SONI Publishes T-4 Capacity Auction Results

5 April 2023

SONI has published the provisional results of the latest capacity auction for the Single Electricity Market.

Capacity auctions are a key element of the all-island wholesale electricity market and are designed to deliver a reliable electricity supply at the least possible cost.  The auctions also aim to encourage new and efficient power plants into market.

This auction, known as a T-4 auction because it secures capacity four years in advance, ran on March 23rd, procuring sufficient capacity to meet security of supply for the period Oct 1st 2026 to September 30th 2027.

This auction secured a total of 7,204 megawatts (MW) of capacity, of which 1,519 is new generation. Gas turbines comprise most of the new generation, complemented by new interconnection, battery storage and demand side units. The auction clearing price was £76,322.95 per MW per year.

A total of £641.5 million of capacity payments will be paid to generators who were successful in this auction.

The capacity required from the auction considered peak demand, security of supply, as well as the reliability and performance of generators, and a range of demand forecasts and interconnection.

The auctions are run by SONI and EirGrid (the Electricity System Operator for the Republic of Ireland) in their roles as Transmission System Operators in Northern Ireland and Ireland respectively, through the joint venture SEMO (Single Electricity Market Operator).

The auctions were designed by the electricity regulators in Northern Ireland and Ireland to ensure sufficient capacity is secured to meet demand across the island. The next T-4 auction is scheduled to take place this September and covers the period 2027 to 2028.

The provisional results are available at Provisional Capacity Auction Results Report on the SEMO website -