Hydropower is a cornerstone of renewable energy

Hydropower fell out of fashion in the late 20th century owing to nuclear power and extremely low electricity prices. But today, hydropower is the undisputed champion of renewable energy. It’s the most widely used carbon-free energy source, generating 15% of the world’s total electricity. In Switzerland, it accounts for nearly 53% of our renewable-energy mix. What’s more, hydropower can play a key role in achieving a net-zero energy supply. But for that, output would need to double by 2050 from its current level (1,400 GW), according to the International Energy Agency.

The biggest advantage of hydropower is its flexibility. Hydropower plants can not only generate electricity on demand, but can also absorb the electricity produced by other types of renewable energy, storing it in pumped-storage facilities. “With hydropower, we can increase our production and storage capacity for other renewables – and therefore build more solar and wind farms,” says Elena Vagnoni, project head at EPFL’s Technology Platform for Hydraulic Machines (PTMH). This R&D platform was established in 1969 and has since become a center of excellence in its field, with world-leading expertise in testing and certifying hydraulic equipment.

A paradigm shift

“At first, hydropower plants were designed for optimal efficiency and not to provide flexibility to power grids,” says Mario Paolone, who heads the PTMH as well as the Distributed Electrical Systems Lab in the School of Engineering. “But now we’re undergoing a paradigm shift, which means we need to completely rethink the way equipment is designed and used. That said, we obviously can’t tear down all our existing plants and build new ones. So we have to find ways to retrofit existing equipment, in addition to designing next-generation systems.”

We’re looking at how we can renovate hydropower plants to reduce their impact on plant and animal life and make them more resistant to the fluctuations in water levels being caused by global warming

EPFL spearheaded the EU’s biggest hydropower R&D program, called XFLEX Hydro, which has just wrapped up. “We developed a range of technology for improving the flexibility of hydropower systems without increasing their installation and maintenance costs,” says Vagnoni. The program included studying ways to optimize the use of existing equipment, analyzing the stresses on equipment in the highly dynamic operating conditions at hydropower plants, and doing research into fluid mechanics and flow control systems.

Gaining megawatts

For example, at pumped-storage plants, the pumps and hydroelectric turbines operate in series. That is, the turbines rotate to generate electricity, and the pumps use the electricity to pump water into a reservoir at a higher elevation, thus storing any surplus energy. When plant operators want to switch the order of operations, the plant has to be shut down for 10 minutes or more. To get around this problem, sceintists has designed what they call hydraulic short circuits, or systems that allow pumps and turbines to operate simultaneously. “This mechanism lets plant operators reverse the process instantly, like what happens inside a battery,” says Paolone. “We’ve already tested it successfully at several hydropower plants in Europe.”

The engineers are also examining methods for boosting the output of hydropower plants. “It’s always better to rely on a carbon-free source of energy,” says Vagnoni. They’re exploring various options, such as increasing a plant’s energy-storage capacity by installing additional pumps, placing microturbines within pipes to supply power to small villages, addressing system fatigue, dealing with sediment more effectively, adopting digital processes for monitoring, maintenance and production schedules, mapping out more granular production schedules, and gaining insight into still-obscure physical phenomena.

Of course, environmental preservation is also important. “We’re looking at how we can renovate hydropower plants to reduce their impact on plant and animal life and make them more resistant to the fluctuations in water levels being caused by global warming,” says Vagnoni.

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