Demand charges are fees on an electricity bill based on a site’s highest power draw (kW) during a billing period, not just the total energy consumed (kWh). They are common for commercial and industrial customers and can significantly impact the operating cost of EV charging sites—especially depots, hubs, and locations with many chargers operating simultaneously.
What Are Demand Charges?
Demand charges are calculated from the peak demand a site reaches over a defined interval, such as:
– The highest 15-minute or 30-minute average kW in a month
– The highest measured kW during specific “peak” time windows (tariff-dependent)
The bill typically includes both:
– Energy charges (€/kWh) for total consumption
– Demand charges (€/kW) for the peak power level reached
Why Demand Charges Matter for EV Charging
EV charging can add large, simultaneous loads to a site, making demand charges a key cost driver. They matter because they:
– Can increase OPEX disproportionately when multiple vehicles plug in at once
– Penalize short peak events even if total monthly kWh is moderate
– Influence charging station profitability and charging ROI calculations
– Make unmanaged charging risky for fleets and high-utilization sites
For depots, a single uncontrolled “everyone plugs in at 18:00” event can set the month’s demand peak and raise costs across the whole billing period.
How Demand Charges Are Triggered in Practice
Demand charges often spike when:
– Many chargers start sessions at the same time (shift change, dispatch return)
– DC chargers ramp to high power simultaneously (DC fleet charging)
– EV charging overlaps with building peaks (HVAC, production equipment, kitchens)
– Curtailment or load management is missing or misconfigured
Even brief peaks can matter if the utility measures demand as an interval average.
Demand Charges vs Connection Tariffs
These terms are related but not identical:
– Demand charges: billing based on measured peak kW usage over time
– Connection tariffs: broader network charges tied to connection capacity, tariff structure, and contracted terms
In many markets, both concepts can apply and should be evaluated together when planning site economics.
How to Reduce Demand Charge Impact
Demand charges are often manageable with smart design and operations:
Load Balancing and Power Caps
– Apply load balancing to distribute available power across chargers
– Set a site-wide power cap to stay below a chosen kW threshold
– Use current transformers (CTs) or EMS data to coordinate with building load
This prevents uncontrolled peaks while still delivering meaningful daily kWh.
Smart Charging and Scheduling
– Stagger charging start times to avoid simultaneous ramps
– Prioritize vehicles based on dispatch scheduling and departure deadlines
– Shift charging to off-peak periods when operationally possible
Scheduling is especially effective for fleets with predictable return-to-base patterns.
Infrastructure and Tariff Strategy
– Phase the rollout: start with controlled capacity and expand with data
– Evaluate tariff options and peak windows during site design
– Consider on-site energy storage for peak shaving where economics justify it
– Align charger count and power levels with real duty cycle needs, not only nameplate ratings
What to Include in a Business Case
When modeling EV charging economics, demand charges should be explicitly included in:
– Cost-benefit analysis and total cost of ownership (TCO)
– Scenario modeling for peak events and seasonal demand
– Sensitivity analysis for peak kW, utilization growth, and tariff changes
Ignoring demand charges often leads to unexpected OPEX and underperforming ROI.
Common Pitfalls
– Designing around total kWh and ignoring peak kW behavior
– Installing high-power chargers without power caps or operational rules
– Assuming “rare peaks don’t matter” when tariffs are based on monthly maxima
– Misconfigured load balancing due to CT phase mapping errors
– Not coordinating EV charging with building peak loads
– Treating demand charges as fixed and not exploring tariff structures or control strategies
Related Glossary Terms
Peak Charging Power
Load Balancing
Current Transformer (CT)
Connection Tariffs
Curtailment Signals
Dispatch Scheduling
Charging ROI
Charging Station Profitability
Charging Session Analytics