Considerable confusion exists regarding the differing tidal energy technology designs that are generically referred to as "tidal power" or "tidal energy". Listed below are the three main types of tidal energy turbines. |
||
|
Shrouded Turbines
Figure 1  |
Barrage Systems
Figure 2  |
Open Turbines
Figure 3  |
| The shrouded turbine system above researched, developed and Patented by Tidal Energy Pty Ltd in Queensland Australia, can use tidal river or ocean currents - accelerating the water across the turbine using a unique hydro dynamic shroud. The shroud allows the turbine to achieve at least 3 times the power output over the same turbine without the shroud. Shrouded systems are eco benign and combined with low cost at around AU$1.25 million per Mega Watt installed can operate in slow or fast flow thresholds over a wide variety of sites. | The Barrage System resembles a dam and is sometimes called a tidal fence. It captures the rise and fall of tides with turbines installed in the dam wall. The Rance River concept in France has operated since 1976. These systems have few viable sites worldwide. There are a number of barrages that have been proposed – Severn River in the UK and Derby in Western Australia - but all suffer from the dual problems of high installation costs, environmental issues and disruption to transport. | The open or free flow turbine system resembles an under water windmill. Similar systems have been used since Roman times. Open or free flow turbines need fast moving water to be commercially viable. The open turbine system above shows an open turbine deployed in the UK. Compared to barrage systems open free flow systems are less costly and have little if any impact on the environment. However open free flow turbines systems require very fast flowing sites with very large turbines to be commercially viable. |
Along with the rapid development of wind energy systems, the potential of hydro-kinetic energy is receiving more and more attention. The distinct advantages of hydro-kinetic energy includes the greater predictability of water currents, little if any impact on the visual amenity with turbines placed underwater, and a lower cost of energy production.
While water energy has been harvested since Roman times, and several free flow or open propeller-type turbines have been installed in ocean currents, there has been little development in the core technology for harnessing this huge yet largely neglected source of renewable energy. The Tidal Energy Pty Ltd concept is to maximize the transfer of energy from the moving water stream to the turbine using venturis. This has led to the development of the Davidson-Hill Venturi Turbine (DHV) capable of efficiencies of 60% from a single turbine rotor.
DHV turbines employ two Patented components to harness hydro-kinetic energy – a pitching blade rotor that produces more torque and an earlier starting moment and a venturi shaped shroud that increases and accelerates the flow of water over the turbine, working in harmony to extract more energy from moving water than any other design. This advance, similar to the development of the jet engine and the breaking of the sound barrier, translates into greater power production from sites previously not commercially viable.
SHROUDED - VENTURIS VS. OPEN FREE FLOW TURBINES
The are many and varied types of open turbines sometimes called free flow or open turbines that do not accelerate water flow and increase the power the turbine is capable of producing. These all resemble the basic windmills or a "propeller on a stick" of the middle-ages and produce less power then the DHV shrouded turbine. Free flow or open turbines usually have larger rotors then shrouded turbine rotors – or multiple rotors – to make up for the lower efficiency and need very fast moving water to compare with shrouded turbines. Free flow or open turbines can be easily damaged by debris without protection afforded by the shroud.
This is the key to understanding the major differences between hydro kinetic technologies and the turbine performance claims by manufacturers.
Using simple to understand charts below open or free flow turbines are compared on a level playing field. All turbine rotors compared are the exact same size. All turbines are compared in the same water speed of 4m/s. All power produced is in kilo-watts with energy sold at 10 cents per kilo watt.
There is a clear cost advantage in choosing the DHV turbine over any other turbine. In order for an open turbine to compare equally with a DHV Turbine two or three turbine rotors need to be added as per Figure 3 Hydro Alternative Energy.
MANUFACTURING
Tidal Energy is now manufacturing turbines from durable marine grade stainless steel and aluminium for water speeds up to and including 6 meters per second (6m/s) of water velocity, and for water speeds over 6m/s from super strength composite materials. All Tidal Energy turbines come with the protective venturi shroud that increases performance and come in 5 sizes from 1.5 meters in diameter to 10 meters in diameter. DHV turbines can be flat packed for shipping to almost any location reducing shipping costs.
EASE OF SHIPPING AND INSTALLATION
Once a DHV Turbine is unpacked it can be easily assembled and handled for transported on a car trailer or the back of a truck to the site ready for deployment.
Free flow turbines can be easily damaged during assembly, transport and deployment as they have no exo-skeleton frame similar to a DHV Turbine protecting the turbine and for ease of handling and installation.
