Tidal Bridge
Concept
BEC’s turbines are designed to be configured in a linear array across waterways with significant tidal flows to form a bridge to be used by auto, truck, and rail transportation. These tidal bridges will increase the ambient flow of the tidal currents by channeling the water through the turbines like a venturi. In crossing between two land masses, Blue Energy will employ a specific build solidity to generate both a static and a kinetic head along the “upstream” or “flood” side of the tidal bridge that will range from one to two meters. The ratio of the number of turbines to open water will generally be on the order of 50%, and will be finely tuned to engage the specific hydrographic conditions for each site in relation to annual tidal frequencies. The low head developed by this blockage ratio will work to increase the volume of water moving through the turbines for a given amount of time, effectively increasing the velocity of the water to upper operational limits. The blockage ratio may be tuned to optimize the hydrographic resource and take advantage of sites that would generally be too slow for free stream technologies while effectively increasing the amount of electricity that may be produced in more desirable and energetic sites.
Turbine Design
The BEC tidal turbines will be configured as several different sizes and nameplate capacities to operate in different depths ranging from 10 to 50 meters. These turbines will be exactly the same except for heights and generator sizes. The turbines, except for the rotor, drivetrain and power electronics, are made of durable marine grade pre-cast concrete. This will lower fabrication costs and provide reliability and longevity of the turbines as the concrete members are designed to last in excess of 75 years.
Each turbine will have five essential elements a base, the caisson, the rotor/drivetrain, the machinery room, and the road decking. The turbines will be gravity mounted on a prepared leveled sea bed. A concrete base section will carry the load of the other turbine elements and hold the bottom bearing for the rotor. The caisson will house the rotor and have specifically shaped walls that act as a venturi which increase the water velocities to the rotor. The rotor has four vertically oriented hydrofoils that have three to four horizontal struts per hydrofoil depending on the length of the foil sections. The shaft will be made of coated steel and the foil sections will be made of a composite material. Each rotor will be The lifespan of each rotor is expected to last for 10 years and will be maintained and replaced at regularly serviced intervals. The machinery room is a vertically integrated structure supported by the caisson and is situated above it. The machinery room is a dry climate controlled structure that Houses the generator and power electronic controls in a dry climate controlled space that is located above the high tide line. This way sensitive electronics and generators are easily accessed and safe from the pervasive effects of the ocean. On top of the machinery room is the road decking. A rail line is installed several meters to either side of the centerline of the turbine to accommodate a gantry crane that straddles the machinery room. This gantry crane can remove and install the entire drive train assembly from a dry, controlled surface on top of the road decking. Transportation infrastructure is located laterally to this and can be designed to meet many different transportation needs, accommodating road and rail traffic. Designs can also accommodate marine traffic of all sizes.
Sizing
Turbines will come in several sizes to accommodate different water depths. The turbines will have various outputs for the changing velocities of the given sites tidal flows. The rotors will be stackable to accommodate greater and more varied depths with the turbine outputs being additive when stacked. All rotors will be ten meters in diameter and will vary in length from 10 to 20 meters. The turbines may be installed in depths of up to 50 meters and span several kilometers in length making this one of the largest scale renewable technologies to be employed.
Given the following:
Length: 1000m
Average Depth: 35m
Peak flow rate:5 m/s
Efficiency: 45%
Rotor Diameter: 10 meters
peak nameplate capacity: 907MW
Operational Advantages
All of the machinery equipment, controls, and generators are housed in a climate-controlled powerhouse above the water line. This allows for a majority of the maintenance to be done without the need for diving in a challenging marine environment. This also means that there are no critical seals to fail; threatening the viability of power electronics and generators, which over a 25+ year lifespan will be a significant factor in longevity.
For ease of maintenance a gantry crane will run along the entire length of the tidal bridge. This will have the capacity to remove the generator, coupler, rotors, and bottom bearings without the need for divers or marine barges. This will significantly lessen the costs of maintenance over the lifespan of the turbines. The traffic lanes on the bridge are on the outside of the rails for the gantry crane, so any maintenance being conducted will not affect the flow of traffic. Blue Energy will employ a direct drive variable speed permanent magnet generator. This obviates the need for a gearbox which is typically the weakest link in any mechanical system. This choice of generator eliminates downtime due to maintenance and mechanical failure, adding to the reliability and durability of the tidal bridge.
There are no fuel costs as the turbines are fuelled by the free forces of the ocean's tidal currents. The turbines also have a long operational life – the rotor and bearings are designed to last 10 years, the mechanical equipment is designed to last for 50 years, and the marine caissons for 75 years or more. As mentioned above, almost all maintenance may be conducted from the bridge itself by an electric gantry crane. This will save on significant fuel usage over the lifespan of this project. Power projects are generally financed over 10 to 15 years, which means that the system will continue to produce fuel free electricity revenues long after it has paid for itself.
The tidal bridge is environmentally benign due to the free-stream open sluice design. This eliminates the need for expensive and high impact dam structures. This results in lower capital costs and also allows fish, nutrients, and silt to pass through the turbines with minimum ecological impact. The turbine operates at a low rotor speed in the range of 5 to 30 RPM, which is not expected to significantly affect the movement of water life and fish stocks. The Blue Energy turbine produces no greenhouse gas emissions and will play a significant role in the reduction of harmful greenhouse gases.
Synergistic Design
Because of high energy densities, enhanced flow shaping to create faster water velocities, a modular design that employs simple materials, nd dual infrastructural role as a transportation solution, the Blue Energy tidal bridge will be able to approach grid economies of scale while reaching grid prices for clean fuel-free electricity. With the Blue Energy tidal bridge the whole is greater than the sum of its parts
Intellectual Property
Blue Energy Canada Inc. protected the tidal bridge and a system-wide claim is patent pending under US Patent Law.