The grid operator in Ireland has always required back up generation, known as operating reserves, in the event that a power station fails which could cause a widespread blackout. Usually, these are powered by fast acting fossil fuel plant which can be switched on in an instant. But Ireland's transition to a wind powered based grid has not resulted in less back-up, but more back-up generation which obviously has an impact on the ability of wind to reduce emissions.
The first table below is from a few years ago and shows four different types of operating reserve with a minimum requirement of 110MW during the day and 75MW during the night.
The next table is from 2020 and shows that Reserves have increased to 155MW during the day and 150MW during the night - a 40% increase during the day and a doubling during the night.
"Generally, the demand for replacement reserves increases with
increasing wind power capacity installed.
The occurrence of high demands for replacement reserves isIn another 2005 study by R. Doherty and M. O’Malley of UCD Dept of Electronic and Electrical Engineering, titled “A new approach to quantify reserve demand in systems with significant installed wind capacity” it was stated that :
mainly driven by a high number of simultaneous forced outages that happens
simultaneously to relatively high wind power. The value of these peaks tends to increase with increasing wind power capacity installed."
The methodology is applied to a model of the all Ireland electricity system, and results show that as wind power capacity increases, the system must increase the amount of reserve carried or face a measurable decrease in reliability [i.e. increase the risks of a blackout - blog note].
So this was well known, that as you increase wind energy, the grid becomes more unstable, and more back-up reserves are needed. It's becoming increasingly clear that Ireland has already reached it's limit on wind generation, where the benefits are more than offset by the costs.