Have you heard of "battery drain syndrome"? It's that flash of anxiety - one that virtually every modern person has felt at least once - when the battery indicator on a smartphone turns red. But what if that moment of "drain" struck not an individual, but an entire nation's power grid? Here is the solution to this massive energy anxiety that we've largely overlooked: pumped-storage hydropower. It is a “battery made of water”, which is both a great gift of nature and the most reliable large-scale energy storage system there is.

The Largest Battery in the World, Granted by Nature

Renewable energy sources such as solar and wind power, which are leading us into the era of carbon neutrality, are a precious gift from nature - but they have a critical weakness: "intermittency," meaning that power generation stops the moment the sun sets or the wind dies down. When energy supply fluctuates with the weather, what is the solution for filling in the missing pieces of the massive puzzle that is the national power grid? The answer lies in pumped storage hydropower - a technology that harnesses "gravity," nature's simplest principle, to generate and store energy.

Pumped-storage hydropower begins with a fascinating shift in perspective. First, two large reservoirs are built on a mountain at different elevations. During late-night hours, when electricity demand is low and power rates are inexpensive, or during the daytime, when renewable energy is produced in excess, surplus electricity is used to pump water from the lower reservoir up to the upper reservoir - a process known as “pumping.” Then, at critical moments for the power grid - when electricity demand suddenly surges or renewable energy generation drops sharply - the water stored in the upper reservoir is released downhill, turning turbines to generate electricity. While conventional hydropower generates electricity in a single burst by collecting water from a flowing river and allowing it to fall in one direction, the key to pumped storage hydropower lies in its ability to generate electricity by continuously circulating water between the upper and lower reservoirs.

As the global race toward carbon neutrality accelerates, the value of pumped storage hydropower is gaining momentum. In the past, pumped storage hydropower was confined to a passive role of storing surplus power from “base-load sources” such as nuclear and coal-fired plants. Now the paradigm has shifted completely: it serves as a “control tower” that regulates renewable energy to prevent grid overloads and delivers power the moment it is needed. Thanks to the latest variable-speed turbine technology, even the charging and discharging output can now be fine-tuned.

In fact, according to the International Hydropower Association's (IHA) “2025 World Hydropower Outlook,” global pumped storage installed capacity is projected to grow sharply from roughly 189 GW at the end of 2024 to around 280 GW by 2030.

Starting with Cheongpyeong in 1980, Korea currently operates seven pumped-storage hydropower plants, including Samnangjin, Muju, Sancheong, Yangyang, Cheongsong, and Yecheon, and plans to further expand the construction of such facilities. Three projects, including Yeongdong, Hongcheon, and Pocheon, which Hyundai E&C won, have already been ordered and are now fully underway (1,800 MW, approximately KRW 4.3 trillion, under the 9th Basic Plan for Long-Term Electricity Supply and Demand), while six additional projects (3,900 MW) are expected to be pursued going forward, opening up a vast energy civil engineering market.

The “Power Sector’s 3-Minute Standby Team” That Prevents Blackouts

You might wonder, "With lithium-ion battery ESS (Energy Storage Systems) available, why do we need to build dams in the mountains?" People tend to think of lithium-ion batteries when they hear "ESS," but the overwhelming mainstream, accounting for over 90% of the world's large-scale energy storage, is actually pumped storage hydropower. Strictly speaking, pumped storage hydropower is effectively the “original” ESS and the most advanced form of long-duration energy storage. For the past 100 years, it has flawlessly carried out the core roles of an ESS: storing surplus power, responding to peak loads (demand during periods of highest electricity use), stabilizing the grid, and supplying high-quality power. If an ESS is an electric battery, then pumped storage hydropower is essentially a "water-powered battery."

Although pumped storage hydropower demands considerable capital and time to build initially, once completed it can readily operate for at least 50 years. Viewed over the long term, it offers overwhelming economic efficiency and stability.

Pumped storage hydropower truly proves its worth when the national grid faces the threat of a blackout. Whereas nuclear and coal-fired plants take anywhere from several hours to several dozen hours to resume generation, pumped storage hydropower starts generating the moment a valve is opened, which only takes three minutes. Even during the rolling blackout of September 15, 2011, which was a close call in South Korea's power history, it was pumped storage plants that first supplied emergency power, effectively serving as the system's “firefighters.” This is why they are known as the “power sector's 3-minute standby team.”

Core Civil Engineering Technologies That Transform Natural Terrain into Energy Dams

Unlike conventional energy storage systems (ESS), which simply pack batteries into shipping containers, the task of safely constructing these massive physical storage facilities within the natural environment falls squarely within the realm of civil engineering. Because these structures must withstand the immense weight of water and the force of gravity for decades on end, the success of a pumped storage plant hinges on the precision of its civil engineering. The core technologies for managing vast mountains and water can be grouped into three main categories.

“Waterway Tunnel & Shaft”: Mastering Enormous Hydrostatic Pressure

When tens of metric tons of water per second cascade from the upper dam down to the lower dam, the hydrostatic pressure and friction acting on the interior of the tunnel that serves as the waterway are beyond imagination. Even a minuscule crack or an error of just 1 mm can cause a sharp drop in generation efficiency or a major structural accident; tunnel excavation and lining (wall reinforcement) technologies capable of fully withstanding this immense water pressure are therefore crucial to the plant's safety.

In particular, to maximize power generation through high head, vertical shafts reaching hundreds of meters in depth are excavated using specialized equipment such as RBMs (Raise Boring Machines). This process demands highly precise construction techniques, keeping the deviation between the starting and ending points within 0.2% (e.g., within roughly 0.6m for a 300m shaft).

“Underground Construction”: Burying a Building as Tall as Dozens of Stories Beneath the Ground

The turbine and generator - the core equipment of pumped-storage hydropower - are installed deep within the bedrock inside the mountain to minimize environmental damage and maximize the efficiency of the water’s head. Excavating a massive artificial cavern (chamber) as tall as a multi-story apartment building right in the heart of a solid mountain requires advanced rock mechanics and structural reinforcement technologies to withstand the immense earth pressure and weight of the entire mountain pressing down from above.

“Ground Waterproofing” to Prevent Water Leaks 

Building upper and lower dams, capable of stably maintaining massive reservoirs at the mountain’s summit and base, respectively, is both the foundation and the culmination of pumped storage hydropower. In particular, if water seeps through minute cracks in the dam’s base or through the interface between the foundation and the surrounding ground, areas subjected to high water pressure, the structural stability of the entire dam can be compromised. Therefore, precision grouting technology, which completely seals even the finest cracks in the ground to prevent water leakage, ultimately determines the lifespan of the power plant.

Precision Engineering Harnessing the Power of Nature: Hyundai E&C’s Pocheon Pumped Storage Power Plant

In the pumped-storage hydropower market, which has emerged as key infrastructure in the era of carbon neutrality, Hyundai E&C has recently demonstrated an overwhelming presence. The Pocheon Pumped-Storage Power Plant Units 1 and 2 Civil Works Project is a large-scale pumped-storage development undertaken by Korea Hydro & Nuclear Power for the first time in nearly 20 years. Located in Dopyeong-ri, Idong-myeon, Pocheon-si, Gyeonggi-do, the 700 MW facility is expected to help stabilize the power grid in the northern Seoul metropolitan area.

The upper dam, which will stand high atop the mountain, will rise 86.5 meters, while the lower dam below it will reach 58.5 meters. The rated head between the two, the height difference over which the water falls, is an impressive 307 meters. Hyundai E&C plans to bring together all of its accumulated core expertise to complete this massive “water battery.”

The success of pumped-storage hydropower depends on the technology used to build dams that can reliably contain water. Hyundai E&C’s water resource management expertise built over more than 50 years through projects such as the Samrangjin Pumped-Storage Power Plant, the pioneer of pumped-storage hydropower in Korea, the Seongdeok Multipurpose Dam, and the Peusangan Hydropower Plant in Indonesia, has become the strongest foundation for the Pocheon project.

The most challenging and critical processes in this project involve excavating the underground powerhouse cavern, which stands as tall as a 20-story apartment building, and constructing 7.8 km of tunnels, including a 3.8 km headrace tunnel. This work will fully leverage Hyundai E&C’s unrivaled expertise in rock mechanics, gained through the flawless construction of massive underground spaces that have drawn global attention, such as the Boryeong Undersea Tunnel and Singapore’s Jurong Rock Caverns.

Hyundai E&C has built unrivaled civil engineering capabilities by successfully completing numerous water-related projects at home and abroad. Through the construction of the Pocheon Pumped Storage Power Plant, the company plans to further strengthen its high-precision construction expertise while cementing its standing as an unmatched "leader in civil engineering" in the global energy market in the years ahead.