[Objective] With the comprehensive implementation of China ’s dual carbon goals and the full -scale construction of modern new power systems, Hainan ’s isolated island power grid has maintained a clean energy installed penetration rate steadily above 87.1%. Large -scale grid integration of onshore and offshore wind power, as well as centralized and distributed photovoltaic power, brings about prominent system challenges: insufficient peak shaving and frequency regulation capacity, continuous decline in system equivalent inerti a, volatile power flow and severe voltage fluctuations. These issues create major hidden risks to the secure, stable and economical operation of the provincial power grid. Restricted by local policies that ban the construction of new coal -fired generating units, existing in-service coal-fired units serve as the only multi-functional supporting power source for Hainan Power Grid. They can provide essential ancillary services including deep peak regulation, fast primary and secondary frequency modulation, dyn amic reactive power and voltage support, emergency spinning reserve, and system black -start capability. Against the backdrop of ultra -high renewable energy penetration, this paper systematically explores feasible flexible retrofitting modes for operational coal-fired units, defines their multi dimensional core functional positioning and quantifiable technical indicators, and constructs a complete low-carbon flexible transformation framework together with targeted grid security support strategies tailored to the unique operating characteristics of isolated island power grids. 

[Methods] This study sorts out Hainan ’s current power supply mix, seasonal and diurnal load variation patterns, main grid structure and annual peak-valley balance status. On this basis, it clarifies the technical requirements for retrofitted units and proposes six transformation pathways: thermoelectric decoupling, deep peak -load retrofitting, energy storage coupling, intelligent digital operation upgrading, complementary coordination wit h new energy stations, and low -carbon emission reduction reconstruction. A multi-layer collaborative control strategy is established to mitigate grid operational risks, and the economic performance of retrofitted thermal units is quantitatively analyzed un der the rules of the provincial electricity spot market and auxiliary service market. 

[Results] Statistics indicate that Hainan’s total social electricity consumption reached 54.473 billion kW·h in 2025, with a year-on-year growth of 4.97%. Forecasts show the grid’s maximum peak shaving deficit will expand to 1.83 million kW by 2027. Comprehensive flexible retrofits can lower the minimum technical output of coal-fired units to below 25% of their rated capacity. 

[Conclusion] When combined with capacity compensation p ricing and standardized auxiliary service trading mechanisms, renovated thermal power assets can achieve coordinated optimization of grid safety operation, low -carbon energy transition and sustainable economic profitability. The research conclusions and tr ansformation pathways provide valuable engineering references for new power system construction in other isolated island power grids with high renewable energy penetration worldwide.