I have written about a number of underwater generating systems in past posts. All of these systems rely on propeller or turbine technology in one form or another. Problem is that it takes a fairly fast flowing current, 5 to 6 knots or more, to turn a propeller sufficiently fast to generate electricity. Slow rivers, estuary waters, and most sea bed currents would therefore not have a fast enough current for normal turbine generation.
Vortex Power a New Approach
A completely new approach has been developed by Professor Michael Bernitsas and his international team at the University of Michigan Department of Naval Architecture and Marine Engineering.
Their idea uses the power of a vortex. All currents in air or water can cause a vortex when the flow is made to deviate. A visually stunning example of this effect is the vortex caused in the wake of a jet plane. I have included a couple of photos that show the effect.
Vortices contain powerful energy. Jet liner vortices have been know to knock small aircraft to the ground quite some time after the big plane has landed. The power of a vortex is a power to be reckoned with.
It is this very vortex power that Professor Bernitsas and his team have learned to harness in a completely new way.
How is it done?
A vortex is created when a current passes over an object that distorts the flow. In the above examples it is the airflow over the aircraft’s wings that causes the air current to spin into a vortex.
Professor Bernitsas and his team have built a beautifully simple machine that creates a vortex by presenting a cylinder, or series of cylinders to the flow, and then utilises the lateral spin force of the created vortex to push the cylinder from side to side, or up and down as in the test rig shown.
I believe that the idea was sparked from observing fish using the vortices created by other fish to increase the efficiency of their movement.
The New Machine.
The new machine can harness power from very slow moving currents hitherto considered of no value for energy generation. A Vivace device occupying one cubic meter of water in a 3 knot current can produce 51 watts of electricity. While they might be considered a bit bulky, these machines can produce very usable amounts of power. One place for sure that bulk does not present a problem is in the seabed. The machine can operate in very low speed currents. The test tank has a current of only 1.5 knots.
The team call their new device “Vivace”, an acronym for vortex-induced vibrations for aquatic clean energy.
How’s it perform?
Estimates suggest that array the size of a running track and the height of a two-story building would power 100,000 houses.
Electricity generated by VIVACE is estimated to cost approximately 5.5 US cents per kilowatt-hour. Wind turbine energy costs run at around 6.9 US cents per kW hour.
VIVACE cylinder moves at a relatively slow speed and would therefore have minimal impact on marine life and environment.
I contacted Professor Bernitsas to ask permission to quote and use photos. I was delighted to receive his reply:
Yes, Tony, you have permission and thank you for asking.
Here is the status of development. We have several models and we are building a prototype with the US Navy which we expect to be tested by the end of 2009.
Michael M. Bernitsas, PhD
Professor of Naval Architecture and Marine Engineering
Professor of Mechanical Engineering
Director, Marine Renewable Energy Laboratory
University of Michigan
Fellow ASME, Fellow SNAME
Here are links to the university and to the development company:
May I wish the VIVACE team every success in the development and implementation phases. Hope for all our sakes that this proves an effective and reliable source of energy.