Island energy systems should aim for a better integration of local resources and exploit their potential for local energy supply to increase their independence and security of supply besides other benefits. Two trends addressing this problem can be observed: On the one hand, increasing the local use of renewable electricity in the electricity sector by investing in Battery Energy Storage Systems (BESS). On the other hand, the integration of all energy sectors into a Smart Energy System (SES) with the conversion of renewable electricity to heat - thus enabling the usage of Thermal Energy Storage (TES). In this paper, these two potential approaches are investigated through energy systems analyses using EnergyPLAN for the Danish island Samsra and the Orkney islands in Scotland. This investigation shows that BESS tend to address only the electricity sector, while TES furthermore improves issues in the heating sector and enables possibilities in the transport sector. The TES approach results in overall reduced energy system costs, while the BESS has a stronger effect on the exchange of electricity. Depending on the various energy systems, both approaches present potential solutions, while the SES approach with the use of TES demonstrates more advantages for the whole energy system. (C) 2019 Elsevier Ltd. All rights reserved.