Troubleshooting
Find out why your solar panels are producing less electricity than expected before calling an engineer.
Your solar panels output changes significantly with the seasons, so lower generation in winter is completely normal. A UK solar PV system can generate several times more electricity in summer than in winter because winter has shorter daylight hours, lower sun angles and more frequent cloud cover. For example, generating only a fraction of your summer output in January is not necessarily a sign of a fault.
Compare monthly solar generation in your inverter monitoring app rather than comparing individual days. Month-to-month trends give you a much better indication of whether your solar PV system is performing normally.
Look at the status light and display on your solar inverter. A normal operating indication generally means the system is producing electricity correctly, while an amber, red or fault indicator may mean the inverter needs attention. The exact meanings vary by manufacturer, so check your inverter manual rather than assuming every colour means the same thing.
If the inverter displays a fault code or error message, record the code and check the manufacturer’s troubleshooting guidance. Do not open the inverter or carry out electrical repairs yourself. Your system’s commissioning and handover documentation should include the manufacturer’s instructions, shutdown procedures and guidance on what to do if the system fails.
Open your solar monitoring app and compare generation over a meaningful period with the same period in previous years. A small difference is normal because weather, sunshine levels and shading vary from year to year. A persistent and substantial fall in solar panel output, particularly when weather conditions are broadly comparable, is worth investigating.
Rather than relying on a single day, compare several weeks or the same month across different years. This can help distinguish normal weather variation from genuine solar PV underperformance.
Shading is a common cause of reduced solar panel generation, and it can change after installation. Trees grow, neighbouring buildings change and new extensions, aerials or other structures can cast shadows across your roof.
Walk around the property and look at the roof from different angles throughout the day. Compare what you see with the surroundings when your solar panels were installed. New or increased shading can reduce solar generation, particularly when it falls across multiple panels.
If your solar installation was installed under the Microgeneration Certification Scheme (MCS), check that your installation documentation and certificate are available. MCS-certified installations should be formally commissioned and handed over with documentation including the system performance estimate, key equipment information and commissioning records.
Rather than paying someone simply to “restore” an MCS registration, contact your original installer first if you cannot find your certificate or installation records. If the installer is no longer operating, contact MCS or an appropriately certified installer for advice on what documentation is available and what needs to be done.
Find your solar commissioning report, handover pack or original installation documents and look for the estimated annual system generation. MCS standards require the installer to provide an estimate of system performance as part of the commissioning and handover documentation.
Compare that estimate with your actual annual solar generation, but allow for differences in weather and operating conditions. Being below the original estimate does not automatically mean your system is faulty. If generation remains significantly below expectations after accounting for factors such as shading and weather, arrange a professional inspection with a qualified solar PV installer. A specialist can check the panels, inverter, electrical connections and overall system performance.