Why Is My Solar System Generating Less Than Expected? 8 Common Reasons Explained

First: What Is "Expected" Production?

Your Sunollo installation report includes a simulated annual yield — a computer-modelled estimate of how much energy your system should generate each year based on your roof orientation, panel capacity, and Singapore's historical solar irradiance data. This is a guideline, not a guarantee.

Real-world production will naturally vary ±15–20% from the simulation due to Singapore's variable tropical weather. A reduction of more than 20% over a full month compared to the simulation (weather-adjusted) is worth investigating.

1. Panel Soiling (The Most Common Cause)

In Singapore's tropical climate, solar panels accumulate a layer of dust, bird droppings, algae, and haze particulate over time. This can reduce output by 5–15% without visible degradation from the ground.

Fix: Schedule a professional cleaning once or twice per year. See our guide: How to Clean Solar Panels in Singapore.

2. Shading from New Sources

Has anything changed on or near your roof since installation? New shading — from a tree that has grown, a new neighbouring structure, or a satellite dish — can dramatically reduce output on affected panels. Because solar panels are connected in strings, one shaded panel can pull down the output of the entire string.

Fix: Walk around your property at different times of day to identify new shade sources. Contact Sunollo if you need a shading analysis — we can advise on whether optimisers or panel repositioning would help.

3. Seasonal and Weather Variation

Singapore's solar irradiance varies throughout the year. The monsoon seasons (November–January and June–July) bring increased cloud cover and lower generation. Year-on-year comparisons are more meaningful than month-on-month.

Fix: Compare your current month's yield to the same month last year using your monitoring app's history. If your system is newer than one year, compare to the installer's monthly simulation figures.

4. Inverter Clipping

If your system was designed with more kWp of panels than the inverter's rated output (called "overclipping" or "oversizing"), the inverter deliberately caps output at its rated maximum on very bright days. This is a deliberate design choice — it increases annual yield by optimising for average conditions while sacrificing the very highest peaks.

Fix: Check your system spec — if your panels are 10 kWp but your inverter is rated 8 kW, clipping is normal. This is not a fault.

5. Panel Degradation

Solar panels naturally lose a small amount of output each year — typically 0.5–0.7% per year for quality panels. A 10-year-old system should produce about 95% of its first-year output under the same conditions. Accelerated degradation (more than 1% per year) is unusual for quality panels and may indicate a manufacturer defect — covered under panel product warranty.

Fix: Compare your current year's total yield to your first full year. If the drop exceeds 1% per year, contact Sunollo to request a warranty assessment.

6. A Failed Optimiser or Microinverter

If your system uses SolarEdge optimisers or microinverters, a single failed unit will reduce total output proportionally. For example, on a 20-panel system, one dead optimiser reduces maximum output by approximately 5%.

Fix: Check the panel layout view in your monitoring app. Any panel showing red or grey persistently on clear days should be reported to Sunollo for warranty replacement.

7. Inverter Operating in Derating Mode

In high ambient temperatures (common in Singapore's summer), some inverters automatically reduce output to protect internal components from overheating. This is called thermal derating and is normal for short periods on very hot afternoons.

If your inverter is mounted in a poorly ventilated space (e.g., a sealed utility cupboard), it may derate more frequently. Ensure there is at least 30 cm clearance around the inverter and that the space has adequate airflow.

Fix: Check inverter placement. If derating is persistent, Sunollo can assess whether additional ventilation or inverter relocation is warranted.

8. Monitoring Data Lag or Communication Issues

Sometimes the production is fine but the app is not updating — giving the false impression of low output. Check:

• Is your home Wi-Fi working normally?
• Is the monitoring data logger connected? (Check the LED on the logger dongle)
• Has it been offline for more than 24 hours? Real-time data may be lagging.

Cross-check by reading the inverter's built-in display for today's energy total — if this is higher than what the app shows, it is a communication lag, not a generation issue.