Korea Hydro & Nuclear Power is speeding up development of pumped storage, known as a giant water battery, to ease power supply instability, cited as the biggest obstacle to building the Honam semiconductor cluster. With the surge in solar installations pushing the grid to its limits, the plan is to use energy storage systems (ESS) first and, in the mid-to-long term, use pumped storage to offset ESS's fire-risk drawback.
Pumped storage means using electricity to pump water from a lower reservoir to an upper one when there is surplus power, then releasing the water to generate electricity when power is needed. Its feature is that it can supply power immediately when supply and demand wobble. In this sense, it is also called WESS (Water ESS), or a "water battery," by analogy to ESS (energy storage system).
◇ Semiconductor plants run 24 hours… filling solar's gaps with "water batteries"
According to the industry on the 18th, KHNP issued a bid notice earlier this month for a "pre-feasibility study on pumped storage in renewable energy-concentrated areas" and began a study to build a medium-scale pumped-storage plant of more than 200 megawatts (MW) in the Honam region. The contract for the related service is planned to be signed as early as early next month.
The push for pumped storage construction in Honam is due to the "three mega projects." The Ministry of Climate, Energy and Environment expects the Honam semiconductor cluster will need 6.3 gigawatts (GW) of power. Adding data centers on top of that will require a massive amount of electricity.
Honam has abundant generation from renewables and nuclear, leaving about 3–5 GW of surplus power, but that is not enough to cover expected demand. In particular, solar generates only during certain hours between 1 p.m. and 5 p.m., creating intermittency. Semiconductor plants and data centers must run around the clock, making stable power supply essential.
In Honam, the rapid increase in solar installations frequently causes saturation of transmission and distribution networks and delays in grid connections. While power generation has jumped, the grid infrastructure to carry it is severely lacking. On spring and fall afternoons, "output control" measures—forcing generators offline to prevent grid overload—occur often.
Pumped storage is emerging as a "grid stabilization device" to offset renewable intermittency. It absorbs excess solar power generated during the day to store energy (water) in the upper dam, and when supply and demand are unstable, it can immediately release water to supply power.
In fact, according to Korea Hydro & Nuclear Power, the seven pumped-storage plants recorded a total of 9,947 starts (switching from a stop to a generation-ready state) last year. In other words, in urgent situations they released water to generate electricity nearly 10,000 times.
◇ ESS fire risks must be addressed… using existing dams slashes timeline and expense
Typically, pumped-storage plants require building both an upper and a lower dam, making the construction period long at about 10 years, and environmental damage concerns follow. It is easier and cheaper to stack ESS to store power, but many experts emphasize that even if the schedule is longer, pumped storage should be built from a long-term perspective, due to ESS's critical drawback: fire risk.
Yoo Seung-hoon, a professor in the Department of Future Energy Convergence at SeoulTech, said, "For a 500 MW buildout, pumped storage construction costs about 1.5 trillion won, while ESS can be done for 1 trillion won, so ESS is advantageous in terms of expense," but noted, "A 1 MW battery is the size of a single container, so to build 500 MW you would have to field 500 containers, creating serious site and public acceptance problems."
He added, "If a fire breaks out in an ESS, it becomes a big problem," and said, "There are not many countries that use only batteries as storage. It is ideal for ESS and pumped storage to split the role half and half."
As a construction approach, a realistic option under review is to use major dams in Honam as "lower dams (waterways)" and add only "upper dams" on nearby high mountains. This would reduce expense, construction time, and environmental impact altogether.
New pumped-storage candidate sites include Hwasun (Dongbok Dam), Jangheung (Jangheung Dam), Boseong (Boseong River Dam), and Naju (Naju Dam). However, the recent plan to supply industrial water to the southwestern semiconductor complex is entangled with this, requiring a comprehensive redesign of infrastructure.
In practice, dams are sometimes used for multiple purposes such as pumped storage and water supply. The Cheongpyeong pumped-storage plant uses the Cheongpyeong Dam as the lower reservoir while also supplying water to the greater Seoul area. It sometimes stores more water in the upper dam and releases it to the lower dam when water is short.
A KHNP official said, "We have reviewed new sites every year for Honam, where there is a lot of renewable energy," and added, "We can disclose the exact candidate sites only after the study results come out."
Considering the expected start of operations for the Honam semiconductor cluster is 2035, ESS will be more useful for now. As semiconductor fabs (manufacturing plants) are built in sequence within the cluster, pumped storage is expected to contribute to power supply starting with the later-phase fabs.