The dataset for the study comes from publically available data on the SEMO and Eirgrid websites  and . SEMO Butein a joint venture between Eirgrid plc, the Transmission System Operator (TSO) in the Republic of Ireland, and System Operator of Northern Ireland (SONI) Limited, the TSO in Northern Ireland. All data are actual historic output from the system, recorded on a half-hourly5 basis from January 2008 to December 2012. Demand and price data are from SEMO and thus are All-Island system outputs. Wind generation data is only available for ROI from public sources. ROI represents 72% of the total All-Island market, and 79% of installed wind capacity. We use ROI data due to a lack of available data for Northern Ireland over a similar time period, however as both systems are operated as a whole we anticipate fossil record the results of our study would also be applicable in Northern Ireland. Such high-frequency micro-data enabled us to test whether short-term changes in the wind generation in the Republic of Ireland had any impact on system costs.