Renewable Energy Grid Integration Challenges in Island Nation Power Systems

Abstract

Small, electrically isolated island grids are frequently cited as ideal proving grounds for high-penetration renewable
energy, yet the same characteristics that make islands attractive for decarbonisation, small system size, limited
interconnection, and high delivered electricity costs, also make them unusually vulnerable to the frequency stability
and curtailment problems that variable solar and wind generation introduce. We compiled operational data
(2016-2023) from eight island power systems ranging in installed capacity from 6 MW to 210 MW, spanning the
Mediterranean, Caribbean, Atlantic, Pacific and Southern Ocean, and analysed one-minute frequency records,
dispatch logs and curtailment reports against each system's instantaneous variable renewable energy (vRE)
penetration to characterise the relationship between penetration level, system inertia, and operational reliability.
Across the sample, annual vRE curtailment rose approximately linearly with average annual penetration once
penetration exceeded roughly 30%, reaching a median of 18% of available vRE energy at the three
highest-penetration systems (annual average 42-61%), and instantaneous penetration above 65% was associated
with a more than fourfold increase in the frequency of under-frequency load-shedding events relative to periods
below 40% instantaneous penetration. Systems that paired high vRE shares with fast-responding battery storage
sized above roughly 15% of peak demand sustained instantaneous penetration exceeding 80% for cumulative
periods of several hundred hours per year with frequency nadirs remaining within statutory limits, while systems
lacking comparable storage or synthetic inertia provision required conservative synchronous-generator
minimum-loading rules that constrained vRE penetration well below the resource's technical potential. We found no
single penetration threshold beyond which stability degraded uniformly; rather, the effective ceiling was set jointly by
minimum system inertia, storage power and duration, and the flexibility of remaining thermal plant. These results
suggest that island decarbonisation targets expressed purely as an annual renewable energy share understate the
operational engineering required to reach them reliably, and that storage sizing and inertia provision, not generation
capacity alone, are the binding constraints on how far island systems can practically be pushed toward full
renewable supply.