Using a Microgrid to Minimize Costs at an Electric Vehicle Charging Center

July 6, 2023
This article walks through how to address some of the inherent complexities arising from configuring a microgrid around an EV charging center.
When you own a gas station, there’s not much you can do to influence the cost you’re paying per barrel of oil. However, when you own an electric vehicle (EV) charging center, there are a number of strategies you can employ to bring down your electricity costs. One method that aligns several strategies under a single umbrella is to design the center as a microgrid. This way, you can generate and manage your own power and reap a whole host of other benefits.

But as you probably already know, a microgrid that combines solar photovoltaics, battery storage and dozens of EV chargers is a relatively complex beast. This scenario led  Rove, a full service EV charging center startup in Southern California, to seek out a microgrid controller that was up to the challenge, along with a supportive team who could help find cost efficiencies along the way.

Let’s set the stage: In terms of load, Rove’s EV charging center includes 40 Level 3 EV chargers, a market and lounge, and car wash. Some power generation comes from solar PV panels, and a battery energy storage system (BESS) acts as a buffer to absorb and dispatch power as needed. In Rove’s case, the microgrid controller needs to manage the point of interconnection with the utility to a net-zero export while also managing the facility’s generation capability.

The center is grid-connected to a local utility, but its setup involves nonexport of power to the utility grid, meaning none of the power generated by the on-site solar PV is sent outside of the microgrid. This leaves the following opportunities for cost reductions:

1. Right-sizing the BESS

The first place to start is with the equipment and infrastructure setup. It stands to reason that a smaller BESS will be less expensive, but it’s important to understand what limitations a smaller BESS capacity poses in terms of being able to achieve system optimization. A larger BESS may result in a greater return on investment (ROI) over time. Plus, the ability for the center to charge customer EVs during a grid outage is a revenue and competitive advantage opportunity that shouldn’t be overlooked (as noted in other benefits below).

Many of these elements are discussed in  Finding that battery size and ROI sweet spot and involve modeling optimal power profiles that minimize the sum of electric billing and investment costs. These models form the basis of an economic analysis where the maximum cost savings for a BESS are calculated by factoring in time-of-use, time-of-generation, demand costs and investment costs over a fixed amortization time.

2. Time-of-use and peak demand reduction

Once the center is up and running, it will be up to the microgrid controller to use the BESS to optimize the site demand based on on-site generation and load availability. Taking into consideration the current state of charge of the BESS, system load and generation, and factoring in the forecasted generation, the microgrid controller will avoid drawing power from the utility grid during periods where time-of-use and peak demand rates are high.

Other benefits

So far, we’ve focused on the economic benefits that the microgrid controller will provide, but the microgrid controller offers additional benefits that support Rove’s business autonomously:

1. Resiliency and business continuity

While the microgrid controller will control the energy storage device to power the site load, it will also reserve a minimum BESS state of charge for reliability purposes. In the event the utility grid goes down, the center will continue to operate under its own power.

With EV charging at the heart of Rove’s business, the microgrid controller needs to support EV charging even when the microgrid is disconnected (or islanded) from the utility grid. In such circumstances, the microgrid controller calculates an estimated remaining battery duration given current generation, load and forecasted generation. Real-time generation and load (including EV charging sessions) data are continuously fed to the microgrid controller, which updates remaining battery life projections and optimizes loads based on priorities set by Rove. These priorities could include curtailing EV charging to distribute battery life equitably among customers and serving critical loads such as safety features, lighting and heating, ventilation and air conditioning systems.

2. Safe power restoration

When the utility grid goes down, the microgrid controller will safely disconnect from it and continue operating under the microgrid’s own power. During this time, it will monitor the utility grid and facilitate reconnection once power is restored. Problems with relays tripping offline can result when re-energizing power lines that have lost power for a while so to mitigate this risk the microgrid controller will need to manage the center’s load during reconnection. It will leverage the BESS to absorb any excess power, ensuring a smooth transition as the center’s microgrid resynchronizes with the utility power grid.

One software solution

Given the inherent complexity of Rove’s microgrid configuration, Rove opted to collaborate with PXiSE Energy Solutions and put the PXiSE microgrid controller through its paces, managing power flow at its EV charging centers. Consisting of hardware-agnostic software,  PXiSE’s AI-enhanced microgrid controller is positioned to handle the plethora of inputs related to the smooth operation of Rove’s centers, resulting in happy customers all around.

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