You’re checking your solar monitoring app, and one panel is producing noticeably less than the rest. Or maybe you climbed up to clean the array and noticed a small, discolored patch on one panel that wasn’t there last year. Either way, you’re probably wondering the same thing: is this normal wear, or something you need to deal with now?
That patch has a name — a hot spot — and it’s worth understanding, because ignoring one can shorten a panel’s life or, in rare cases, become a genuine fire risk.
What Is a Hot Spot, Exactly?
A hot spot is a small area on a solar panel that gets significantly hotter than the cells around it — sometimes well above 100°C, with some documented cases reaching 130–150°C in severe situations. That’s hot enough to scorch the backsheet or crack the glass over time.
Here’s the mechanism, and it’s simpler than it sounds. The cells inside a panel are wired in series, like a string of old-style Christmas lights. Current has to pass through every cell in that string, one after another. If one cell can’t produce as much current as its neighbors — because it’s shaded, dirty, or damaged — the healthy cells around it keep pushing current through it anyway. That mismatched cell can’t handle the load the same way, so instead of converting the energy into electricity, it dumps it as heat. Localized. Concentrated. That’s the hot spot effect.
It’s a good example of how a solar array is only as strong as its weakest cell.
What Causes Hot Spots
Five things typically trigger this chain reaction:
- Partial shading. Anything that blocks light on part of the array — a tree branch, a neighboring wall, an antenna, or, very commonly on Bangladeshi rooftops, a water tank or satellite dish sharing the same space. Even a shadow crossing one corner of one panel for a couple of hours a day is enough to start the process.
- Soiling. Dust, dried mud, or bird droppings sitting on part of a panel block light the same way shade does. During the monsoon, debris and organic matter tend to accumulate faster, and open rooftop mounting — common in residential setups here — makes panels more accessible to nesting birds than fully enclosed ground-mount systems elsewhere.
- Manufacturing defects. Microcracks, weak solder joints, or inconsistent cell material can create a point of higher resistance from day one. This isn’t something you can inspect for visually, and it’s part of why panel quality matters more than price alone.
- Cell mismatch. Cells age at slightly different rates. Over years, small performance gaps between cells widen, and the weaker ones start absorbing more of the load than they should.
- Bypass diode failure. This is the one most homeowners have never heard of, and it’s arguably the most important. Bypass diodes exist specifically to reroute current around a struggling cell so it isn’t forced to carry a load it can’t handle. When a diode fails, that safety valve disappears — and a shading or mismatch problem that would have been minor becomes a genuine hot spot.
Are Hot Spots Dangerous?
Not every hot spot is an emergency, and it’s worth resisting the urge to panic the moment you spot one. A mild, early-stage hot spot mostly just means a small efficiency loss — a bit less output from that one panel. Left unaddressed for a long time, though, it can degrade the encapsulant, delaminate the panel’s layers, or crack the glass. And in the more severe cases — usually where a bypass diode has failed alongside sustained shading or soiling — hot spots are a recognized contributor to solar panel fires.
The honest way to think about it: hot spots range from “cosmetic and worth monitoring” to “a real fire and safety consideration,” and the difference usually comes down to how long the underlying cause has gone unaddressed.
How Would You Actually Know You Have One?
This is the part most articles skip, and it matters, because almost nobody has a €2,000 thermal camera sitting in a cupboard.
What you can check yourself:
- Watch your monitoring app, if your system has panel- or string-level monitoring. A single panel consistently underperforming its neighbors on a clear day is the earliest and most reliable clue.
- Do a visual walk-around every few months. Over time, a hot spot can show up as browning, a faint bubble under the surface, or discoloration on the backsheet — not always dramatic, but usually visible if you know where to look.
- Never touch a panel to check its temperature. Surface heat from ordinary sun exposure and a genuine hot spot can feel similar to the hand, and there’s no safe reason to be testing electrical equipment by touch.
What genuinely needs a professional:
- Confirming a suspected hot spot with an infrared or thermal imaging inspection
- Replacing a failed bypass diode — this involves opening the junction box and isn’t a reasonable DIY job for most homeowners
- Any repair involving the panel’s internal wiring
If your instinct after a visual check is still “something’s off but I can’t tell what,” that’s the point to call someone rather than keep monitoring it yourself.
Fixing and Preventing Hot Spots
| Cause | Typical Fix | DIY or Professional |
| Soiling (dust, droppings, debris) | Regular panel cleaning | DIY, with basic care and the right technique |
| Partial shading | Trim vegetation, or reposition/adjust obstructions where possible | Often DIY; sometimes limited by shared walls or fixed structures like water tanks |
| Manufacturing defect | Panel replacement under warranty, where applicable | Professional |
| Cell mismatch (age-related) | Panel-level monitoring to catch early decline | Professional inspection recommended |
| Bypass diode failure | Diode replacement | Professional only |
A few of these deserve a bit more context. Cleaning is the most accessible fix and prevention step available to a homeowner — it’s worth doing on a regular schedule rather than only when output visibly drops. Shade management sounds simple in theory, but in dense urban settings it isn’t always fully solvable; you can’t always relocate a neighbor’s structure, and in those cases the more realistic response is accepting some shading loss and monitoring the affected panel more closely rather than expecting a total fix.
For larger systems, adequate airflow underneath the panels also matters more than people expect — it’s a passive way to help dissipate heat and reduce how quickly minor mismatches turn into real hot spots.
For Larger and Industrial Installations
A homeowner with eight or ten rooftop panels can manage most of this with an occasional visual check and a cleaning schedule. A commercial rooftop array or an industrial ground-mount system is a different scale of problem entirely.
For facility managers and EPC teams, the more realistic approach is scheduled thermal inspection — increasingly done with drone-based thermography on larger sites — combined with string-level monitoring and IV curve tracing to catch underperforming strings before a site visit is even needed. The economics usually favor this: a proactive O&M contract that includes periodic thermal scans is cheaper than losing a string to a diode failure that went unnoticed for months, and it matters for insurance and liability considerations too, particularly at industrial scale where a fire risk isn’t just a financial loss.
Does a Hot Spot Affect Your Warranty?
This varies enough by manufacturer and installer that it’s worth treating as general guidance rather than a fixed rule: a hot spot traced back to a manufacturing defect is generally the kind of issue panel warranties are meant to cover, while one caused by shading, soiling, or a site condition usually isn’t, since it’s not a fault in the product itself. If you suspect a hot spot on a relatively new system, it’s worth reviewing your specific warranty terms — or asking your installer directly — before assuming either way.
A reputable installer sourcing quality panels with reliable bypass diode design from the outset is one of the more effective ways to reduce hot spot risk over a system’s lifetime, and it’s a reasonable thing to ask about when comparing quotes. Muspana, like other established installers, can also carry out professional thermal inspections for homeowners and businesses who’d rather have a confirmed diagnosis than guess from a monitoring app.
None of this means every warm patch is a crisis. Most hot spots start small, and most are catchable with a bit of regular attention — a clean array, an occasional visual check, and taking a persistent underperformance reading seriously instead of writing it off. That’s really the difference between a minor efficiency dip and a panel that needs replacing early.
FAQs
Are solar panel hot spots dangerous?
Not always. A minor hot spot mostly reduces efficiency, but if it’s left unaddressed — especially where a bypass diode has failed — it can damage the panel and, in severe cases, contribute to a fire risk. It’s worth taking seriously rather than ignoring.
Can a solar panel hot spot be fixed?
It depends on the cause. Soiling and mild shading are usually fixable through cleaning or shade management. A failed bypass diode or a manufacturing defect typically requires professional repair or panel replacement.
How do I detect a hot spot without a thermal camera?
Watch for one panel consistently underperforming its neighbors on your monitoring app, and do a periodic visual check for browning, bubbling, or discoloration. A confirmed diagnosis still requires a professional thermal inspection.
Do hot spots void my solar panel warranty?
It depends on the cause. Defect-related hot spots are generally covered by manufacturer warranties; those caused by shading or soiling usually aren’t, since they’re site conditions rather than product faults. Check your specific warranty terms to be sure.
What causes hot spots on rooftop solar panels in Bangladesh specifically?
The same five mechanical causes apply everywhere, but rooftop realities here — shared space with water tanks, monsoon debris, and bird activity on open mounts — make shading and soiling especially common triggers worth watching for.
