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Battery-Supported Bus Charging in Martha’s Vineyard Is the Latest Example of Islands Leading in Energy Innovation

Alex Eller
Nov 13, 2018

EV Fleet

Like many islands around the world, Martha’s Vineyard in Massachusetts relies primarily on imported fossil fuels for electricity. With ambitious goals to transition to cleaner local sources of energy, a plan has been enacted to replace the island’s fleet of diesel buses with new electric models. These buses will reduce reliance on fuel imports and improve local air quality. Islands have been early adopters of electric bus technologies—in addition to high fuel costs, bus routes on most islands are relatively short and geographically restricted, which reduces the need for very long-range vehicles and the expensive battery packs they require. 

Going Wireless

The Vineyard Transit Authority (VTA) has announced plans to develop a network of wireless charging stations both at individual bus stops and at its maintenance facility. This network will allow the buses to automatically recharge and extend their range while picking up passengers. These charging stations will be integrated with distributed energy storage systems to mitigate the spikes in demand caused by charging. The three battery systems currently being developed will each have a capacity of 250 kW/500 kWh. The pairing of energy storage with vehicle charging is quickly gaining traction among utilities as well as commercial and industrial building owners, as it can lower operating costs for EV charging stations and limit the need for new grid infrastructure to serve the higher power demand. Navigant Research’s recent report, Energy Storage for EV Charging, explores this technology combination and the associated business models in greater detail. 

For Martha’s Vineyard, the flexibility and intelligent software controls provided by these energy storage systems will be critical to deploying a cost-effective electric bus fleet. Battery systems provide a load-leveling service on the grid and ensure that total demand does not exceed available supply. Currently, the island does not have sufficient generation resources available to charge all the electric buses at the same time. With the addition of storage, the energy needed to charge the buses can be pulled from the grid at a steady rate and at times when overall demand is lower. Rather than charging each bus from 0% to 100%, the control software will ensure that buses take turns charging numerous times throughout the day, charging only partially at each stop. This charging pattern reduces strain on the existing electrical grid and can theoretically enable unlimited driving range. 

Multifunctional Batteries

A key feature of the island’s battery-backed bus charging system is that the stations will each be designed as small microgrids capable of disconnecting from the wider power grid and operating independently. This design will allow the stations to continue providing power during an emergency or large-scale outage. For example, the VTA’s maintenance and operations center in Edgartown will integrate battery energy storage with a new 700 kW solar PV array, a diesel generator, and vehicle charging stations. This center will be able to operate independently and provide power for emergency services, including vehicle charging, if the island’s grid is down. 

The benefits of combined energy storage and EV charging are becoming clear as the industry continues to evolve. This project on Martha’s Vineyard provides a replicable framework for other transportation agencies around the world by both reducing the costs to transition to an electric bus fleet while also enhancing resiliency and emergency response capabilities.