The Blue Energy tidal energy system has a number of synergistic design characteristics that set it apart from other efforts at tidal energy capture. Blue Energy’s patented design generates benefits far greater than the sum of its individual parts.
Four fixed hydrofoil blades of the Blue Energy Turbine are connected to a shaft that drives a variable speed electrical generator assembly. This rotor is mounted in a durable concrete marine caisson which anchors the unit to the ocean floor, directs the water flow through the turbine and supports the coupler, generator, and electronic controls above it in a dry, climate controlled machinery room above the water surface. The hydrofoil blades employ a hydrodynamic lift principle that causes the turbine foils to move proportionately faster than the speed of the surrounding water. A computer optimized cross-flow design ensures that the rotation of the turbine is unidirectional on both the ebb and the flow of the tide. The turbine is designed to work through the entire tidal range with a typical cut-in speed of 1 metre per second.
The design of the Blue Energy Turbine requires no new construction methodology: It is structurally and mechanically straightforward. The transmission and electrical systems are similar to thousands of existing hydroelectric and wind turbine installations. A standardized high production design makes the system economical to build, install and maintain. The technology also lends itself to take advantage of recent improvements in generators, composite materials, manufacturing processes, and grid inter-tie and transmission controls from developments in the wind industry. All of these factors serve to enhance the efficiencies, cost benefit ratios, and ultimately the net saleable power output of the turbines.
SIZE AND SCALABILITY
Blue Energy turbines can be built in smaller units than our Ocean Class Bridge system. We have developed a small modular 125KW design that can be combined into arrays of up to 4 units and used in free stream applications to provide community power.
However, Blue Energy’s greatest potential rests with its ability to scale to gigawatt sizes and provide a cost competitive alternative to coal and nuclear power plants. Combine a closely packed rotor array with channel crossings measured in kilometres, and you have the potential to substantially impact the electrical capacity of entire nations.
The tidal bridges will be composed of modular turbine units that are stacked to extend from the ocean floor to the water surface. The turbine modules are of pre-formed thin-shelled concrete. In that the rotor in the module is a vertical axis the length of the rotor is independent of its diameter. This makes the application of the bridge suitable to a number of different depths as great as 60 metres by stacking turbine modules on top of each other to suit the conditions of the project site. These are large scale, site specific installations that will vary in size and output capacity by location. The power of the combined caisson modules in a tidal bridge will range from 200 MW to 2,000 MW, making this technology one of the largest scale renewable technologies available today.
Free-standing underwater turbines have their place in our energy future, but they simply cannot meet the need for utility scale energy. Imagine if you will the difficulty of maintaining a field of 1,000 one-megawatt underwater turbines in a tidal environment, to say nothing of simply finding enough space to place them.
MECHANICAL SIMPLICTY & LONGEVITY
When formulating scientific theories one of the guiding principles is called Occam’s Razor, which holds that the simplest explanation that accounts for the observed facts is the best one. A similar principle holds for industrial design.
The marine environment, and especially an energetic tidal stream, is no place for lightweight aircraft design & materials. Even static components like the fiberglass venturi ducts of ducted fan devices are subjected to tremendous pounding forces. Our design foundation is based in proven marine engineering rather than adaptations of devices suitable for low density air. Our drive shafts and bearings are derived from the drive lines that have been propelling cargo ships over the world’s seas since the turn of the century. The lifting foils that provide the thrust to turn the drive shafts are simple, straight foil-shaped blades that are easily manufactured with overkill safety factors. Generators capitalize upon decades of development in the wind industry. Bridges have been built of reinforced concrete for centuries.
The Davis turbine design that is at the core of the Blue Energy system has undergone a long development history involving in-water testing of five different units, including two grid connected trials, followed by extensive refinement using CFD (computational fluid dynamics) modeling and 1375 tow tank experiments providing verification for the numeric modeling.
The secret of manufacturing efficiency is standardization and modular construction. For this reason our rotors, foils, concrete bridge ducting elements, machinery rooms, and generators are all individual modules.
MAINTENANCE
Ease and economy of maintenance will be the deciding factor in determining market penetration in the marine energy industry. Blue Energy starts with one overwhelming advantage--- our machinery is all housed in climate controlled rooms located above the highest wave point. We don’t even have to rely on a shaft seal to keep our generators and electronic controls perfectly dry. The advantage of a direct access hatch permitting rapid and inexpensive changing of generators, some of which can be as large as a locomotive engine, is obvious.
Our venturi-shaped bridge elements and rotor foils are not as critically sensitive as some other designs to surface disruption by marine growth, but marine life always triumphs over the best efforts to prevent it. The design provides for the removal of the generator rotor bearing assembly with no underwater service requirements. We can then perform any maintenance task from applying new anti-fouling to changing complete rotor and foil units.
The primary structural housing of the bridge has a service life that can be measured in centuries. Primary structural materials used are concrete and steel-common low cost industrial materials. Individual components, drive shafts, bearings, foils, generators & electronic controls can be replaced or updated in accordance with their individual service requirements without interrupting the output of the entire system.
The inner edge of the roadbed contains a guide way for a purpose-designed crane that handles all the heavy service and maintenance jobs far more economically than is feasible with offshore wind turbines or underwater tidal turbines. Our generators and rotors may be removed and serviced without the need of divers.
TRANSPORTATION BRIDGE
The bridge that spans our turbine array serves two functions. It is first of all the key to economical long term maintenance and service of the turbines. In many locations, the value as a transportation link can create secondary market value that approaches that of the electricity produced. In our discussions with potential Joint Venture partners we are finding that the transportation value generates a high degree of interest. For the cost of the electric plant you get a free bridge--- true synergy in action!
The Blue Energy Tidal Bridge uses the concrete ducts of the turbine housings as the support structure for the bridge, another case of using one design element to serve two functions. Multiple lanes of traffic can use the roadway located above the machinery rooms of the full ocean class design.
China just completed the world’s longest bridge (36km) at a cost of 1.4 billion US. The Hangzhou Bridge saves 120 km of travel distance between Shanghai and Ningbo, but it also spans one of the three largest tidal flows in the world. If the bridge had incorporated Blue Energy tidal energy turbines into its design it also could have replaced many of the coal plants China is building at a furious pace while providing the same transportation benefits as the chosen design.
In a sense this represents a lost opportunity, but there are scores of other locations worldwide with the same type of potential, as verified by the nearly 30 billion dollars of pre-commercial project inquiries that we have received about our Tidal Bridge design.
HIGH EXTRACTION EFFICIENCY
It might seem that a high-tech-looking open centered turbine with a computer-optimized fiberglass duct channelling the water flow would have much higher extraction efficiencies than a simple Davis turbine that has to push its foils against the tidal flow for part of its cycle. As it turns out, once again the whole is greater than the sum of its parts.
When you place an object into a moving fluid the fluid flow moves around it. If the object is partially porous, part of the flow will be through it and part will still divert to the sides. Any device that extracts energy from a moving flow does so by obstructing the flow, and is therefore subject to a limitation on how much energy can be extracted before the fluid simply bypasses the device. This is a simple laymen’s explanation of the Betz Effect. Herein lies the key to why the Blue Energy Tidal Bridge will always generate higher extraction efficiencies than any individual stand-alone turbine or propeller. In crossing a channel completely, a hydraulic head is developed along the tidal bridge structure, significantly increasing the power output of the tidal installation. This is accomplished by designing the appropriate blockage ratio of turbines (build solidity) to open water to generate the desired head height for a given set of hydrodynamics for a particular tidal site. The blockage ratio of a tidal bridge will be on the order of 50%, leaving a significant part of the waterway open to sea life, sediment, and water flow. Blue Energy's synergistic design permits us to set rotor bay velocities (the power output of the turbine is a function of the water velocity cubed) so that they maximize the power output of the tidal resource. This design element is not trivial and can yield an overwhelming advantage in the cost of energy produced.