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http://pesn.com/2007/08/07/9500489_VAOT_v_HAOT/
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PureEnergySystems.com > News > August 7, 2007

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Horizontal versus Vertical Axis Ocean Turbines

A review of the leading tidal power technologies and a comparison of the advantages and disadvantages of the horizontal axis design versus the vertical axis design.

by Adrian Akau
for Pure Energy Systems News

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Blue Energy tide turbine diagram

 


Vertical Axis Ocean Turbines (VAOT) compared to Horizontal Axis Ocean Turbines (HAOT)

Vertical Axis Ocean Turbines have been proposed by FreeFlow69, a new company in Cornwall England for the San Francisco Bay area and the Bristol Channel in England. The question this article wishes to examine is whether it is possible to access relative merits of the VAOT as proposed and to compare it with HAOT technologies presently being tested or developed. 

The FreeFlow Osprey VAOT is proposed to work in a multiple system. It would have its gearbox and generator above the water level and be anchored in place where tidal currents are strong. An individual VAOT would be designed similar to the Blue Energy tide turbine.

Blade sections might also be designed as follows:

Neo-AeroDynamic
Wind/Water Turbine
Windaus Vertical Axis Wind Turbine

The Osprey plant is proposed to link a number of vertical axis turbines linked together for underwater generation of power with fixed wind turbines above:

The orange knobs in the center are the gearbox and electric generator of each Osprey.

The VAOT is in competition with several HAOT that are already being tested. Let us look at a few examples of the more common horizontal type:

Verdant's turbine producing power
in New York's East River.


The "Wando" type HAOT that the Voith Siemens Hydro Tidal Corporation (51% owenership) is preparing to construct with a plant in Wando, South Korea. Each of the three turbines is rated at 1 Mw and the plant is to manufacture 600 Mw of turbines per year. Note that the horizontal axis can swing 180 degrees as the current changes direction and that it can be raised above ocean level for repairs ("The crossbeam can be lifted from the water for maintenance purposes.").

The 1.2Mw SeaGen tidal energy system will commence testing during the week of August 20th in Northern Ireland’s Strangford Lough. It is a prototype for commercial technology to be replicated on a large scale over the next few years. Note that the clockwise and anticlockwise torque are in balance.



In comparing the VAOT type produced by FreeFlow to the standard HAOTs, we come to some general conclusions:

1. A VAOT having its gearbox and generator above sea level does not seem to have any advantage over the horizontal axis type. Both are subject to corrosion and the Osprey turbine and gearbox would have to be just as watertight as the Verdant, Wando or SeaGen units. What really counts is the energy of the currents passing through that can be converted.

2. The Wando and SeaGen units are designed to be raised out of the water for repairs by rotation on the horizontal axis in the case of the Wando and lifted vertically on the post for the SeaGen. The gearbox and electric generator portion would be accessible on the Osprey without lifting but a special hoist would have to be used to raise up the generator to examine the blade section. Normally, it is much safer to work on ocean current turbines out of the water since the currents are swift and can be dangerous. 

"Twix Hartland Point and Padstow Bay,
Is a sailor's grave by night or day."
(a saying about currents in the Bristol Channel)

3. The energy accumulators for the Osprey VAOTs which are to provide a narrow channel for the water to flow in order to increase its velocity may not prove cost effective. The Osprey Turbine may be of good design and function well, but the entire platform system seems bulky and unwieldy. The Verdant, Wando and SeaGen HAOT units seem less complex in overall design with both the Wando and SeaGen units set up for safe, above water repair. 

4. The introduction of wind turbines to the top of the VAOT energy accumulator platform would not seem to be cost effective in comparison to the system requirements, i.e. that the units be placed in areas of maximum current velocity and that these areas may or may not have suitable wind velocities. Also, floating platform wind turbines are outside the discussion of ocean current generating units at this time and the addition of wind generators to the VAOT's would not necessarily produce power at the same KWh rate. The idea here was to continue producing power during the change of tides since at that time, tide velocity reduces to zero before starting up in the opposite direction.

5. It would seem that just a few large Verdant, Wando or SeaGen type HAOTs would be adequate to replace an entire flotilla of Osprey VAOTs. If channeling is required for the VAOT's, then these additional costs should be included.

6. My tentative conclusion therefore is to prefer the design of the standard HAOT''s as I believe they would be less complex to install and safer to maintain. However, I believe the VAOT's such as the Osprey should also be tested. It is difficult to imagine a single VAOT being anchored in place due to the fact that the axis of the turbine itself is vertical. Therefore, the necessity of the anchored flotilla and probable increased cost of the system.

# # #

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Page poted by Sterling D. Allan August 7, 2007
Last updated August 08, 2007

 
 

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