How a Pumped Storage Power Plant Is Turned Upside Down

You did read that correctly: Turning a pumped storage power plant upside down is an innovative idea for meeting the growing demand for storage capacity as renewable energies are expanded. My report explains how it works, why it is a forward-looking concept for numerous regions, and what key tasks Fichtner is handling to make it a success.

The expansion of renewable energies is clearly one of the greatest challenges of our time. One of the hurdles to this is the storage of electricity to balance supply and demand.

The Name Says It All: Zero Terrain Technology

Pumped storage power plants have been a proven solution to this problem for a hundred years and currently make up about 97 percent of the world’s electricity storage capacity. But building new plants is often difficult because sites with suitable topological conditions are rare. One solution that can overcome this is Zero Terrain Technology, developed by Energiasalv Pakri OÜ from Estonia.

The idea is to turn the pumped storage power plant upside down by using natural waters as the upper reservoir and a cavern as the lower reservoir. This is an idea with huge potential, as it is equally suitable for coastal regions and inland locations with large lakes or rivers if a rocky subsoil is present to permit the construction of a cavern.

“The idea of inverted pumped storage sounds simple,
but it requires special know-how”,
says Peep Siitam, founder of Energiasalv.

The first power plant employing this new concept is being built in Paldiski, in northwestern Estonia, where the Baltic Sea will be used as the upper reservoir and an artificially created cavern as the lower reservoir. Funded by the EU, a pumped storage power plant with a capacity of 500 MW is to be constructed by 2029, which can be expanded in future by building further caverns. Fichtner was contracted to find the best solution for the construction of this innovative plant.

Mining Knowledge Meets Energy Know-How

“The advantage of the Paldiski project is its simple principle, but the underground infrastructure requires much more underground work than normal,” says Peep Siitam, and he adds: “The biggest challenge is constructing the large shafts that extend 700 meters into the ground.”

The construction of ten large caverns as the lower reservoir, as well as the powerhouse and transformer caverns, poses another challenge.

For this complex task, Fichtner assembled multidisciplinary teams of energy and mining engineers, as well as geological and geotechnical experts, so that the project can be managed and supported from the design phase through to implementation.

First of all, the team worked out design alternatives, studied their feasibility and economic viability, and finally made a recommendation on the option that will now be implemented. “In a consortium with the engineering firm ‘Ingenieurbüro Steiger’, Fichtner carried out a geotechnical investigation and came up with a technical solution that is convincing in its flexibility and efficiency,” concludes Siitam.

Technical Solutions and Economic Options

In addition to complex technical and geological conditions, economic criteria naturally also play a key role in this project.

“To assess economic viability, we have to calculate such projects relative to the market,” reports Dr. Sebastian Palt, Hydropower Projects Director at Fichtner.

In this case, this means including the options on the Scandinavian power exchange ‘Nord Pool’ or on the market for balancing energy (primary, secondary and tertiary control), while also estimating future marketing potential.

Hydropower plants usually have long construction periods and are planned for decades of use. Since long-term forecasts entail numerous uncertainties, adaptability is vital. Presently, the experts see the best sales opportunities in the day-ahead market, but expect balancing energy to grow in importance.

Increasing Flexibility, Minimizing Risks

In the context of long-term economic considerations, the choice of pump-turbines, for example, is a key factor in terms of flexibility. For this reason, the choice was made to use three large pump-turbines that can react extremely quickly to changes in load and direction, thus enabling participation in the balancing energy market.

According to Peep Siitam, the project is also adaptable in other respects: “One of the biggest technical advantages of the Paldiski project is that the storage capacity could be expanded cost-effectively at any time without having to interrupt operations. That’s unique. And Fichtner’s greatest contribution to the project lies in the development of precisely this solution.”

Thinking Ahead – and About the Environment

An environmentally significant contribution that Fichtner’s team made to the plant layout is the arrangement of the inlets and outlets in the Baltic Sea. This is because during operation of the pumped storage plant, enormous masses of water are sucked in during turbine operation and pumped back into the Baltic Sea during pumping operation. If this were done by a classical inlet and outlet structure at a central point, it would result in strong currents of a magnitude of 1 m/s velocity, carrying sediments into the cavern system and affecting the flora and fauna. “To avoid this, we designed a six-arm inlet and outlet system, similar to the inlet structures of seawater desalination plants. The openings are located at a depth of about 15 meters and are so large that the velocities are less than 0.2 meters per second at full load during pumping and turbine operation,” explains Dr. Sebastian Palt. “This drastically reduces the velocities of the currents, especially at the seabed, and prevents damage to marine flora and fauna.”

Teamwork – Across All Disciplines

The importance of interdisciplinary knowledge in developing and assessing this unique facility in its entirety is illustrated by another example. The specialist expertise of Fichtner Water & Transportation’s mining department is crucial for drawing up the fresh air concept for the underground works. Ventilation of the entire plant was a key criterion for determining the diameters of the 650-meter-deep vertical shafts for supplying fresh air to the construction works.

Conclusion

The Paldiski project demonstrates the importance of interdisciplinary knowledge. And Fichtner made key contributions to the design, enabling the implementation of a technology that makes pumped storage power plants possible in regions that previously appeared unsuitable. When there is a surplus of electricity, the cavern will be emptied with the help of pump-turbines; when there is a demand for electricity, the force of the water flowing down through the pump-turbines will be used to drive the generators.

“Zero Terrain Technology enables pumped storage power plants that no longer require mountains”,

says Peep Siitam. Fichtner’s networking of knowledge and its interdisciplinary way of thinking and working are also to thank for this.

July 2023