I have another cool method of generating energy. There are researchers who are trying to harvest energy from various sources that are now working with a power generator that works in slow moving currents where traditional turbines have not worked effectively. This means that tidal streams and slow moving rivers in the US could generate something like 140 BILLION killowatt-hours per year or about 3.5% of our entire electricity demand. This is all according to the EPRI (Electric Power Research Institute).

In the past, most efforts to tap energy from slow moving current have used underwater windmills that use the force of the lift to turn their blades. This is because we have usually tapped air for energy and use it support boats and other water devices. But when you watch the way fish use water to propel themselves, you realize that they create vortices in the water that allow them to push off and propel themselves forward. This is why they are currently referring to this application as fish as fuel. But it has nothing to do with using actual fish as a source of fuel. Nobody is grinding up fish and putting it in an engine somewhere.

When researchers realized that these natural vortices could be used to drive generators, a new concept for creating energy emerged. A group of researchers have now created a machine called the VIVACE (Vortex Induced Vibrations for Aquatic Clean Energy) and yes I know it sounds sort of funky and even kinda geeky. But the cylinders in this new machine oscillate up and down in actual moving water. This is a first. It is especially exciting because the device works naturally in the marine environment and is non invasive.

VIVACE Photo courtesy of Vortex Hydroenergy

A description of VIVACE appears in a recent issue of the Journal of Offshore Mechanics and Arctic Engineering.

A group of engineers has built a working prototype in their lab. The spring-supported cylinder bounces up and down in a tank of moving water. This is called vortex shedding. As water drives the cylinder, the induced turbulence builds up into what we know as a “vortex” and this eventually rolls back off the cylinder, giving it a push as it goes. The next vortex that forms spins in reverse and gives a push in the OPPOSITE direction. The opposing energies force the cylinder to vibrate up and down, creating energy.

To get the whole picture, imagine a flag pole as the wind rushes past, the flag flapping one way and then the other. But you could not use this same principle with air because the medium is too thin and will not create enough of a push. Water creates waves and they can be very forceful. This is because the high density of water makes vibrations that are as much as 800 times more energetic than air would create at the same speeds. This means that VIVACE can extract 10 times more energy from a volume of moving water than the currently used tidal turbines.

Combine this high energy generation with the fact that it can work anywhere, even in currents as slow as 2 knots or 2 mph. Current tidal turbines cannot create energy from tides that do not reach at least 5 to 7 knots and therefor must be used in larger bodies of water like fast moving rivers, oceans and rushing mountain streams. This new machine will work in any body of water. Which makes it more accessible and, ultimately, much more economical.

This whole idea simply came from studying fish and how they utilize the water for energy. Fish move through the water by using vortices generated by their own movements but they gain even more speed by sharing vortices with other fish. This is why fish moving in schools can be seen daring at high levels of speed while single fish seem to move more slowly. And the roughness of their skin (or scales) is what allows them to propel the water much more efficiently. The makers of the VIVACE tried to duplicate this roughness, finding that a rougher cylinder surface increases power output by up to 70% over and above a smoother surface. This is apparently done by conversion of kinetic energy into vortices. So much has been learned from the activities of fish. They are even copying the tails of fish in their design, experimenting with passive tail designs that keep vortices from interfering with each other.

The group of researchers who are developing this machine is working with the Navy currently to install two VIVACE systems within the next year. One will be in the Detroit river and another in the ocean. The Navy design will call for modules with several cylinders grouped together (like rungs on a ladder). The sizes will vary with the cylinders for the Detroit River project being about a foot in diameter and as as high as 20 feet. This machine is planned to generate from 3 to 5 kw of power from this slow moving river (moving only about 1.5-knots).

The Navy project is important to establish the viability of the machine. A commercial plant is still far in our future so for now none of us will benefit. The estimated cost of electricity from an established VIVACE installation would be about 5.5 center per kw hour, which is similar to the current cost of wind generation. And even if we can’t benefit from it right now, anything that saves the military, and hence the government, too, is a darn good thing.

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