I'm wondering if there's been any investigation into why the RTD prices oscillate so much. The image below is a chart from WITS, the RTD prices are in shades of blue, the PRS in orange/purple. I've observed that the RTD prices either ramp up through a trading period then reset, or ramp down (generally corresponding with the direction demand is changing in), with the average somewhere around the PRS. For example in the chart below there's a large oscillation between $75 and $175 around 6am this morning. At the time the PRS prices were fairly stable around $120.
My understanding is the gate is closed, so the only inputs which should be changing in the RTD solves should be demand, wind and any system security constraints Transpower invokes/revokes. But why is there such a big difference between the last 5 minute of the trading period and the first 5 minute of the next? Surely when the PRS prices haven't changed indicating the generators offers haven't changed substantially and the price~demand curve is fairly flat around the margin there shouldn't be such a big swing in the RTD? And why are the RTD prices starting below the PRS and ending above?