Path-Q Solar
How can I tell whether an existing solar system is still producing as expected?
Answer
Compare measured production with the system's historical output and a weather-adjusted expectation for the same period, while checking for shading, outages, soiling, and monitoring gaps. A single cloudy month is not enough to establish a fault; a persistent unexplained deviation is more significant.
Key points
- Review daily, monthly, and seasonal energy production rather than relying on one day's result.
- Compare similar periods and account for weather, snow, shading changes, and curtailment.
- Check inverter status, monitoring communications, utility bills, and any system alerts.
- Compare output by inverter, string, or module group if the monitoring system provides that detail.
What it depends on
- Original production estimate and system size
- Weather and irradiance conditions
- Shading, soiling, snow, outages, and equipment changes
- Accuracy and completeness of monitoring data
Risks and trade-offs
- Comparing raw output without weather adjustment can produce false alarms.
- A monitoring outage can look like a production outage.
- Roof or electrical work may temporarily change output or access.
Information you may need
- At least several months of production history
- System design, commissioning date, and expected production
- Monitoring alerts and inverter status
- Weather, outage, shading, and maintenance records
Your next step
What to do next
Export recent production data, compare it with comparable historical and weather-adjusted periods, and contact the installer if the unexplained shortfall persists.
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