As EV charging is added to a property or fleet operation, the cost of electricity is not always determined by kilowatt-hours alone. Many commercial utility rates also include a demand charge: a fee tied to the site’s highest level of power drawn from the grid during a billing period. A brief period when multiple chargers are operating at once can set that peak and influence the bill for the entire month.
A battery energy storage system (BESS) is a rechargeable, on-site energy asset that stores electricity for use later. At an EV charging site, it can charge when the site’s grid demand is lower and discharge when charging activity would otherwise push grid demand to a new peak.
How a BESS works
A BESS combines battery cells with equipment and controls that manage the flow of energy. When the system is charging, it draws electricity from the grid or, where available, from on-site renewable generation. When the site needs additional power, the system converts stored energy and delivers it back to the site’s electrical loads.
Software is central to the process. It monitors site load, charging sessions, battery state of charge, electricity pricing, and operating limits. Those controls determine when the battery should store energy and when it should support the site.
| Site condition | How storage can respond |
|---|---|
| Lower-demand hours | The battery can recharge while the site’s grid use is below its target limit, subject to the operating plan and electricity rate. |
| Multiple vehicles begin charging | The system can discharge stored energy to supplement the grid and limit the size of the new demand peak. |
| On-site renewable generation is available | Excess generation can be stored for use later, instead of relying exclusively on immediate grid consumption. |
| Utility demand-response event | Storage can help reduce grid draw, if the site, tariff, controls, and program rules support that use. |
Peak shaving: reducing the demand-charge driver
The most common use case is called peak shaving. It does not eliminate the energy required to charge vehicles; the vehicles still need the same energy. Instead, it changes where some of that power comes from during the moments when grid demand is highest.
For example, if a site has a target grid limit, the BESS can discharge whenever EV charging and other building loads approach that threshold. By supplying part of the load locally, the battery can keep the site’s measured grid demand below the level it otherwise would have reached. After the peak has passed, the BESS can recharge according to the site’s energy-management plan.
Why EV charging sites are a strong fit
EV load can be dynamic. Vehicles arrive at different times, charging power can vary by vehicle and charger, and a fleet may have concentrated return-to-base periods. That makes it difficult to predict the precise moment a site will set a new monthly peak.
Storage gives site operators another tool besides limiting charging power or upgrading utility capacity. It can support vehicle throughput during high-demand windows while helping the operation manage the portion of its bill that is based on peak power demand.
What should be evaluated before deployment
- Utility tariff: Demand charges, time-of-use rates, ratchets, and billing rules vary by utility and location.
- Load profile: Interval data helps reveal when peaks occur, how long they last, and whether storage can address them.
- Charging operations: Vehicle arrival patterns, charge durations, and required state of charge determine the right operating strategy.
- Battery sizing and controls: Both power capacity and stored energy matter; a system must be sized for the height and duration of the peaks it is designed to manage.
- Safety, permitting, and interconnection: Local codes, utility requirements, and site conditions should be assessed early.
Managing energy as an operating system
The best outcome comes from coordinating storage with chargers, building loads, utility pricing, and fleet schedules. That enables a site to prioritize vehicle readiness while treating peak demand as an operating variable that can be monitored and managed.
For EV fleets and properties, the goal is straightforward: deliver the energy vehicles need without allowing short periods of simultaneous charging to create avoidable grid-demand costs.
This independent EVODS article was informed by a general overview of battery energy storage systems from Driivz. Actual energy and demand-charge savings depend on the utility tariff, site load profile, storage design, controls, and local requirements.
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