Solar power has been getting a lot of attention of late, as prices fall and efficiencies improve. But solar is by no means the only weapon in clean energy advocates' arsenal. With over 70 percent of Earth's surface covered in water, hydropower may also help give fossil fuels a run for their money. 

Here are some of the projects we've been keeping an eye on.

Pumped seawater offers on-demand hydroelectric power

One of the big drawbacks of many renewables is their relative intermittency. The sun doesn't always shine, the wind doesn't always blow, and even the oceans are sometimes calm. As reported over at TreeHugger, The Searaser aims to get around this problem using the motion of the waves to pump water uphill, which can be released again later to create on demand power. The idea has gained some prominent support, with clean energy mogul Dale Vince purchasing Searaser and announcing his ambitions for 200 commercial units in the first five years

Tidal lagoons replace controversial barrage

The Bristol Channel, which separates Southern Wales from the Southwest of England, has some of the highest tides in the world. At one point, the government was intent on building a huge tidal barrage which, it was claimed, might provide between 5 percent and 10 percent of the U.K.'s energy needs. But the plan proved controversial among environmentalists, with many arguing that the disruption to ecosystems was too high. Instead, focus has now shifted to tidal lagoons which will be much less disruptive, while still providing power to hundreds of thousands of homes. The proposed lagoon in Swansea Bay, shown in the video above, is just the first of several planned installations around Britain, three of which should be operational by 2021. 

Micro-hydroelectric power harnesses toilet flushes and showers

Large-scale hydropower tends to grab most of the headlines, but as Matt Hickman reported last month, South Korean researchers believe we may soon be able to generate electricity from toilet flushes, showers, faucets and gutters. Using a transducer that harnesses flowing water to generate small amounts of renewable energy, such devices might one day contribute to keeping the lights on. 

Harvesting hydroelectric power and cleaning up ocean plastic

Global climate change isn't the only manmade problem we are facing. We've also managed to choke up our oceans with plastic. But what if we could clean up the Great Pacific Garbage Patch and generate clean, renewable energy at the same time? Created by South Korean designer Sung Jin Cho, the Seawer Skyscraper (shown at top) is a proposed self-supported hydroelectric power station that generates electricity from waves, sun and plastic, and separates plastic particles and fluids, releasing cleaned water back into the ocean.  

Be warned, however, no such thing exists in the real world. While the project received an honorable mention in the 2014 eVolo Skyscraper Competition, be aware that what is being proposed is extraordinarily ambitious and difficult. When I wrote about a similar project, Boyan Slat's concept for floating automated ocean clean-up arrays, I quickly became aware of countless experts who were deeply skeptical of these end-of-pipe, magic-bullet solutions to such an intractable problem as marine plastic pollution. From the harsh marine environments to biofouling to the relatively fragile nature of zooplankton, their criticisms were as numerous as they were convincing. I'd love to see the Seawer prove them wrong, but I won't be holding my breath. 

Using wind power technology to harness tidal hydroelectric power

Engineering giant Siemens has long been at the forefront of wind turbine technology. The company is now operating one of the first commercial-scale tidal power plants off the Irish Coast, generating enough power for over 1,500 homes. True, that's small fry compared to wind, coal, nuclear or gas.

But you've got to start somewhere.  

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