Battery Optimisation Guide: Charging on Off-Peak Tariffs

If you're on a tariff with cheaper electricity at night, you can set your battery to charge from the grid during those hours. You then use that cheap energy in the day and evening, instead of paying peak prices. This makes the biggest difference in winter, when your panels generate less.

Before you start

• Find your exact off-peak times. They're in your supplier's app, on your bill or on your tariff's web page. Many overnight tariffs give you around 4 to 7 cheap hours, somewhere between about 11pm and 7am, but every tariff is different.
• Check whether the times change when the clocks go forward or back. Some tariffs follow UK time and some don't. Your battery's schedule follows the inverter's clock, so check the times again each spring and autumn.
• Decide how full you want the battery to get. In winter, charging to full overnight usually makes sense. In summer, leave some room so the battery can still soak up your solar during the day.

Fox ESS

Fox ESS uses the Mode Scheduler to change how the battery behaves at set times.

1. Open the FoxCloud app and go to your plant.
2. Open Work Mode, then the Mode Scheduler.
3. Add a time slot that matches your off-peak hours, and set its mode to Forced Charge. If there's a setting for the level to charge to, set it now.
4. Leave the rest of the day on Self-use.
5. Save the schedule and make sure it's turned on.

Don't let time slots overlap. While the Mode Scheduler is on, you can't change battery settings in Quick Settings. There's more detail in Charging your Fox ESS battery on a cheap overnight tariff.

Duracell Energy

1. Open the Duracell Energy app and tap the menu at the top right, or the battery icon on the home screen.
2. Choose Schedule Control, then Charge / Discharge.
3. Tap Edit on a charge session.
4. Set the start and end times to match your off-peak hours. You can also set the charge rate and which days it repeats.
5. Save, then turn on the toggle on that session. A grey toggle means it's off.

You can have up to three charge sessions and three discharge sessions. Make sure they don't overlap. Sessions keep running every day until you turn them off. There's more detail in Using the Duracell Energy app.

Tesla Powerwall

Tesla doesn't use fixed charging times. Instead, you tell the app your tariff, and the Powerwall works out when to charge and when to use its stored energy. Tesla calls this Savings mode. It used to be called Time-Based Control.

1. Open the Tesla app and tap Settings, then Powerwall.
2. Under Operational Mode, choose Savings.
3. Open Utility Rate Plan and enter your tariff's off-peak, peak and any other periods, with their prices.
4. If there's a Grid Charging option, make sure it's on.
5. Set your Backup Reserve.

There's more detail in Using your Powerwall with an off-peak tariff.

Checking it's working

The morning after you set it up, check the app. You should see the battery charging from the grid during your off-peak hours, and its level higher at the end of them. If nothing happened, check the times, that the schedule is switched on, and that the inverter's clock is right.

If you'd rather not set this up yourself, we're happy to help.