The test was scheduled to take place over Thursday until 19.50 GMT, but National Grid data shows that the maximum available output from the plant unexpectedly fell from 780MW to zero shortly after 14.00 GMT.
Both SSE and National Grid declined to comment on the outright generation achieved by the plant before its availability was cut.
“We cannot comment in detail on the proving test, but we will be discussing the results of the test with SSE,” a spokesman for National Grid told Utility Week.
The 32 year-old plant is under contract with National Grid to be availble to provide back-up generation over the coming winter months in the event that demand outstrips the UK’s dramatically tightening supply margins.
To ensure security of supply National Grid has set a monthly test for each of the three units contracted as back-up through the supplemental balancing reserve (SBR), which is paid for at the full contract rate.
Peterhead is contracted at a rate of £250/MWh through the SBR and stands alongside RWE’s Littlebrook and Scottish Power’s Ryehouse gas-fired power plant on the reserve bench.
“They should have awarded the contract to a more reliable plant,” one UK power trader said of the Peterhead outage.
The unit was seldom used within the market but successfully completed a discretionary unpaid test on 5 November ahead of the mandatory monthly tests required as part of the contract.
“National Grid will undertake a proving test every month for all three units, through to the end of February,” a spokesman for National Grid told Utility Week. He added that £250/MWh “is the contracted price for Peterhead and that this is reflected in the offer prices that we are paying today for the test.”
The Littlebrook and Ryehouse plants have both generated power in regular market conditions in the weeks before the SBR contract began 1 November so opted to forego unpaid testing. Paid testing took place at the Ryehouse plant 19 November while Littlebrook is yet to undergo its November test.
A spokeswoman for SSE declined to comment on the cause of the outage.