The Republic of Ireland and Northern Ireland have ambitious targets for 40% of electricity to be supplied by renewables by 2020, with the majority expected to be supplied by wind power. There is, however, already a significant amount of wind power being turned down, or ‘curtailed’, and this is expected to grow as wind penetrations increase. A model-based approach is taken to estimate curtailment using high-resolution wind speed and demand data covering four years, with a particular focus on the temporal characteristics of curtailment and factors that affect it. The model is validated using actual wind output and curtailment data from 2011. The results for 2020 are consistent with previously published estimates, and indicate curtailment levels ranging from 5.6 to 8.5% depending on assumptions examined in this study. Curtailment is found to occur predominantly at night, and to exhibit stochastic variability related to wind output. To accommodate high penetrations of wind power, the findings highlight the value of flexible demand over relatively long time-periods. The model's output data have been made publicly available for free for further investigation.