Solar Panels Not Generating: Troubleshooting Guide
Solar PV systems are remarkably reliable, but occasionally something goes wrong and generation drops off — sometimes suddenly, sometimes gradually. This guide explains the most common causes, what you can safely check yourself, and when to call in an MCS-certified engineer.
Welsh Solar provides repair and diagnostic services across Wales for systems we did not originally install. If you need urgent help with a system that has stopped working, call us on 0330 223 7664.
First checks you can do safely
Before anything else, check whether the system is actually offline or just appearing offline in the monitoring app. Monitoring platforms sometimes lose connection to the inverter while the system itself continues to generate normally. Walk to the inverter and look at the status lights or screen — most modern inverters show clearly whether they are producing power, in fault, or shut down.
If the inverter shows a fault or has no power at all, check whether your AC isolator (usually next to the inverter or in the consumer unit) has tripped. A tripped breaker is the most common simple cause of a stopped system. Reset it once; if it trips immediately, do not keep trying — call an engineer.
Common causes of reduced generation
Gradually declining generation is usually caused by panel soiling — bird droppings, moss growth, or accumulated dust. A panel cleaning service can restore lost output, particularly on installations with low pitch angles where rain does not naturally clean the surface. We offer panel cleaning as a standalone service across Wales.
Sudden drops in generation are more likely to be electrical: a tripped breaker, a faulty inverter, a damaged DC connector, or a string fault caused by water ingress at a panel junction box. These require diagnostic equipment to identify properly, and we always recommend professional diagnosis rather than guesswork.
- Tripped AC isolator (most common cause)
- Inverter fault or failure
- DC connector water ingress or failure
- Panel soiling or moss growth
- Shading from new vegetation growth
- String or panel failure (rarer)
- Monitoring fault rather than actual system fault
When to call an engineer
Anything beyond checking and resetting the AC isolator needs an MCS-certified electrician with solar-specific diagnostic equipment. Solar DC systems can carry hundreds of volts even when isolated from the grid, and the electrical work involves specialist tools and safe-work procedures that domestic electricians may not be trained on.
For systems still under their original warranty, call the original installer first if they are still trading. They have an obligation to honour the warranty terms. For systems out of warranty, or where the original installer has ceased trading (sadly common in this industry), Welsh Solar provides diagnostic and repair services across Wales.
Our diagnostic and repair process
A typical diagnostic visit takes 60-90 minutes and includes an electrical check of all isolators and protective devices, a string-level test on the DC side, an inverter status check including stored fault history, a check of monitoring connectivity, and a brief visual inspection of accessible parts of the array. We charge a flat call-out fee for the initial visit and provide a written report with our findings.
If the issue is straightforward — a tripped breaker, a failed DC connector, a contamination issue — we usually repair it on the same visit. Inverter replacements and other significant repairs are quoted separately, and we always provide a written quotation before any major work begins.
Frequently asked questions
How do I know if my solar is actually broken?
Look at the inverter display or status light. If it shows no power or a fault code, the system has a problem. If it shows normal output, the issue may just be the monitoring app losing connection.
Is it safe to investigate my own solar system?
It is safe to look at the inverter display and check the AC isolator. Anything else — opening enclosures, working on the DC side, going on the roof — needs a qualified solar engineer.
Do you repair systems you did not install?
Yes. We provide diagnostic and repair services across Wales for any solar PV system, regardless of who installed it originally.
How much does a diagnostic visit cost?
We charge a flat call-out fee for the initial diagnostic. The exact cost depends on location; please call 0330 223 7664 for a current quote. Repairs are quoted separately.
My original installer has gone out of business. What now?
This is unfortunately common. We can take over service for systems originally installed by ceased-trading companies and provide ongoing support. Manufacturer warranties on panels and inverters often remain valid even if the installer is no longer trading.
Preventive measures to reduce future faults
Many faults that cause solar systems to stop generating can be prevented or detected early through routine maintenance. We recommend a basic service every two to three years, which includes electrical testing of all isolators and protective devices, a visual inspection of accessible parts of the array, a check of monitoring connectivity and data, and panel cleaning if required.
For systems with batteries, more frequent service is appropriate — typically annual — because battery systems are more complex and benefit from firmware updates and cell balancing checks. Our service plans cover both PV-only and PV-plus-battery systems with appropriate visit frequencies and reporting.
The cost of routine service is small compared to the cost of an unexpected major fault and the lost generation while it is being diagnosed and repaired. Customers who service regularly experience significantly fewer unscheduled callouts than those who do not.