Solar shutting down at midday, battery not discharging

Start in the app, not at the inverter

Very few domestic inverters have a screen any more. What you have is a coloured light on the unit and a fuller message in an app or monitoring portal, and the portal is where the event name or number actually lives. A light can only tell you that something happened, not which of a dozen things it was. So before anything else, find the event history — SMA's is in the Results menu of the inverter's web interface or the system logbook in Sunny Portal; Tesla's is the app's alerts with their exact notification wording; other makes are similar. The three complaints below are sorted by what that history shows, and two of them usually show nothing at all, which is itself the diagnosis.

Shutting down in the middle of the day

A system that generates happily in the morning, drops out around midday and comes back in the afternoon is the commonest complaint in this category, and the explanation is almost never your equipment. An inverter is required to disconnect if the grid voltage goes outside its permitted band, for the same reason a chargepoint does: equipment that keeps pushing into an out-of-range network makes the problem worse. The timing gives it away. An inverter exports by holding its output a little above the grid voltage, and several systems in one street doing that on a bright afternoon lift the local voltage until inverters begin dropping off. They wait, the voltage falls because they have stopped pushing, and they reconnect — which is why the pattern is intermittent rather than a clean stop.

Look at a week of the monitoring app. Midday drops on bright days, with normal generation either side and dull days unaffected, is the signature of a network voltage problem; if it began around the time neighbours had solar fitted, that fits too. Find the event in the history rather than trusting the light, because the event name is what separates a grid disconnection from something on the DC side. Then report it to your distribution network operator — the company that owns the cables and the substation, not your electricity supplier — and ask them to monitor over several days, since a single reading can miss the peak entirely. They do not charge to investigate or correct network voltage. Export limiting configured on the system is not a shutdown but is often reported as one; it caps output by setting.

If the drops are unpredictable rather than at midday, or the history shows an insulation, isolation or residual current event, stop here and read the DC section below instead.

A battery that will not discharge

A battery sitting at a percentage while the house draws from the grid looks like a fault and is usually a setting. Take them in order. A time-of-use tariff makes a system charge and hold deliberately, and a schedule set up months ago will not match a tariff that has since changed; look at what the system has been told to do before deciding it is not doing it. A backup reserve — Tesla publish it as a setting that keeps a floor of charge for a power cut — means the house cannot draw below that percentage, so the battery looks stuck there. A weather-anticipation mode overrides normal behaviour while it runs: Tesla's Storm Watch charges ahead of bad weather, and Solis publish export limiting as a named state. And on a dull morning there may simply not be enough generation to engage the battery; GivEnergy’s commissioning guidance says the inverter must be generating at least 180 watts to activate the battery, so you can see solar production and no storage activity with nothing wrong.

A settings explanation leaves no event in the history. A genuine communication fault between battery and inverter, or a battery management fault, normally does, with a name. If there is one, contact your installer rather than trying to clear it, and do not update firmware to try to fix it — GivEnergy's instruction is not to update firmware while the battery is in a fault state or not operating correctly. On a system in warranty that visit should be at no cost.

Generating less than expected

Most of this is weather and the way panels are rated. The headline figure is measured at a standard test condition — a set irradiance and a set cell temperature — that a British roof rarely meets, and output falls as cells heat up, which is why a clear March day can beat a hazy July one. Shading changes with the season too: a system commissioned in summer can be shaded by the same tree in autumn when the sun is lower. Compare against the same period last year rather than against the rated figure, look for shade on the array around midday, and check whether export limiting is set. An inverter that goes dark overnight is normal — SolarEdge publish a night mode below six volts of input, and microinverters stop communicating in low light. What is worth acting on is a step change in the monitoring rather than a drift, or one string or section down against the others in the per-string data. That is an installer's visit with the monitoring data, not a reason to go near the roof.

The one reset, and what it does not do

There is one owner-safe action on a solar system: switch the alternating current side off at its breaker, wait, switch it back on, and let the inverter run through its start-up checks. Understand exactly what that does. It makes the inverter safe to stand next to. It does not make the panels, or the wiring between them and the inverter, safe — because there is no switch that stops a panel generating in daylight. GivEnergy's own fault guidance has the installer check that a string does not exceed 580 volts DC; that is the ceiling for a domestic roof, and an ordinary string in daylight sits at several hundred volts, more than anything else in the building. Direct current at that level is also less forgiving than mains, because there is no zero crossing to help an arc extinguish itself. Do not open the inverter and do not attempt to measure anything on the array. On the DC isolator the manufacturers differ: this site's cross-brand advice is not to operate it as a troubleshooting step, while GivEnergy's owner diagnostics guide does include switching the DC and AC isolators off to restart the inverter, with the instruction to contact the installer if unsure. If your manufacturer publishes that step for owners, follow their sequence exactly, and do not mistake it for making the array safe. The panels are still live page sets out the manufacturers' wording in full.

Installing this equipment means a new circuit, which is notifiable electrical work under Part P of the Building Regulations in England and Wales — the Welsh Approved Document names photovoltaic supplies outright — normally done by a scheme-registered electrician — which is not the same thing as gas being criminally restricted, and nobody should tell you it is. But the DC side is where the certification earns its keep, and it is where the owner's part ends.

When the DC side reports a fault

SMA publish the clearest wording in the category. Event 3501 is insulation resistance too low, and SMA say directly that the error is not caused by the inverter — it is in the DC installation — and that it can come and go with the weather, because damp finds its way into a connector or a cable that is dry the next afternoon. Event 3701 is residual current, and unlike the insulation event it trips a running system; SMA publish the threshold as a sudden jump of 30 milliamps or more. Their safety statement covers both, and it reaches further than people assume: danger to life due to electric shock, high voltages can be present in the event of a ground fault, and do not touch the cables, the substructure, the frame or the modules of the PV array. Not just the cables. There is no owner reset for either event and SMA do not offer one; their corrective measure for both is to contact your installer. Their diagnostic procedure says why: the insulation resistance can only be measured with a suitable device for safe disconnection and short-circuiting of the PV modules, and if no suitable device is available the measurement must not be carried out.

Other makes publish the same shape. SolarEdge's ground fault procedure has the switch off and then a five-minute wait for the input capacitors to discharge before AC and then DC are disconnected, and the work is a qualified technician's. Whatever the badge, an insulation, isolation or residual current event is the installer's, and the roof is nobody's until they have made it safe.

Powerwall and other batteries

Tesla publish no fault code list for the Powerwall. What they publish is a set of named app alerts, and one instruction repeated before every troubleshooting section: do not troubleshoot during a grid outage or in extreme weather conditions. The reason is specific. During an outage the Powerwall is supplying the house, so the wiring is live from the battery even though the grid is dead — Grid Outage is the system doing the job it was bought for, not a fault. On a Powerwall 3 the single light behind the logo is solid white in normal operation, flashing white when idle and heading for sleep, off when off or asleep, and flashing red for an inverter fault; Powerwall 3 Expansion units have no light at all, so an unlit expansion is not a fault. Breaker Open means a breaker has tripped and may simply need resetting once; if it trips again or there is heat damage at a connection, that is an electrician or a Tesla visit and should not be delayed. Tesla's position on the hardware is unambiguous: Powerwall 3 and Backup Gateway 2 are not user-serviceable and must be repaired by Tesla or a Certified Installer, and the deadfront cover inside the Gateway is not to be opened because exposed wiring can present a risk of electrical shock.

Right now

Switch off at the isolator or the breaker for that circuit rather than waiting for a call, and understand that on a solar or battery system this makes the alternating current side safe and leaves the panels and their wiring live while it is daylight. If you can smell burning or see scorching at the inverter, the battery or a connection, leave it isolated and do not use it again until it has been looked at. Do not go onto the roof.

What it costs

Nothing, for most of this guide. Network voltage is the distribution network operator's to investigate and correct, and they do not charge. A schedule, a reserve, a storm mode or a tariff mismatch is a setting. Where the code pages carry a bracket: a communication or battery management fault is an installer visit, up to about £300 and at no cost in warranty; an insulation or residual current event is an installer's inspection with the right test equipment at £120 to £600, the top end being a fault traced across several strings with roof access; an inverter that will not connect to the grid is nothing if it is light, weather or a tripped breaker, and up to about £300 once there is a DC-side event; a Powerwall breaker that keeps tripping, up to about £250 for the electrician's or Tesla's visit.

Sources

• SMA published articles on events 35xx (3501, 3503) and 37xx (3701), and SMA technical information on insulation errors in PV systems, including the safety statement and the diagnostic procedure quoted; SMA Sunny Portal and web interface documentation.
• Tesla Powerwall support (tesla.com/en_gb/support/energy/powerwall): the LED states, Powerwall 3 Expansion, the named alerts Breaker Open and Grid Outage, the grid-outage instruction, backup reserve, Storm Watch, and the non-serviceable statement.
• GivEnergy published guidance: the commissioning-portal note that the inverter must generate at least 180 W to activate the battery, the PV over-voltage check against 580 V DC, the owner diagnostics guide’s isolator restart, and the instruction not to update firmware in a fault state.
• SolarEdge published ground fault procedure. Solis documentation on export limiting.
• Approved Document P (2013) on notifiable work; the distribution network operators' responsibility for network voltage as described on this site's "Inverter shutting down in the middle of the day" page.
• Cost brackets are those on the code pages named, each with its own sourcing.