Solar Panel Low Output: Full Diagnosis and Fixes

Key Takeaways

• The most likely causes of low solar panel output are degradation mechanisms like PID and LeTID, or physical damage such as hot cells and cell cracking.
• The first check for low output involves visual inspection for physical damage and measuring voltage/current at the module level.
• Always disconnect power from the solar array before inspecting or tightening electrical connections to prevent severe electrical shock or fire.
• Stop DIY troubleshooting and call a qualified technician if you detect internal module damage, persistent electrical faults, or if output remains low after basic checks.

Why is your solar panel output low?

Low solar panel output is often caused by degradation mechanisms that reduce the module's efficiency over time, or by physical damage. The most common causes include Potential-Induced Degradation (PID), Light and Elevated Temperature-Induced Degradation (LeTID), hot cells, and cell cracking. The first step to address low output is a thorough visual inspection of the panels and their connections.

Diagnosis Steps for Low Solar Panel Output

Follow these steps to systematically diagnose why your solar panels are producing less power.

Step 1: Visual Inspection for Obvious Damage

Inspect each solar panel for any visible signs of damage.

1. Check for soiling: Dust, dirt, bird droppings, or leaves can block sunlight. Clean the panels if necessary.
2. Look for cracks: Examine the glass surface and individual cells for any visible cracks. Cell cracking, even micro cracks, can reduce output.
3. Inspect for discoloration or burn marks: These can indicate hot cells or other internal damage. Hot cells can reach temperatures exceeding 150°C.
4. Check for delamination: Look for bubbles or separation between the layers of the module. This can be a sign of encapsulation degradation.
5. Examine the backsheet: Look for any signs of cracking, chalking, or browning. Backsheet cracking can compromise insulation and safety.
6. Inspect the junction box: Ensure the junction box is intact and sealed. Look for any signs of physical damage or overheating. Trina Solar Vertex NEG21C.20 modules, for example, feature an IP 68 rated J-Box.

Step 2: Electrical Measurements at the Module Level

Use a multimeter to measure the voltage and current of individual panels. Ensure safety precautions are followed.

1. Measure Open-Circuit Voltage (Voc):

• • Disconnect the panel from the rest of the array and any load.
  • Measure the voltage across the positive and negative terminals.
  • Compare this reading to the datasheet's Voc value for your specific module under Standard Test Conditions (STC: Irradiance 1000W/m², Cell Temperature 25°C, AM=1.5). For instance, a Jinko Tiger Neo JKM580-605N-72HL4-(V) 605 Wp module has a Voc of 53.11V at STC. A Canadian Solar TOPHiKu6 CS6.1-72TD 625W module has a Voc of 52.8V. Trina Solar Vertex NEG21C.20 695W module has a Voc of 48.3V.
  • Note that actual Voc will be lower in real-world conditions due to higher operating temperatures. For example, the Jinko JKMxxxN-54HL4-V series has a temperature coefficient of Voc of -0.25%/°C. Canadian Solar TOPHiKu6 CS6.1-72TD modules have a temperature coefficient (Voc) of -0.25% / °C. Trina Solar Vertex NEG21C.20 modules have a temperature coefficient of Voc of -0.24%/°C.

2. Measure Short-Circuit Current (Isc):

• • Carefully short the positive and negative terminals of the disconnected panel through an appropriate ammeter.
  • Compare this reading to the datasheet's Isc value. For example, a Jinko Tiger Neo JKM580-605N-72HL4-(V) 605 Wp module has an Isc of 14.31A at STC. A Canadian Solar TOPHiKu6 CS6.1-72TD 625W module has an Isc of 14.84A. Trina Solar Vertex NEG21C.20 695W module has an Isc of 18.28A.
  • Isc is less affected by temperature than Voc but can be reduced by shading or internal resistance.

3. Compare readings: Significant deviations from expected values (considering temperature and irradiance) indicate a problem with the specific panel.

Step 3: Check for Degradation Mechanisms

Some degradation issues are not immediately visible but can significantly reduce output.

1. Potential-Induced Degradation (PID):

• • PID can cause power loss, reduced photocurrent, and voltage. It involves electric charge transfer through the encapsulation of PV modules.
  • PID-polarization (PID-p) is a common type, accounting for 83% of PID power loss failures, as commonly reported by installers and noted in PVEL scorecards.
  • In the field, PERC modules in open racks with -1500V system voltage have exhibited PID-p within several weeks, while those with +1500V did not.
  • PID-p in TOPCon modules with EVA encapsulation can rapidly and repeatedly recover under sunlight when the voltage potential across the front glass is removed.

2. Light and Elevated Temperature-Induced Degradation (LeTID):

• • LeTID causes power degradation under combined thermal and light stress, followed by slow recovery. It mainly affects p-type PERC modules.
  • This mechanism is linked to hydrogen-related defects and can lead to significant yield loss, sometimes over 10%, in field operation.
  • Modules containing n-type TOPCon cells are substantially less susceptible to LeTID than early p-doped PERC cells.

3. UV-Induced Degradation (UVID):

• • Modern TOPCon, HJT, PERT, and PERC solar cells frequently show high degradation rates in accelerated UV degradation tests.
  • A study of 14 TOPCon types showed power loss from 0.5% to 8% (median 3%) after 60 kWh/m² UV dose under short-circuit conditions.
  • UVID is caused by UV-triggered changes in the passivation efficiency of the passivation stack/silicon interface.

Cause and Fix Table

Fault-Fix Considerations for Solar Panels

When troubleshooting low solar panel output, it is important to distinguish between issues that can be addressed on-site and those that require module replacement or professional intervention.

Module-Side Checks: Many issues originate within the module itself. Degradation modes like PID, LeTID, and UVID are inherent material and design challenges. For instance, PID involves electric charge transfer through the encapsulation, leading to power loss. LeTID is a degradation mechanism mainly affecting p-type PERC modules, causing reduced power output under combined thermal and light stress. These are typically not field-repairable.

Physical damage such as cell cracking, hot cells, and backsheet degradation also fall into this category. Hot cells, caused by partial shading or cell cracking, can lead to localized temperatures exceeding 150°C and result in discoloration or burn marks. While cleaning soiling is a simple fix, internal damage like cell cracks, which can cause 0.2% power loss per dendritic-like cracked half-cell for multi-wire modules, usually necessitates module replacement.

System-Side Checks: Before concluding a module is faulty, ensure the problem isn't external. Check wiring for loose connections or corrosion. Verify that the inverter is operating correctly and its settings are appropriate for your array. Ensure there is no external shading from trees, buildings, or other obstructions.

When the Panel is Dead vs. Settings are Wrong: A "dead" panel typically means it produces significantly less power or no power at all, often due to internal failure or severe physical damage. This is indicated by very low or zero Voc and Isc readings. If the panel is dead, replacement is usually the only option.

Incorrect inverter settings, while not a panel fault, can mimic low panel output. For example, if the inverter's maximum power point tracking (MPPT) range is not optimized for your array's voltage, it may not extract full power. Always consult your inverter manual to ensure settings are correct. However, this article focuses on panel-specific faults.

Safety

Working with solar panels involves high voltages and currents, which can be extremely dangerous. Always prioritize safety.

• Read Manuals: "Please read the safety and installation manual before using the product." PV modules should be handled and installed by qualified people who have professional skills.
• Disconnect Power: Before inspecting or tightening any electrical connections, always kill power first. Disconnect the solar array from the inverter and any loads.
• Insulated Tools: Use only insulated tools when working with electrical components. A spanner across a live solar panel string can short hundreds of amps, leading to severe electrical shock or fire.
• Module Fire Performance: Be aware of the fire performance ratings of your modules. For example, Canadian Solar CS6.1-72TD modules are rated "TYPE 29 (UL 61730) or CLASS C (IEC 61730)".
• Protection Class: Canadian Solar CS6.1-72TD modules are rated "Class II".
• Junction Box: Ensure junction boxes are properly sealed. Trina Solar Vertex NEG21C.20 modules have an "IP 68 rated" J-Box.

When to call a technician instead

While basic visual inspections and electrical measurements can help identify common issues, there are clear limits to DIY troubleshooting.

• Persistent Low Output: If output remains consistently low after you have performed basic checks, cleaned the panels, and verified connections, a deeper problem likely exists.
• Internal Module Damage: If you detect signs of internal damage such as severe discoloration, delamination, or burn marks within the cells or encapsulation, the module requires professional assessment. Attempting to repair internal module damage can be dangerous and may void warranties.
• Electrical Faults: If you measure unexpected voltage or current readings that you cannot explain, or if you suspect a ground fault or short circuit, do not proceed. High voltage DC systems can be lethal.
• Warranty Concerns: Many manufacturers offer warranties against certain types of degradation or manufacturing defects. For example, Jinko Solar, Canadian Solar, and Trina Solar provide product and performance warranties. Attempting unauthorized repairs can void these warranties.
• Safety Risks: If you are uncomfortable working with electricity, or if the problem requires accessing the roof or working at heights, it is always safer to call a qualified solar technician. They have the training, tools, and safety equipment to diagnose and fix complex issues safely.