Tidal range
The tidal bar/barrage structure - a structure which crosses the tidal estuary.
A tidal lagoon - an enclosure that is either attached to the coast or offshore.
Both require tide levels which vary by several metres and are constructed in shallow water.
Tidal stream
Relies on the tidal current to produce energy.
They require a large depth of water and a fast tidal current.
Tidal range vs Tidal stream
Both forms of tidal energy are important and complement each other - because generation sites rarely overlap.
Frequently Asked Questions
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Predictability, tides come twice a day and at different times around the coast of the UK.
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Where else do you see the tide going out half a mile? The UK has a unique geography with one of the highest tidal ranges in the world and one of our greatest assets.
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The river Severn for example, has a tidal range of 15m, Thames 7m, Mersey 10m, Humber 7m.
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Yes, tidal energy harnesses the predictable rise and fall of tides while wave power harnesses the kinetic energy of waves generated by wind.
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Tidal range uses the vertical difference in water levels between high and low tide whereas tidal stream relies on the kinetic energy produced by a strong tidal current. Tidal stream is a wind turbine under water and requires deep water with high current usually located between islands such as Anglesey in Wales, UK.
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A recent study commissioned by the British Hydro Association (BHA) that the levelised cost of energy (in line with government assessment) is cheaper than nuclear power.
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Yes triple regulated Bulb Turbines could be used in the centre of an estuary where the turbine can be set low as the machine requires 6m of head above the turbine. The total energy produced is 30% less than with a Very Low Head Turbine (VLHT).
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The VLHT is bi-directional and generates in ebb and flow and works on a differential head of 3-6m and significantly reduces the impact on the ecology.
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We plan to use concrete caissons sitting on the bed of the estuary and letting the water flow through the turbine opening thereby creating a tidal bar rather than a barrage (sometimes referred to as a tidal fence). A barrage would let the water in and hold the water until the tide dropped and then generated in one direction.
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A tidal bar would be one side of the triangle in an estuary where a lagoon is generally circular and should not close off an estuary.
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A shipping lock will be incorporated into the structure.
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The turbine operates at low speed 25rpm - similar to a water wheel - and will not harm the fish. There are no harmful pressure gradients or shear forces in the turbine flow that could stun the fish.
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Most hydro schemes have an asset life of at least 125 years with
mechanical/electrical refurbishment every 50 years. -
The impact of corrosion from seawater is generally around the splash zone where the water is oxygenated. A submersed turbine with the correct materials will have a good life span.
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The towers have a life of 60 years but the mechanical and electrical machine has a life of 25 years.
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The seabed will be levelled with stone and steel or concrete caissons will be manufactured in dry docks and floated into position. This is a proven method of construction.
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It would take between three and four years once planning consent and funding are in place.
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The River Severn for example could produce 6% of UK power requirement and utilising all our estuaries could deliver 30% of UK power requirements.
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Existing technology impacted on ecology and fish mortality and was not considered economical. These issues have generally been mitigated and the VLHT resolves the main objections to tidal range energy overcoming the issues of ecology, fish mortality and economics.
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The main hydro suppliers are waiting to see if the government changes its view on the cost of tidal range energy.
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The Tidal Range Alliance is a subset of the British Hydro Association whose members are potential tidal range developers, engineers and suppliers. It brings together various stakeholders interested in developing tidal range energy.