Despite Korea’s 2050 carbon neutrality pledge, the country still relies on fossil fuels for roughly 60% of its power generation, while the transition to renewables has lagged. Accelerating this transition requires strong policy support, yet recent measures—such as the 2024 restriction on new renewable energy grid connections for roughly one-third of the country's substations—have instead restricted renewable deployment. These actions cannot be regarded as unavoidable from a system operation standpoint, particularly in light of global energy transition trends.

This issue brief highlights the reduction of thermal power plants’ minimum generation levels as a key task for expanding renewable energy. Minimum generation levels refer to the guaranteed minimum output of generators, justified by claims of safety and environmental compliance, and typically applied to large-scale coal, gas, and nuclear facilities. In Korea, excessively high minimum generation levels—averaging 50–60% of capacity—are guaranteed, inevitably constraining renewable output (see table).

Under current grid operation rules, the combined minimum generation levels of must-run generators are guaranteed first, and renewables are permitted only within the remaining demand range. Once projected renewable generation exceeds this threshold, curtailment begins (Detailed Rules on Grid Evaluation and Operation Article 8.3.1). Conversely, lowering must-run generators’ minimum generation levels would reduce curtailment and enhance system stability (see figure).

International practice demonstrates that safer and more flexible operation is possible. Global guidelines recommend 20–40% as a technically sound minimum generation range, and major countries have already reformed accordingly. Japan lowered thermal plant minimum generation from 50% to 30% in 2024; India reduced from 70% to 55% in 2023 with a roadmap to reach 40%; and China, through retrofits and compensation schemes, cut levels from 60–70% to 30–40%, significantly reducing curtailment.

Korea has made limited progress. In August 2024, Jeju’s grid introduced the concept of an “output floor below minimum generation,” enabling must-run generators to operate below their conventional thresholds. However, such reforms have yet to be applied on the mainland grid, where curtailment is worsening and new renewable projects face connection bans. Mainland reforms must be expedited to enhance flexibility of existing plants and unlock fuller use of the existing grid infrastructure. The starting point is minimum generation level adjustment.