Why Has My Solar Output Dropped? (UK 2026)

Updated: June 2026 • Energy Solutions NW This guide covers why solar output drops — season, dirt, shading, degradation and faults — and how to tell which it is, for NW homeowners.

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Read the Pattern First

Before assuming the worst, look at how the output has dropped — the shape of the drop usually points to the cause.

• • Gentle dip over weeks in autumn/winter: almost always normal seasonal change.
  • Drop only at certain times of day: usually shading.
  • Sudden drop that stays low: more likely an inverter, wiring or panel fault.
  • App shows low but your bill looks normal: often a monitoring glitch, not a real drop.

Keeping a rough sense of your usual monthly generation makes these patterns far easier to read.

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Season and Weather

By far the most common reason for lower output is simply the time of year. UK solar generation is much higher in summer than winter — shorter days and lower sun mean far less to work with in the darker months. A big difference between June and December is completely expected. Counter-intuitively, very hot days can also reduce output slightly — panels are a little less efficient as they heat up. Our guide on whether solar panels work in winter explains the seasonal side.

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Dirt and New Shading

If the drop isn’t seasonal, the next things to rule out are dirt and shade — both block light from reaching the cells. Soiling from dust, pollen, leaves or bird droppings can shave off a few percent, sometimes more if it’s heavy. A quick visual check often shows whether the panels need a clean. New shading is a sneakier culprit: a tree that’s grown, a new extension, or a neighbour’s building can cast shade that wasn’t there before. On many systems, shading one panel drags down others on the same string. Our cleaning guide covers the soiling side.

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Natural Degradation

All solar panels lose a little output as they age — this is normal and built into their performance warranties. Typical degradation is only a fraction of a percent per year, so many panels still produce around 80–85% of their original output after 25 years. Because it’s so gradual, degradation shows up as a slow decline over many years — not a sudden drop. If your output fell quickly, degradation isn’t the cause.

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Inverter and Other Faults

A sudden drop that stays low points more towards a fault — and the inverter is the usual suspect. Because the inverter handles all your generation, a fault can cut output sharply or stop it entirely, often with an error code on the display. Less commonly, wiring problems or panel-level faults like micro-cracks can be behind it. Our guide to common solar panel faults covers how these show up and how they’re diagnosed.

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What to Do

A simple, safe order of checks will get you a long way:

1. 1. Consider the season: is this just a normal winter dip?
   2. Look at the panels: any obvious dirt, droppings or new shading?
   3. Check the inverter: note any error code or warning light.
   4. Compare to last year: is output really down on the same month previously?
   5. Call a professional if there’s an error code, no clear cause, or the drop is significant.

As always, don’t attempt electrical checks or roof work yourself — the system carries high voltage in daylight.

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Why Choose a Professional Installer?

• • Safe diagnosis: the right tools for high-voltage systems.
  • Accurate fault-finding: identifying the real cause of a drop.
  • Warranty support: help with claims where a fault is covered.
  • MCS certified installations: work to recognised standards.

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What Happens When You Request a Quote?

1. 1. Submit the form: tell us what you’ve noticed.
   2. We review: our team looks at your setup and the symptoms.
   3. Free consultation: we discuss your options with no obligation.
   4. Tailored quote: you receive a solution designed around your specific needs.

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Related Guides

• • Solar Panel Maintenance UK: Cleaning, Faults & Repairs
  • Common Solar Panel Faults & How to Spot Them
  • How to Clean Solar Panels (and Should You?)
  • Do Solar Panels Work in Winter in the UK?

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Frequently Asked Questions

Why is my solar output lower in winter?

This is normal. Shorter days and a lower sun mean far less daylight to work with, so UK solar generation is much higher in summer than winter. A large seasonal difference is expected and not a sign of a fault.

Should I worry about a gradual drop in output over years?

Usually not. Panels degrade slowly — a fraction of a percent a year — and many still produce around 80–85% of original output after 25 years. A slow decline over many years is normal and built into the warranty.

What causes a sudden drop in solar output?

A sudden drop that stays low more often points to a fault — most commonly the inverter, sometimes wiring or a panel issue. New shading or heavy soiling can also cause sharper drops. An error code on the inverter is a strong clue.

Can I diagnose a solar output drop myself?

You can do the safe checks: consider the season, look for dirt or new shading, note any inverter error code, and compare with the same month last year. For anything electrical, an active error code, or a big drop, call a professional. Last updated: June 2026