Hydrogen as an energy vector can increase penetration of renewable and intermittent sources in the energy supply of the islands and it can serve as an energy vector that may allow reaching 100% renewable energy supply of island communities. This article presents summary of the results of several case studies: Island of Mljet-Croatia, Porto Santo-Madeira, Terceira-Azores, and Malta. The islands were analysed by RenewIslands methodology and it was decided to apply hydrogen as an energy vector. Different scenarios for each island were modelled by H2RES software and required installed powers of necessary technological options are described for chosen scenarios. Basically, there were two types of scenarios. Scenarios with 30% hourly penetration limit for electricity generated by intermittent sources, as a proxy to the current conversion technology being installed in island, and scenarios without this limit, as a proxy of available conversion technology that can also provide output control and ancillary services. When hydrogen as an energy vector was introduced in the scenarios with penetration limit, it was possible to increase penetration by 4-6% of total yearly electricity demand and it was possible to satisfy 100% of transport load by hydrogen from renewable energy sources. In scenarios without penetration limit it was possible to satisfy all electricity demand and hydrogen demand for transport from renewable sources. (C) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.