On-site energy storage is the use of batteries (and sometimes other storage technologies) installed at a charging location to store electricity and discharge it when needed. In EV charging, on-site storage—most commonly battery energy storage systems (BESS)—helps manage peak demand, reduce grid connection constraints, improve resilience, and support the integration of renewables.
What Is On-Site Energy Storage?
On-site energy storage is a system that can charge from the grid or onsite generation and later supply power to site loads.
– Typically installed as a stationary BESS with power conversion equipment (inverters)
– Stores energy (kWh capacity) and delivers power (kW capability) on demand
– Can be controlled by an energy management system (EMS) or a site controller
In charging applications, storage may support the chargers directly or manage total site demand at the point of connection.
Why On-Site Energy Storage Matters in EV Charging
Storage solves common constraints that limit charging rollout and performance.
– Enables more chargers without immediate grid upgrades by shaving peaks
– Keeps a site within a contracted import limit and reduces capacity tariffs or demand charges
– Stabilizes charging performance when the grid connection is weak or constrained
– Improves utilisation by allowing higher power delivery during busy periods
– Supports sustainability goals by storing excess solar PV and increasing self-consumption
For depots and public hubs, storage can be the difference between “grid-limited” and “operationally reliable.”
How On-Site Energy Storage Works With Charging
Storage is coordinated with chargers and site load.
– The BESS charges during low-demand or low-price periods, or when PV is producing excess energy
– During peak charging demand, the BESS discharges to reduce net grid import
– Site controls enforce limits and decide how power is allocated across loads
Common operational modes include:
– Peak shaving: cap grid import at a defined threshold
– Load smoothing: reduce sudden ramps when multiple chargers start simultaneously
– Backup support: maintain limited operation during outages (site-dependent)
– Renewable shifting: store midday PV for evening charging needs
BESS is often paired with energy throttling and dynamic load management to coordinate charger output.
Typical Use Cases
– Fleet depots with many vehicles charging overnight
– Public charging hubs where peak demand is concentrated
– Sites with limited grid connection capacity and long upgrade lead times
– Retail and workplace car parks that want to avoid building peak demand penalties
– Solar canopy sites that want to maximize renewable usage for charging
Key Benefits of On-Site Energy Storage
– Faster site deployment and scaling under grid constraints
– Lower operating costs through peak reduction and tariff optimization
– Improved charging availability and performance during high demand
– Better renewable integration and lower carbon intensity potential
– Added resilience and operational control for critical fleets
Limitations to Consider
– Adds CAPEX, permitting, and integration complexity
– Needs careful sizing (kW and kWh) based on peak profiles and charging behavior
– Battery degradation and lifecycle costs must be included in business cases
– Safety, siting, and fire risk management require proper engineering and compliance
– Benefits depend strongly on local tariff structures, grid limits, and utilization patterns
Related Glossary Terms
Battery Energy Storage System (BESS)
Energy Management System (EMS)
Peak Shaving
Grid Congestion
Capacity Tariffs
Energy Throttling
Renewable Integration
Power Plant Controller