Large-scale hybrid energy storage systems that combine pumped hydro storage (PHS) with battery storage are emerging as a critical solution for long-duration energy storage and grid stability. These systems leverage the complementary strengths of both technologies to address the challenges of variable renewable energy integration, providing fast response times, scalability, and sustained energy delivery. By integrating the high energy density and long-duration capabilities of pumped hydro with the rapid response and flexibility of batteries, grid operators can optimize performance across multiple timescales.
One of the key synergies in hybrid PHS-battery systems lies in their complementary ramp rates. Batteries excel at near-instantaneous response, capable of discharging or absorbing power within milliseconds to seconds. This makes them ideal for frequency regulation, short-term balancing, and smoothing out sudden fluctuations in supply or demand. Pumped hydro, while slower to start—typically requiring several minutes to reach full output—can sustain energy delivery for hours or even days due to its large storage capacity. By combining the two, grid operators can deploy batteries for immediate grid stabilization while relying on pumped hydro for sustained energy release, ensuring seamless transitions between short-term and long-term storage needs.
Scalability is another major advantage of hybrid PHS-battery systems. Pumped hydro facilities often require specific geographic conditions, such as elevation differences and water availability, limiting their standalone deployment. However, when paired with batteries, the overall system can be optimized for locations where pure PHS may not be feasible. Batteries can be deployed modularly, scaling up or down based on demand, while PHS provides the bulk energy storage backbone. This hybrid approach allows for more flexible site selection and reduces the need for oversized PHS reservoirs, lowering environmental and capital costs.
Several national grids are already exploring or implementing hybrid PHS-battery systems to enhance grid reliability and renewable integration. In the United Kingdom, the Dinorwig Power Station in Wales, one of Europe’s largest pumped hydro facilities, has been paired with battery storage to improve grid response times. The batteries handle rapid frequency deviations, while the pumped hydro system manages longer-duration energy shifts, creating a balanced storage portfolio. This configuration has proven effective in maintaining grid stability amid increasing wind power penetration.
Australia’s Hornsdale Power Reserve in South Australia provides another example. While primarily known for its large-scale lithium-ion battery system, the facility is being integrated with pumped hydro projects in the region to extend storage duration. The batteries provide immediate grid services, such as inertia and frequency control, while the pumped hydro component stores excess solar and wind energy for overnight or multi-day discharge. This hybrid approach has helped South Australia achieve higher renewable energy shares without compromising reliability.
In the United States, the Bath County Pumped Storage Station in Virginia, the largest PHS facility in the country, is being evaluated for hybridization with battery storage. The goal is to enhance the plant’s ability to respond to rapid changes in demand while maintaining its role as a long-duration storage asset. Preliminary studies suggest that adding battery capacity could reduce the wear and tear on PHS turbines by minimizing the need for frequent starts and stops, thereby extending the lifespan of the infrastructure.
The operational benefits of hybrid PHS-battery systems extend beyond technical performance. Economically, these systems can optimize revenue streams by participating in multiple energy markets. Batteries can capitalize on high-value, short-duration services like frequency regulation, while pumped hydro earns revenue from energy arbitrage and capacity markets. This dual-market participation improves the financial viability of storage projects, making them more attractive to investors.
From a grid resilience perspective, hybrid systems offer redundancy. If one component is unavailable due to maintenance or unforeseen outages, the other can compensate to a degree, reducing the risk of supply shortages. This is particularly important in regions with high renewable penetration, where storage systems must be highly reliable to back up intermittent generation.
Challenges remain in deploying hybrid PHS-battery systems at scale. Coordinating the control systems of two fundamentally different technologies requires sophisticated energy management software capable of real-time optimization. Additionally, regulatory frameworks often lag behind technological advancements, creating barriers to market participation for hybrid systems. However, as more pilot projects demonstrate success, policymakers are beginning to adapt regulations to accommodate these innovations.
Future developments in hybrid PHS-battery systems will likely focus on increasing efficiency and reducing costs. Advances in battery chemistry, such as solid-state or flow batteries, could further enhance the synergy between the two technologies by improving energy density and cycle life. Similarly, innovations in pumped hydro, such as underground or seawater-based systems, could expand the geographic feasibility of these hybrids.
In summary, large-scale hybrid energy storage systems combining pumped hydro and batteries represent a transformative approach to long-duration storage and grid stability. By harnessing the rapid response of batteries and the enduring capacity of pumped hydro, these systems provide a balanced solution for renewable integration. Real-world implementations in the UK, Australia, and the US demonstrate their viability, offering a blueprint for other nations seeking to enhance their energy storage infrastructure. As technology and markets evolve, hybrid PHS-battery systems are poised to play a pivotal role in the global transition to sustainable energy.