A model of the 2020 Irish All-island electricity system has been developed and solved in PLEXOS, an economic dispatch, unit commitment tool. The model also includes a simplified British power system, the proposed installed wind capacity of Great Britain and interconnectors between the two systems. From the model wind curtailment was determined under two offshore/onshore wind mix scenarios (installed offshore wind capacity ranging from 25-2700MW) while considering three different system non-synchronous penetration limits (ranging from 50-70%). The onshore wind capacities of each scenario are adjusted in order to achieve the 2020 renewable generation targets for the island of Ireland. Results clearly indicate the need to increase the system non-synchronous generation penetration limit as high as possible due to the large amount of additional installed wind capacity required to achieve the renewable targets otherwise. Additionally there is a clear benefit in having a portion of the wind capacity installed offshore in terms of reducing wind curtailment and wholesale electricity prices on the electricity system.