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River Mouths Could Offer Hundreds of Gigawatts of Clean Energy

Gradient between fresh and salt water could be used to provide power

2 min read
River Mouths Could Offer Hundreds of Gigawatts of Clean Energy

There are a lot of rivers in the world, and a lot of places where those rivers discharge into an ocean. And according to a study published recently in Environmental Science & Technology, taking advantage of even 10 percent of those interfaces of fresh and salt water could provide more than 150 gigawatts of power.

The process is called pressure-retarded osmosis. Basically, a membrane divides fresh water coming in from the river with the salt water of the ocean or sea. The fresh water flows through the membrane due to the salinity gradient, and the pressure difference spins a turbine to generate electricity. Simple, no fuel required, and clean.

The total river discharge globally is about 37,000 cubic kilometers (somewhere in the vicinity of 10 quadrillion gallons); the new study suggests that if 10 percent of that could be exploited using pressure-retarded osmosis, it would generate 157 gigawatts of power. (For comparison: The U.S. has an electricity capacity of just over 1,000 gigawatts.) And that's 157 gigawatts of emissions-free power; the same amount from coal-fired power plants would release a billion tons of CO2 every year.

The authors of the study, Ngai Yin Yip and Menachem Elimelech of Yale University, might overshoot a bit with one number: they estimate that this power could provide electricity for 520 million people. They base that on the DOE's Energy Information Administration per-capita electricity consumption numbers, but somewhere between one and two billion people still lack electricity access. So, a couple of caveats to what seems like a really good idea: somehow using 10 percent of the world potential for river discharge power is an immense undertaking and extremely unlikely to happen on time scales that matter for emissions reductions; and no, 157 gigawatts will not provide power for half a billion people.

Still, this seems worth doing. There is one prototype facility already in place, in Norway, which we'll watch closely to see if it delivers on the concept's promise.

Image via Environmental Science & Technology

The Conversation (0)
This photograph shows a car with the words “We Drive Solar” on the door, connected to a charging station. A windmill can be seen in the background.

The Dutch city of Utrecht is embracing vehicle-to-grid technology, an example of which is shown here—an EV connected to a bidirectional charger. The historic Rijn en Zon windmill provides a fitting background for this scene.

We Drive Solar

Hundreds of charging stations for electric vehicles dot Utrecht’s urban landscape in the Netherlands like little electric mushrooms. Unlike those you may have grown accustomed to seeing, many of these stations don’t just charge electric cars—they can also send power from vehicle batteries to the local utility grid for use by homes and businesses.

Debates over the feasibility and value of such vehicle-to-grid technology go back decades. Those arguments are not yet settled. But big automakers like Volkswagen, Nissan, and Hyundai have moved to produce the kinds of cars that can use such bidirectional chargers—alongside similar vehicle-to-home technology, whereby your car can power your house, say, during a blackout, as promoted by Ford with its new F-150 Lightning. Given the rapid uptake of electric vehicles, many people are thinking hard about how to make the best use of all that rolling battery power.

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