In 2007 Ireland supplied 96% of the total energy demand with fossil fuels (7% domestic and 89% imported) and 3% with renewable energy even though there are enough renewable resources to supply all the energy required As energy prices increase and the effects of global warming worsen it is essential that Ireland begins to utilise its renewable resources more effectively Therefore this study presents the first step towards a 100% renewable energy-system for Ireland The energy-system analysis tool used was EnergyPLAN as it accounts for all sectors of the energy-system that need to be considered when integrating large penetrations of renewable energy the electricity heat and transport sectors Initially a reference model of the existing Irish energy-system was constructed and subsequently three different 100% renewable energy-systems were created with each focusing on a different resource biomass hydrogen and electricity These energy-systems were compared so that the benefits from each could be used to create an optimum scenario called combination Although the results illustrate a potential 100% renewable energy-system for Ireland they have been obtained based on numerous assumptions Therefore these will need to be improved in the future before a serious roadmap can be defined for Ireland s renewable energy transition (C) 2010 Elsevier Ltd All rights reserved