Ground-breaking upgrade at hydropower plant provides unexpected boost to energy security

OZ-EN-OISANS, 17 October 2022 – With energy experts scrambling to find a solution to the looming gas supply crisis in Europe, a relatively simple upgrade to a hydropower plant in France signalled that existing renewable energy assets could provide an alternative to gas-fired power plants for certain energy services. This breakthrough could help reduce the reliance on imported fossil fuel at a sensitive time for energy policies.

Since September 2021, Grand’Maison hydropower plant has been testing a new operating mode that allows it to generate and store energy at the same time. This feature, which may at first sound counter-intuitive, is actually giving the plant an edge in the liberalised European energy market, where storing excess power and providing energy at the right time is an advantage.

“Energy security is just another positive externality”, explains Prof. Francois Avellan, energy expert and advisor on the R&D project. “Our initial objective was to increase the value of existing hydropower assets,” he explains. “We wanted hydropower plants to respond to energy demands more rapidly and help them provide more services to the power grid.”

Grand’Maison pumped storage plant lower reservoir, France. Credit: Mathias Magg

After twelve months of testing and operation, EDF, France’s main power utility and the owner of the power plant, is more than satisfied with the outcomes. “Doing more with the same equipment makes sense economically, but also environmentally and strategically” explains Frédéric Corrégé, Regional Director at EDF. “Looking at the results, it’s clear that we’ve avoided the use of gas-fired power plants and reduced greenhouse gas emissions.”

The international consortium supporting the trial estimates that the new operating mode has helped the power grid save over 19,000 tons of CO2 emissions during the first six month of operation. Over the course of a year, this would be like taking 24,000 cars off the road. (1)  

The upgrade makes the power plant an attractive alternative to gas-fired power plants in the energy market. In Europe, the day-to-day operation of power plants are dictated by two factors: the fluctuations in energy consumption and the demands of power grid operators, who must ensure that the electricity distributed maintains basic quality. This means keeping voltage and frequency within tight boundaries. To do so, power plants are asked to inject or store specific quantities of power throughout the day while the system seeks to balance power supply and demand. All of this is done by advanced computer systems working 24/7.

Not all power plants can produce small quantities of energy to respond to the demand at short notice. Wind farms can’t order the wind to blow, and other power plants take a longer time to adjust. Grid operators are left to rely on two options: gas-fired power plants, which rely on fossil fuel, and hydropower plants, which use renewable energy.

Grand’Maison is one of these hydropower plants. It functions as a giant battery that pumps and stores energy in the form of water, and releases it when it is needed, to produce electricity.

Since the upgrade, Grand’Maison also does something that other pumped storage plants can’t do: running a turbine when it is in pumping mode. Generally, the two standard operating modes are mutually exclusive: at any given time, a pumped storage plant can either generate power or use the grid excess power to pump water into a reservoir.

Grand'Maison pumped storage plant high-voltage connection to the grid
Grand’Maison pumped storage plant high-voltage connection to the grid (France). Credit: Mathias Magg

The new ‘hydraulic short-circuit’ mode, or XFLEX mode, that has been tested with success at Grand’Maison will enable the power plant to enter a third state: simultaneously pumping water for energy storage and running its turbines to finely adjust power excess, if any, and provide enhanced services to the grid.

This transformation has proved so effective that the new dual mode is now used 50-70% of the time in place of strict pumping. “There is a clear added value to this upgrade” Mr Corrégé explains.  

The upgrade is part of an international initiative supported by the European Commission under the Horizon2020 research programme. The XFLEX HYDRO (2) project uses digitalization technologies to explore the operating limits of current power plants.

More power plants are due to release the results of real-life testing over the coming months. EDP, Portugal’s main utility is currently testing the new XFLEX mode at its Frades II power plant.

[1] Estimated average emissions over 15,000km:

[2] The Hydropower Extending Power System Flexibility (XFLEX HYDRO) project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 857832