Members of the European parliament have recently voted in favour of an energy strategy report which describes hydropower as playing “a crucial role in energy storage”. MEPs in the Industry, Research and Energy Committee said that energy storage will be essential for the transition to a decarbonised economy, acknowledging that they already know pumped storage is a technology that works well.

The report calls on EU member states to fully explore their energy storage potential looking at a range of solutions including pumped hydro. It also requests the European Commission develops a comprehensive strategy on storage in line with renewables targets. In addition the report:

  • Urges EU member states to seek ways to enhance pumped storage hydropower capacity, alongside multi-purpose uses of existing and new reservoirs.
  • Calls on member states to remove any administrative obstacles to delayed projects, and provide regulatory support for innovative approaches.
  • Points to the opportunities and environmental benefits of upgrading existing capacity for storage applications.

“The resounding vote by the European Parliament recognises the obvious: we need more energy storage. That will not happen by magic,” says Eddie Rich, Chief Executive of the International Hydropower Association. “European politicians have a huge opportunity as part of green economic stimulus packages to facilitate pumped storage hydro development through enabling policies and incentivising markets,” he added.

Recent developments

Interesting developments have been taking place at the Drax Group’s Cruachan pumped storage project in Scotland. In July 2020, the scheme begun supplying critical system support services to keep the UK’s power system secure. This was a ‘world-first’ power system stability contract with National Grid Electricity System operator (ESO).

As part of a six-year contract, one of the power station’s generating units will provide support services such as inertia to keep power supplies secure without generating any electricity, enabling more wind and solar power to come online. Drax is the first of five providers to supply system support services to the grid in a move expected to save consumers more than £120 million over the course of the contracts.

The new partnership with National Grid Electricity System Operator (ESO), which is responsible for balancing supply and demand for electricity in Great Britain, is part of a world-leading approach to managing the decarbonisation of the grid – securing electricity supplies, saving consumers money and helping to enable more wind and solar power.

Cruachan Power Station has four generating units and under the terms of the contract awarded in January one of those will provide the grid with support services including inertia, which helps to keep the electricity system running at the right frequency to reduce the risk of power cuts.

It will achieve this through using a small amount of power from the grid to spin the turbine 600 times every minute offering inertia to the grid to manage changes in frequency without generating unneeded electricity.

“Drax is a leading provider of system support services in Great Britain. This new partnership underlines our commitment to enabling a zero carbon, lower cost energy future,” commented Will Gardiner, Drax Group’s CEO. “Cruachan has played a critical role in the growth of renewables over the last decade and this new contract will enable more wind and solar power to come onto the grid in the years ahead.”

Inertia was traditionally a by-product of the kinetic energy in the spinning parts of large traditional power stations. As the country’s electricity system has transitioned from traditional sources of power like coal to renewables, there has been an increased need to separately procure inertia to maintain stable, secure supplies of power.

Through the stability tender the ESO has procured the equivalent amount of inertia as would have been provided by around five coal-fired power stations – and in the process will save consumers up to £128 million over six years.

“The GB electricity system is one of the most advanced in the world, both in terms of reliability and the levels of renewable power, and we’re really excited to be adding to that with this new approach to operating the grid,” said Julian Leslie, ESO Head of Networks. “Our contracts for stability services with providers such as Drax are cheaper and greener, reducing emissions and saving money for electricity consumers.

“This approach – creating a market for inertia and other stability services – is the first of its kind anywhere in the world and is a huge step forward in our ambition to be able to operate the GB electricity system carbon free by 2025.”

Testing and development

In July, Voith announced that model tests for two individual Pelton turbines and a storage pump have been successfully completed for the Ritom pumped storage plant in Switzerland, confirming guaranteed values and expectations.

At its research and development center, the Brunnenmühle in Heidenheim, Voith technology group successfully completed three fully homologous model acceptance tests on a 5- and 6-nozzle Pelton turbine and a storage pump.

The Voith experts determined the efficiency, maximal output, runaway speed and the hydraulic forces of the machines on the basis of the fully homologous models. The specialists also controlled the cavitation behaviour at different operating points. As a result, the subsequent behaviour of the machines were analysed and the guaranteed parameters verified. The contractually assured guarantees were confirmed by the measurements and in some cases exceeded.

Even before the model acceptance tests were carried out, the electromechanical parts of the new machines were examined with detailed simulation models and optimized with regard to all requirements, said Voith, with its team initially starting testing on the two-stage storage pump.

“The results of the model acceptance tests for the storage pump were very positive. We were able to achieve parameters that exceeded the contractually guaranteed performance,” said Christian Matten, Project Manager at Voith Hydro.

Afterwards the model acceptance tests of the two Pelton turbines were carried out. Despite the high efficiency guarantees, the parallel development of two completely different Pelton turbines and numerous conversions on the test stand, the Voith team was able to achieve the guaranteed parameters and thus successfully complete the model acceptance tests.

“Currently, the engineering of all components of the hydraulic and electric machines is in progress. The components from earlier construction phases, for example, the turbine housing and the distribution piping, are already in production. If everything goes according to schedule, these components can be installed on site in May 2021,” explained Matten.

The four Pelton turbines with a total rated output of 44MW used in the existing Ritom storage power plan will be replaced by significantly more powerful machine groups in the new power plant. Voith will supply two Pelton turbines, each up to 60MW capacity and with a 60MW storage pump.

The first machine unit will supply power for the 16.7-Hz-grid of the Swiss Federal Railways and for operating its trains. The second machine unit will feed electricity into the public 50-Hz-grid. In conjunction with the turbine, the storage pump can provide control power for rapid grid regulation and stabilization with maximum flexibility.

The new hydropower plant will provide a control band from 60MW of feed-in to 60MW of power consumption for the Swiss 50-Hz-grid. In addition, the storage pump can be accelerated and synchronized with the grid using the 50-Hz-Pelton group by means of back-to-back startup.

Connected to the grid

The Nant de Drance pumped storage project in Switzerland is probably one of the best known projects in developments, with the 900MW project expected to be complete and fully operational at the end of 2021. In August, one of the project’s pump turbines was connected to the extra-high-voltage grid for the first time, marking a major step in the current test phase.

The Nant de Drance teams have been testing some of the machines since March 2020, and on 5 August 2020  they synchronised one of the pump turbine with the extra-high-voltage grid for the first time. These grid connection tests, which were a success, are a major step in getting the power plant up and running, a process that began in November 2019 when the intake valves were opened. Numerous tests are being carried out on the pump turbines and other installations during this period to ensure that every component meets the safety, quality and reliability requirements needed for the Nant de Drance power plant.

There are currently close to 150 people working on site. Around 50 of them are involved in getting the power plant up and running, while the others are working on building the groups in the machine cavern and completing the finishing works. Commissioning is progressively carried out on several machines in parallel, which requires perfect coordination of these complex operations. The machine cavern holds a total of six pump turbines, each with a capacity of 150MW. Work will continue until the end of 2021, when the Nant de Drance plant will be fully operational.

A cutting-edge power plant

Nant de Drance SA shareholders have invested about CHF 2.2 billion in the construction of the pumped storage power plant. This investment demonstrates a long-term vision and a willingness to meet the challenges of future electricity supply. Depending on demand, the 900MW plant will be able to produce or store large quantities of energy in a very short period of time. This flexibility will play a decisive role, as electricity production becomes increasingly volatile due to the expansion of new renewable energies and the growing demand for flexibility. The balancing energy provided by Nant de Drance can balance short-term differences between electricity production and consumption. The plant will make a decisive contribution to the stability of the European electricity grid and the security of supply within Switzerland.

Construction work began on the plant back in 2008, and in July 2011, the project was modified, increasing capacity from 600 to 900MW and the upper dam raised. The machine cavern for the project was fully dug out in March 2014, with work to raise the Vieux Emosson dam completed in September 2014. Just over four years later, In December 2018, the major construction work was completed. In November 2019,  the intake valves were opened for the first time, with the turbines at the project turned on for the first time in May 2020.

Expanding capacity

The La Coche pumped-storage hydroelectric power plant located in the Tarentaise Valley, Savoie, France, was expanded with the commissioning of a new 240MW turbine generator unit late last year.

Owned and operated by state-owned Electricite de France (EDF), the existing 360MW pumped storage facility has been operational since 1976.

Preparatory earth works for the £131m (€150m) expansion of the plant was started in 2015, while the construction of the new generating unit was started in 2016.

The commissioning of the new plant, along with the upgrades to the existing pumped storage units, increases the annual generation capacity of the La Coche facility by 20% to 650GWh,  enough to meet the electricity needs of approximately 270,000 people in the Savoie region.

The La Coche power plant expansion involved the construction of a 240MW Pelton turbine generator unit in an outdoor power house, as well as modification to the water-intake pipeline system for the existing underground powerhouse.

The existing water intake shaft for the underground powerhouse was bifurcated with the installation of a Y-shaped connector, and a 2.6m-diameter steel penstock was installed to provide water supply to the new plant. The pipeline bifurcation work involved the digging of approximately 300m of tunnel.

Unlike the existing generating units of the pumped-storage power plant, the new unit will operate only in turbine mode without reversible pumping operations, due to the significant increase in water flow because of the melting snow upstream.

A new operation building and a 765kV transformer have also been built at the site, as part of the expansion.

A 240MW Pelton turbine generator unit supplied by Andtiz Hydro is installed in the new 33m-high surface power station, which is built adjacent to the existing underground power station.

The 3.6m-diameter Pelton wheel weighing 15 tonnes (t) is positioned at the bottom of the powerhouse. It rotates by water jetted by five surrounding injectors at a rate of approximately 500km/h. The rotating wheel drives the main generator positioned above to generate electricity.

The main generator weighs more than 630t comprising a rotor and a stator. The stator measures 4.5m-high and 7.5m in diameter and weighs approximately 330t, while the 4.25m-high and 4.5m-diameter rotor weighs approximately 300t. The generator components lie enclosed within an 80cm-thick reinforced cement concrete (RCC) structure.

The pre-existing pumped-storage plant comprises four reversible Francis type turbine and pump units housed in an underground power plant. Each turbine is capable of producing up to 80MW of electricity.

Located in the Tarentaise Valley, Savoie, France, the height difference between the upper and lower reservoirs of the pumped storage facility is 900m. The upper reservoir is the La Coche basin, which is fed by the tributaries of the Isère river, especially during the snowmelt season. Water from the upper reservoir flows into the lower reservoir at Aigueblanche dam, via the underground powerhouse.