A balcony solar panel that isn’t producing normally comes down to one of five things: too little light, a socket circuit that’s switched off or tripped, a monitoring fault rather than a generation fault, shading or dirt across the panel, or an inverter that has disconnected itself from the grid on purpose. That last group catches people out.
Work through them in that order and you’ll usually find the answer.
One piece of framing first. Compliant plug-in solar can be lawfully sold and used in Great Britain from 27 August 2026 under SI 2026 No. 848. If you’ve already got a solar kit running, which side of that line it sits on changes what support you can expect. Our summary of what changes on 27 August 2026 has the detail.
Two things never to do while diagnosing
Don’t open the inverter, and don’t touch the fixed wiring or the consumer unit beyond reading the labels. Everything here happens from the socket outwards. Anything further in is a job for a qualified electrician.
The Fault That Usually Isn’t One
Start here, because it explains several of the symptoms people report as faults. Every grid-connected micro-inverter has to shut itself down when the mains supply goes away. The Interim Product Specification covers this at clause 6.2.3.3, Anti-Islanding Provisions, and its note records what the network standard is doing: "According to G98, interface protection and loss-of-mains protection are intended to disconnect the generating unit from the network during over/under voltage, over/underfrequency and loss-of-mains conditions."
Clause 6.2.3.3.3 sets the timing. "The inverter shall automatically disconnect from the mains supply within 100 ms", and "the voltage at accessible plug pins shall decrease to below 34 V within 100 ms following disconnection from mains supply". That behaviour is verified during type testing, which is what a listing on the ENA Type Test Register evidences.
So all of these are a compliant device working as designed:
- A street power cut and no solar power. The unit drops out in a tenth of a second and stays out until the grid returns. This isn’t a backup supply or an off-grid solar setup. To power your home through a cut you need battery storage on a different route.
- Nothing generated after you switched the circuit off. Kill that circuit at the consumer unit and the balcony solar system has no grid to synchronise with.
- Brief dropouts during voltage or frequency excursions on your street. The protection watches over and under voltage and frequency as well as loss of mains.
- A delay before generation resumes. The device needs a stable supply again first.
Never try to prove anti-islanding works by throwing the main switch. It interrupts supply to the whole property and the specification doesn’t ask it of you. For the mechanism, see how plug-in solar panels work.
No Output At All
When you plug in solar panels and nothing happens, and the grid is up, work outwards in this order, using your eyes and the manufacturer’s manual.
- Is the socket live and switched on? Plug a lamp into it. A switched socket knocked off by a vacuum cleaner lead is worth ruling out first.
- Has the circuit breaker tripped? Find the breaker or RCBO feeding it. The specification’s own guidance gives the method: outlets on the same breaker are on the same circuit, and you identify them by seeing which lose power when that breaker is switched off.
- Is the plug fully home? A compliant device has a factory-fitted BS 1363 plug with a fuse rated no higher than 5 A. If you suspect the fuse, follow the manufacturer’s instructions and use the rating they specify. Never fit a higher one.
- Are the DC connectors seated? Check visually. The specification requires manufacturers to tell you that DC connectors "shall not be disconnected under load and that the AC supply shall be turned off before disconnecting DC connections", so unplug the device from the socket before you go near the DC side.
- Is there enough light? A panel in winter dusk produces almost nothing.
If all five check out and the installation still delivers nothing on a bright day, that’s a warranty conversation with the manufacturer or retailer, not a job for an installer.
Output Far Below What You Expected
Low output is a common complaint and rarely a fault. Solar energy arriving on a UK balcony is seasonal and modest, and three things decide how much electricity the panels produce.
The output is capped, and the panel rating isn’t the cap. Plug-and-play solar of this class is sold across Europe as 800W kit, and the UK device ceiling is a declared maximum apparent power of 800 VA with current at the point of connection limited to 3.5 A. You’re allowed up to 2,000 W of DC panels behind that, so a kit can be rated well above what it pushes into your ring. Panel ratings are measured under standard test conditions, a laboratory reference of 1,000 W/m² at 25°C that a UK balcony rarely sees.
Season. Our own PVGIS-based modelling for a south-facing London system puts roughly 60% of annual generation in the six months from April to September, with June producing close to five times December’s figure. On cloudy days the panels generate electricity from diffuse daylight rather than stopping, but at a fraction of clear-sky figures. The detail is in our guide to balcony solar in winter.
Orientation and tilt. A near-vertical panel on a balcony railing sits a long way from the annual optimum, and east or west facing costs you again. A rooftop solar installation on a pitched roof starts closer to the ideal. See the best direction for balcony solar panels for what each aspect delivers.
Shading, and Why a Small Shadow Costs So Much
Partial shade is disproportionately expensive. A shadow across one corner of a cell string pulls that string down, and depending on how the module and inverter are arranged it can cost more than the shaded area.
The usual culprits are the railing, a downpipe, the balcony above, a neighbouring block that bites in winter when the sun sits low, and a washing line nobody thinks about. Shade that moves through the day is easy to miss, because the kit looks fine when you check it.
Microinverters are the mitigation. One per panel, or independent MPPT channels within a single microinverter, lets a shaded panel drop its own output without pulling its neighbour down with it. Our inverter types guide covers how the options differ. If your kit puts two panels through a single tracking channel, expect shade on one to cost you on both.
Dirty Panels, Bird Mess and Winter Debris
Uniform dust costs a little. Concentrated soiling costs more, because a solid opaque patch behaves like shade rather than grime. Bird droppings and a leaf plastered on by rain make solar panels produce a sudden step change in the data, not a gradual decline.
The specification requires manufacturers to supply "recommended intervals and procedures for inspection and maintenance, including visual checks of fixings, cables and connectors", and "instructions for safe cleaning where applicable". Use those: some backing materials and coatings don’t tolerate detergents or pressure.
The safety point matters more than the cleaning point. A first-floor balcony is high enough to kill you, so clean from inside the guarding with both feet on the floor, or don’t clean it at all. If the face can only be reached by leaning over the rail, change the mounting position instead.
The App Won’t Pair, or the Inverter Shows Offline
Monitoring and generation are separate paths. Losing the first tells you nothing certain about the second, and plenty of "offline" alerts arrive while the kit is quietly producing.
The specification requires the device to have "an interface, either integrated on the device or accessible via a third-party device like a mobile phone, that can display status information and error messages to users together with mitigation guidance". The documentation also has to carry an "explanation of indications of operating status" and a "procedure to follow in the event of faults or defects". Read both before any forum: error codes are manufacturer specific.
Common causes of a comms failure, not a generation failure:
- The unit is outside and the router is inside, through a masonry wall. Signal strength at the balcony is often the whole story.
- A dual-band network under one name. Many home routers publish 2.4 GHz and 5 GHz under a single network name, and a device that can only join 2.4 GHz may fail to pair. Check what the manufacturer says about band selection.
- It’s dark. Many micro-inverters take their own power from the panels, so they stop reporting at night. Confirm the expected behaviour in your documentation before treating an overnight gap as a fault.
If the app pairs but reports an error code, send that code to the manufacturer’s support channel instead of guessing at it.
The RCD or RCBO Trips
Of everything on this page, this is the symptom where the right response is to stop.
An RCD detects current leaking out of a circuit and breaks the supply. An RCBO combines that with overcurrent protection. When either operates it has measured something, and repeatedly resetting it is not diagnosis.
The specification handles the interaction from the product side. A plug-in solar device "shall be designed such that it does not adversely affect the operation of upstream residual current devices", and any smooth DC residual current fed to the mains must not exceed 5 mA in normal operation or under relevant fault conditions. That limit exists because older protective devices can be desensitised by DC leakage from equipment on the circuit, a category that includes plug-in EV chargers, IT equipment and power supplies as well as solar. The wiring regulations sit behind all of it: the specification requires compliance with BS 7671:2018+A4:2026.
There’s one self-test the specification does put on you, and it runs the other way round. Press the test button on the RCBO periodically while the plug-in solar unit is producing power. If it doesn’t trip immediately, the guidance is to "contact a competent professional electrician to discuss replacing the RCBO with a more modern unit".
Two things you must not do. Don’t fit an RCD adaptor, a multi-way adaptor or an extension lead to work around it, because all of those are prohibited for this connection. And don’t use an outlet that’s damaged, degraded or non-compliant: the specification says users should seek inspection by a qualified electrician wherever there’s doubt about the condition or suitability of the installation. Our balcony solar electrical safety guide covers RCD types and consumer unit age in full.
Stop and call a registered electrician if
The RCD or RCBO trips when the device is plugged in or generating. The socket is warm, discoloured or scorched. There’s a smell of hot plastic. The lead, plug or a DC connector is damaged. Your consumer unit uses rewireable fuses, or you can’t tell what protection the socket circuit has.
Where DIY Diagnosis Stops
The appeal of plug-in solar is that you generate your own electricity from a solar panel system you can connect yourself. It’s still a renewable generator tied to your mains supply, so it doesn’t follow that every fault is a DIY solar job.
Safe for you: everything outside the socket. Checking light, shade and soiling. Reading status indicators and error codes. Following the manufacturer’s documented procedure for faults and defects.
Not safe for you, ever: opening the inverter, working on fixed wiring, altering the consumer unit beyond operating a labelled switch, or bypassing a protective device that has operated. None of that becomes acceptable because the device itself needed no professional installation.
If the answer needs the circuit tested and not just the kit checked, that’s a registered electrician’s job. Ask for the circuit and its protective device to be tested, and say a generating device is plugged into it.
When It’s the Kit, Not Your Installation
Some kits can’t be diagnosed usefully because there’s nothing behind them. Compliance under the UK route runs through two gates: a declaration on the product that it complies with the specification, and a listing on the ENA Type Test Register assessed and confirmed as compliant. Submitting a device for registration "shall not, in itself, be regarded as demonstrating compliance". As at 11 August 2026 four devices were listed under the register’s "Plug-in Solar" device type, from GoodWe, Anker and InstaGroup, and all four were assessed Non-compliant, so nothing had been verified compliant at that point. ENA’s own wording is that such a device "cannot be deemed compliant at this stage" and will be reviewed again.
A device with no verified UK listing has no UK type-test evidence behind its anti-islanding behaviour, and often no UK support route or installer to call either. If the kit came from a European retailer, check the plug first: the UK route requires a factory-fitted BS 1363 plug, and a Schuko plug on an adaptor sits outside the specification. Only one device per household can be connected while the current G98 restriction stands, so a second unit isn’t a diagnostic step either.
Our certification tracker carries the current state of the register, and the plug-in solar compliance checker runs a kit against the full set of limits.
Frequently Asked Questions
Why is my balcony solar panel not producing power? Check in this order: light levels, whether the socket is switched on and its breaker hasn’t tripped, whether the plug is fully home, whether the panel is shaded or soiled, and whether the app is reporting a comms fault instead of a generation fault. A device that shut down during a power cut was doing what it’s required to do.
Does plug-in solar work during a power cut? No. Anti-islanding protection disconnects the inverter from the mains supply within 100 ms of losing it, and the specification requires the voltage at accessible plug pins to fall below 34 V in the same window. That protects anyone working on the network. A plug-in device isn’t a backup supply and can’t be made into one.
What are the common reasons for low balcony solar output? Season and sun angle first, then orientation and tilt, then shading, then soiling. The output ceiling matters too: a compliant unit is capped at 800 VA and 3.5 A whatever the panels behind it are rated at, so a high panel rating won’t give a high peak.
Why does my inverter show offline at night? Many micro-inverters draw their operating power from the panels, so they stop communicating once there’s no light. Check your documentation for the expected overnight behaviour first. An overnight gap with normal daytime figures either side is normally the design working as intended.
My RCD trips when the solar is generating. Is that normal? No, and it shouldn’t be reset repeatedly. A compliant device is required not to adversely affect upstream residual current devices, with smooth DC residual current to the mains limited to 5 mA. Unplug the device, leave the circuit alone, and get a registered electrician to test the circuit and the protective device.
When should I stop and call an electrician? As soon as the problem involves the fixed installation instead of the device. That means any RCD or RCBO tripping, a warm or discoloured socket, a burning smell, damaged cabling or connectors, or a consumer unit whose protection you can’t identify. Never open the inverter, and never work on a circuit yourself.
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