Tidal energy differs from wind or solar on two critical dimensions: predictability and energy density. Seawater is a non-compressible medium with 832 times the density of air. The wind is as variable as the weather and the sun only shines with a high degree of reliability in desert areas.  Tidal flows are as reliable as the orbit of the moon and the gravitational forces that it generates.  Recovering energy from the tides is not a new concept, but with growing awareness of the need for renewable sources of energy, many new ideas are being proposed to capture their energy. Blue Energy’s tidal energy system overcomes the limitations of both the oldest and newest designs.

OPTIONS FOR CAPTURING TIDAL POWER

Tidal Barrages:  A direct adaptation of conventional hydroelectric dam technology.  
A tidal estuary is closed off by a dam incorporating movable flood gates.  The incoming tide fills the reservoir behind the dam, gates are closed at high tide, and the ensuing hydraulic head of water is used to turn Kaplan turbines as the water flows back out. This method represents the first commercial system, with proven cost metrics from La Rance, France where a 240MW plant has operated since 1966.  Largely under the radar, Korea is building massive tidal energy capacity using this approach.  
Barrage systems have multiple disadvantages, the biggest one being capital cost.  When an estuary is turned into a reservoir, its ecology and marine productivity are irrevocably altered, and valuable fisheries may be destroyed.  Another factor is that power can only be generated for half of the tidal cycle, substantially limiting the capacity and moving power cycles away from the ideal 24/7 output. 

Underwater Devices:

Underwater Windmills:  The tidal energy devices receiving the most attention are adaptations of wind technology.  They have propellers mounted on a fixed piling, tethered by anchoring systems, or held in place on the seabed by heavy gravity mount bases. All propellers employ the same principles of lift that allow airplane wings to support the weight of a plane in flight.  They are subject to conversion efficiency limits known as the Betz effect (explained in more detail below). Since water is so much denser than air, underwater windmills necessarily have short, low aspect foil sections and are limited in span by structural requirements and water depth.

Ducted Fan:  These devices resemble giant versions of common air conditioning and heating fans.  They use a venturi-shaped duct to increase the velocity of the water flow over blades attached to an outer housing. This housing contains permanent magnet elements that form part of the generator.  From an engineering standpoint, this is an elegant design in that it eliminates the driveshafts and reduction gears that are major maintenance and failure points for underwater windmills. However, it creates challenges for long-term maintenance. The electrical components are spread around the perimeter of a housing that can be 50 meters in circumference. They must be perfectly sealed against water intrusion under conditions where they experience amplified pressure from water depths. Marine growth has a significant impact upon the efficiency of the device, and anti-fowling paints have a limited performance lifetime.  Any major service requires removal of the device from its underwater mounting.  This operation can only be accomplished by divers and large floating cranes operating in extremely difficult conditions. Assuming they can achieve a projected five year maintenance cycles, six major installation operations will be required in the life of the turbine. This method also suffers from Betz Effect limits and long term maintenance will be the largest factor in life-cycle costs of power production.
When we examine any of the tidal energy designs that house their machinery and electrical equipment underwater, it becomes obvious that they do not pose a technical solution that is truly scalable to replace coal or nuclear power plants.

TIDAL BRIDGES

Blue Energy Tidal Bridge Power System

A propeller placed in a moving stream of water is subject to the limitation technically known as the Betz Effect (58% kinetic energy conversion limit).  Fluids tend to flow around rather than through energy capture devices.  What this means is that laws of physics handicap the bottom mounted underwater windmill conversion methods to only a percentage of their ambient stream kinetic energy potential.   Blue Energy recognizes the unique nature of tidal hydrographic regimes and that power conversion outputs are a cubed function of the water velocity. 
Generating tidal power is one thing, maximizing value in tidal resource developments is quite another.   Flow shaping, static/current head, Betz Effect, resource by-pass – all subtleties in method yet to be appreciated in the early phases of tidal technology commercialization. By using thin shell concrete structure and rock fill causeway to develop blockage, we expand the kinetic energy capture ratio to achieve higher build efficacies. There are a number of advantages to the Blue Energy Tidal Bridge System.  Taken separately they are obvious factors and common sense, but when combined, they form a less obvious synergy that serves to optimize performance and costs of construction, installation, and operation and maintenance.    Increasing the channel blockage ratio develops a static head across the bridge (water levels are slightly higher on one side) allowing us to generate the maximum amount of energy.   Incorporating the static head with venturi flow shaped turbine rotor bays also permits us to set the fluid media conversion velocities to just under the pressure limits for cavitation, (remember power output is a cubed function of the water velocity) thereby developing maximum power for a given sectional area.  It is these subtleties that will be the bottom line determining factors as to who will be left standing after the inevitable consolidation of the tidal power space.
Understandably, the above is difficult to understand, and a bit technical but necessary to explain Blue Energy’s power yields of potentially 400% to 1000% over that of bottom mounted free stream methods.

Affirming that the company is on the right track with its tidal bridge methodology, Blue Energy has already received in excess of $30 Billion in transportation tidal bridge solution inquiries from around the world. This distinguishes our conversion method and is an indicator that our tidal bridges will enjoy a billion dollar supplemental market driver. Billion dollar transportation sector propagation drivers and low price point, mean the Blue Energy technology will NOT require billion dollar subsidies (as did wind power) to move this technology very quickly into the energy mix.
Blue Energy is the value proposition tidal power technology, and building bridges to our future.