Demand metering is the measurement of a site’s electrical demand (kW) over defined time intervals, typically to calculate demand charges and to monitor peak load against contracted capacity limits. For EV charging sites, demand metering is critical because charging can create large, simultaneous loads that drive peak demand costs and operational constraints.
What Is Demand Metering?
Demand metering records how much power a site draws from the grid and calculates demand over an averaging interval such as:
– 15-minute demand
– 30-minute demand
– In some cases, shorter intervals for internal monitoring
Utilities use the highest interval demand during a billing period to set demand-related fees, while site operators use it to control charging load and prevent peak spikes.
Why Demand Metering Matters for EV Charging
Demand metering matters because EV charging influences peak kW, which can be more expensive than total energy (kWh). It helps:
– Identify peak events caused by simultaneous charging
– Manage and reduce demand charges with power caps and scheduling
– Verify that site demand stays within contracted limits and connection tariffs constraints
– Support cost-benefit analysis and charging ROI models with real peak data
– Detect abnormal load patterns that may indicate misconfiguration or faults
For depots and workplaces, demand metering is often the foundation for cost control.
How Demand Metering Works in Practice
Demand metering typically follows this logic:
– The meter measures instantaneous power draw continuously
– Power is averaged over a fixed interval (e.g., 15 minutes)
– The highest interval value becomes the “peak demand” for that period
Even a single short peak can influence the month’s maximum demand if it raises the highest interval average.
Where Demand Metering Data Comes From
Demand metering can be captured through multiple layers:
Utility Revenue Meter
– The main utility meter used for billing
– Typically the official source for demand charges and contracted demand compliance
Sub-Metering and Site Monitoring
– Additional meters in distribution panels to track EV charging feeders separately
– Often used in depots, multi-tenant sites, or complex facilities
– Supports internal cost allocation and troubleshooting
CPMS / EMS Calculated Demand
– CPMS or energy management systems can calculate demand using charger telemetry
– Useful for operational control, but may not match utility billing exactly
For accurate financial reconciliation, utility meter data is usually the reference.
Demand Metering and Load Control
Demand metering data is frequently used to drive real-time charging control:
Power Caps and Load Balancing
– Use load balancing to distribute power across chargers
– Enforce a site-wide kW cap based on measured demand
– Adjust charging limits dynamically using current transformers (CTs) and EMS inputs
This keeps total site demand below a target threshold to reduce cost and avoid overload.
Curtailment and Demand Response
– Apply curtailment signals during peak windows or grid stress events
– Reduce EV charging load temporarily while maintaining fleet readiness priorities
This is common when participating in flexibility programs or when tariffs penalize peak demand.
Typical Use Cases
Demand metering is used for:
– Fleet depot charging cost control and peak management
– Workplace charging where EV load overlaps with building peaks
– Public hubs with multiple chargers and variable high-load events
– Commissioning and validation of load management systems
– Ongoing monitoring to detect growth in peak demand as utilization increases
Common Pitfalls
– Assuming energy (kWh) is the only driver of cost and ignoring peak demand (kW)
– Using CPMS power values as a billing proxy without reconciling to utility meter rules
– Misconfigured CT mapping causing incorrect demand readings and unstable controls
– Failing to account for building load spikes when managing EV charging
– Not documenting demand intervals and tariff logic, leading to wrong peak predictions
– No monitoring alerts, so peak events are discovered only after the bill arrives
Related Glossary Terms
Demand Charges
Demand Factor
Load Balancing
Current Transformer (CT)
Curtailment Signals
Connection Tariffs
Charging Capacity Planning
Charging ROI
Charging Session Analytics