Pumped Hydro Storage (PHS) is a renewable and sustainable approach for grid-level energy storage that uses the power of water to store and release electricity. As many countries look to transition to renewable energy sources like solar and wind, large-scale energy storage will play a key role in ensuring a stable supply of electricity even when the sun isn’t shining or the wind isn’t blowing. PHS holds great potential to meet this emerging need with its vast energy capacities and mature technology.
How Pumped Hydro Storage Works
At its core, pumped hydro storage uses surplus electricity, often from renewable sources like solar and wind, to Pumped Hydro Storage water from a lower elevation reservoir to a higher elevation reservoir. When power is needed, the process is reversed – the stored water is released through turbines back to the lower reservoir, generating electricity in the process.
More specifically, PHS consists of two reservoirs – an upper and lower reservoir, connected by pipes and reversible turbines/pumps. During off-peak periods or when renewable supply exceeds demand, surplus electricity is used to pump water from the lower reservoir uphill to the higher reservoir. This pumping process stores the energy in the form of gravitational potential energy of the water. Later, when electricity is in high demand, typically during evening peak hours, the water stored in the upper reservoir is released back down through turbines, which spin generators to convert the kinetic energy of the flowing water back into electrical energy that can power homes and businesses. The water then returns to the lower reservoir, completing the cycle.
Current Applications of PHS
There are over 150 PHS facilities currently in operation around the world with a combined power capacity of over 100 GW – more than all other energy storage methods combined. The largest facilities can store energy equivalent to billions of smartphone batteries. Some examples of major PHS plants include:
The Dinorwig Power Station in Wales, UK has the largest underground caverns in the world that can generate nearly 2 GW of power, enough for over 1 million homes.
The Bath County Pumped Storage Station in Virginia, US at 3.0 GW can power over 3 million homes for 8 hours.
Japan has over 30 PHS facilities providing valuable balancing services for its grid dominated by solar and wind.
India’s Kodagu PHS plant spanning 4 reservoirs generates over 1 GW.
Switzerland relies heavily on PHS to balance its hydropower and imported power.
Many other countries like China, South Korea, Germany, Italy and Canada also utilize PHS for grid balancing, renewable firming, capacity provision and energy arbitrage. With huge subterranean or mountain reservoir possibilities, PHS capacity worldwide is estimated to be over 1,000 GW ultimately.
Advantages of Pumped Hydro Storage
Some key advantages that make PHS well suited for large-scale energy storage include:
Maturity – PHS technology has been in commercial use for over 100 years giving it a proven track record. Its mechanical components have a lifespan of over 50-100 years with little maintenance required.
Scale – PHS facilities can scale from tens of MW to multiple GW, far larger than other storage options. The largest single plant stores 9.3 tWh which no other technology comes close to matching.
Cost – At scale, PHS has energy costs as low as $0.04/kWh making it very economical for grid-level storage applications. Levelized costs are already lower than many emerging storage technologies.
Sustainability – PHS is a renewable resource that utilizes the natural water cycle without GHG emissions or toxic materials as in battery technologies. Facilities operate year-round for decades.
Load Flexibility – PHS is highly flexible and able to soak up excess renewable supply within minutes or provide power within seconds during outages making it ideal for grid stabilization.
Large Energy Capacity – PHS systems can sustain peak power output for 8 hours or more depending on reservoir sizes, far exceeding other storage methods. Multiple plants chained together provide even longer discharge durations.
Multi-use Infrastructure – Upper/lower reservoirs double as recreational areas, fisheries, flood control, irrigation and municipal water supply increasing societal benefits.
Challenges of Pumped Hydro Storage
Despite its clear advantages for bulk energy storage, PHS also faces some challenges:
Long Lead Times – Sourcing suitable topography and gaining approvals for large civil works like dam construction means new PHS projects take 5-10 years to develop and complete.
High Upfront Costs – Installing complex civil infrastructure in remote mountainous areas requires billions of dollars of capital investment for projects measured in multiple GWs or more.
Geographic Limitations – Appropriate paired upper/lower reservoir sites with sufficient elevation differentials are limited worldwide constraining where PHS can be deployed.
Public Acceptance Issues – Environmental and social impacts of reservoirs and water diversion may face public opposition depending on the location. Suitable reservoir sites are often in protected areas.
Potential Impact of Climate Change – Less predictable rainfall and snowpack patterns with climate change could impact the viability of some existing and future PHS projects over the long run if water availability decreases.
Role of PHS in the Energy Transition
As the world aims to transition electricity grids to run predominantly on renewable energy, PHS plays a vital and indispensable role in providing large-scale, long-duration renewable energy storage. As the amount of variable solar and wind power increases on national grids, PHS provides the indispensable stabilizing service of soaking up excess renewable generation when supply surpasses demand and later releasing it when grid demand rises and renewable output falls off.
This balancing function allows more solar and wind capacity to be added to a grid while still maintaining grid reliability. PHS also enables renewable energy to meet continuous base load demand that today is served primarily by coal and natural gas power plants. As the renewable energy share increases to 50% or more, PHS will be essential to guarantee electricity security.
With ongoing technical innovations to improve plant efficiency, new project configurations, and exploring joint-use designs that also deliver hydropower, water supply or other benefits, the potential for PHS to store massive volumes of renewable energy globally remains largely untapped. Sensitive siting and strong community consultation will be needed given the infrastructure scale, but with costs continuing to drop and zero emissions, PHS deserves greater policy attention and targeted deployment support in the coming decades.
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1. Source: Coherent Market Insights, Public sources, Desk research.
2. We have leveraged AI tools to mine information and compile it.
