Why are my solar panels underperforming? — UK

Solar panel underperformance is more common than most owners realise. Over time, every system loses some efficiency — but the question is how much, and whether the loss is within normal range or a sign of a fixable problem. Here are the most common causes of solar energy loss and what you can do about each one. This guide is tailored for UK solar owners, where maritime climate conditions and shorter daylight hours create different challenges.

Symptoms to watch for

Signs that this issue may be affecting your system

Natural panel degradation

Common

All solar panels lose efficiency over time at roughly 0.5–0.8% per year. Accelerated in extreme heat or poorly manufactured panels.

Loss: 3–15%Detection: monitoring

Cell hotspots

Common

Localised overheating in individual cells caused by micro-cracks, shading, or manufacturing defects. Best detected via thermal imaging.

Loss: 5–20%Detection: thermal

Panel soiling

Common

Dust, pollen, bird droppings, or debris accumulation reducing light absorption. More severe in arid or agricultural areas.

Loss: 2–15%Detection: visual

Inverter efficiency loss

Moderate

Degradation or malfunction in the inverter reducing DC-to-AC conversion efficiency. Often indicated by error codes or unexpected shutdowns.

Loss: 5–25%Detection: electrical

What you can check yourself

Actions you can take today without professional help

1

Natural panel degradation

Compare current annual production to your system's first-year output. A decline beyond 1% per year may indicate accelerated degradation.

2

Panel soiling

Visually inspect panels from ground level. If you can see a visible film or debris, cleaning may restore 2–7% production.

3

Inverter efficiency loss

Check your inverter display for error codes or red/amber warning lights. Compare current output to the inverter's rated capacity.

When to get a professional inspection

Signs you need professional help

-Your system is over 7 years old and you've noticed a production decline
-Production has dropped more than 1% per year compared to year one
-Your system has experienced hail, storms, or physical damage
-You see visible damage: discolouration, bubbling, or cracked glass
-Your inverter shows frequent error codes or unexpected shutdowns

Expected inspection costs

Drone thermal audit

Most comprehensive option

Handheld thermal scan

Best for smaller systems

Electrical inspection

Inverter and wiring only

Find inspection providers

CaliforniaTexasFloridaArizonaColoradoNew York

Is your system affected?

Use our free Solar Loss Checker to get a personalised diagnosis with an action plan.

Check my systemShould I get an audit?

Based on conservative solar performance modelling and published degradation data

NRELIEA-PVPSSunSpecPVsyst+ published research

Updated April 2026 · Structured performance modelling

How we calculate →

More guides

→Solar Panel Hotspots Explained→Is Your Solar Inverter Losing Efficiency?→How Dirt and Soiling Reduce Solar Panel Output→When Should You Get a Solar Thermal Inspection?

Solar inspection by state

→California (CA)→Texas (TX)→Florida (FL)→Arizona (AZ)→Nevada (NV)→Colorado (CO)