FAQ
What is a pumped hydro storage facility?
A pumped hydro storage facility is the most advanced and cost-effective long-duration, large-scale energy storage technology available today. It helps balance the energy system by storing and supplying electricity at times when most needed.
The Paldiski 500 MW Pumped Hydro Storage Plant is Estonia’s first large-scale energy storage facility. In a water storage system, energy is produced when seawater is passed through turbines into reservoirs built 750 meters deep. When wind turbines and solar panels generate more electricity than is consumed – i.e., when electricity prices are low – seawater previously pumped into the reservoirs is returned to Paldiski Bay, thus storing energy.
Read more about the Zero Terrain technology HERE.
Why do we need pumped hydro storage?
The Paldiski underground pumped hydro storage is a strategic solution that enables Estonia’s transition to renewable energy while maintaining a reliable, stable power system and lowering electricity prices.
Just as electric cars need batteries, renewable energy requires storage. Without it, we can’t use wind or solar energy when the weather isn’t favorable or when demand peaks. Energiasalv can provide energy for up to a week—far more than any battery that is currently on the market.
Moreover, Energiasalv’s underground facility is more than a storage solution—it also enables the development of a multi-purpose underground infrastructure that can later support defense, logistics, data centers, and critical services.
How and where is the storage facility being built?
Estonia’s first large-scale pumped hydro storage facility will be built approximately 750 meters below sea level in the Pakri Peninsula, at Paldiski. The location was selected due to its favorable natural and geological conditions: sufficient sea depth, crystalline bedrock, and proximity to energy infrastructure.
Key components include underground water reservoirs carved into the bedrock, inlet channels, a turbine hall, access shafts, ventilation and cable shafts, and service tunnels.
Why is energy storage needed?
Because there always isn’t enough wind, and the sun doesn’t always shine. When more electricity is produced than needed, it can be stored and used later. This improves energy security and helps stabilize electricity prices.
Long-duration storage—ranging from tens of hours to several days—is critical. Without it, a significant share of renewable energy would be wasted, which would make the energy system inefficient.
How does pumped hydro help reduce electricity prices?
When renewable energy production exceeds demand, the Paldiski facility stores electricity by pumping water into the bay. When renewable output falls short, the system releases water through turbines to generate power.
In a 30-hour operating cycle, Energiasalv can deliver 15 million kWh of electricity to the grid—more than the daily consumption of all Estonian households combined. This reduces consumer energy costs by an estimated €131 million annually.
Why is the Paldiski PHS so important?
Paldiski’s energy storage facility is the largest renewable energy storage solution in Estonia and the Baltics, playing a key role in the region’s clean energy transition. It keeps the grid stable during production fluctuations—on calm or cloudy days, for example.
The future power system needs reliable storage not just for minutes or hours, but for entire days. Paldiski can operate at full 500 MW capacity for 30 hours straight. With a total storage capacity of 15 GWh, it’s a long-duration, high-capacity solution.
By comparison, a 100 MW industrial battery with 0.13 GWh capacity can only supply electricity for 1–2 hours. Achieving the same output as Paldiski would require dozens—or even hundreds—of battery parks, which is neither technically nor economically feasible.
Beyond storage, Paldiski is a strategic underground infrastructure project with a 100-year lifespan, strengthening Estonia’s energy security, stabilizing prices, and enabling economic growth. The space can also support data centers, manufacturing of critical goods, and emergency shelters.
How does PHS help keep energy prices low?
Pumped hydro is currently the most cost-effective technology for controlled electricity production and storage. Its use significantly reduces peak energy prices and lowers electricity costs for households and businesses alike.
The storage supplies 500 MW and 15 GWh of electricity over a 30-hour cycle—precisely when other sources can’t meet demand. This balances the grid and ensures stable prices.
Watch how it works -> Zero Terrain video
How much energy can be stored at Energiasalv?
The Paldiski facility can store up to 1.2 TWh of renewable energy per year, providing a stable and dispatchable electricity supply. Its long-duration storage system has a maximum output of 500 MW.
How much electricity does the PHS generate and consume?
A 500 MW facility can generate up to 15,000 MWh of electricity in 30 hours. It doesn’t “create” electricity from nothing but converts it—pumping water up when surplus energy is available (e.g., midday sun or nighttime wind), then generating power as the water flows back down through turbines.
The system’s efficiency is around 80%—meaning for every 100 units stored, about 80 units are returned. Around 20% is consumed by the pumps and turbine generators.
Does pumping water consume energy?
Yes, energy is used to pump water—this is true of all storage technologies. The Paldiski plant has a round-trip efficiency of around 80%, with 20% energy loss. In return, it offers immense value: flexibility, stability, and reliability.
It stores energy when renewables are abundant and releases it when demand spikes—e.g., during evening peaks—reducing the need for expensive and polluting backup generators. This makes renewable energy a reliable base load source, not just a weather-dependent addition.
Why is the Paldiski project crucial for Estonia?
The storage project saves the need to build excess generation capacity. It enables efficient use of variable sources like wind and solar—critical for a decarbonized future.
What kind of jobs and business opportunities does PHS at paldiski create?
The project brings over €1 billion in investment to Estonia and creates hundreds of direct and indirect jobs—mostly in construction, engineering, logistics, and services.
It also attracts foreign investment from businesses needing clean, reliable base-load power—like data centers, manufacturing, and critical infrastructure providers.
Paldiski is more than an energy project—it lays the foundation for a new industrial era based on clean and secure electricity.
Does the EStonian phs project harm the environment?
Environmental impact assessments concluded that, due to the project’s specific location (outside Natura-protected areas) and design, there will be no significant habitat loss or fragmentation, nor adverse effects on water resources or protected species in nearby nature reserves.
What happens to the rock excavated during construction?
A large amount of GNEISS—a durable, high-quality rock—will be excavated and reused as a valuable construction material for roads and infrastructure.
According to TalTech studies, gneiss is stronger and more weather-resistant than the commonly used limestone in Estonia. Using it means more durable roads, fewer potholes, and lower maintenance needs.
Reusing gneiss could eliminate the need for up to 400 hectares of new limestone quarries—reducing dust, noise, traffic, and environmental strain, especially near populated areas.
This approach also helps address Estonia’s estimated €500 million road maintenance backlog—as stronger materials extend road lifespans and lower public and private costs.
Gneiss reuse is circular economy at its best:
- Reducing the need for new quarries and their impact on communities
- Strengthening infrastructure with cost-effective materials
- Cutting CO₂ emissions by replacing imported crushed stone
- Supporting sustainable public construction with local resources
