We don’t talk about hydropower much in the U.S. when we talk about renewable energy. Many states don’t even count it as renewable. But as a new International Energy Agency report highlights, around the world, hydropower is seen as a significant weapon in the battle against climate change.

Check it out: Since 2005, there’s been more new hydropower generation -- around 600 terawatt-hours -- than wind, bioenergy, solar and geothermal combined (which account for less than 550 terawatt-hours combined).

According to the IEA’s Technology Roadmap for Hydropower (PDF), global installed hydropower capacities have been growing in recent years at an average of 24.2 gigawatts per year. By the end of 2011, total capacity was at 1,067 gigawatts and the new capacity under construction will drive the figure up to 1,300 gigawatts by 2017.

The IEA is enthusiastic about this expansion -- in fact, it wants to see more, aiming for a doubling of hydroelectricity output by 2050, which if accomplished would prevent up to 3 billion tons of CO2 emissions annually.

What about the other environmental angle? In the U.S.,  the damming of the Columbia and Snake rivers has decimated native salmon runs, and the loss of the Hetch Hetchy Valley in Yosemite National Park has caused similar problems. In China, the Three Gorges projects, while an aid in flood control and a big power producer, are widely considered to be an environmental disaster.

In the Technology Roadmap, the IEA argues that advances in hydropower technology and careful planning, design and implementation can make hydropower a truly sustainable form of energy. For instance, it cites new “fish-friendly” turbine designs like the Alden turbine, a project that has been backed by the U.S. Department of Energy.

The DOE, for its part, isn’t looking to use such technology on big, new dams, however. It says it wants to modernize hydropower infrastructure in the U.S., “increasing efficiency and reducing environmental impacts at existing facilities.”

In the early days of the Obama administration, $30.6 million in stimulus funding went to test innovative technologies that the department said could add power generation at just 4 cents per kilowatt-hour, a rate that is highly competitive for renewable energy. One of those backed projects was the Boulder Canyon Hydroelectric Facility in Colorado, where two older turbines were replaced by one new unit that can put out 30 percent more energy, according to the DOE.

The DOE is also excited about the possibilities for small hydro. Last November, it announced $17 million in grants for sixteen projects in eleven states, with $7.3 million of that going to ten small hydro projects. The goal, the department said, was “to research, develop and test low-head, small hydropower technologies that can be quickly and efficiently deployed at existing non-powered dams or constructed waterways.”

Another $6.8 million of the money was earmarked for two storage projects, where pumped storage hydropower is used to enable the integration of wind and solar energy, intermittent renewable sources that basically need to be used when they become available.

The challenge for pumped storage projects in the U.S. right now, however, is the price of natural gas, the IEA points out in its report. For pumped storage to be viable, there needs to be a big gap between the price of peak and off-peak power, and the shale gas boom has made gas-fired plants an economically attractive way to produce peak power at a relatively cheap cost. That leaves little incentive for investment in pumped storage.

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Editor's note: This article is reposted in its original form from EarthTechling. Author credit goes to Pete Danko.

Tags: doe, hydropower, iea