of those energy costs because they can offset your energy use and fuel economy efficiency benefits. So even though you may have better fuel economy for your battery electric bus if the cost for electricity is high or higher than what it would be for your conventional baseline fuel economy it's going to offset those benefits.

So thanks for listening. That does now conclude Module 2 of the Flipping the Switch series, Electric School Bus Vehicle In-Use Performance. To complete the modules of this series, continue to listen on to Module 3 where I will provide information on electric school bus range and reliability.

And remember that you can find the content for the Flipping the Switch on Electric School Bus series, including each part of the series and associated modules, as well as handouts with the summary of information and links to all those resources mentioned today on the Alternative Fuel Data Center's Electric School Bus Page.