Hot spots, microcracks and potential-induced degradation are three of the main ways solar panels lose output early. Learn what causes each one, the symptoms to watch for, how professionals detect them and how careful handling and installation prevent them. Most solar panels age slowly and predictably, but a few failure mechanisms can cut output much faster. The three most common are hot spots, where a cell overheats because it cannot carry the current of its neighbours; microcracks, fine fractures in the thin silicon cells; and potential-induced degradation (PID), a slow electrical leakage driven by high system voltage. They are linked: cracks can create hot spots, and all three show up as lost production. Much of the prevention happens long before a problem is visible, during manufacturing, transport, handling and installation.
Hot spots: when a cell turns power into heat
Cells inside a panel are connected in series, so the same current must flow through all of them. If one cell produces less current than the rest, the others push current through it anyway. The weak cell is forced into reverse bias and, instead of generating power, it dissipates power as heat. Bypass diodes limit the damage by diverting current around a group of cells, but the affected cell can still run far hotter than its neighbours.
Common causes include:
- Persistent partial shade from a vent, antenna, satellite dish or overhanging branch.
- Concentrated dirt, such as a bird dropping or leaves trapped against the frame.
- A cracked cell, or a poor solder joint that raises resistance.
- A manufacturing defect in an individual cell.
Over time, sustained heat can brown the encapsulant, blister or burn the backsheet and, in severe cases, crack the glass. From ground level, the early signs are usually invisible; the first clue is often lower output from one string.
Microcracks: fractures in thin silicon
A solar cell is a slice of crystalline silicon typically well under a quarter of a millimetre thick. It is strong for its thickness but brittle, and the glass and frame protect it only up to a point. Microcracks form when a panel flexes or takes an impact:
- Dropping or jolting pallets, or transporting panels flat without support.
- Carrying a panel by one corner or edge so it bends.
- Kneeling, walking or placing tools on panels during installation.
- Clamping panels outside the manufacturer's specified zones, which lets the glass flex in wind.
- Hail, heavy wind loads and years of thermal cycling that widen existing cracks.
A small crack may cost almost nothing at first. The risk is progression: as the panel heats and cools each day, cracks can grow until they electrically isolate part of a cell. That inactive area reduces current, can trigger a hot spot and may eventually activate a bypass diode. Occasionally, cracks become visible as thin brownish lines across cells, often called snail trails.
Potential-induced degradation
Panels in a string are wired in series, so the cells at one end sit at a high voltage relative to the earthed aluminium frame, which can reach hundreds of volts in residential systems and more in commercial ones. That voltage difference can drive a small leakage current through the glass and encapsulant. Over time, charged particles, including sodium from the glass, migrate towards the cell surface and create paths that short out, or shunt, part of the cell.
PID is typically worse in heat and high humidity, at coastal sites and at the end of a string with the greatest voltage difference. The symptom is gradual, progressive power loss affecting some panels much more than others, rather than a sudden failure. Early PID can sometimes be partly reversed, and some inverters include functions designed to counteract it, but prevention through PID-resistant cells, encapsulants and glass is far more reliable.
Comparing the three faults
| Fault | Main causes | Typical symptoms | How it is detected |
|---|---|---|---|
| Hot spot | Shading, concentrated soiling, cracked cells, poor solder joints | Lower string output; browning or burn marks in advanced cases | Thermal imaging, visual inspection |
| Microcrack | Handling, transport, foot traffic, incorrect clamping, hail | Often none at first; later power loss, snail trails, hot spots | Electroluminescence imaging, thermal imaging, IV curves |
| PID | High string voltage, heat, humidity, susceptible materials | Progressive loss, worst at one end of a string | IV curves, thermal patterns, electroluminescence imaging |
Electroluminescence imaging works by running current backwards through the panel in darkness. Working cell areas glow faintly in the near-infrared, while cracked or inactive areas appear dark, making it the clearest way to see microcracks.
What owners can safely watch for
None of these faults requires anyone to climb onto a roof to notice the early signs. Monitoring data is the best indicator: one string or panel group producing consistently less than a similar one on clear days, or output that keeps sliding year after year faster than normal ageing, deserves investigation. From the ground or a window, owners can also look for brown or yellow discolouration, thin dark trails across cells or new shading from growing trees. After hail or a severe storm, it is sensible to compare production with previous clear days and arrange a professional inspection if it has dropped.
Prevention starts with handling and installation
- Store panels upright in their packaging on a flat surface, away from traffic and weather.
- Carry each panel by two people, holding the frame on its long edges, with the glass kept flat and unstressed.
- Never stand, kneel or place tools on panels. Walkways and roof access are planned so panels are not used as platforms.
- Follow the installation manual for clamp zones, clamp torque and rail spacing, so the panel is supported as it was tested.
- Design out shading from vents, dishes and future tree growth, and route cables so they do not rest on backsheets or pull on junction boxes.
- Choose appropriate products for the site, including panels tested for PID resistance and, near the coast, salt mist corrosion.
Following the manual also matters for warranty cover, because installation outside the manufacturer's instructions can affect a product warranty claim. The differences between warranty types are explained in solar panel warranty types explained, and normal long-term output loss in solar panel degradation explained. Roof access is hazardous, so inspection and any work on panels should be left to accredited professionals.
Next steps
If one part of an array is producing less than it should, or panels show discolouration, a professional inspection can identify which of these faults is involved. To have your system checked, request a free assessment from Blue Energy Solar. The energy market lists a Solar Fault Diagnosis at $249 for the call-out and first hour, and Solar Panel Replacement from $450 per panel, supplied and installed, with a minimum charge of $650 per site attendance; prices are indicative and confirmed after a site assessment.
Frequently asked questions
Are hot spots a fire risk?
A severe, long-running hot spot can damage the backsheet and surrounding materials, and heat at a faulty connection is a recognised safety concern, which is why these faults should be investigated rather than ignored. Most hot spots are found as a loss of output long before any hazard develops. If burn marks, melting or a burning smell are noticed, keep clear and have a licensed professional isolate and inspect the system.
Can a panel with microcracks be repaired?
Generally no. Cells are laminated between glass and backsheet during manufacture, so individual cells cannot be replaced in the field. If cracking is causing meaningful power loss or hot spots, the usual fix is replacing the panel with one electrically compatible with the rest of the string. Minor cracks with no measurable loss are often monitored rather than replaced, since the panel may keep performing for years.
Do half-cut cell panels reduce these problems?
They can reduce the impact. Half-cut designs split each cell in two, which lowers the current in each piece and reduces resistive heating at connections. A crack or shaded area also affects a smaller portion of the panel's cell area. They are not immune to cracking, hot spots or PID, however, so correct handling, installation and material choice still matter just as much.
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