The rules below are fixed in advance and apply identically to every zone. A forecast record only means anything if the rules could not have been chosen after seeing the results, so they are published here in full.
One value per zone per day: onshore wind output at 11:00 local time on the following day, expressed as a load factor, which is generation divided by installed capacity. The forecast is issued at the day-ahead gate and published before 12:00 local time, ahead of the day-ahead auction. A forecast published after the auction has closed is not a day-ahead forecast.
Load factor rather than megawatts, because fleets grow. A record kept in megawatts would appear to improve on its own every time a wind farm is connected.
The benchmark is the transmission system operator's own published day-ahead wind forecast for the same zone and the same 11:00 target: Elia, Energinet, Fingrid, the German transmission system operators, Red Eléctrica, PSE, REN, NESO, EirGrid and SONI, Terna and APG. It is the bar to be beaten, and it is never an input.
The benchmark is frozen on first capture. Operators can and do return revised values for a past hour on a later query, and if those revisions were allowed through, the bar would move after the fact and every comparison built on it would be worthless. Metered output is the one exception, because realtime estimates are legitimately replaced by settled values. That is the outcome being measured, not the bar.
The published forecast record is write-once for the same reason. A published forecast is never rewritten after the fact.
The headline metric is nMAE, the mean absolute error as a share of installed capacity. One sample per day, on the 11:00 target, for both forecasts, over the same set of days.
Resolution is not the same thing as horizon. Averaging error across all 96 quarter-hours of a day produces a considerably smaller and much more flattering number than measuring the single day-ahead value a market participant has to commit to. Only the latter is reported here.
Where a difference between the two forecasts is too small to be meaningful, it is described that way rather than presented as a win.
An 80% interval is published alongside each forecast and is calibrated to cover approximately what it claims to cover. It is context for the point forecast rather than the product. What is measured, published and scored here is the point forecast against the operator's own.
Every zone page publishes the full daily record under these rules. Start from the zone index. Terms are defined in the glossary.