Power curtailment is the intentional reduction of available power to EV chargers (or a charging site) below their maximum capability. Curtailment can be temporary or scheduled and is typically applied to stay within a site capacity limit, comply with grid constraints, reduce costs, or maintain operational stability.
Curtailment may be applied at the site level (total kW limit) or per charger/per connector (individual power caps).
Why Power Curtailment Matters in EV Charging
EV charging demand can exceed available electrical capacity, especially at fleets, workplaces, and multi-tenant sites. Power curtailment helps:
– Prevent exceeding import capacity or tripping the main breaker/fuse
– Reduce peak demand and demand charges (tariff-dependent)
– Avoid costly grid upgrades by operating within existing limits
– Maintain stable operation during grid stress events or utility requests
– Allocate limited power fairly across multiple vehicles (improve throughput and uptime)
How Power Curtailment Works
Curtailment is usually implemented via load management controls:
– Real-time metering measures total site load (or feeder load)
– A control system (CPMS/EMS/controller) enforces a maximum power setpoint
– Chargers are throttled dynamically (e.g., reduce from 22 kW to 11 kW)
– Priority rules determine who gets power (fleet critical vehicles, earliest departure, paid priority)
– When capacity is available again, chargers ramp back up to normal limits
Common Curtailment Triggers
– Site demand approaching a maximum site demand limit
– Utility demand response or grid constraint events
– High building loads overlapping with charging (HVAC, production lines)
– Transformer or feeder thermal limits (hot days, sustained high load)
– Pricing strategy: align with peak/off-peak tariffs or energy procurement constraints
– Fault conditions requiring safe derating (overtemperature, cooling issues)
Types of Power Curtailment Strategies
– Static curtailment: fixed maximum power per charger or per site (simple, conservative)
– Dynamic curtailment: adjusts continuously based on real-time headroom
– Time-based curtailment: reduced limits during peak margin windows
– Priority-based curtailment: allocates power based on rules (SoC, departure time, user type)
– Emergency curtailment: immediate reduction during faults, overheating, or grid events
Benefits
– Enables more chargers on limited electrical capacity
– Improves reliability by preventing overloads and nuisance trips
– Reduces cost exposure to peak-driven tariffs
– Supports grid-friendly operation and demand response participation
– Provides operational control during abnormal conditions
Limitations and Practical Considerations
– Slower charging during curtailment can affect user satisfaction and fleet readiness
– Requires accurate metering and stable communications for dynamic control
– Poorly designed rules can create perceived unfairness (some vehicles consistently throttled)
– Curtailment can reduce revenue if pricing does not reflect reduced power or longer session times
– For public sites, messaging is important (clear expectations and transparent tariffs)
Related Glossary Terms
Load Curtailment
Load Management
Dynamic Load Balancing
Maximum Site Demand Limit
Import Capacity
Peak Demand
Demand Charges
Peak Shaving
Load Shifting
Scheduled Charging