When it comes to electrifying your school buses, there’s a lot of new information to go through. We recently explained the different types of charging or energy services that clarify the benefits of technology like Vehicle-to-grid (V2G), but there are also some important differences when it comes to charging stations or EVSEs ( power supply equipment for electric vehicles).

Here is a breakdown of some of these differences and why they are important to school bus operators.

AC vs. DC

AC stands for “alternating current”. Alternating current is the type of energy that flows in and out of the power grid that we all connect to. DC stands for “direct current” and is the type of power we get from batteries like the standard AA batteries you use for personal electronics.

Electric bus batteries can only store energy in the form of direct current, which means that a conversion must take place to allow different levels of charge.

In AC and DC loads, an inverter is required for power conversion, but the place where the inverter lives differs: it is either inside the bus (AC) or inside the charger (DC ).

How AC Conversion Works:

(Click to enlarge the image.)

How the DC conversion works:

DC bus load
(Click to enlarge the image.)

Side by side comparison

For a quick reference, here are some differences between AC and DC charging.

Tips for AC Charging

1. Make sure you have the right power level

For example, you need an 80 amp charging station if your electric bus needs 19.2 kW

2. Choose a smart charging option

Choose an AC charging solution that goes beyond “mute charging” and lets you recharge when prices are low to save on utility bills.

3. If you are considering V2G, consider DC option

V2G with AC load is possible but rare; confirm that your electric buses are V2G compatible with a two-way on-board charger

Tips for DC charging

1. Not all DC charging is “fast”

The term “DCFC” (DC Fast Charger) refers to a range of different power levels depending on the supplier of the charging station.

To make sure that your DC station is really “fast charging” you can do a simple calculation: electric bus battery size (kWh) / charging station size (kW) = charging time.

For example, a DC charger with a capacity of 25 kW will take more than 6 hours to fully charge a bus with a 155 kWh battery; a DC charger with a capacity of 60 kWh will take less than 3 hours to charge a bus with a 155 kWh battery

2. Check the specifications of the DC charging station

For direct current charging, you must have the correct output voltage, so check the compatibility between the electric bus and the charging station.

For example, if you have an electric bus with an 800V DC battery but your charging station has a maximum output voltage of 400V, you will not be able to properly charge your bus.

3. Enjoy V2G with DC charging

Due to utility interconnection requirements, DC load is preferred for V2G operations.

Make sure your DC charger has a CCS1 connector and your bus is V2G compatible.

V2G charge with CC

V2G has many savings benefits, in addition to the opportunities to generate revenue from grid services and sell power back to the grid, when utilities permit. To take full advantage of the V2G benefits, you will need a V2G compatible DC charger, a V2G compatible power bus with a two-way on-board charger, and a V2G software platform built into both.

Here is a recap of the differences between V1G, bidirectional, and V2G charging.

Nuvve EVSE options

Nuvve offers Level 2 AC and DCFC options optimized for charging electric school buses. Our DCFC 60kW and 125kW charging stations are preconfigured with our proprietary V2G software which helps maximize savings and create revenue generation opportunities (where applicable).

But don’t worry, you don’t have to memorize these details. Nuvve’s team of experts can guide you through the electrification process to create a customized solution for your school bus operation.

We also offer flexible funding options, including full funding and no upfront fees, so you don’t have to wait for grants or funding to go green.

See answers to frequently asked questions below.

To learn more, visit nuvve.com/stn or email us at [email protected]

Faq

  • Can any electric bus perform V2G services?

No, the electric bus must be V2G compatible, use a CCS1 connector plug and have technological integrations allowing bidirectional energy flow.

  • Can I do V2G with an AC charger?

While AC load can be V2G compatible, in USA, electric buses cannot use AC load for full V2G two-way load due to the nature of the on-board inverter.

  • How does Nuvve do V2G with a CCS1 plug?

Nuvve has developed and deployed a custom integration with selected bus manufacturers that enables two-way energy flow between an electric bus and a DC charging station using this type of connector.

  • Which electric school buses are V2G compatible?

Today, Nuvve has software platform integrations with several electric bus manufacturers; Contact us for more information.

  • What is the difference between two-way charging and V2G?

Bidirectional charging allows you to charge and discharge energy from an electric bus battery; V2G is a more sophisticated level of control that allows grid services and participation in the energy market. See the matrix above for reference.

  • What is the difference between a DC fast charger with V2G and a DCFC not V2G?

A DC fast charger with V2G will help you save money more efficiently by precisely controlling the flow of energy in and out of a bus battery and into the power grid. In addition to recharging when prices are low, in some areas V2G enables electric buses to generate income by selling additional energy from the bus batteries back to the grid.

  • Do Nuvve DC fast chargers only work with V2G compatible buses?

No, we can charge any vehicle that accepts DC fast charging, even if the vehicle is not V2G compatible.

  • How do I decide which electric bus charging solution to buy based on my journeys?

Evaluate your bus routes to determine if you will have enough time to recharge with a level 2 charger compared to the DCFC charger.

If you plan to expand your fleet, consider making your charging infrastructure sustainable. The battery capacities of the bus keep improving, so the power of your charging station should keep pace.

Choose a charging station that goes beyond “silent charging” and allows flexibility in scheduling charge times to save on utility costs and more.


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