Why are my solar panels underperforming?

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.

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

Browse providers — US · UK · Australia · Spain

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 June 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?

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Frequently asked questions

How much performance loss is typical for this solar problem?+

Cell hotspots typically causes 5–20% output loss on residential solar systems, depending on severity, panel count affected, and how long the defect has been present.

Can I detect this issue without a professional inspection?+

Some signs (visible discolouration, hot panels on a clear day, inverter error codes, year-on-year kWh drop > 8%) are observable from monitoring data. For confirmation, a thermal imaging inspection — drone or handheld FLIR — is the gold standard and costs $299–$549 for a residential system.

Is this covered under my panel or inverter warranty?+

Most tier-1 panel warranties cover defects causing performance below 80–85% of nameplate within 25 years, and inverter warranties run 10–12 years. Claims almost always require third-party diagnostic evidence (thermal images, IV-curve traces, or written performance reports).

How fast does this defect get worse if I ignore it?+

Untreated, cell hotspots can compound — a single hot cell can degrade neighbouring cells through reverse bias, and a failing optimiser or inverter often cascades across strings. Typical degradation acceleration is 2–4× normal once a fault is present.

What does a thermal inspection cost to confirm this?+

A residential thermal solar inspection in the US costs $299–$549, UK £249–£449, and Australia AU$399–AU$699. Drone-based audits are usually at the lower end and complete a 10 kW array in under 20 minutes.

Should I repair, replace, or claim warranty?+

Rule of thumb: if defect-affected panels represent < 10% of array output, repair (e.g. bypass diode replacement, junction box rework). If 10–25% and within warranty period, file a claim. If > 25% and out of warranty, model the payback of partial re-power vs full replacement against current $/W pricing.