Hotspots are one of the most damaging faults a solar panel can develop. They occur when one or more cells in a panel overheat, creating localised thermal stress that accelerates degradation and can even cause permanent physical damage to the panel.

For solar owners, hotspots represent a hidden threat — they're almost always invisible to the naked eye, but they can silently reduce your system's output by 5–20% and shorten your panel's lifespan by years.

What causes hotspots?

Hotspots form when there's a mismatch in current flow within a panel. When one cell can't carry as much current as its neighbours, the excess energy is dissipated as heat. The most common causes include:

Micro-cracks

Tiny fractures in silicon cells are the most frequent hotspot trigger. These cracks can occur during manufacturing, transport, or installation — even walking on panels during maintenance can cause them. Micro-cracks are invisible to the naked eye and may not cause problems immediately, but over time they worsen under thermal cycling stress.

Cell mismatch

When cells within a panel have significantly different electrical characteristics — due to manufacturing variation, localised degradation, or partial damage — the weaker cells can become reverse-biased. Instead of generating electricity, they consume it, converting the energy to heat.

Persistent shading

If part of a panel is consistently shaded — by bird droppings, fallen leaves, a chimney shadow, or accumulated debris — the shaded cells operate at reduced output. In string configurations without bypass diodes (or with failed bypass diodes), this can force the shaded cells into reverse bias, creating hotspots.

Bypass diode failure

Bypass diodes are built into panels specifically to prevent hotspots from shading. When these diodes fail, a single shaded cell can drag down an entire string and overheat. Bypass diode failure becomes more common as panels age, particularly in hot climates.

Solder joint degradation

Over years of thermal cycling, solder joints connecting cells can develop high-resistance connections. These create localised heating that behaves similarly to cell-level hotspots.

Why hotspots are dangerous

The damage from hotspots goes beyond reduced output:

Accelerated degradation — The overheating cell and surrounding area degrade far faster than the rest of the panel, creating a compounding problem.
Encapsulant damage — Sustained high temperatures cause the transparent encapsulant material to brown or bubble, permanently reducing light transmission.
Delamination — Repeated thermal stress at the hotspot can cause layers of the panel to separate, allowing moisture ingress.
Glass cracking — In severe cases, the thermal stress can crack the glass cover, destroying the panel's weather seal.
Fire risk — Extreme hotspots can reach temperatures above 150°C, creating a genuine fire hazard. While rare, hotspot-related fires do occur.

Research published in the journal Solar Energy found that hotspots can cause 5–20% performance loss depending on severity, with the worst cases exceeding 25% loss on affected panels.

Can you spot hotspots yourself?

In most cases, no. Hotspots are invisible in normal lighting conditions. However, some advanced cases produce visible symptoms:

Browning or discolouration on the panel surface, visible as darker patches
Bubbling in the encapsulant layer — looks like small blisters under the glass
Burn marks on the back of the panel (if you can access the underside)
Snail trails — silvery discolouration lines along micro-cracks, caused by moisture interacting with cell metallisation

These visible signs typically indicate that hotspot damage has been ongoing for a significant period. By the time you can see them, the cell is usually permanently damaged.

What monitoring data can tell you

If you have panel-level monitoring (via microinverters or power optimisers), you can spot potential hotspots by looking for:

Individual panels consistently underperforming compared to neighbours
Panels showing an unusual production curve shape (steep dropoff in afternoon heat)
Sudden drops in output from a specific panel that don't recover

String-level monitoring is less useful for hotspot detection since a single panel's loss is diluted across the string.

Thermal imaging: the definitive detection method

Professional thermal inspection using infrared cameras is the only reliable way to identify hotspots. Under sunlight, hotspot cells show up as bright spots on a thermal image — the temperature differential makes them unmistakable.

There are two main approaches:

Drone thermal inspection ($200–500)

A drone equipped with a radiometric thermal camera flies over your array, capturing thermal images of every panel. This is the best option for:

Large arrays (20+ panels)
Roof-mounted systems that are difficult to access
Commercial installations
Situations where you want a comprehensive survey of every panel

Handheld thermal scan ($150–350)

A technician uses a handheld thermal camera from ground level or roof access. Better for:

Smaller systems (under 20 panels)
Ground-mounted arrays with easy access
Targeted investigation of specific panels flagged by monitoring data

Both approaches work best during peak sunlight hours (10am–2pm) when the panels are under full load and temperature differentials are most pronounced.

When to get a thermal inspection

Consider thermal inspection if:

Your system is more than 7 years old — hotspot risk increases significantly with age
You've noticed a production decline beyond normal degradation (more than 1% per year)
You're in a hot climate with high thermal cycling stress
Your system has experienced hail, storm damage, or physical impact
Your monitoring shows individual panels underperforming compared to the rest of the array
You see visible signs of panel damage (browning, bubbling, cracking)

For new systems (under 3 years), hotspots are relatively unlikely unless there was a manufacturing or installation defect. For systems over 10 years old in hot climates, periodic thermal inspection every 3–5 years is a sensible precaution.

What to do if hotspots are found

If thermal inspection identifies hotspots, the appropriate response depends on severity:

Minor hotspots (temperature differential under 20°C): Monitor and re-inspect in 12–18 months. May not require immediate action.
Moderate hotspots (20–40°C differential): The panel is degrading faster than normal. Consider warranty claim if within coverage period.
Severe hotspots (above 40°C differential): The panel should be replaced. Continued operation risks further damage and potential safety hazard.

Use PanelAudit's Solar Loss Checker to estimate whether your system's profile suggests hotspot risk based on age, location, and equipment type.

How to Identify Solar Panel Hotspots