Pumped storage gets a new look for alternative energy
RIBEIRA DE PENA, PORTUGAL
When Portugal’s electrical — system needs a boost, a signal activates a power plant buried deep in a hillside in the country’s scrubby, pine-covered north. Inside the human-made cavern, valves, 9 feet in diameter, suddenly open, allowing water draining from a reservoir 4 miles away to begin streaming through four massive turbines.
Up close, the spinning turbines make an earsplitting din. At full power, they generate enough electricity to rival a nuclear reactor.
This is the heart of a vast hydroelectric project that is reshaping a rugged river valley about 65 miles east of Porto, Portugal’s second-largest city after Lisbon. Besides the underground power plant, Iberdrola, the Spanish energy giant, has built three dams in the area — two on the Tâmega River and one on a feeder stream — and the three resulting reservoirs sprawl over nearly 4 square miles.
“This is my pyramids,” said David Rivera Pantoja, the project manager, who has been working on the project for almost 15 years.
But the 1.5 billion-euro ($1.6 billion) complex of concrete, tunnels and water is not just massive. It is also providing an answer to one of the most vexing questions facing renewable energy.
Hundreds of billions of dollars are being spent across the globe on solar energy and wind power. But when the sun goes down, or the breezes become still, where will the electricity come from? Iberdrola’s giant project — which uses water and gravity to generate power on demand, and then pumps the water back to the upper reservoir when rates drop — is part of the solution.
The concept of storing energy in the form of water on top of a mountain has been around for more than a
century, but interest waned in the 1990s, when plants burning natural gas became the go-to source for on-call power, shaving the price differences between peak and off-peak power.
Now, however, a kind of global renaissance in the technology, known as pumped storage, is taking place.
What has changed in countries such as Portugal is the rapid growth of clean sources of power such as wind and solar farms. While these technologies churn out electric power free of greenhouse gas emissions, they generate an energy stream that is less steady than a traditional power plant fueled by coal, natural gas or a nuclear reaction.
The ongoing shift to renewable power sources and away from fossil fuel plants is creating a need for other sources of electricity that can help bridge the gaps.
“You can’t have just solar and wind,” said Fabian Ronningen, an analyst at Rystad Energy, a consulting firm. “You need something to balance.”
Tapping a reservoir and using its water to spin underground turbines allows engineers to create renewable energy on demand. The rise and fall of the dammed water serve as visible markers of the process taking place.
A facility such as this one on Portugal’s Tâmega River stores energy in the form of water when the wind is blowing hard or on sunny days, and then lets it flow, generating electricity and causing the water level in the upper reservoir to fall, when energy is less abundant and more expensive.
Iberdrola executives say plans by governments in Europe and elsewhere to increase wind and solar energy mean more demand for facilities like the one on the Tâmega.
Because pumped storage plants are so useful for keeping a power grid humming, they are finding favor in many countries, including China, India and Australia. Several proposals are also making their way to reality in the United States.
But projects this large also bring substantial downsides. In Europe, the scope for building such huge facilities may be limited by high costs, long lead times and opposition from environmentalists and local residents objecting to flooding river valleys. And the flooding from dams can hurt the riverine habitats of fish, birds and plants and inundate antiquities.
In addition, the better sites already have dams on them, so it was quite unusual for such a large complex as the Tâmega to go ahead in a western European country.