Jeju Island is being mentioned as a new pumped-storage power project site for Korea Hydro & Nuclear Power Co. (KHNP). As renewable power generation on Jeju has surged, forcing frequent curtailments, the intent is to build a pumped-storage plant to use it as a kind of battery for grid stabilization. There are seven pumped-storage plants on the mainland, but this is the first time an island region has been floated as a project site.
Pumped storage stores water by pumping it from a lower reservoir to an upper reservoir when there is surplus power, then generates electricity by releasing the water during periods of peak demand. In effect, the upper reservoir serves as an energy storage system (ESS). Accordingly, pumped-storage plants are also called WESS (Water ESS), or "water batteries."
According to the energy industry on the 4th, KHNP is conducting a site study to build at least two pumped-storage plants on Jeju Island, a region dense with renewables. The installed capacity would be 100 megawatts (MW) or less, qualifying as small pumped-storage plants. The preliminary feasibility study is in its final stage, with results expected within the third quarter.
KHNP is reviewing a pumped-storage project on Jeju because grid instability has been highlighted by the concentration of renewables. According to the Korea Power Exchange, total generation on Jeju last year was 6,607,830 MWh, of which renewables such as solar and wind accounted for 24.3%. The province plans to continue increasing renewable generation.
A drawback of renewables is that generation fluctuates with weather and time. Problems also arise when power production exceeds demand. In such cases, the grid faces strain and plants are sometimes forcibly curtailed. On Jeju, renewable curtailment rose annually to 61 times in 2021, 132 in 2022, and 181 in 2023.
Then it fell to 83 times in 2024, and did not occur at all in 2025. That is because the third high-voltage direct current (HVDC) subsea link between Wando and East Jeju entered operation, allowing surplus power to be sent out immediately.
Installing HVDC has addressed curtailment for now, but if the share of renewable generation rises, the problem could recur. Another lingering concern is that South Jeolla Province, which exchanges power with Jeju, already has high renewable output and must also absorb the electricity sent from Jeju. In short, to fundamentally stabilize the grid, Jeju needs to build ESS on the island.
Batteries for ESS are easy to install but carry fire risks. As a result, pumped storage is emerging as a long-term alternative. With pumped storage, water can be lifted to the upper reservoir when power is excessive and released to generate electricity when it is scarce. In other words, it can contribute to grid stability and peak demand support.
KHNP did not disclose which areas on Jeju it is surveying. Actual construction is expected to be possible only if the related details are included in the 12th Basic Plan for Long-term Electricity Supply and Demand.
Given Jeju's terrain, reinforcement work is a challenge when building a pumped-storage plant. The island is formed of porous volcanic rock such as basalt and volcanic ash. Because pumped storage requires impounding massive volumes of water in upper and lower reservoirs, leakage issues can arise. Ground reinforcement and leakage-blocking technologies must be employed.
A KHNP official said, "We have nearly completed the site study on whether a pumped-storage project is feasible in specific areas on Jeju," adding, "Small pumped storage can be used for grid stabilization and frequency regulation (adjusting output when supply and demand differ in the power system)."
Meanwhile, KHNP operates seven pumped-storage plants on the mainland: Cheongpyeong (400 MW), Samnyangjin (600 MW), Muju (600 MW), Sancheong (700 MW), Yangyang (1,000 MW), Cheongsong (600 MW), and Yecheon (800 MW).
In addition, under the 9th Basic Plan for Long-term Electricity Supply and Demand, new pumped-storage plants are being built in Yeongdong (500 MW), Hongcheon (600 MW), and Pocheon (700 MW). Hapcheon (900 MW) and Yeongyang (1,000 MW) are under preliminary feasibility study.