World's Biggest Batteries - (Pumped Storage)

Have you ever used small batteries or power banks and wondered how their larger counterparts could successfully store energy on a city or national scale? With the growing reliance on renewable energy sources, can we store enough power to energize entire cities—or even countries—repeatedly?

The short answer is yes. The detailed exploration of how this is achieved begins now.

Key Findings

• Dominance of Pumped Storage: Pumped storage hydroelectricity accounts for over 90% of global grid-scale energy storage capacity.
• Efficiency: These systems achieve a round-trip efficiency of 70-85%, making them one of the most efficient large-scale storage solutions.
• Longevity: With lifespans ranging from 50 to 100 years, pumped storage offers significant durability advantages over other technologies.
• Global Capacity: The total installed capacity worldwide exceeds 160 GW, with China, Japan, and Europe leading in adoption.
• Enduring Backbone: Despite the rapid growth of battery technologies, pumped storage continues to be the foundational technology for grid-scale energy storage.

The Mechanics of Pumped Storage Hydroelectricity

Pumped storage hydroelectricity (PSH) operates on a remarkably simple yet powerful principle. These systems utilize two water reservoirs situated at different elevations. During periods of low energy demand or excess electricity generation—often from renewable sources like wind or solar—surplus electrical energy is used to pump water from the lower reservoir to the upper reservoir.

By elevating the water, the system stores energy in the form of gravitational potential energy. When electricity demand increases, this stored energy is released by allowing water to flow back down to the lower reservoir through turbines. The flowing water converts potential energy into kinetic energy, which the turbines transform into electrical energy via generators. This process provides a rapid response to fluctuations in energy demand.

By RCraig09 - Own work, CC BY-SA 4.0, link

The operation occurs in two distinct phases:

1. During periods of excess electricity (typically at night or during peak renewable generation), water is pumped upward, storing energy.
2. When electricity demand rises, water flows downward through turbines, generating electricity much like a conventional hydroelectric plant.

Most pumped storage plants use reversible Francis turbine designs, which function as both pumps and generators depending on the water flow direction. This dual functionality minimizes the need for separate equipment, thereby reducing costs and complexity.

The Energy Storage Challenge

Electricity consumption patterns rarely match energy generation. This fundamental mismatch presents one of the greatest challenges for modern power grids.

This chart illustrates the disconnect between energy generation and consumption:

• Daily Demand (red line): Electricity demand varies throughout the day, peaking in the late afternoon and evening as household usage increases.
• Nuclear/Fossil Baseload (green line): These plants maintain steady output, providing reliable power but lacking the flexibility to adjust to demand fluctuations.
• Solar Generation (yellow line): Solar power peaks during midday but drops to zero by evening, creating a significant gap when demand rises.

The Duck Curve Phenomenon

When we subtract solar generation from total demand, energy experts refer to the resultant graph as the “duck curve” due to its distinctive shape. This curve reveals two critical challenges:

The purple “Duck Curve” line highlights:

1. Midday Surplus: During daylight hours, solar generation can create energy surpluses, resulting in negative values on the graph.
2. Evening Ramp: As solar production diminishes and demand rises, grid operators must rapidly increase output from other power sources, producing a steep upward curve.

This dramatic evening ramp creates significant stress on power grids. Conventional power plants were not designed for such rapid output changes. Energy storage systems like pumped hydro provide a crucial buffer, absorbing midday surpluses and releasing energy during evening peaks.

Engineering Challenges of Pumped Storage

While pumped storage presents powerful benefits, it faces two significant constraints:

Geographic Requirements

The ideal location for a pumped storage facility must meet several criteria:

• Two large reservoir sites located in close proximity.
• A significant elevation difference (several hundred meters).
• Suitable geological and terrain conditions.
• Minimal environmental impact.
• Access to power grid infrastructure.

Unlike battery systems, which can be deployed almost anywhere, these geographical requirements significantly restrict where pumped storage plants can be built.

Efficiency Considerations

Although pumped storage is highly efficient compared to other large-scale storage options, energy losses still occur during operation. Modern installations achieve round-trip efficiency rates of 70-85%, which means that 15-30% of input energy is lost during the storage and retrieval process.

These losses occur through:

• Friction in pipes and turbines.
• Evaporation from reservoirs.
• Inefficiencies in electrical conversions.
• Losses in pumps and generators.

Despite these challenges, pumped storage remains the most cost-effective solution for grid-scale energy storage over long operational lifespans.

Comparison of Energy Storage Technologies

This comprehensive comparison highlights how pumped storage stacks up against competing technologies:

Key Insights

Each storage technology offers distinct advantages and limitations:

The comparison reveals pumped storage’s unique value proposition: although lithium-ion batteries offer higher efficiency, pumped storage excels in cost and longevity metrics, making it particularly suited for grid stabilization and long-duration energy shifting.

Global Distribution of Pumped Storage Capacity

While this technology is widespread, installation capacity varies significantly by region:

Asian countries lead global deployment, with China and Japan together accounting for over 100 GW of installed capacity. This concentration reflects both geographical advantages and strong policy support for energy storage in these regions. Europe maintains significant capacity through facilities in mountainous areas like the Alps and Pyrenees, while the United States has developed approximately 23 GW of pumped storage, primarily in Appalachia and the western states.

Energy Storage Technology Adoption Trends

Examining global adoption trends reveals compelling insights:

While pumped storage has maintained its dominant position, lithium-ion battery deployment has shown explosive growth. Between 2015 and 2023, lithium-ion capacity increased from just 1 GW to approximately 185 GW worldwide, approaching parity with pumped storage. This rapid rise reflects declining battery costs, shorter development timelines, and greater siting flexibility.

Despite this competition, pumped storage continues to expand steadily. New facilities are under development in China, Europe, and Australia, underscoring the technology’s continuing relevance in an increasingly diversified energy storage ecosystem. Each technology seems to find its niche: pumped storage for long-duration and large-scale applications, batteries for rapid response and distributed deployment, and emerging technologies for specialized use cases.

Conclusion

Pumped storage hydroelectricity represents a remarkable achievement in large-scale energy storage technology.

While often overshadowed in the headlines by newer battery technologies, it remains the backbone of global grid-scale energy storage. Its unique blend of scale, efficiency, and longevity ensures that pumped storage will continue to play a vital role in electricity grids as renewable energy integration accelerates.