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System security and resilience

Improving the accuracy of intermittent generation forecasts

Improving the accuracy and frequency of intermittent generation forecasts in the spot market.

  • Generation
  • Policy

    • Overview

    On 31 July 2025 the Electricity Authority is introducing a new hybrid forecasting arrangement to improve the accuracy of intermittent generation forecasts and offers. 

    To give effect to the hybrid arrangement, we have decided to implement several key policy design measures. These changes aim to ensure intermittent generators’ offers are as accurate as possible during all trading periods.

    Intermittent generators can use an alternative to the centralised forecast, if they meet minimum performance standards, but need to obtain the Authority’s approval to do so. Please read this guidance on the process and requirements and apply using this application form. For any queries, contact forecasting@ea.govt.nz

    Timeline

    Past activity

    Project background

    Incorrect forecasting by wind generators was a contributing factor in the 9 August 2021 grid emergency, which resulted in the disconnection of approximately 34,000 customers without warning.

    In response to this grid emergency, the Electricity Authority (and other organisations) conducted a number of reviews and investigations to:

    • understand the causes of power supply interruptions
    • understand the industry’s response on the night
    • learn lessons from the event to identify and recommend improvements to ensure similar circumstances are better managed in future.

    In response to one of the review’s recommendations, we published an information paper about the accuracy of wind generation, demand forecasts and bids leading up to real time from April 2021 to March 2022. We found that intermittent generation forecasts are often inaccurate and unreliable until the last three and a half hours before real time.

    Inaccurate forecasting is prevalent because there are minimal obligations around the accuracy of intermittent generation forecasts. Intermittent generators have few incentives to forecast accurately as there is little correlation between forecasting accuracy and revenue earnt in the spot market.

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