New Zealand has more than 200 electricity prices. Britain has one.
New Zealand's market sets a price at every point where power enters or leaves the national grid, every half hour, so a megawatt-hour is worth more where the grid can't easily bring it. Here is one day of it, point by point.
Each square is a point on the grid, stacked by its price that half hour; the map shows where each point is, with New Zealand's wind farms as white triangles. Hover for a point's name and price.
Two islands, two prices
In 40 of the day's 48 half hours, the South Island's points averaged under NZ$15 a megawatt-hour. The North Island's averaged more than NZ$100 for most of the day, peaking at NZ$281 at 19:30, and its dearest point reached NZ$330. The islands' prices part like that when the link between them, the high-voltage cable across Cook Strait, can't carry any more: the South Island's hydro has power to spare, while the North Island, where most people live, has to run dearer plant closer to home. Only in the morning peak, around 07:30, were both islands dear at once. The dearest point was Wellsford, north of Auckland, in 38 of the 48 half hours, near the far end of the grid from where most power is made; in the other ten it was Hangatiki, in the Waikato.
Why this matters for wind
A wind farm in a nodal market earns the price at its own point. Two farms with the same wind can earn very different sums depending on where they connect, and a farm behind a full line can see its price fall towards nothing on a windy day. Britain has one national price instead, and when its lines are full it pays wind farms to turn down through the Balancing Mechanism: see a day of it, and the cost every day on our Curtailed page. New Zealand, Texas and much of the US price by point on the grid, Australia by region, and most of Europe, Britain included, by country or zone.
How this was made
Final energy prices for each point of connection and each half-hour trading period, and each point's position, from the Electricity Authority's EMI datasets (CC BY 4.0). The day is the one of the last 30 on which prices differed most from place to place. 246 points had a price that day; the 216 with a price in every half hour are shown. Times are New Zealand time, at the start of each half hour. The wind farms come from our own database. The coastline is Natural Earth's (public domain).
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