Is a dam in rural Portugal the key to our alternative energy future?


When the Portuguese power grid needs more electricity, a large multinational electricity company releases millions of gallons of water from a dammed reservoir.

Stanley Reed and Matilde Viegas traveled to Ribeira de Pena in northwest Portugal to explore the project and photograph it in depth.

When Portugal’s electrical system needs a boost, a signal activates a power plant buried deep in a hill in the scrubby, pine-covered north. Inside the man-made cavern, sluices nine feet in diameter suddenly open, allowing water flowing from a reservoir four miles away to begin flowing through four massive turbines.

Up close, the spinning turbines make a deafening din. At full power, they generate enough electricity to rival a nuclear reactor.

It’s the heart of a massive hydroelectric project that is reshaping a rugged river valley about 65 miles east of Porto, Portugal’s second-largest city after Lisbon. As well as the underground power station, Spanish energy giant Iberdrola has built three dams in the area – two on the Tâmega River and one on a feeder stream – and the resulting three reservoirs span nearly four square miles.

“These are my pyramids,” said David Rivera Pantoja, the project manager, who has worked on the project for almost 15 years.

But the 1.5 billion euro ($1.6 billion) complex of concrete, tunnels and water isn’t just huge. It also provides an answer to one of the thorniest questions facing renewable energy.

Hundreds of billions of dollars are spent worldwide on solar power and wind power. But when the sun goes down or the breeze dies down, where will the electricity come from? Iberdrola’s giant project – which uses water and gravity to generate electricity on demand, then pumps water to the upper reservoir when rates drop – is part of the solution.

The concept of storing energy in the form of water on a mountaintop has been around for over a century, but interest faded in the 1990s when natural gas-fired power plants became the go-to source. of electricity on demand, thus reducing the price differences between peak and off-peak power.

Now, however, something of a global renaissance in technology, known as pumped storage, is happening.

What has changed in countries like Portugal is the rapid growth of clean energy sources like wind and solar farms. Although these technologies produce electricity without greenhouse gas emissions, they generate a less stable flow of energy than a traditional power plant fueled by coal, natural gas or a nuclear reaction.

The ongoing shift to renewable energy sources and the move away from fossil fuel power plants creates a need for other sources of electricity that can help fill the gap.

“You can’t just have solar and wind,” said Fabian Ronningen, an analyst at Rystad Energy, a consultancy. “You need something to balance.”

Mining a reservoir and using its water to spin turbines underground allows engineers to create renewable energy on demand. The rising and falling of the dam water serve as visible markers of the ongoing process.

A facility like this on the Tâmega River in Portugal stores energy in the form of water when the wind blows strong or on sunny days, then lets it flow, generating electricity and causing the water level to drop in the upper reservoir, when energy is less abundant and more expensive.

It is like a huge battery, but produces much more electricity for a longer duration than large electricity storage facilities used for similar purposes. And reversing the flow of the turbines to pump the water into the tunnel allows it to be recharged infinitely.

Iberdrola executives say plans by governments in Europe and elsewhere to increase wind and solar power mean greater demand for facilities like Tâmega’s.

Pumped-storage power plants can also provide, essentially, energy insurance to install even more sources of clean energy generation, helping efforts to combat climate change, analysts say. Iberdrola, for example, plans to install a large wind farm nearby.

Because pumped storage power plants are so useful in keeping an electrical grid running, they find favor in many countries, including China, India, and Australia. Several proposals are also making their way to reality in the United States.

But projects of this magnitude also have substantial downsides. In Europe, the ability to build such massive facilities may be limited by high costs, long delivery times, and opposition from environmentalists and local residents who oppose flooding of river valleys. And flooding from dams can damage river habitats for fish, birds and plants and flood antiquities.

Additionally, the best venues already have dams on them, so it was quite unusual for a complex as large as the Tâmega to go ahead in a Western European country. “It was quite an exceptional project,” said Martin Burdett, editor of the International Journal on Hydropower and Dams. And the construction work is not finished yet.

For this reason, energy companies can focus on retrofitting existing hydroelectric facilities with pumps and other equipment so that they can continue to reuse water lost as it passes through a conventional hydroelectric dam.

“We are going to turn them into something better suited for the future,” said Ivar Arne Borset, senior vice president of Statkraft, a Norwegian company that is one of the world’s leading operators of hydroelectric facilities.

Yet as the climate warms, southern European countries like Portugal are becoming increasingly vulnerable to droughts, including a brutal one last summer that cut Portugal’s hydropower output by more than 50% compared to 2021.

“It’s a very expensive and very destructive way of producing energy,” said João Joanaz de Melo, associate professor in the department of environmental sciences at NOVA University in Lisbon.

Despite this, the Tâmega project obtained the stamp of approval from the European Investment Bank, the lending arm of the European Union, which granted a loan of 650 million euros.

“The planned investment for this project will reduce the Iberian market’s dependence on fossil fuels as well as carbon dioxide emissions,” the European Investment Bank said in an emailed message. The bank also wanted to stimulate the local economy and create jobs.

A Spanish government agency, the Instituto de Crédito Oficial, is granting another loan of 400 million euros. Portugal has also pledged an annual payment of €12.74 million for 10 years as an investment incentive.

Building the Tâmega facility was a long and difficult process involving much more than obtaining financial support. Iberdrola won an auction for the site in 2008, paying just over 300 million euros to use the site for 70 years, then negotiated compensation for the approximately 50 homes that were to be flooded by the reservoirs. The company agreed to pay €50 million for roads, playgrounds and sports facilities to compensate local governments. And the company has accepted environmental improvement projects like planting trees on an area of ​​land comparable to that which the dams flooded.

To ensure enough water for the power station even during droughts, Iberdrola built two dams on the Tâmega, about six miles apart. These barriers will each have turbines so that they too can generate electricity and income when the water is released.

The company also dammed a small river that flows into the larger one, creating a third reservoir high on a plateau about 2,000 feet above the valley. A four-mile, 24-foot-wide water tunnel connects this man-made lake to caverns dug deep underground where turbines and other equipment are installed.

For most of its length the tunnel is level, but as it approaches the power station it begins to drop and eventually dips vertically, creating enormous water pressure. If all four turbines are running, the water shoots out at 42,000 gallons per second. Above, at the level of the reservoir, the water level drops slowly. A one-hour release lowers the level of the upper reservoir, which is about 100 feet deep when full, or about two feet.

Construction continues at the facility. One of the dams, the Alto Tâmega, will not be completed until 2024.

The underground power plant, however, is already working. There, a team of technicians works in an underground world. This facility has started generating electricity while undergoing final adjustments.

So far, as a system that can reuse water, it proves more resilient in times of drought than conventional dams. Mr. Rivera says the facility operated almost at full capacity in the fall, releasing water when electricity prices were high and returning it when they fell. The same water went up and down, up and down all day, he said.

Iberdrola says the severe drought last summer and low water levels from traditional dams have increased the use of the storage system. The company also says periods of high and low wind and solar power generation are expected to increase demand to tap into the reservoir. The more frequently the wind turbines are used, the more revenue they will generate for Iberdrola, executives say.

The plant is installed in a large cavernous space. Technicians in yellow vests and helmets are sometimes present to carry out maintenance but are not compulsory at all times. The turbines are switched on and off from Madrid, where Iberdrola is based.

And so after 15 years, Mr. Rivera has nearly completed his monument. While countries like Portugal may lack places to build conventional dams, water is such a useful medium for storing electricity that it seems almost inevitable that more of these centers will be built.

But in the future, there may not be many more projects in Europe as huge as this one. Innovations are likely to reduce water losses and make facilities less destructive to the environment. Mr Burdett, of the International Journal on Hydropower and Dams, said existing hydropower plants would be upgraded to conserve water. He added that depleted mine shafts and excavations near the sea were all seen as alternatives to damming up rivers.


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