This simple dam trick is a big win for green energy

Some countries are already taking advantage of this potential. Since 2000, 36 dams in the United States have been retrofitted with turbines, adding more than 500 megawatts of renewable generation capacity. There’s more potential out there: A 2016 US Department of Energy report found that an additional 4.8 gigawatts of electricity could be generated by modifying non-powered dams over the next three decades. In places like the United States and Western Europe, where the dam-building boom of the mid-20th century has long since faded, retrofitting may be the only option left for governments looking to ramp up hydropower. “If there are dams that are going to stay in place, let’s try to find solutions and work together to reach the optimal solution,” says McManamy.

But before anyone starts upgrading all of these dams, they might want to take another look at the numbers. It is not easy to predict accurately how much electricity a retrofitted facility will actually produce, because it turns out that not every dam is suitable for conversion. Suppose someone wants to install turbines in a dam built to hold water so that it can be used to irrigate farmers’ fields. During the growing season, much of that water is usually directed toward the crops, rather than flowing over the dam to generate electricity. Or perhaps in an area where the water is high enough to generate electricity for part of the year. Suddenly, these modified dams might not seem like a smart idea.

One recent study of modified dams in the United States, also commissioned by the Department of Energy, found that projections for their energy production skewed toward the optimistic side: On average, those forecasts were 3.6 times greater than actual output. The study found that the most successful retrofits tended to be concrete dams that were initially built to aid in navigation. (Dams are often used to widen or deepen waterways to facilitate the passage of boats.) “This is a complex issue. It is not an easy solution,” says McManamy.

But in countries like Brazil, large dams are still on the agenda. “If they are going to really develop and raise the standard of living for the country as a whole, they need energy. That’s how long and short it is,” says Michael Golding, a senior aquarist at the Wildlife Conservation Society. The country’s latest 10-year energy plan outlines the lines The petition for nine large new dams due to be completed before 2029. Rather than hope that these dams will not be built, it is important to make sure that appropriate studies are done to ensure that they are built in a way that minimizes environmental destruction, Golding says: “Often impact frameworks are The environment is not very good. They will define an area of ​​interest close to the dam and this area of ​​interest does not include all downstream impacts and upstream impacts as well.”

The Belo Monte Dam is a good example of how large dams can affect the surrounding environment. The dam complex has redirected 80 percent of the Xingu flow away from the 62-mile stretch of the river known as the Big Bend. This section of Xingu happens to be the only known wild habitat of the Zebra Pleco – a striking striped catfish loved by aquatic life. Thiago B says Koto, a postdoctoral researcher at the Tropical Rivers Laboratory at Florida International University: “There is a high risk of extinction of this species.” The effect of dams on fish species is well documented elsewhere in the world. In Washington State, the Elwha Dam has separated the upper and lower Elwha watersheds, reducing the available habitat for salmon by 90%. Some native species on the river have completely disappeared, while the numbers of others – such as the Chinook – have declined to a fraction of their previous levels.

However, in the end, even large dams may outlive their usefulness. In 2014, the last remnants of the Oasis Dam were removed for good. Chinook salmon, which for decades had been locked behind two dams, is now slowly making its way upriver. A full recovery is expected to take decades. “Dams don’t last forever,” Koto says. “There are a lot of them in abundance, but they don’t provide the minimal benefits they are supposed to.”

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