Pyranometer Drift Analysis

Performance ratio divides measured generation by measured irradiance. That makes the pyranometer as consequential as the plant itself — and pyranometers soil, age and drift.

A sensor reading high depresses PR and triggers investigations into plants that are performing perfectly well. A sensor reading low inflates PR and conceals genuine degradation. Both failure modes cost money, and neither announces itself.

Each sensor is cross-checked three ways: against its redundant pair in the same plane of array, against a clear-sky model on cloud-free days, and against the plant's own aggregate DC current.

Weather moves all references together. Drift does not. Consistent one-way divergence across the whole irradiance range — not just at the extremes — is the signature that separates a failing instrument from a cloudy afternoon.

• Cross-check each sensor against its redundant pair
• Compare against a clear-sky model on cloud-free days
• Validate against the plant's own aggregate DC current
• Test for one-way divergence across the full irradiance range
• Rank sensors by drift magnitude for calibration

Drift-corrected irradiance and a calibration priority list — so PR trends describe the plant rather than the sensor watching it.

• Irradiance baseline corrected for measured drift
• False investigations into healthy plants avoided
• Genuine degradation no longer concealed by an optimistic sensor
• PR becomes defensible in front of a board