When a solar system underperforms or shuts down, the cause is rarely mysterious. Most problems fall into a handful of familiar categories: shading and soiling, loose or damaged connections, inverter faults, insulation or earthing problems, grid issues and battery management. Knowing what to look for helps you decide what you can safely check yourself and when to call a qualified technician.
This guide covers 12 common faults, their typical symptoms, likely causes and practical fixes for effective solar system troubleshooting.
Safety First
Solar systems involve dangerous voltages. DC circuits remain live whenever there is light, and batteries can deliver very high currents. Before any inspection:
- Never open junction boxes, disconnect DC connectors under load or touch exposed conductors.
- Follow the manufacturer’s shutdown procedure and isolate AC and DC sides.
- Wear suitable personal protective equipment and use insulated tools.
- Do not climb onto roofs without fall protection.
- Leave electrical testing, battery work and inverter repairs to qualified personnel.
Visual checks, reading display codes and reviewing monitoring data are generally safe for owners and operators.
1. No Power Output at All
Symptoms: The inverter is dark, shows no output or displays a standby or fault message. Energy production is zero during the day.
Likely causes: A tripped AC breaker, an open DC isolator, a blown fuse, a grid outage, or a failed inverter.
What to check and fix:
- Confirm grid supply is present. Grid-tied inverters shut down during outages for safety.
- Check that AC breakers and DC isolators are switched on.
- Read the inverter display for error codes and consult the manual.
- Look for tripped residual current or surge protection devices.
- If the inverter is powered but not exporting, check grid voltage and frequency.
- If the inverter will not start, contact the installer or manufacturer.
2. Low Energy Production
Symptoms: The system works, but yield is lower than expected, or lower than the same month last year.
Likely causes: Soiling, new shading, seasonal weather, module degradation, string faults, inverter derating or an undersized system.
What to check and fix:
- Compare current production with similar periods and the expected yield for recent weather.
- Inspect panels for dirt, bird droppings and leaves, and clean as needed.
- Look for new shading from trees, buildings or equipment.
- Check monitoring data for a single string or inverter that is lagging.
- Check inverter temperature, since overheating can reduce output.
- Request an IV curve test or thermal scan if the cause is not obvious.
3. Inverter Fault or Error Codes
Symptoms: The inverter displays a fault code, flashes a warning light or repeatedly restarts.
Likely causes: Grid problems, DC input faults, overheating, internal component failure or settings errors.
What to check and fix:
- Record the exact code and consult the manual or manufacturer.
- Restart the inverter following the shutdown and start-up procedure. One-off faults sometimes clear on restart.
- Check ventilation and clear dust from vents and fans.
- If the fault returns, contact a technician. Repeated faults can indicate hardware failure or wiring issues.
4. Ground Fault or Insulation Resistance Alarm
Symptoms: The inverter reports a ground fault, insulation fault or leakage current alarm, and often refuses to start, especially in the morning or after rain.
Likely causes: Damaged DC cable insulation, water in connectors or junction boxes, a pinched or rodent-damaged cable, or a faulty module.
What to check and fix:
- Inspect visible cable runs and connectors for cuts, burns, moisture and animal damage.
- Check junction boxes for water ingress.
- Have a technician measure insulation resistance string by string to isolate the faulty section.
- Repair or replace damaged cables, connectors or modules. Never ignore ground faults, as they present shock and fire risks.
5. Overheating and Hot Spots
Symptoms: Discolouration on cells, burnt marks on backsheets, localised heating visible under thermal imaging, or inverters derating in hot weather.
Likely causes: Partial shading, cracked cells, faulty bypass diodes, soiling patches or poor ventilation around inverters.
What to check and fix:
- Inspect modules visually for browning, burn marks and cracks.
- Use thermal imaging to find hot cells, hot junction boxes and warm connectors.
- Remove sources of shading and clean localised dirt.
- Replace damaged modules.
- Improve shading and airflow around inverters and electrical equipment.
6. Loose or Damaged Connectors and Cabling
Symptoms: Intermittent output, string failures, melted connectors, burning smell or visible arcing marks.
Likely causes: Poorly crimped or mismatched connectors, loose terminals, UV-degraded cable, thermal cycling, or mechanical strain.
What to check and fix:
- Inspect connectors for discolouration, melting or looseness.
- Ensure connectors are the same make and type on both sides. Mixing brands can cause overheating.
- Re-terminate or replace faulty connectors and use proper crimping tools.
- Secure cables with UV-resistant clips and avoid sharp bends or contact with sharp roof edges.
- Treat any burning smell or melted connector as urgent and isolate the system.
7. String or Module Mismatch
Symptoms: One string produces noticeably less current or voltage than identical strings, or performance drops after a module replacement.
Likely causes: Different module types or ages in the same string, shading on part of a string, failed bypass diode, damaged cells or incorrect string configuration.
What to check and fix:
- Compare string currents and voltages at the same time of day under similar sunlight.
- Verify that strings contain the same number and type of modules.
- Remove sources of partial shading.
- Test and replace faulty modules.
- When replacing modules, match electrical characteristics with the existing array as closely as possible.
8. Grid Overvoltage or Frequency Trips
Symptoms: The inverter shuts down during sunny periods with messages about grid overvoltage, voltage out of range or frequency fault. Production drops at midday.
Likely causes: Weak or heavily loaded local network, long cable runs with voltage rise, or inverter settings that do not match grid requirements.
What to check and fix:
- Measure grid voltage at the inverter terminals during production hours.
- Check that cable sizes are adequate to limit voltage rise.
- Confirm inverter grid-code settings are correct for your region and approved by the utility.
- Discuss network issues with the utility, since a transformer tap adjustment or network upgrade may be needed.
- Do not change protection settings without approval, as this may breach connection agreements and safety rules.
9. Battery Not Charging or Discharging Properly
Symptoms: Battery state of charge stays low or high, batteries do not supply power during outages, or capacity seems far lower than expected.
Likely causes: Incorrect charge settings, tripped battery breaker, communication failure between battery and inverter, battery management system protection, ageing cells or temperature extremes.
What to check and fix:
- Check battery breaker, fuses and connections.
- Review inverter and battery management system alarms and event logs.
- Confirm that charge and discharge limits match the battery manufacturer’s specification.
- Check communication cables between the battery and inverter.
- Inspect battery temperature, since very high or low temperatures limit operation.
- If capacity has declined sharply, arrange a capacity test and consult the supplier about warranty.
10. Battery Over-Discharge or Rapid Capacity Loss
Symptoms: Backup time is much shorter than designed, the battery shuts down early or cells show imbalance.
Likely causes: Loads larger than designed, sustained deep discharge, high temperatures, cell imbalance or ageing.
What to check and fix:
- Audit actual loads and compare them with the design.
- Move non-essential loads off the backed-up circuit.
- Increase solar charging capacity or adjust settings to reserve more capacity.
- Improve ventilation or shading around the battery.
- Replace or expand the battery if it has reached its end of life.
11. Monitoring or Communication Failure
Symptoms: The portal shows no data, intermittent data or an offline inverter while the system seems to operate normally.
Likely causes: Router or internet outage, changed Wi-Fi password, loose data cables, data logger failure or expired mobile data subscription.
What to check and fix:
- Check internet connectivity and restart the router and data logger.
- Verify Wi-Fi credentials and signal strength.
- Inspect communication cables and connectors.
- Check SIM card status and data balance for cellular gateways.
- Update firmware where recommended by the manufacturer.
- Remember that loss of monitoring hides performance problems, so fix communication faults quickly.
12. Tripping Breakers, Surge Damage and Lightning Effects
Symptoms: Frequent breaker trips, failed inverters after storms, damaged surge protection devices or burn marks on equipment.
Likely causes: Lightning-induced surges, poor earthing, undersized protection, overloaded circuits or insulation faults.
What to check and fix:
- Inspect surge protection devices for status indicators and replace any that have operated.
- Test earthing continuity and resistance, and repair corroded or loose connections.
- Check that breaker ratings match cable sizes and inverter output.
- Look for moisture, burnt terminals or damaged cables.
- Review the lightning protection and earthing design, particularly in high-lightning areas such as the Lake Victoria region.
- Consult a qualified electrician if trips persist or recur after storms.
A Simple Troubleshooting Routine
When something looks wrong, a methodical approach saves time:
- Observe. Record the symptoms, error codes, date and weather conditions.
- Check monitoring data. Compare production, voltage and current across strings and inverters.
- Inspect visually. Look at modules, cables, connectors, enclosures and inverter surroundings from a safe position.
- Check the basics. Confirm that breakers, isolators and grid supply are healthy.
- Restart carefully. Follow the manufacturer’s shutdown and start-up procedures.
- Escalate. If the problem persists, contact a qualified technician with your notes, photographs and error codes.
Prevention Is Cheaper Than Repair
Most faults can be avoided or caught early through good design, quality components, careful installation and routine maintenance. Use proper connectors and cable management, maintain adequate ventilation, install surge protection and earthing, keep monitoring active and schedule inspections and cleaning. A small annual service often costs far less than the energy lost through an undiagnosed fault.
Conclusion
Solar systems are reliable when well designed and maintained, but faults will occur over a 25-year life. Understanding the 12 problems above, from simple soiling and loose connectors to ground faults, grid trips and battery issues, helps you spot trouble early, act safely and restore performance quickly. Keep clear records, use monitoring data, respect safety limits and involve qualified professionals for anything beyond a visual check. With a sensible troubleshooting routine, your solar system can stay productive for decades.
