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Description Thumbnail
Posters
Run-of-river poster.
Tidal Impoundment poster.
Tidal Stream poster.
Wave poster.
Offshore Wind poster.
Resource Maps
Run-of-river resource map based on rainfall and river gradients.
Tidal impoundment resource map based on tidal range.
Tidal stream resource map based on velocity of currents.
Wave resource map based on size of swell and windblown waves.
Offshore wind resource map based on wind speed at 40m above ground.
Sources of Aquatic Energy
Rainfall arises from evaporated surface waters.
Run-of-river projects exploit the head and flow of water in rivers and streams.
The gravitational pull of the sun and moon give rise to tides.
Tidal impoundment exploits the head created by high and low tides.
Strong tidal streams arise when the tidal flows are constrained by land, islands and shallows.
Surface winds create waves.
Swells travel across oceans.
Atmospheric circulation which gives rise to winds.
Coastal winds can be generated by thermal convection of heated air over land.
Energy Processes
The larger the elevation drop of a river over a set distance, the greater the energy in the water flow.
The strongest currents in a river are located in the centre and close to the surface, where they are not slowed by friction with the river banks and bed.
As water flows, it accelerates around the outside of a river bend, with slower moving water flowing around the inside of the bend.
Tidal ranges can be increased in areas such as estuaries, where the upstream tidal flows are funnelled into a narrow channel.
Useful heads of water can be created in areas with high tidal range by impounding the inflow or outflow of water, as the tide rises or falls.
Laminar flow in a tidal stream.
Where a tidal stream flows over a ridge, overflows can form.
Where the seabed is rough, turbulence can be created forming up-welling and down-welling areas.
Where waves meet tides, extremely turbulent seas can develop.
Eddies form downstream of a restriction in a tidal current.
Eddies form downstream of a restriction in a tidal current.
The strongest currents in a tidal stream form in different places when the floods and ebbs.  The ‘sweet spot,’ shown in orange, of universally strong tides is therefore quite limited.
Waves are created by a circulation of water near the surface that dissipates with depth.
The energy contained by waves diminishes as they reach the shore due to seabed friction effects.
Waves cause floating objects to articulate around a pivot point.
Waves create a pressure differential in the water column.
The energy in offshore wind increases with height above the water surface, avoiding energy loss due to friction with the water.
Onshore winds are generally slower than those at sea because of friction caused by obstacles such as trees, cliffs and mountains.
Onshore winds are generally slower than those at sea because of friction caused by obstacles such as trees, cliffs and mountains.
Technology Animations Still Images Animations
Run-of-river Technologies
Diversion plants exploit diverted flows where there is sufficient gradient over the diversion.
Weir Type plants  exploits flows created by weirs that still allow water the flow freely.
Kinetic Energy Devices exploit the direct flow of water in larger river systems, similar to tidal stream technology, though usually on a smaller scale.
Tidal Impoundment Technologies
Tidal Barrages involve building a dam across an estuary with a high tidal range.  The tidal barrage plant generates energy by allowing water to flow in and/or out of the estuary through low head hydro turbines.


Bunded tidal barrages operate in a similar way to conventional tidal barrages but do not fully obstruct an estuary.
Single Basin Offshore tidal lagoons would be built on tidal flat in areas with high tidal ranges.
Multiple Basin Offshore Tidal lagoons are built on tidal flat in areas with high tidal ranges.
Tidal Stream Technologies
Horizontal axis turbines work in a similar manner to wind turbines.  The turbine is placed in the water and the tidal stream causes the rotors to rotate around the horizontal axis and generate power.
Vertical axis turbines work in a similar manner to horizontal axis turbines but the tidal stream causes the rotors to rotate around the vertical axis and generate power.
Reciprocating Hydrofoils have a hydrofoil attached to an oscillating arm.  The lift caused by the tidal stream causes the arm to oscillate and generate power.
Venturi Effect Devices are devices which funnel the water through a duct, increasing the water velocity. The resultant flow can drive a turbine directly or the induced pressure differential in the system can drive an air turbine.
A tidal kite is tethered to the sea bed and carries a turbine below the wing. The kite ‘flies’ in the tidal stream, swooping in a figure-of-eight shape to increase the speed of the water flowing through the turbine.
The Archimedes Screw is a helical corkscrew-shaped device (a helical surface surrounding a central cylindrical shaft). The device draws power from the tidal stream as the water moves up/through the spiral turning the turbines.
Wave Technologies
Attenuators are floating devices that are aligned perpendicular to the waves.  These devices capture energy from the relative motion of the two arms as the wave passes them.
Surface point absorbers are floating structures that can absorb energy from all directions.  They covert the motion of the buoyant top relative to the base into electrical power.
Oscillating wave surge converters are near-surface collectors, mounted on an arm which pivots near the sea bed.  The water particles in the waves cause the arm to oscillate and generate power.
Oscillating water column technologies convert the rise and fall of waves into movements of air flowing past turbines to generate power.
Overtopping devices have a wall over which waves break into a storage reservoir which creates a head of water.  The water is released back to the sea through a turbine to generate power.
Submerged pressure differential devices capture energy from pressure change as the wave moves over the top of the device causing it to rise and fall.

Bulge wave technology consists of a rubber tube filled with water, moored to the seabed heading into the waves. The water enters through the stern and the passing wave causes pressure variations along the length of the tube, creating a ‘bulge’. As the bulge travels through the tube it grows, gathering energy which can be used to drive a standard low-head turbine located at the bow, where the water then returns to the sea.



Two forms of rotation are used to capture energy by the movement of the device heaving and swaying in the waves. This motion drives either an eccentric weight or a gyroscope causes precession. In both cases the movement is attached to an electric generator inside the device.



Offshore Wind Technologies

Horizontal axis three-bladed turbines are the most popular configurations.  Energy output is related to the area of air swept by the blades.
An array of horizontal axis three-bladed wind turbines.
Horizontal axis two-bladed turbines; less common but may be more efficient and easier to maintain.
An array of two-bladed horizontal axis wind turbines.
Vertical axis wind turbine technology; the rotas spin in less space than horizontal mounted alternatives.
An array of vertical axis wind turbines.
Moorings and Foundations
A tidal foundation device which uses hydrodynamic forces to keep the structure firmly pinned to the seabed.
Plied steel jacket attached to the bottom of a mono-pile.
Piled steel jacket extending above the sea surface.
Tension legged mooring; the buoyancy of the surface structure keeps the mooring lines under tension.
Solid structural link between the device and the anchor.
Simple catenary link between the device and the anchor.
Lazy “S” link between the device and the anchor.
Gravity base with a penetration skirt, suitable for a sedimentary seabed.
Shoreline deployment from a solid pier.
Shoreline deployment in a natural gully.
Shore line deployment in coastal defences.
Barge based deployment platform.
Four point tension-legged mooring.
Four point catenary mooring.
Guyed tower; suitable in shallow sediments and rock.
Drive monopole; suitable for deep sediments.
Steel jacket tower; wide-spread suitability.
Gravity base; wide-spread suitability.
Surface lying barrier.
Embedded barrier.
Tension-legged mooring with a piled foundation.
Floating mooring with catenary anchors.
Tension-legged mooring with a gravity base foundation.
Spar buoy concept where catenary anchors hold a buoyant tower in place.
Twin piles, drilled or driven into seabed.
Structural base secured to seabed by rock pins/anchors.

Supporting activities

Anchor Handling Tug Supply (AHTS) vessels

Cable laying ship

Crane barge

Embedment anchor

Types of foundations and moorings for offshore wind turbines

Types of foundations and moorings for offshore wind turbines

Gravity anchor

Grid connection of wave test site

Grid connection of wave array

Example of a bespoke device specific installer

Jack-up barge

Jack-up barge underway

Multicat underway

Offshore Construction vessel

Rock anchor

Survey vessel

Test site infrastructure

Tug

Vertical loaded anchor

Work boat

llp logoThis project has been funded with support from the European Commission (EU Lifelong Learning Programme Agreement no LLP/LdV/TOI/2009/IRL – 515). This publication reflects the views only of the author, and the Commission cannot be held responsible for any use which may be made of the information contained therein.

Aqua-RET Project © 2012. All Rights Reserved

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