There are three main types of conventional or fossil fuel generation plant installed on electricity systems worldwide, including Ireland's electricity system. These are baseload generating plant, flexible/mid-merit generating plant and peaking generating plant. The Open Cycle Gas Turbine (OCGT) plants are in essence peaking generating plants.
Peaking generating plants are, in general, relatively costly to operate when they are producing electricity, but are the cheapest form of capacity to install as capital costs are comparatively low. Critically, peaking plants have the distinct operating advantage of being capable of switching on or off very quickly. Therefore they are utilised on electricity systems worldwide in order to cater for those periods when electricity demand might exceed the supply available from other generators. The extent to which such plants generate electricity can be more than 2% depending on the type of plant.
In scenarios where there is a potential supply/demand imbalance on a given day peaking capacity may only be needed to cover a few hours before switching off again. Without the back up of peaking plants, systems would be vulnerable to a shortfall in electricity supply at certain periods which would require other forms of generating capacity to be called upon that are not as flexible as peaking plants, resulting in a higher cost to the energy consumer.
In determining generation licence applications including peaking plants the Commission for Energy Regulation (CER) requires that each plant has the necessary permits including planning permission and a connection offer to the grid from EirGrid before a licence is granted.
Electricity generators include peaking plants are required to fund the cost of their connections to the gas and electricity transmission networks themselves so there is no extra cost to the consumer by virtue of where a generator decides to locate.