Maturity status | Beta |
This article explains what Time-of-Use Optimization is, how it schedules EV charging based on electricity prices, and how to configure it for a site.
What is Time-of-Use Optimization?
Time-of-Use (ToU) Optimization shifts EV charging to periods when electricity prices are lower. The Energy Management System (EMS) ensures each EV reaches its minimum energy target by the expected departure time in the most cost-efficient way, using a price forecasts and modelled EV behavior to decide when to charge at full power and reduce power.
How does Time-of-Use Optimization work?
The EMS receives tariff forecast data from a connected tariff and modulates each EV's power to reach its minimum energy target by the expected departure time in the most cost-efficient way. Furthermore, a price threshold can be set to charge EVs with the maximum power available during relatively cheap periods.
Key behavior:
EVs that have not reached their minimum required energy follow a cost-optimal charging path
A relative price threshold can be defined to allow all EVs to charge at low prices
EVs that have already met their minimum required energy are curtailed to minimum power during expensive periods
If no valid tariff data is available, the EMS treats all time windows as cheap and EVs charge at full power until their targets have been met
All Standard Control constraints — fuse limits and DLM/SLM power limits — always apply and take precedence
EV priorities during curtailment:
When available power must be distributed across multiple EVs, the EMS assigns priority based on how urgently each EV needs to charge:
EVs that have already reached their energy target (lowest priority)
EVs that can reach their target at minimum power
EVs that can reach their target at maximum power
EVs that cannot reach their energy target even at maximum power (highest priority)
What are the requirements for Time-of-Use Optimization?
Standard Control (DLM or SLM) must be active on the site
An electricity tariff must be configured for the site
Parking duration and minimum desired energy must be configured for the site
How do I configure Time-of-Use Optimization?
In XENON, go to the Energy Management Configuration for the site
Under Time of Use, enable the feature set the following fields:
Minimum parking duration — the expected time EVs are parked at the site
Minimum energy — the minimum energy target per charging session
Price percentile — the percentage of cheapest intervals during which EVs charge at full power (for example, 30% means EVs charge at full power during the cheapest 30% of the day's price intervals)
What are the limitations of Time-of-Use Optimization?
Settings for departure times and required energy are set at a site level and not for individual EVs or charging sessions
For very constrained sites, it might not always be possible to reach the target energy for each charging session