Solar Panel Hot Spots: What They Are and Why They're Dangerous

Understanding Hot Spots in Solar Panels

Hot spots are localized areas of a solar panel that become significantly hotter than the rest of the panel. They're usually only visible with thermal imaging cameras, but they indicate internal problems.

What Causes Hot Spots

Cause 1: Shaded or Partially Shaded Cells

When one part of a panel is shaded while the rest is sunny, it creates a hot spot.

• The shaded cells stop producing power but continue conducting electricity
• Other cells in the string try to push current through the shaded cell
• This creates resistance and heat buildup at the shaded cell
• Temperature can exceed 100°C (212°F) in severe cases
• This is called "reverse bias" condition

Cause 2: Cracked or Damaged Cells

• Manufacturing defects or impact damage can crack solar cells
• A cracked cell loses efficiency but still conducts power
• This causes localized heating at the damage site
• More common in cheaper panels with lower quality control

Cause 3: Delamination or Internal Degradation

• The panel's internal layers separate or degrade
• This causes poor electrical contact within the panel
• Localized resistance creates heat spots
• Often a manufacturing defect or installation damage

Cause 4: Solder Joint Failure

• Solar cells are connected by solder joints
• Poor solder work or age can cause joint failure
• Weak connections create resistance and heat
• More common in older or low-quality panels

Cause 5: Bypass Diode Issues

• Each panel has bypass diodes that protect against reverse bias
• A faulty diode can fail to protect, causing hot spot formation
• The diode itself overheats when protecting the panel

How Serious Are Hot Spots?

Minor hot spots (small and rare):

• Isolated small hot spots on one panel, especially from temporary shading
• Panel still operates and produces power
• Hot spot disappears when shade is removed
• This is not necessarily a defect requiring action

Moderate hot spots (larger or persistent):

• Hot spots covering significant area of the panel
• Persist even when there's no obvious shading
• Indicate internal panel damage or defect
• Panel will degrade and fail faster than normal
• Should be monitored and potentially replaced

Severe hot spots (large and critical):

• Very hot spots (over 100°C difference from rest of panel)
• Multiple hot spots on same or multiple panels
• Accompanied by visible damage or discoloration
• These are fire hazards and immediate safety issues
• Panels should be replaced immediately

Fire Risk and Safety Implications

Hot spots can cause fires if:

• Temperature becomes very high (150°C+)
• Nearby materials are flammable (some roof materials, insulation)
• Wiring is close to the hot spot and can overheat
• Bypass diode failure creates sustained, uncontrolled heat

Actual fire risk from hot spots is low if:

• Hot spots are minor and from temporary shading
• System has modern arc fault protection and safety equipment
• Wiring and installation meet current safety codes
• Hot spots are identified and corrected

Diagnosing Hot Spots

Professional thermal imaging:

• Thermal cameras can see temperature differences on panels
• Professional inspection cost: $300-$800
• They can identify which panels have hot spots and severity
• Some installers offer this as part of maintenance services

Visual inspection:

• Walk around your roof and look at panels from the ground
• Use binoculars to look for visible discoloration or burn marks
• Look for areas that are notably darker or lighter than surrounding panel
• This is less precise than thermal imaging but cost-free

Production analysis:

• If a panel has hot spots, it usually produces less power
• Check your monitoring for unusually low-producing panels
• A panel with significant hot spots might produce 20-30% less than similar panels
• This is not diagnostic proof, but combined with thermal imaging confirms the issue

What to Do About Hot Spots

If hot spots are from temporary shading:

• Trim trees or remove obstructions causing shade
• No panel replacement needed; issue resolves with shade removal

If hot spots are from internal panel damage:

• The panel is defective and should be replaced under warranty
• Contact your installer with thermal imaging results
• Manufacturer should cover replacement if within warranty period
• If out of warranty, replacement cost is $350-$550 per panel

If hot spots are severe or a fire risk:

• Stop operating the system immediately
• Turn off the DC disconnect switch
• Contact your installer urgently for inspection
• Do not restore operation until problem is resolved
• This is a safety hazard that requires immediate attention

Preventing Hot Spots

During installation:

• Ensure quality panels from reputable manufacturers
• Verify proper installation workmanship
• Check that bypass diodes are functional
• Proper grounding and protection design prevents diode failures

During operation:

• Prevent shading from trees, buildings, or new structures
• Keep panels clean; dirt buildup can create localized shading
• Annual inspection for visible damage or discoloration
• Professional thermal imaging every 3-5 years in warranty period