Review of off-peak prices

In May 2023, off-peak prices were particularly high for trading periods 21-34 at between $78/MWh and $245/MWh. Our Market Monitoring team has conducted analysis to understand what caused these higher off-peak prices.

Market Monitoring concluded that demand and wind forecasting differences led to pre-dispatch prices being lower than final prices for all the off-peak trading periods on 18 May 2023. This would have affected generators’, and especially thermal operators’, decision making about their offers into the market.

The issue was made worse by low wind generation, as there was less ability to run hydro in a flexible way. More hydro had to run to meet the baseload.

Other contributing factors included hydro outages on 18 May 2023 which removed ~100MW of cheaper generation in the North and South Islands. These outages were impacted by a line constraint along the Aviemore-Benmore line, which limited generation from Aviemore and others downstream of the constraint to be exported north. These outages and constraints led to more generation from Huntly 5 being cleared between trading periods 21-34.

Overall, prices were consistent with underlying conditions, so no further action is proposed.

Find out more: Review of off-peak prices on Thursday 18 May 2023.