Vanuatu has set ambitious plans to decrease carbon emissions and has advocated strongly on the international stage for climate change mitigation. However, the adoption of renewable energy in the country remains far short of stated targets, despite substantial efforts and investments. Small island developing states face unique challenges and opportunities in transitioning to renewable energy sources, yet there is a scarcity of published studies that offer comprehensive strategies to attain renewable energy goals. At the 5th PRETMM in May 2023, the Pacific regional energy ministers called for the implementation of improved planning frameworks and the adoption of capacity expansion tools to assist electricity sector planning for transition to renewables, while also ensuring the security and resilience of island grids that have a high proportion of variable renewable energy. However, given the planning capacity constraints of these small countries and unique characteristics of their grids, it is not clear how to select appropriate modelling tools and build capability to use them.

This study provides comparison of two well-known software tools, HOMER Grid and PyPSA, for capacity expansion modelling in this context, with a focus on capabilities for the integration of renewable energy on isolated island grids. The objective of 100% renewable energy by 2030 for the Efate Grid in accordance with Vanuatu's National Energy Road Map (NERM) is the test case for the study. The study evaluates the overall capabilities, advantages, and constraints of both tools, with a focus on their suitability in the context of the Pacific Island nations.

HOMER Pro is well-known for its intuitive interface and comprehensive collection of renewable energy components and has been extensively used for design and optimisation of off-grid electricity systems, however, with the launch of Homer Grid, it is increasingly being considered for on-grid applications. PyPSA is characterised for its open-source platform, adaptability and capacity to manage complex power system models with provision for generation dispatchability. A comparison of outcomes for modelling the dispatch of a base year and the least-cost capacity expansion trajectory is conducted. Validation is undertaken against the base year, and deviations in the outcomes are investigated to better understand the sources of these differences. Advantages and drawbacks of both tools considering the unique characteristics of the smaller isolated island grids are assessed.
The modelling utilises field data pertaining to the Efate Grid, the current grid architecture, energy consumption trends, geographical characteristics, and accessible renewable energy sources. The analysis examines several technological scenarios that make use of indigenous resource endowment such as wind, solar, geothermal, and coconut oil while incorporating the use of Battery Energy Storage Systems (BESS) to meet grid stability constraints and renewable energy targets.

This research makes original contributions by conducting an analysis of the suitability of HOMER Grid and PyPSA, and how they might be adapted, to inform planning within the unique characteristics of the Efate Grid and within the framework of Vanuatu's NERM objectives. The primary findings derived from the comparative analysis provide insights into least cost planning pathways, system stability, and pragmatic approaches of reaching 100% renewable energy for the Efate Grid specifically, but also more generally for other relatively smaller isolated grids.

The research underscores the importance of considering the specific needs of small island grids and provides valuable recommendations for policymakers and energy planners working towards sustainable and resilient energy systems for the broader Pacific Island region.