National Grid ESO wants to contract power operators who can offer so-called ‘SuperSEL’ (stable export limits) services to help it keep the grid stable at times of very low demand. It wants to know about plants’ reactive power, inertia and response characteristics.
It said it was likely to call on transmission-connected plant that would support system inertia and voltage.
It is also considering reviving its ‘Demand Turn-Up’ contract, which rewarded large customers who are able to increase their usage at specific times. It is not clear that the product is permitted under the EU’s ‘Clean Energy Package’ legislation, but NGESO invited companies to provide information about their capability while that issue was addressed.
The products are part of the system operator’s response to managing the system through periods of record low demand while few industrial and commercial customers are drawing power.
On Easter Monday, demand fell to 15.2GW, compared to the previous record of 15.8GW. The system operator admitted it had not predicted such low levels: its prediction was 17.4GW, but it had overestimated consumer demand and underestimated the effect of warmer weather and embedded wind generation.
With such low levels of demand, NGESO brought 17 generating units on line to maintain system stability, a level of intervention it would not normally expect until the June or July during summer lows. It said that the cost of the day’s balancing actions meant Monday was “more expensive than average” and predicted that demand could go even lower in the bank holidays in early and late May, although that depends on weather conditions. Long term, it expects to have more, and longer, periods of very low demand as the system evolves to include more renewables and distributed generation.
The system operator is continuing to investigate whether it can source inertia from “non-traditional sources” – it usually calls on thermal plant with large rotating masses to provide the service – but said that work would not be implemented this summer.