Fleet peak shaving is the practice of reducing a depot’s maximum power draw (peak kW) caused by EV charging—so fleets can avoid demand charges/capacity fees (where applicable), prevent overloads, and delay or reduce costly grid upgrades, while still ensuring vehicles are ready by departure time.
What is fleet peak shaving?
Peak shaving keeps charging load from spiking when many vehicles plug in at once (typical “return-to-depot” wave). It’s achieved by controlling charging power using:
– A site power cap (hard limit on total EV charging power)
– Dynamic load management / load balancing across chargers
– Charging schedules that shift sessions away from peak periods
– Optional battery storage (BESS) or PV coordination to reduce grid import
Peak shaving focuses on kW (power), not just kWh (energy).
Why fleet peak shaving matters
– Reduces demand charges and capacity fees in markets where peak drives costs
– Prevents breaker/transformer overload and nuisance trips
– Avoids evening peaks that coincide with high electricity prices
– Enables more EVs per depot without immediate grid upgrades
– Improves overall energy predictability and operational resilience
Common peak shaving methods for fleet depots
1) Hard site cap + dynamic allocation
– Example: site cap 120 kW shared across 20 AC chargers
– Vehicles charge at lower power when many are connected, then ramp up as others finish
2) Staggered start / wave scheduling
– Charge early-departure or low-SoC vehicles first
– Delay flexible vehicles to off-peak hours (e.g., after 22:00)
3) Priority-based throttling
– Critical routes get power; non-critical vehicles are slowed or paused
– Keeps readiness protected while peaks are controlled
4) Integration with building load
– Limit EV charging when HVAC/production loads are high
– Requires real-time metering at the main incomer
5) BESS-based peak shaving (optional)
– Battery discharges during peak charging demand to reduce grid import
– Can be combined with off-peak charging or PV charging of the battery
Key inputs needed
– Site electrical limit (transformer/main breaker) and any sub-board limits
– Tariff structure and demand charge rules (how peak is measured)
– Vehicle arrival/departure pattern and target SoC/kWh needs
– Charger power ratings and minimum effective charging power
– Metering setup to include non-EV building load if needed
KPIs to track
– Peak kW (daily/monthly) and peak duration
– Demand charge or capacity fee impact (before vs after)
– Readiness rate (% vehicles meeting departure target)
– kWh shifted to off-peak windows
– Public charging fallback rate and exception causes
– Charger utilization and queue/rotation effectiveness
Best practices
– Treat peak shaving as “readiness-first”: cap power, don’t sacrifice critical departures
– Model unmanaged vs managed peak before sizing grid upgrades
– Set minimum power floors to avoid “too-slow charging” that never catches up
– Build an override workflow for urgent vehicles and late arrivals
– Review peak events weekly and adjust caps, priorities, and schedules
– Contractually define responsibility for connectivity/firewall issues (controls must be reliable)
Common mistakes
– Only setting a cap without scheduling logic → peaks shrink but readiness fails
– Ignoring building loads → EV cap is wrong and trips still happen
– No monitoring/alerts → peak shaving fails silently when chargers drop offline
– Overcomplicating early—start with caps + priority tiers, then refine
– Assuming BESS alone solves it without operational scheduling discipline
Related glossary terms
Demand charges
Dynamic load management
Fleet load balancing
Fleet charging scheduling
Active power throttling
Fleet energy optimization