Is energy’s future dammed?
Large hydroelectric project in Portugal may point way to new alternative power source
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 humanmade cavern, valves, 9 feet in diameter, suddenly open, allowing water draining from a reservoir a few 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 reshaping a rugged river valley about 65 miles east of Porto, Portugal’s second-largest city. Besides the underground power plant, Iberdrola, the Spanish energy giant, has built three dams in the area — two on the Tamega River and one on a feeder stream — and the three resulting reservoirs sprawl over nearly 4 square miles.
But the $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 sets, 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.
While clean sources of power such as wind and solar farms 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.
Tapping a reservoir and using its water to spin underground turbines allows engineers to create renewable energy on demand. The facility stores energy in the form of water when the wind is blowing 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.
It is like a huge battery, but one that produces far more electricity for a longer duration. And reversing the flow of the turbines to pump the water back up the tunnel lets it be recharged endlessly.
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 to flooding river valleys.
And the flooding from dams can hurt riverine habitats and inundate antiquities.
In addition, the better sites already have dams on them. For that reason, energy companies may focus on upgrading existing hydroelectric facilities with pumps and other equipment so that they can keep reusing water that is lost when it flows through a conventional hydroelectric dam.