Thursday, August 16, 2007

Catching the Flow

Of all the different technologies for producing energy, I've probably devoted the least space in this blog to those that extract energy from flowing water. Large hydroelectric dams are hardly novel; they generate about 7% of our electricity. But at least in the US, most of the attractive locations for large-scale hydropower have already been dammed or determined to be too pristine to exploit. "Mini-hydro", in the form of small dams or "run of river" installations is an interesting alternative, and it looks a lot more palatable than its larger cousin. The other day I ran across a link to a video report on a project that has fascinated me since I first heard about it in the late 1990s. It is a hybrid of hydropower and tidal power, tapping the tidal energy of the East River alongside Manhattan with turbines installed on the riverbed.

The initial size of this project is tiny; it will only power a supermarket and parking garage, when it runs, but the developers hope to scale up to 10 MW--still a lot smaller than the typical power plant or wind farm. This kind of tidal power application falls somewhere in the middle of the spectrum of renewable electricity sources: much more predictable than wind, but less reliable than geothermal or conventional hydro. Where it shines is in its unobtrusiveness, which might enable it to fly under the NIMBY radar in a way that wind turbines can't.

For that matter, the turbines used in the East River ought to work just as well in a river flowing due to gravity, like the St. Laurence, instead of one that reverses flow when the tide changes direction. It could provide a useful alternative to the standard approach to mini-hydro, which avoids large dams and reservoirs, but still entails diverting and empounding a portion of the flowing river. The reliability and environmental impact of "kinetic hydropower" remains to be determined, however. I will be watching the East River project with interest to see whether this emerges as a viable competitor or ends up as another interesting, but not very practical energy idea.

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