Why Is My Solar Battery Not Discharging?

Usually, because it has been told not to. A battery that sits full while the house buys electricity from the grid is most often following a setting: a reserve level it won’t go below, a work mode that holds charge back, or a schedule that is waiting for a different time of day.

Genuine faults do happen, and one of them is invisible from the app. But the settings are where to start, because you can check all of them from your phone.

Key points

• Check the battery’s reserve (minimum charge) setting first. At or below it, the battery stops on purpose.

• Some work modes hold charge for a power cut or put export first. In those modes, not discharging can be normal.

• A charging schedule on a time-of-use tariff can stop the battery discharging during the cheap window.

• In the middle of the day your solar may already be covering the house, so the battery has nothing to do.

• A full battery, an evening house load and grid import in normal self-use mode is a red flag worth reporting.

First, the settings that look like faults

It is sitting at its reserve

Most systems let you set a minimum state of charge that the battery won’t discharge below in normal use. The point is to keep something back for a power cut, or to protect the battery. If the app shows the battery resting at the same percentage every evening, compare it with the reserve setting. If they match, the battery is doing what it was told.

The work mode is holding charge back

Batteries run in a work mode that decides what they prioritise, and the names differ between brands. Taking FoxESS, a brand we fit, as an example, its published guide to work modes says:

• in Self-use, the battery powers the home when solar falls short

• in Feed-in, solar goes to the house and then to the grid, rather than being stored for later

• in Back Up, discharging is not allowed until the battery is above its backup level

So a battery in a backup-style mode, or one set to put export first, can look as if it is ignoring the house. If the mode was changed recently, perhaps during a power cut or by someone trying a new setting, that is the likely explanation.

A schedule is running

On a time-of-use tariff, your battery is probably scheduled to charge from the grid during a cheap overnight window. Many systems also stop the battery discharging during that window, because there is no point running the house from the battery while grid electricity is cheap. If the house is importing in the small hours and the battery is idle, check whether the time matches your cheap window.

Schedules can also outlast the tariff they were set up for. If you have changed tariff, check the schedule still matches the new one. Our guide to Octopus Flux explains how one common time-of-use tariff works with a battery.

Solar is already covering the house

On a bright day, your panels may be supplying everything the house is using. The battery has nothing to do until the solar drops off in the late afternoon. That is normal.

It is cold

Batteries have temperature limits for discharging as well as charging. A battery in an unheated garage or outbuilding can limit or stop discharging in very cold weather. The limits differ by product, so check the datasheet for yours.

It is set not to power the car

Some systems are set up so the battery doesn’t discharge into an EV charger, so the car charges from the grid or solar instead. If the battery stays put only while the car is charging, that is the likely reason.

It is discharging, but the app says otherwise

If the monitoring has dropped out or the app is showing an old reading, the battery may be working perfectly. Our guide to monitoring your solar panels through an app explains how to tell.

When it is probably a genuine fault

This combination is worth reporting: the battery is well above its reserve, it is evening, the work mode is a normal self-use mode, no schedule is running, and the house is importing from the grid.

The likely causes are:

• A CT clamp problem. The battery decides when to discharge using a current sensor on your incoming supply. If that sensor is misreading, the system may not see the house using power at all. Our guide to why a solar battery is not charging explains CT clamps in detail. Never touch one yourself: they sit on live incoming cables.

• Communication loss between the battery and the inverter, which often makes the battery park itself.

• A battery management system protection trip, where the battery has shut itself down to protect a cell.

• A firmware mismatch after one part of the system updated and another didn’t.

• A tripped breaker or an isolator left off, sometimes after unrelated electrical work.

• A failed module in a stacked battery, which can take the whole stack offline.

What you can safely check yourself

• Read the app: state of charge, work mode and any alarm or error code.

• Compare the battery’s resting level with its reserve setting.

• Check the work mode, and whether anyone has changed it recently.

• Check any charge or discharge schedule against your tariff’s cheap window.

• Check whether the battery stops only when the car is charging.

• Look at the front of the consumer unit for a tripped breaker. Reset it once. If it trips again, stop and call an engineer.

• Check any clearly labelled external isolator.

• Note when it started, and anything around then: a tariff change, a firmware update, a power cut, new electrical work.

Do not open the battery, the inverter or the consumer unit, touch the CT clamp or anything at the meter, or reset a breaker repeatedly.

Frequently asked questions

My battery stops at 10 or 20 per cent every night. Is that a fault?

Probably not. That is very likely your reserve setting.

The battery is full but the house is using grid power at night.

Check the work mode and any schedule first. If both look normal, this is worth reporting.

Will changing the work mode damage the battery?

Choosing a standard mode in the app is designed to be safe. If you are unsure which mode suits your tariff, ask your installer.

Can you look at a battery you didn’t install?

Yes. We inspect and repair battery systems whoever fitted them.

Book a solar system inspection. If your battery won’t discharge and the settings all look right, we’ll find out why.