Battery Optimisation Guide: Charging on Off-Peak Tariffs
Taking advantage of off-peak energy tariffs is one of the best ways to maximise your solar battery investment, especially during the UK winter months when solar generation is lower.
By setting your battery to charge from the grid overnight when electricity is cheap, you can power your home cost-effectively during expensive peak periods. Below are step-by-step instructions for scheduling grid charging on three popular battery systems: Fox ESS, Duracell Energy, and Tesla.
1. Fox ESS
To schedule your Fox ESS battery to charge during an off-peak window, you will need to switch it into "Time of Use" (TOU) mode.
-
Open the FOX ESS Cloud App (available on iOS and Android) or log into the web portal.
-
Select your inverter from the device menu and navigate to Settings.
-
Find the Work Mode (sometimes called Energy Management Mode) and change it to Mode Scheduler
- Mode Scheduler allows you to submit different "modes" at different times. You can use not just to charge your battery from the grid, but also to discharge directly to the grid, or send energy straight to the grid instead of your property, if you would like to.
-
Enter your desired start and stop times for your selected mode.
-
You can set up to two different time periods.
-
Ensure that the "Enable charge from grid" option is selected.
-
Press Save (you should receive a 'Success' message).
2. Duracell Energy
The Duracell Energy app allows you to easily set timed charges and discharges directly from your smartphone.
-
Open the Duracell Energy app and navigate to the "Scheduled Control" page from the main menu.
-
Here, you can schedule up to 3 charges and 3 discharges at once.
-
Tap 'Edit' on one of the available charge slots.
-
Set your Start Time and End Time to match your off-peak tariff window.
-
You can also adjust the charge rate (which defaults to 6000W) and set the frequency, such as having it repeat every day.
-
Once configured, save the settings and toggle the status switch (the grey button) to the ON position to engage the charge.
-
These cycles will run automatically until you manually turn them off.
3. Tesla Powerwall
Tesla’s grid charging system is uniquely intelligent; instead of blindly charging to 100% during a set time frame, it uses an algorithm designed for cost-efficiency and battery health. It factors in historical data, weather forecasts, and your home's energy usage.
To set up Time-Based Control for off-peak charging:
-
Open the Tesla app and tap Settings at the bottom of the main screen.
-
Select Utility Rate Plan to input when your electricity is cheap and expensive.
-
Tap Edit next to your plan details to enter your provider's specific peak and off-peak times.
-
Under the Schedule section, set the specific times when power is at its cheapest.
-
Ensure your system mode is set to Time-Based Control and that Grid Charging is enabled.
-
Tap Change Rate Plan to save and confirm your settings.
Note: Because Tesla uses predictive algorithms, your battery may prioritise solar generation and might not charge fully from the grid if it anticipates you will have enough solar energy to meet your home's needs the next day.