GB2477872A - Floating tidal stream electricity generating platform - Google Patents

Abstract

A floating platform which extracts energy from coastal tidal streams to drive an onboard electricity generating plant 14. The platform may comprise two hulls 1 linked at the bottom by a sole plate 2 with a paddle wheel 8 located in between. The hulls are shaped to passively accelerate the tidal stream driving the waterwheel by up to three times. The platform is moored by anchors fore and aft in an orientation parallel to the local tidal stream and is designed to operate during both ebb and flow tides without being re orientated. Ballasting tanks are provided which are empty when the platform is towed into position before being flooded to lower the platform to its operating draught. Nine tenths of the deck is covered by sloped steel canopies 6 to allow large waves approaching from the quarter or beam to break across the platform thereby reducing rolling.

Description

DESCRIPTION

The invention is a device for the acceleration of coastal tidal streams and for the conversion without repositioning of both the ebb and flow of such streams into mechanical energy and the transmission of that energy to on-board electricity generating plant and having the capability to perform all these functions without interruption in extreme wind and wave conditions.

The structure of the device is a twin-hulled floating platform whose hulls 1 are linked at their lowest level by a reinforced submarine sole-plate 2 and above deck-level by two substantial bridges 3. At the longitudinal mid-points of the inner hull sides are two turrets 4 which act as supports for the axle-bearings of a paddle-wheel 5. This paddle-wheel can revolve freely in either direction.

The paddle-wheel axle 8 enters the top of each turret via waterproof glands where it is seated upon bearings and linked to a transmission system which conveys mechanical power down through the turrets to electricity generators within the hulls 1.

The hull-sides are vertical, their outermost sides being perfectly straight to present no obstruction to the flow of the tidal stream. The innermost hull sides are straight and run parallel to the outer sides for only approximately half the total length of the platform, then taper outwards in a gentle curve until they meet the outer hull sides at pointed bows. The platform may then be described as having two bows at both extremities.

The sole plate 2 extends from a point approximately one eighth of distance along the overall platform length to one eighth of that distance from its other extremity. The sole plate is not flat but gently sloped 10 at each extremity so that it may both house transverse reinforcement members 11 that extend across the beam of both hulls and also form a hydrofoil profile. *1

The platorm is anchored both fore and aft to the sea-bed so that its longitudinal orientation is held parallel to the known direction of flow of the local tidal stream.

The rate of flow of water passing between the inner hull-sides and across the sole-plate will be approximately three times that of the natural velocity of the tidal stream. Additionally, the number of hours per day during which quantities of energy viable for driving electricity generators will be extended.

The device is capable of being constructed to any desired scale.

However, its scale and size must be determined by reference to the amplitude of the highest historic or anticipated wave at the intended site of use. The clearance between the waterline 9 and the underside of the paddle-wheel axle 8 needs to comfortably exceed this known or anticipated height, so that solid water could not drive the upper half of the paddle-wheel 5 in a direction diametrically opposite to that of its lower half, thus incurring shock loads. Freak waves as high as 16 metres have, for example, been reported around the coasts of the UK, and the device here described would need to be constructed with this parameter in mind. Although the device is represented in the attached diagrams on a scale of 1:1,000 and would have an overall length of metres, this must be regarded as the smallest scale on which the design should be executed in order to be effective. Nevertheless, greater size yields the important benefit of greater energy yields and proportionally higher electrical output. Size matters.

The device incorporates vertical bow strakes (sometimes referred to as "wave-piercing bows") at both extremities so that waves approaching longitudinally do not generate an undesired lifting effect and thus induce pitching..

Nine-tenths of the deck area is covered by sloped steel canopies 6 to allow larger waves approaching from the quarter or beam to break across them and thus reduce rolling. An optional feature for sea-areas with exceptionally heavy weather would be the alternative of a larger steel canopy linking the outboard slopes of the bridges 3. *1

The outward faces of the two bridges 3 and of the two axle-support turrets 4 are also sloped to assist the dispersal of larger waves breaking across the superstructure.

The parts of the hulls between the bridges and the bows incorporate ballasting tanks 12. These are kept empty when towing the platform to its site of operation and are then flooded to lower the platform to its correct operating draught thus endowing the platform with greater mass and stability in heavy seas.

Internally,some space is occupied by the massive support columns and beams of the bridges 3 and turrets 4. The space forewa rd/aft of the bridges is occupied by ballasting tanks 12. Space between the bridges 3 is available for transmission components, electricity generating plant 14 and storage compartments 13 for tools and materials.

The paddle-wheel 5 should be constructed as a steel or aluminium skeleton lattice and to present as little aerodynamic drag as possible to winds from the beam or quarter. It is also desirable to specify paddle-to-wheel attachments and wheel-to-axle attachments which fracture under shock loads, obviating possible damage to fixed structures such as bearings or turrets.

The device is symmetrical in its longitudinal dimension and thus designed to function with equal efficiency during both the flow and ebb of tidal streams without needing to be re-positioned or to swing around a single anchor.

Constructional materials suitable for the device include: Hulls: steel plate or marine-grade ferrocrete (steel-reinforced concrete) Sole-plate: galvanised steel plate enclosing steel tubing or girders Bridges and turrets: high-tensile steel Paddle-wheels: galvanised steel or aluminium Paintwork below waterline: barnacle/marine growth repellent polymer coating A design feature of the bridges and turrets is that their lower structure passes through the canopies and decks and is both seated upon the sole of the hull and rigidly attached its side(s). The generator compartment requires to have a very strongly reinforced steel floor both to support the massive weight of generators and to resist the huge torque they generate.

To prevent the ingress of larger sea-creatures and flotsam into the channel between the hulls, wide-gauge steel mesh netting is fitted between the tops of the bows and the leading edges of the sole-plate.

Smaller sea-creatures can pass through the paddle-wheel 5 unharmed.

Electricity generated aboard the platform would be fed ashore by submarine cable and where appropriate into the National Grid system.

The device possesses several major advantages over alternative technologies for electricity generation: a) it uses no fossil or nuclear fuel b) It has almost no environmental or ecological impact c) It generates zero pollution d) Its construction ensures an extremely prolonged service-life e) Maintenance work is minimal (lubrication and bearing-replacement) f) It occupies no land g) It draws energy from a source which is as predictable as the rotation of the Earth upon its axis h) The abundance of available tidal stream energy amounts to many times the level of peak demand for electrical power in the UK.