Short answer
If the inverter switches off around midday with a message about grid voltage, it is seeing too high a voltage at its end. That comes from loss in the cable, from the connection or from a lot of feed-in in the street. A thicker cable, a shorter route or a report to the grid operator are the solutions.
Who this article is for Anyone with solar panels who sees the yield drop on exactly the best days. Reading and noting it down you can do yourself; testing and adjusting is work for an installer.
What happens
An inverter pushes power into the grid. To do that, it has to make its own voltage slightly higher than the grid's. If the voltage at the inverter is already high, it goes above the limit set by the standard, and then it is obliged to switch off.
That limit is around 253 volts, measured over ten minutes. So your inverter is doing nothing wrong: it is following the rules.
Why the voltage at the inverter is higher
Three causes, usually in combination:
1. Loss in your own cable. The longer and thinner the cable from the meter cupboard to the inverter, the more the voltage at the inverter rises while it feeds back. This is the cause I come across most often, and the only one you can solve yourself.
2. The neighbourhood feeds back a lot. If the whole street is full of panels, the grid voltage rises on sunny afternoons. That is a matter for the grid operator.
3. The connection is light. An old connection or a long branch to an outlying home causes more loss.
What you can establish yourself
- When does it happen: always around midday, or at random?
- What exactly does the message say: note the code and the text
- How many volts the app or the display shows at the moment it switches off
Those three details tell me almost immediately where the problem is. Take a photo of it, that is quicker than typing it out.
What can be done about it
| Cause | Solution |
|---|---|
| Cable too thin or too long | Heavier cable, or the inverter closer to the meter cupboard |
| Everything on one phase | Spread over three phases |
| High grid voltage in the street | Report to the grid operator, who can adjust the transformer |
| Bad connection or termination | Retest and tighten, sometimes a burnt terminal block |
Without measurements you rarely get anywhere with the grid operator; with them you usually do.
Adjusting the voltage limit in the inverter is not a solution. You are not simply allowed to do it either: that limit is there to protect the grid.
Reporting it to the grid operator
If my measurements show it is not your installation, I record that in a test report over several days. With that report the grid operator takes a report seriously, and they can change the setting of the local transformer. Without measurements you rarely get anywhere.
What else you need to know about your connection is in the grid congestion check and in solar panels and the consumer unit.
From my own work
A customer in Nuth had an installation that stopped around half past one every sunny day. The inverter reported grid voltage too high. The cable from the meter cupboard to the loft was 2.5 mm² over more than thirty metres. After replacing it with 4 mm² the measured voltage at the inverter dropped by almost five volts and the switching off stopped. The yield went up by about a tenth.
When to call an electrician
- The inverter switches off on sunny days, often around midday
- The message is about grid voltage, grid or overvoltage
- The inverter is warm or shows an error code that comes back after a restart
I measure what the voltage at the inverter actually does and where the loss is. See also the 24/7 fault service.
Frequently asked questions
Can I raise the voltage limit in the inverter?
You are not simply allowed to, and it is not a solution. That limit protects the grid and your equipment.
How do I know whether it is my cable or the street?
By measuring at the inverter over a whole day. If the voltage drops as soon as it stops feeding back, the loss is in your own cable.
What does the grid operator do if I report it?
With a test report they can change the setting of the local transformer. Without measurements you rarely get anywhere.
Further reading
A dynamic contract and a home battery: is it worth it
With a dynamic contract the battery can charge when electricity is cheap. That works, provided you let it be controlled automatically.
The net metering scheme is ending: what changes for my panels
Your panels keep generating just as much. What changes is the value of the electricity you feed back.
Feed-in charges: why you pay for your own electricity
More and more suppliers charge for feeding your solar power back into the grid. Your bill shows what that costs you.
Questions and comments
Ask your question below. Ask before 17:00 on a working day and you get an answer from Kevin himself the same day. No account needed, and your email address does not appear on the site.