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Imagine standing here next to this reservoir. Somewhere underneath the water's surface lies the town you used to live in. When this massive hydropower plant in India was constructed, up to 100,000 people had to pack up their things and leave. This is not an unusual story. Hydropower dams are monuments to progress, though they come at a huge cost. But what if we could harness the immense power of water without having to build destructive megastructures? Here are some promising examples: Let's follow the water - starting with a small creek, following the river downstream, and ending at the ocean.
We begin our journey here, where the stream is still quite small. We find a little side-arm, a canal leading into the stream. In it sits: a whirlpool, generating energy. This is a vortex power plant. The idea is simple: water flows into a round basin. This one is about four meters wide. In the middle there's a small turbine with wide blades. As the water swirls down, like in the bathtub drain, it spins the turbine - which drives a generator. The result: enough electricity for around 15 average European households. That's not huge. But imagine a couple of these along existing canals or streams, hidden away on the side, powering nearby homes, farms, or public buildings.
They can be installed quickly, and maintenance is simple too: a filter at the inlet keeps out large debris, and if something clogs, you just let water flow through the bypass. This cleans the filter in a matter of seconds. Usually, fish the size of a small trout can swim right through. Unlike big dams that block migration routes, these small power plants barely disturb the river. Still, these vortex power plants can change how the river flows and the habitats within it. That's why some people have developed different designs, like this Belgian company.
They've coated their turbine blades with rubber to make sure fish and other animals aren't harmed. In fact, the vortex basin often turns into a little biotope. Mosses and algae grow, crustaceans and small fish settle in, oxygen levels rise - creating a mini ecosystem. But despite these advantages, there are just about 35 of these power plants in the world. Because they are less efficient than their bigger cousins, their output is naturally smaller too, given their much smaller size. So, these plants are best for supplying small communities, factories, or mini-grids. For areas with bigger power needs, they're a hard sell.
"One thing is, small hydropower is fairly complicated compared to, let's say, solar." That's Lydia Powell, a public policy adviser and expert on renewable energies. But in remote areas with small streams or canals, it could be a smart, cheap, minimally invasive and decentralized solution. Our next stop: a big river. Here, the fundamental idea is even simpler: just float a turbine in the current. That's the principle behind the Stromboje, or "power buoy". It looks a bit like a submarine hull with a propeller. Anchored in the flow of the river, the rotor spins as the water pushes past it - turning the kinetic energy of the river's current into electricity.
The technology has been in development for nearly two decades and suffered many setbacks. Some designs clogged too easily; others didn't produce enough power or had a tough time transmitting the energy onto land. However, those working on improvements now claim that earlier flaws have been fixed and that output is finally high enough to make the floating power plants commercially viable. The idea is to have dozens of these buoys lined up in a stream - forming a floating "power farm" in the river. And this is where the world's first hydrokinetic turbine power farm was supposed to be built. But the installed turbine didn't meet expectations.
After a successful start, output kept dropping. And no quick fix could be found. So the project was abandoned in early 2025. But shortly after, another company took over the existing infrastructure. Using a smaller and slightly different design, their planned farm would boast 124 devices, delivering power to hundreds of households with their so-called Energyfish. They claim tests have shown the plan is feasible. But if it works at scale, remains to be seen. Still, the advantages are tempting: no dams, no flooding, fish can swim past, and the buoy can be moved or removed if needed.
Proponents of the technology see huge potential in big streams all over the world. There might also be potential in using it in strong tidal currents. An initial analysis by the inventor of the hydrokinetic turbine puts the untapped potential of peak output in South- and Southeast Asia's streams at 70 Gigawatts. That's equivalent to the capacity of almost 30 dams like the one in Tehri, in India. So, if this technology proves sufficient enough, for island nations or river communities, kinetic turbines could eventually become a local and renewable power source.
Now we've reached the mouth of the river - the place where freshwater meets the sea. And here is where another interesting hydropower idea is being tested: osmotic energy. The concept makes use of the different salinity of each water type. DW visited the world's first osmotic power plant in Norway in 2010. Let's travel back in time to see how this works: "An osmotic power plant exploits the difference between river water's low salt concentration and the high salinity of seawater to generate energy.
River water and seawater are separated by a membrane. The fresh water, shown in green, flows through the membrane to balance the salt concentration and pushes water to the top on the seawater side. That osmotic pressure can be used to run a power-generating turbine." "The membrane, that is really the heart of the system." This is Stein Erik Skilhagen, a Norwegian energy expert. Back then, he was the project lead of the first pilot osmotic power plant in Tofte, in Norway. And this is him today. "I must say that was quite a great experience when we saw that we did, in fact, create the pressurized water
which could operate the turbine." The concept of osmotic energy has been around for decades. Norway really had high hopes for the technology, but announced in 2013 that it would discontinue its efforts and "leave the technology development to other players in the global market." "The amount of water needed to transport in pipes, channels, tunnels, whatever, that in itself was very expensive. We have shown that it works. But the next step is to make it commercially viable." One of the takeaways from the test plant in Norway was that most river mouths likely aren't ideal places to set up such a plant.
Osmosis works best where there are even higher differences in salt concentrations. "As long as you have high concentrations versus low, then you can sort of harvest energy this way." That's Sandra Kentish, a chemical engineering professor and membrane researcher at the University of Melbourne. Today there are two working osmotic power plants in the world: one in Denmark and one in Fukuoka, Japan. Neither of them uses the difference between river and seawater. The Danish project uses the brine from a salt mine. This brine has a much higher salt concentration than seawater. And it's not only regular salt, sodium chloride, that can be used
for osmotic power generation. "Sodium chloride, potassium chloride, lithium chloride, it doesn't matter as long as you have a high ionic strength. So a lot of ions, a lot of salt. It doesn't matter what salt it is." The other existing osmotic power plant in Fukuoka in Japan just opened in 2025. Here, osmosis works its magic using treated wastewater and concentrated brine from a desalination plant to power its turbines. The goal is to replace the brine altogether in the future and figure out a way to use seawater instead. Because, well: about 97% of the world's water is seawater.
Cost remains the biggest challenge. Membranes are still expensive and only efficient under certain circumstances. That means electricity from osmotic power still costs way more than from other renewables. "I honestly don't think it's ever going to be river water, seawater. But maybe somebody comes up with a spectacularly better membrane next week. And, you know, we get there." These three examples show that it's possible to harness the power of water in gentle ways and in certain circumstances. If villages can generate, use and sell electricity, - they become economic agents of transformation."
"I think we need to look at these niche solutions as much, because they can affect the demand side of the equation." None of these solutions will replace huge dams tomorrow. But combined with other technologies, they could add to the clean energy mix and work as decentralized systems. Around the clock, and in all seasons. And maybe that's the real innovation: learning how to work with the flow of rivers instead of against them. "So, what do you think? Which of these solutions would work best in your country? Let us know in the comments below. And if you like this kind of videos, don't forget to hit subscribe."
