A Spanish government report shows that a lack of conventional power plants — needed to regulate grid voltage — was partly to blame for the Iberian blackout on 28 April.
This report — and May-June's surging power-sector gas demand — have sparked a discussion about gas' role in grid stability.
Conventional plants — combined-cycle gas turbines (CCGTs), nuclear and coal-fired — must provide voltage control across the Spanish grid, according to transmission system operator (TSO) Red Electrica's operating procedure.
Non-synchronous generators — such as solar and wind operators — also provide control, although not usually to the same extent.
Seven CCGTs and three nuclear plants were originally scheduled to be available for voltage control on 28 April, but the night before the blackout, one of the thermal plants — either gas or nuclear — informed Red Electrica it would not be able to operate the next day, and the TSO decided not to select a substitute.
This miscalculation resulted in "resources for voltage control [being] inferior to what they had calculated the previous morning for the middle hours [of 28 April]", the report concludes. Insufficient control at a critical moment caused a cascading disconnection of generation plants, with some disconnections happening in an "improper manner".
Gas takes centre stage
The report raises important questions about the role of CCGTs and other thermal generators in providing grid stability.
Following the blackout, more CCGTs were included in the mix "to reduce the impact that an abrupt output change may have over voltages", Red Electrica said on 13 May.
Gas has since continued to play a greater role in Spain's power mix, with CCGT output rising by 68pc on the year in May and 123pc on the year in June (see graph).
Power-sector gas demand increased to 232 GWh/d in May from 138 GWh/d a year earlier, despite overall power demand edging down to 24.5GW from 24.6GW.
Spain's overall gas burn was 789 GWh/d last month, up from 724 GWh/d a year earlier.
Power-sector gas demand on 1-22 June more than doubled from a year earlier — to 317 GWh/d from 148 GWh/d — as exceptionally hot weather boosted cooling demand. This helped to drive up overall gas use to 842 GWh/d from 701 GWh/d.
Discussions are under way around changes to CCGTs' role in voltage regulation. Market and competition regulator CNMC issued an update on technical voltage control rules on 12 June and plans to create new local markets to "contract local capacity" to better regulate voltage control through conventional generators like CCGTs, as well as renewable generators.
In addition, Spain's vice-president and ecological transition minister, Sara Aagesen, has said a forthcoming decree-law will address the "need for sufficient synchronous generation" — probably by increasing dispatch obligations for CCGTs and nuclear plants.
The energy ministry presented a draft law in December for capacity payments to CCGT operators, aiming to keep plants on line even when operating at low load factors. Such a move should help secure CCGT availability for voltage control.
