Tuesday, August 14, 2007

Using tides to create electric power

Watch out Bonnie, there might be big propellers under the water in the East River.

A company that seems to have some trouble designing cast aluminum turbine blades has installed a small number of test turbines in the East River. The currents are so strong that several of the turbine propellers have been sheared off a third of the way down, and stronger replacements were hampered by insufficiently strong bolt connections to the turbine hubs. The East River is not actually a river; it's a tidal strait, and one can easily observe the current moving in opposite directions with the tides. The plan is to install a field of turbines anchored to the bottom of the East River and use the currents to generate electricity for the city.

It is worrying when the founder of the company, Trey Taylor, thinks that: "The only way for us to learn is to get the turbines into the water and start breaking them." The trial turbines — five generating electricity and one housing the dynamometer that measures water rotational speed — have been installed on the bottom of a narrow strip of the river’s eastern channel.


bonnie said...

Ha! Thanks for the warning! I did know about that. Won't have to worry about those in Jamaica Bay. Currents there are pretty inconsequential. I do pay attention to the tides but mostly to make sure I don't paddle out somewhere on the ebb & get stuck having to take the long way around getting back 'cause there's no water left over the way I got there!

There was actually quite a bit of consternation among the local paddlers when that project got going - they weren't all that far below the surface, and people were worried about whether they could be injured by the spinning blades if they happened to have the misfortune to fall out of their boat in that area. Apparently that's not really a risk. Scuba divers might want to look out but fortunately that's not a scuba hot spot!

It seems like a really good idea, but I can see why they are having problems - the stretch of the East River where I think they put the turbines is pretty effectively corked by Roosevelt Island. Currents on the Hudson get up to close to 3 on the ebb, slightly less on the flood (think there's a bit of a river effect there, the ebb is always a bit longer & stronger than the flood - and in snowmelt season in the spring, the current sometimes never really turns to go north, just sort of slows down & speeds up according to the tides!). I think the East River max current speed along the Roosevelt Island section is around 7 knots. Riding with it is fun - you fly. Having something fixed in place against that power, even if it's spinning - that's a lot of force to handle.

EVK4 said...

A friend of mine is in the renewable energy business; when we were discussing the amount of tidal flow going in and out of SF Bay one day, he mentioned that the one thing keeping it from being a huge source of energy is saltwater. It's just too darned corrosive. The materials just aren't there yet to produce energy anywhere near the $0.08/kwh that they can do with coal.

for reference, photovoltaic is in the high 20s, wind is in the high teens, and some forms of solar are in the low teens.

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