[Inverter shutting down in the middle of the day]what to check

A system that generates happily in the morning, drops out around midday and comes back later is the commonest complaint in this category, and the usual explanation has nothing to do with your equipment. Every grid-connected inverter in Great Britain carries interface protection that must disconnect it when the supply voltage or frequency goes outside set limits. For a domestic system the limits come from the Energy Networks Association’s Engineering Recommendation G98, which covers generators up to 16 amps per phase — about 3.68 kilowatts on a single phase; larger systems fall under G99. G98’s settings are an over-voltage trip at 262.2 volts held for one second or 273.7 volts for half a second, an under-voltage trip at 184 volts for two and a half seconds, and frequency trips outside 47.5 to 52 hertz. Those sit above the legal supply range, which is 230 volts plus 10 per cent and minus 6 per cent — 253 volts down to 216.2 volts — under the Electricity Safety, Quality and Continuity Regulations 2002, and G98 explains why: the settings allow for the voltage rise inside your own installation when you export, and it is the distribution network operator’s responsibility to keep the supply at your terminals within the statutory limits. That last sentence is the one to hold on to.

The mechanism explains the timing. An inverter exports by holding its output voltage a little above the grid’s; that difference is what makes current flow outwards, and G98 acknowledges it as voltage rise within the customer’s installation. Solis put the practical version in their installer article on their OV-G-V grid over-voltage codes: a trip once or twice a day is caused by an unstable grid, continuous tripping needs investigating, and the impedance of the cable run between the inverter and the meter is on their list of things that produce it. Put several exporting systems in one street on a bright afternoon and the local voltage climbs; when it reaches a limit, inverters disconnect, the voltage falls because they have stopped pushing, and they reconnect, which is why the pattern is often intermittent rather than a clean stop. That street-scale picture is the usual explanation rather than a sentence any manufacturer publishes, but the physics it rests on is in G98 and in Solis’s article.

The useful signals are these: it happens around midday on sunny days and not on dull ones, it may have started after neighbours had panels fitted, and the event in your app history names the grid or the voltage rather than insulation, isolation or arcing. Report it to your distribution network operator, not your electricity supplier — a different organisation, determined by where you live rather than chosen. Investigating a voltage complaint is a regulated standard of service for a distributor: under the Electricity (Standards of Performance) Regulations 2015 they must either send an explanation within five working days or offer a visit within seven, and pay you a fixed sum if they miss it. Ohme publish the same escalation for chargepoints and add a detail that applies just as well here: an operator needs to monitor over several days rather than take one reading, because voltage fluctuates through the day and night. What separates this from a genuine fault is repeatability and pattern. A system that stops at unpredictable times, in all weather, or that shows an insulation, isolation or arc-related event in its history, is reporting something else entirely and that does need attention.

1. 1

   Look at the pattern in your monitoring app over a week. Midday drops on bright days with normal generation either side is the signature of a voltage problem on the network.

2. 2

   Find the event history in the app or portal rather than relying on the light on the inverter. The event name is what distinguishes a grid disconnection — grid voltage, grid frequency, over-voltage — from something on the DC side such as insulation, residual current or arcing.

3. 3

   Check whether it started around the time neighbours had solar fitted. More export in one street raises the local voltage for everybody on it.

4. 4

   Report it to your distribution network operator, not your electricity supplier. They own the cables and the substation, G98 makes keeping your supply within the statutory 216.2 to 253 volts their responsibility, and they are the only party who can adjust it. The Energy Networks Association runs a postcode lookup that names yours.

5. 5

   Ask them to monitor over several days rather than take a single reading. That is Ohme’s advice for chargepoints and it applies here for the same reason: voltage varies through the day and a one-off measurement can miss the peak entirely.

6. 6

   If the drops are unpredictable rather than midday, or the history shows insulation or residual current events, stop here and contact your installer instead.