System operators warn of System Alerts risk this winter
20 November 2020
EirGrid and SONI issued their Winter Outlook for 2020-21 on 15 October in which they warned that if high generator forced outage rates continue over the winter period there is a risk of System Alerts.
The transmission system operators (TSOs) said the all-island capacity margin this winter is predicted to be 929MW (see Figure 1), with this margin having reduced every year over the past five years. This is mainly due to increasing demand, dispatchable generation exiting the market and increasing generator forced outage rates. They said that, despite the expected margin, if high forced outage rates continue over the winter, there is a risk of System Alerts, particularly when renewable generation is at a low output and support is not available from GB across the interconnectors. In NI, if the forced outage of just one large generator over the winter period coincides with low renewable generation there is a risk of a System Alert. The margin is predicted to be at its tightest at the end of November and start of December.
Of the all-island capacity margin, 786MW is predicted in RoI and 175MW in NI. Given the impact of COVID-19 this year, the TSOs expect the low demand forecasts in the Generation Capacity Statement (GCS) are more applicable for this winter, so they anticipate a peak demand of up to 6,840MW this winter, split 5,210 MW in RoI and 1,690MW in NI. This peak demand is a different day to that with the lowest margin.
The current capacity of demand side response is 553MW in RoI and 95MW in NI and with an availability factor of 40% of maximum capacity assumed, this gives a maximum availability of around 259MW.
Installed dispatchable generation in RoI is 6,454MW, which is set to reduce to 6,226MW with the closure of West Offaly and Lough Ree peat units in December. Installed dispatchable generation capacity in NI is 1,906MW; neither figures take account of outages.
Installed wind capacity grew in RoI by over 450MW in 2019 and now stands at 4,234MW; the contribution assumed for adequacy purposes is 398MW. NI installed wind capacity is 1,276MW (including small scale) with a corresponding contribution of 120MW to adequacy. Solar capacity in NI is 246MW but this does not contribute to adequacy assessments as the winter peak occurs after sunset.
Available net transfer capacity from GB to RoI for winter 2020-21 is expected to be 500MW via the East West Interconnector and 450MW via the Moyle interconnector. In line with the GCS, the TSOs have assume capacity reliance between RoI and NI of 100 MW north to south and 200MW south to north.
Noting that forced outage rates can vary sharply, with security of supply implications, the report notes that rates have increased every year in the last four years, with the all-island, RoI and NI annual forced outage rates currently standing at 10.6%, 12.2% and 6% respectively. Due to the impact of COVID-19, a number of generators had to postpone maintenance outages from the summer months until later in the year, and later in the year to next year, due to the unavailability of resources and materials from overseas. As a result, there are outages of large generator units extending into December and January where typically there would not be any large generator outages in these months. The TSOs said some conventional generators have been and continue to be, constrained off to preserve run hours ahead of the units’ scheduled maintenance to avoid running out of hours ahead of their outages.