Indonesia has large renewable energy resources that are not always located in regions where they are needed. Sub-sea power transmission cables, or island links, could connect Indonesia's high-demand islands, like Java, to large-resource islands. However, the role of island links in Indonesia's energy transition has been explored in a limited fashion. Considering Indonesia's current fossil fuel dependency, this is a critical knowledge gap. Here we assess the role of island links in Indonesia's full power sector decarbonisation via energy system optimisation modelling and an extensive scenario and sensitivity analysis. We find that island links could be crucial by providing access to the most cost-effective resources across the country, like onshore photovoltaics (PV) and hydropower from Kalimantan and geothermal from Sumatera. In 2050, 43 GW of inter-island transmission lines enable 410 GWp of PV providing half of total generation, coupled with 100 GW of storage, at levelised system costs of 60 US$(2021)/MWh. Without island links, Java could still be supplied locally, but at 15% higher costs due to larger offshore floating PV and storage capacity requirements. Regardless of the degree of interconnection, biomass, large hydro, and geothermal remain important dispatchable generators with at least 62 GW and 23% of total generation throughout all tested scenarios. Full decarbonisation by 2040 mitigates an additional 464 MtCO2e compared to decarbonisation by 2050, but poses more challenges for renewables upscaling and fossil capacity retirement.

Current bioenergy development has emphasized on degraded land, since the sustainability of bioenergy in the forest sector remains a subject of debate related with emissions and deforestation risk. Thus, this study aims to open new perspectives of how degraded land and social forestry can be potentially combined to significantly impact the energy transition and environmental-societal enhancement. Considering sustainability of Bali as a small island with its unique customary governance structure, a model of biomass energy optimization using geospatial fuzzy-multicriteria analysis was developed to select potential green energy source sites. Firstly, potential degraded land and social forestry were mapped to identify potential feedstock, then normalized using Euclidian Distance and Fuzzy Logic based on identified five sustainability criteria. They are availability of raw material, road, port, transmission, and demand proximities. Meanwhile, using identified three restriction criteria, i.e. protected area, slope and land-use restrictions, a restriction map was developed. The two maps were then integrated using Geospatial-based multicriteria analysis, fuzzy logic and Analytical Hierarchy Process (AHP) weighting method, to further identify potential green energy source map. The integration shown a significant increase of 60 % in land availability for bioenergy development. Results of study recognized potential 36,527 ha of degraded land; 21,671 ha of social forestry; and 40 optimal locations for bioenergy facilities, considering various spatial and temporal criteria. To conclude, the identified 120 social forestry sites in Bali involving 78,385 household provide opportunity to a community based socio-economic coupled with revitalizing environment efforts, which lead to massive net zero emissions community participation. Further, the integration of social forestry and degraded land should be highly recommended to policy maker in bioenergy development.

The current focus of offshore wind industry and academia lies on regions with strong winds, neglecting areas with mild resources. Photovoltaics' cost reductions have shown that even mild resources can be harnessed economically, especially where electricity prices are high. Here, we study the technical and economic potential of offshore wind power in Indonesia as an example of mild-resource areas, using bias-corrected ERA5 data, turbine-specific power curves, and a detailed cost model. We show that low-wind-speed turbines could produce up to 6,816 TWh/year, which is 25 times Indonesia's electricity generation in 2018 and 3 times the projected 2050 generation, and up to 166 PWh/year globally. Although not yet competitive against current offshore turbines, low-wind turbines could become a crucial piece of the global climate mitigation effort in regions with vast marine areas and high electricity prices. As low-wind-speed turbines are not yet on the market, we recommend prioritizing their development.