Solar Panels Not Generating? Step-by-Step Diagnosis

You have just checked your solar app and it is showing nothing. Or the inverter has gone dark and silent. That sinking feeling is understandable — but before you call your installer, work through these seven checks. The large majority of apparent zero-generation faults turn out to be something simple: a switched isolator, a standby mode, or a monitoring dropout rather than a real system failure.

Step 1: Check the inverter

The inverter is the box usually mounted on a wall near your electricity meter or consumer unit (fusebox). It converts the DC electricity your panels produce into AC electricity your home can use. Start here.

Look at the LED indicator and display:

• Solid green light — the inverter is working normally. If you are seeing zero on the display during daylight, check the time: most inverters enter standby automatically after sunset and do not "switch on" until there is enough irradiance to generate usefully. On an overcast morning this can be as late as 9–10am.
• Flashing green — the inverter is running but output may be low. This is normal during low-light conditions.
• Orange or amber — a warning state. The inverter is operational but something is outside its normal range. Common causes include a slight grid voltage fluctuation or a momentary communication error. Note any code shown.
• Red light, or an error code on the display — the inverter has shut down. Write down the exact code shown. Your installer can look this up remotely and it saves time on any subsequent callout.
• No lights at all — the inverter has no power. Move to Step 2 first.

If the inverter is simply dark and silent during daylight hours, it almost certainly has no power reaching it — which means an isolator is off somewhere. Move straight to Step 2.

Step 2: Check the isolator switches

A solar installation has multiple isolator switches — physical switches that interrupt the circuit at different points. Any one of them being in the off position will prevent the system from generating. They are sometimes knocked off accidentally during cleaning, storage work in a loft, or a visit from someone who was not expecting them to be there.

There are typically three isolators to check:

1. The AC isolator — usually a red or grey rotary switch mounted on the wall beside or below the inverter, or sometimes on the consumer unit itself. It is labelled something like "solar AC isolator" or "PV array". Make sure it is turned to the ON position.

2. The DC isolator near the inverter — a second switch, also usually close to the inverter, that isolates the DC cables coming down from the panels. It may be black or red and is often labelled "DC isolator" or "PV DC". Again, check it is ON.

3. The DC isolator on the roof — there is often a third isolator mounted on the roof just below the panels, or in the loft space near where the cables enter the property. You should be able to see this from inside the loft hatch without going onto the roof itself. If it is accessible and safely visible, check it is ON. If you cannot see it without climbing or reaching into an unsafe space, leave it alone.

If you find any of these switched off, turn it back on and wait two or three minutes for the inverter to go through its startup sequence. If it starts up normally, the problem is solved. If it trips off again within a few minutes, do not keep resetting it — call your installer, as repeated tripping indicates a fault the switch is responding to.

Step 3: Check the monitoring app

It is easy to confuse "the app is not showing generation" with "the system is not generating". They can be two entirely different problems.

Signs it is a monitoring issue, not a generation issue:

• The inverter has a green light and the display shows a positive generation figure, but the app shows zero or is not updating
• The app shows "device offline", "no connection", or a grey/dashed status
• Your home WiFi was reset recently, or the router was moved
• The app has not updated since a specific date — possibly the date your broadband went down

What to try:

Check that the monitoring device — usually a small dongle plugged into the inverter, or a data logger box nearby — has its indicator lights on. If it has gone dark, try unplugging it from the inverter's data port, waiting 30 seconds, and plugging it back in. Give the app five to ten minutes to reconnect.

If your WiFi password changed recently, the monitoring device will need to be re-paired to your network. Manufacturer apps (SolarEdge, Solis Cloud, GivEnergy, SolarMan) all have a re-pairing process — search for your inverter brand plus "reconnect WiFi" for the specific steps.

The important distinction: if the inverter display shows generation figures and the display is incrementing as you watch it, your system is generating electricity. The issue is monitoring only, and there is no urgency about a professional visit.

Step 4: Check the obvious — weather and time of year

Before going further, step outside and look up.

UK solar panels generate from diffuse daylight, not just direct sunshine — but there is a wide spectrum between "a bit overcast" (you will still see some generation) and "heavy cloud cover all day" (output may be 10–20% of your sunny-day figure, and on a small system that can look like almost zero).

A few things worth confirming:

• Is it actually a bright day? Solid grey cloud, fog, or rain will dramatically reduce output. Generation of 0.3–0.5 kWh on a completely overcast short winter day is not a fault.
• What time is it? In December, effective solar generation in the UK is compressed into roughly 8am–4pm, with the peak between 11am and 2pm. Checking at 8.30am in January and seeing 0.1 kWh is not a fault.
• Has it been snowing? Snow sitting on panels blocks generation almost entirely. It usually slides off once temperatures rise slightly. Do not attempt to clear it yourself by going on the roof.

If you are checking on a clear, bright spring or summer day between 10am and 3pm and still seeing zero, move on to the remaining steps.

For more on what normal seasonal output looks like, the solar winter performance audit article covers monthly expectations in detail.

Step 5: Check the consumer unit

Go to your fusebox (consumer unit — the grey or white box on the wall with the row of switches). Look for a circuit breaker labelled "solar", "PV", "generation", or similar. It may be a dedicated RCBO (a combined RCD and circuit breaker in a single unit) rather than a standard MCB.

If this breaker has tripped — it will be in a middle or off position rather than firmly up — try resetting it once by switching it fully off, then back on.

• If it stays on and the inverter restarts, monitor for the rest of the day. A single trip in isolation can be a transient grid event.
• If it trips again within a few minutes or within the same day, do not keep resetting it. A repeatedly tripping circuit breaker is telling you something is wrong. Call your installer.

Step 6: Check for new shading

Shading is a surprisingly common cause of sudden drops in generation, including what can look like near-zero output if the shading is severe enough or affects panels feeding a string where a microinverter or string optimiser has also failed.

Think about what has changed near your property in the last few weeks or months:

• Tree growth — trees that were bare in winter can cast significant shade once in leaf. If your panels are close to a tall deciduous tree, spring and summer may actually produce less than you expect because of new leaf cover.
• New buildings or extensions — a neighbour's extension, a new dormer conversion, or a newly built property nearby can cast shadows that did not exist when your system was designed.
• Temporary obstructions — scaffolding on an adjacent property, a large vehicle parked nearby, or a satellite dish or aerial that has been moved or added since installation.

Go outside and look at your panels from the garden or street. Is anything casting a shadow across them during the part of the day when you would expect peak generation? Even partial shading on one panel in a string system can reduce output from the whole string significantly.

Step 7: Check the generation meter

Many solar installations include a separate generation meter — a small digital meter usually mounted near the inverter that records every kilowatt-hour your system produces. Unlike the monitoring app, this meter records directly from the system and does not depend on WiFi or a data connection.

Find the generation meter and note the reading. Come back in an hour. If the number has incremented — even slightly — your system is generating electricity. The problem is therefore in the monitoring or app connection, not in the panels or inverter themselves.

If the meter shows a positive number and is incrementing but your energy supplier's app or smart meter display shows nothing, it is likely a SEG (Smart Export Guarantee) metering or reporting delay rather than a generation failure.

If the generation meter has not incremented at all during an hour of reasonable daylight, that is a genuine generation fault — proceed to the next section.

When to call your installer

Work through all seven steps above before calling. When you do call, have the following ready — it makes the conversation significantly more useful:

• The exact error code shown on the inverter display (if any)
• Which isolators you checked and whether they were on or off
• Whether the generation meter is incrementing or not
• The date the problem started (or the last date the app showed normal generation)
• What the weather has been like over the past few days

Call your installer if:

• The inverter shows a persistent red light or error code that does not clear after a restart
• A circuit breaker trips more than once after being reset
• You can smell burning from anywhere near the inverter or electrical enclosures
• You can see any physical damage — cracked panels, damaged cables, discolouration around any electrical box
• The generation meter has not incremented at all on a clear sunny day after confirming all isolators are on
• You cannot identify the cause from any of the steps above

If your system is under the MCS installer warranty (typically two years for workmanship), the installer is obliged to investigate at no charge. If the inverter is under manufacturer warranty — usually ten years — the manufacturer will typically cover the repair cost, though you may still need to pay your installer's callout fee to conduct the diagnosis.

If your installer is unresponsive

If you cannot get your original installer to respond — for example, they have ceased trading — you have options:

• MCS complaints process — if your system was MCS certified, the MCS scheme has a complaints process and can help pursue warranty claims even if the original installer has gone under.
• RECC (Renewable Energy Consumer Code) — if your installer was a RECC member, they have a consumer code and an Alternative Dispute Resolution (ADR) scheme.
• Independent inspection — any MCS-certified solar installer can carry out a system inspection. They are not obliged to use your original installer. A paid inspection (typically £150–£300 plus VAT) will give you a written report you can use to support any warranty claim.

The installer went bust article covers this situation in more detail, including how to trace warranty obligations.

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