Solar output capped when battery is full
Why is my solar output capped when the battery is full?
If your solar battery reaches 100% and your daily solar graph suddenly flattens out or drops, you might think your system is broken. Usually, this is a completely normal feature of your setup, but occasionally it points to a simple settings error we can fix remotely.
There are two very different things that can happen when the battery is full. One is completely normal and needs no action at all. The other is a setting issue that we can usually fix for you over the phone. This page helps you tell the two apart.
Which one applies to you?
When your battery is full, which one of these happens?
...and you are exporting power to the grid. This is normal.
Your generation flattens at roughly 5 kW total instead of climbing further, and your system is still sending power out to the grid. All is working perfectly. Read more about the 5 kW cap.
...and you are not exporting power to the grid. This is likely a mistake in the settings.
Your generation drops to a very small amount, such as 200 to 350 watts, to just match what your house is using. Nothing is being exported. This points to a blocked setting we can easily correct. Read more about this fix.
If neither pattern sounds like what you are seeing, or if the drop happens at random times rather than when the battery is full, please contact us and we will investigate.
Normal: capped at the inverter's limit
Through the morning, the panels produce power. Some of this runs the house, and the rest charges the battery. The moment the battery hits 100%, it stops taking a charge, so all the remaining power is used by the house or sent to the grid.
The 5 kW you are seeing is the output rating of your inverter, which is 5 kW on the systems we normally fit. The inverter is the box that manages your solar system. kW (kilowatts) measures how much power it can send out at any one moment. So 5 kW is the most your inverter can send out, whether that power runs your home or goes to the grid.
ESB Networks sets a separate limit on how much a standard home can send out. A standard home supply, called a single-phase connection, is what almost every Irish house has. It can send out up to 25 amps, and amps measure how much electricity is flowing. That works out at about 5.75 kW. Your inverter's 5 kW output rating sits below that, so the inverter is the limit you meet first. Once the battery is full and the house has taken its share, the inverter caps its output at 5 kW and trims whatever is left. Your panels and battery are working perfectly.
How the export cap works
The 5 kW is the inverter's total output, not just what goes to the grid. Export is whatever is left over after the house takes its share. If your home is using 1 kW at the time, the most you can export is around 4 kW, not the full 5 kW. That is completely normal and not a sign of a fault.
If you would like to understand why we fit panels rated higher than the inverter in the first place, see why oversizing solar panels makes sense.
Needs fixing: export limit left on
The second pattern is different. Instead of flattening safely at the 5 kW cap, the system stops sending power to the grid completely. With nowhere for the extra power to go and no battery left to charge, your system slows the panels right down. They produce only the small amount of power your house needs to run things like the fridge and lights, which is often just 200 to 350 watts.
This is usually caused by an incorrect setting blocking power from leaving your house. On Solis systems it is called the Feed-in Power Limit Switch. Other brands use different names, but the effect is the same: export is blocked even though your connection allows it.
This setting is sometimes left switched on from when your system was first installed. While your connection was waiting for approval to export to the grid, the limit was needed. Once that approval came through, the setting should have been switched off, and occasionally it is missed.
Export limit settings are only accessible to installer accounts. Customers cannot switch this off themselves, but we can usually fix it remotely so no site visit is required.
When we look into it for you, we check the setting and switch it off. Once that is done, your panels will get back to full power and rise to the normal 5 kW cap.
What happens next
There is nothing you need to do to the system itself. Switching this off is a change that only your installer can make, and it can be done remotely. Here is what happens once you let us know your solar is dropping when the battery is full:
- We check the export-limit setting on your inverter.
- If it has been left switched on, we turn it off remotely. No site visit is needed.
- Your system returns to normal, sending spare power to the grid instead of slowing the panels down.
Need a hand?
If your solar generation is capped or dropping when the battery is full and you are not sure which of the situations above apply, get in touch with your installation team at PureVolt.ie.
Tell us what your app is showing, for example whether the generation is flattening at a set level, or dropping to match what your house is using. We can usually tell from that which of the two it is. If it is the setting, we can switch it off for you remotely.
You might also find these guides useful:
- Battery charging and discharging explained, understanding normal battery behaviour.
- Battery percentage jumping up and down, what it means when the percentage moves in sudden steps.
- Solis remote access setup, how to give us remote access to your inverter so we can help faster.