There are two GB auctions that run daily for the sale of firm exit capacity. Bids may be evergreen or reducing. An evergreen bid remains fixed throughout the day. A reducing bid reduces by 1/x with each hour that passes where it remains unallocated (where x is the number of hours remaining in the gas day at time the bid was placed).
There is also one auction that runs daily for the sale of off-peak capacity. All these are detailed below:
Day-Ahead Daily Exit Capacity (DADNEX)
Unsold obligated firm exit (flat) capacity will be made available in the DADNEX auction and is a 'pay as bid' auction.
Bid Window: D-7 05:00 to D-1 14:00
Allocation Window: D-1 15:00 to D-1 16:00
Charges: For information, please refer to the Joint Office website
Within-Day Daily Exit Capacity (WDDNEX)
Any remaining unsold capacity after the allocation of the DADNEX auction will roll over and be made available in the WDDNEX auction, which is a 'pay as bid' auction.
Bid Window: D-1 14:00 to D-0 02:00
Allocation Window: D-0 06:30 to 02:30
Charges: For information, please refer to the Joint Office website
Daily Off-Peak Exit Capacity (DONEX)
In addition to firm NTS exit (flat) capacity users may also bid for and purchase daily off-peak exit capacity. This product is sold via the DONEX auction. This amount depends of the prevailing forecast total system demand for the gas day being less than 80 per cent of the 1-in-20 peak day demand.
Bid Window: D-7 05:00 to D-1 14:00
Allocation Window: D-1 15:00 to D-1 16:00
Charges: For information, please refer to the Joint Office website
General Pricing
All auction bids will be allocated based on price (highest first) until all unsold capacity has been allocated (in line with the allocation principles as described in UNC Section B – Annex B1). Where bids exceed the available unsold quantity, National Grid may allocate these but will do so at their own discretion.