Pumped storage is currently the only energy technology capable of storing electricity on a large scale and in a cost-effective and sustainable way, while also providing flexible supply to grids with a high share of variable renewables. Thus, capacities are expected to grow substantially to 700GW by 2050.

Based on the principle of prioritising renewable energies in the load order, the long-term design of the system should aim at reducing and even preventing situations that will force the system administrator to stop or reduce production due to the risk of system survivability.

Therefore, given the random nature of the availability of solar and wind energies and the volatility that characterises them, the enormous absorption of these technologies (especially in island markets) presents a significant challenge for the designers of the electricity sector.

With the integration of large quantities of renewable energies into the mix, the importance of the development of energy storage potential will also increase. On the one hand, it will contribute to the increasing efficiency of renewable energies by utilising them at the desired time, and on the other will be a valuable tool to ensure the flexibility required in the operation of the electricity sector.

The efficient storage of energy is a crucial piece of the renewable revolution puzzle to fight climate change, reduce greenhouse gas emissions and protect the earth’s resources and biodiversity.

Today, with a share of 96%, pumped storage is the dominant storage technology in the world. It is the ultimate choice for grid-scale energy storage, bulk power management and flexible wholesale ancillary services helping to provide grid stability.

Austrian examples

As part of the Climate and Energy Strategy 2030, Austria has set itself the goal of increasing the share of renewable energy in gross final energy consumption to 45-50% by 2030. In addition, the aim is to cover 100% of total electricity consumption (national balance sheet) in 2030 from renewable energy sources.

The latest generation of pumped storage power plants that will be connected to the Austrian grid in the coming years, such as the Tauernmoos PSPP of the Austrian Federal Railways and Kühtai II PSPP of TIWAG, are strengthening this pioneering role. The new technology used enables maximum flexibility and can thus make a valuable contribution to the future energy system.

As an example, the Kühtai II project is a 130MW pumped storage project planned as the second upper stage of the existing Sellrain-Silz power plant group. It involves the construction of a new underground power plant, a new Kühtai reservoir, and a water diversion gallery with six water intakes.

The new Kühtai reservoir will have a storage volume of 31Mm3 approximately half the size of the existing reservoir Finstertal. It will be created with the construction of a 113m high and 510m long earth core rockfill dam.

A 25.5km long and 5m diameter transmountain water diversion tunnel will be constructed to deliver water into the new Kühtai reservoir, via the central and eastern Ötztal valley and the rear section of the Stubaital valley.

The underground power plant will be equipped with two reversible spiral Francis pump-turbine units of 65MW of power generation capacity each (90m3 in generation mode). The powerhouse is located at a depth of 174m below the surface and the plant is designed for combined turbine and pump operation.

The electricity produced by the Kühtai 2 pumped-storage facility will be evacuated through an underground 220kV power transmission line and tunnel connecting the existing Kühtai power plant for onward transmission to the grid.


Vattenfall has started a feasibility study where the possibility of restoring Juktan’s pumped storage power plant is being investigated. As part of the feasibility study, AFRY’s role will be to investigate the technology areas of the existing units, civil work, electricity and permits.

Juktan’s power plant is located between the Storjuktan and Storuman lakes in the upper part of the Ume River, 20km north of Storuman municipality. This power plant was the first large, pumped storage plant in Sweden and also the largest pumped storage power plant in operation from 1979 to 1996 with a storage capacity of ~30GWh. An unusual advantage of Juktan’s reservoir design is that you can pump water from Storjuktan-to-Blaiksjön with a lower potential and generate with a higher potential from Blaiksjön-to-Storuman.

If Juktan is restored as a pumped storage power plant, it will be Sweden’s largest pumped storage power plant with a storage capacity of approximately 300,000 Tesla batteries. This giant battery can store energy without any major energy losses once the water is pumped to the highest level in the Blaiksjön Dam. Furthermore, this type of large-scale energy storage is necessary to stabilise the electricity grid and to help enable the significant industrial investments that are taking place in northern Sweden.

The feasibility study is ongoing until mid-2023 and when a decision is made on a return to pump operation, commissioning is expected to be in 2031.


The Israel Government through the Electricity Authority and Israel Electric Company is encouraging the private sector to initiate and operate private alternative power systems.

The Manara power station, operated by an operation and maintenance contractor, will serve as a hot reserve for the Israel Electric Company during times of high demand when it is required to supply high production capacities. The scheme for the daily production of electricity will be determined by IEC, which will dispatch the power station for electricity supply to the grid in accordance with its needs. Based on the principles of the tariff arrangements, the pumping costs during production will be totally covered by the Israel Electric Company through its payments for the electricity produced.

Manara is a kibbutz in northern Israel. Located in the Upper Galilee adjacent to the Lebanese border and overlooking the Hula Valley, it falls under the jurisdiction of the Upper Galilee Regional Council. The Manara Pump Storage Project will have an installed capacity of 156MW. The powerhouse is situated in a cavern inside the mountain hills and includes one pump-turbine, one motor-generator and a step-up transformer with a total installed capacity of 156MW. The upper reservoir with an active storage of 1.2Mm³ is designed as the daily reservoir. The power water way with a length of round 1100m and 3m diameter is connected to the lower reservoir with an active storage of 1.24Mm³.

The design of the system is compliant with a daily cycle (generation and pumping). The project includes one pump-turbine unit that is able to convert hydraulic energy into electric energy and vice-versa.

The pump-turbine is capable of fully automatic operation and of providing several operating modes and capabilities. In turbine operation, the pump-turbine is suitable for frequency control within all the load range.

The entire start/stop, dewatering, coupling, operation and synchronisation will be automatically controlled by means of computerised controllers, connected to indicators and sensors on the systems and motors. This will ensure correct operation as a high level of availability, reliability and maintainability is required in order to satisfy grid requirements.

AFRY’s assignment covers Owner’s Engineering services for Ellomay PS Ltd. It will be an important role to ensure timely, cost and quality fulfilment for the owner, working closely with the EPC Contractor, Electra Infrastructure Ltd. Beside the site activities, AFRY will review the full design and will support the client during the commissioning of the project. The overall schedule for AFRY’s services is about 60 months.

At AFRY we are convinced about the dispatch of renewable energy in the near future and are very pleased to bring this important infrastructure project into construction and operation in due time.

This article first appeared in International Water Power magazine.