Insights / Field note · Solar22 April 2026

Not all grid curtailment is uncontrollable

A solar inverter looked like it was suffering normal grid curtailment. The real cause was high grid voltage at the connection point, and it was fixable.

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This image shows a solar inverter curtailment issue identified during a performance assessment, which was having a significant impact on production through repeated trips and power throttling.

Two stacked time series of solar inverter actual versus predicted power. Top, before resolution, shows heavy throttling and fault modes with actual far below predicted and large negative residuals. Bottom, after resolution, shows actual closely matching predicted with small residuals. — Actual against predicted inverter power, before and after resolution. Before, repeated throttling and fault modes drive large negative deltas against the prediction. After, actual tracks predicted closely and the trips are gone.

Investigation revealed the cause was due to a high grid voltage especially on one phase. A check of the voltage at the connection point confirmed it was above the 10% allowable band. The network operator was notified, confirmed the issue through their own monitoring and replaced the grid transformer, bringing voltage back into range and resolving the curtailment.

The root cause, in the voltage

For those interested in the root cause, these voltage scatter plots show the before and after picture clearly.

Before the transformer replacement, L3 AC voltage was regularly breaching the 253 V grid limit and increasing with production to reach the 263 V inverter voltage limit, where it would initially throttle the production and then often trip the inverter.

After the grid transformer replacement, the no load voltage dropped by about 8 V, keeping the inverter comfortably within the inverter limits across the full output range.

Two stacked scatter plots of L3 AC voltage against total active power. Before resolution, points rise with power, cross the 253 V grid limit and reach the 263 V inverter limit. After resolution, the points sit about 8 V lower and remain below both limits across the power range. — L3 AC voltage against total active power, before and after the transformer replacement. Before, voltage rises with output, breaches the 253 V grid limit and approaches the 263 V inverter limit. After, the whole band drops by about 8 V and stays clear of the limits.

This highlights the importance of performance assessments and fully investigating the cause of any unexpected underperformance and derating.

Charts and analysis by PowerVeritas. Where open datasets are used, sources are credited on the attributions page.