Abstract
The British Isles, consisting of the United Kingdom and the Republic of Ireland, were investigated for a sustainable energy system transition towards 100% renewable energy in 2050. Under given framework conditions, three pathways comprising the entire energy system were investigated in 5-year time steps and hourly resolution applying an advanced energy system modelling tool and identifying the lowest cost solutions. The British Isles were structured into 10 sub-national regions. Special attention was paid to the high offshore wind potential of the British Isles, as well as the limited societal acceptance for onshore wind in the United Kingdom. The results indicate that a transition to 100% renewable energy is economically more attractive than the governmental strategy that involves nuclear power and fossil carbon capture and storage. The total annualised system costs can decrease to 63 b€ and a levelised cost of electricity of 40 €/MWh if onshore wind and solar photovoltaics are allowed to be built to a higher extend. High levels of electrification and sector coupling are the main reasons for decreasing primary energy demand. The multiple risks of nuclear technology can be avoided if dedicated action towards 100% renewable energy is taken.