Valley filling is a smart charging and energy management strategy that shifts electricity demand into periods of lower grid usage, often during overnight or off-peak hours. In EV charging, valley filling is used to schedule charging sessions when overall electricity demand is low, helping smooth the demand curve and make better use of available grid capacity.
What Is Valley Filling?
Valley filling means increasing electricity consumption during the “valleys” in the daily load profile — the times when demand on the grid is relatively low. Instead of allowing large numbers of EVs to charge immediately during busy peak periods, charging is delayed, staggered, or controlled so more energy is consumed when the network is under less pressure.
In practice, valley filling is often part of smart charging, load management, and time-of-use optimisation strategies.
Why Valley Filling Matters in EV Infrastructure
As EV adoption grows, unmanaged charging can increase pressure on local distribution networks, especially in the evening when many vehicles are plugged in at the same time. Valley filling helps avoid this by aligning charging demand with periods when spare electrical capacity is available.
For site owners, fleet operators, utilities, and charging network operators, valley filling can reduce peak demand, improve grid efficiency, and support more cost-effective charging without necessarily requiring major infrastructure upgrades.
How Valley Filling Works
A charging management system monitors electricity demand patterns across the site or grid
Charging sessions are delayed or adjusted to avoid peak load periods
Available charging power is shifted into low-demand hours, such as overnight
Charging schedules may respond to time-of-use tariffs, utility signals, or site demand limits
Vehicles are still charged by the required departure time, but energy delivery is spread more efficiently across the low-demand window
This approach is especially effective where vehicles remain parked for extended periods and do not need immediate full-power charging.
Typical Valley Filling Use Cases
Common valley filling applications include:
– Workplace charging where vehicles remain parked for several hours or all day
– Residential charging that shifts energy demand into overnight periods
– Fleet depots charging multiple vehicles outside operational hours
– Apartment and multi-tenant charging where many users share limited site capacity
– Public or semi-public destinations with predictable dwell times
These environments benefit from controlled charging because there is enough flexibility to optimise when power is delivered.
Key Benefits of Valley Filling
– Reduces pressure on the grid during peak demand periods
– Improves use of existing electrical capacity
– Supports lower charging costs where off-peak tariffs apply
– Helps avoid unnecessary grid reinforcement or transformer upgrades
– Enables more efficient operation of load-managed EV charging systems
– Supports wider grid balancing and electrification goals
Limitations to Consider
– Requires smart controls, software, or a charge point management system
– Works best when vehicles have long dwell times and flexible charging windows
– May be less effective where users expect immediate maximum charging power
– Depends on accurate forecasting of site load, user behaviour, or tariff signals
– Poorly configured schedules can affect user satisfaction if vehicles are not ready on time
Valley Filling vs Peak Shaving
Valley filling increases energy use during low-demand periods to smooth the load curve
Peak shaving reduces or limits energy use during high-demand periods
In many EV charging systems, both strategies are used together to improve overall energy management
While peak shaving focuses on cutting the top of the demand curve, valley filling focuses on filling the low-demand gaps.
Where Valley Filling Is Most Relevant
Valley filling is most relevant in locations where charging demand can be scheduled rather than delivered immediately, such as:
– Homes and residential developments
– Workplace and office parking
– Fleet depots
– Hotels and destination charging sites
– Commercial properties with multiple EV charging points
– Multi-tenant buildings with constrained grid capacity
In these settings, valley filling helps balance charging performance, cost control, and infrastructure efficiency.
Related Glossary Terms
Smart charging
Load management
Peak shaving
Time-of-Use (ToU) tariffs
Off-peak charging
Dynamic load balancing
Site power limit
Demand response
Grid balancing
Utilization analytics