The blade shells are sandwich constructions, featuring trademarked SPRINT glass fiber pregreg faceskins surrounding Gurit’s trademarked Corecell structural foam for the core. These materials reportedly allow the very thick laminates of the spar to be built up and cured in one shot under vacuum pressure only, without debulking to remove air between plies.
The spar caps (110 mm/4.33 inches at the thickest point) are manufactured using Gurit’s trademarked SparPreg unidirectional carbon fiber prepreg - designed specifically for use in spar caps - combined with the company’s trademarked SPRINT glass fiber prepreg, also designed for blade applications. The blades themselves consist of a mix of glass and carbon fiber prepregs, all oven-cured. To capture tidal water energy as it ebbs and flows, the turbine remains stationary, but the blades can be adjusted to rotate through 270° to accommodate the change in water flow. Designed for water flows of up to 5m/sec (16.4 ft/sec), the turbine’s 1-MW rating equates, practically, to power that is sufficient for about 500 homes. The blade is 300 mm/11.8 inches thick at the center and 50 mm/2 inches thick at the tip. The blade that Gurit ultimately designed for the HS1000 measures 9m/29.5 ft long, weighs 2,000 kg/4,409 lb, is 1.5m/4.9 ft at its widest point and has a root that is 1.3m/4.3 ft in diameter. The selected solution, however, is considered by Gurit to be subject to confidentiality and, therefore, was not disclosed. Gurit, he reports, considered several ideas, including filling the blades with water prior to installation, filling the blades with foam or flooding them with seawater. To maximize blade-turning and power-generating efficiency, Royle says, it was necessary to equalize the pressure in some way. And because the blade is relatively short, it also means that the blade design must transition much more quickly than a wind blade does from the cylindrical shape at its root to its sculpted hydrodynamic architecture (see illustration, top left).įinally, Royle says, Gurit had to consider the challenge of coping with the pressure differential between the inside and the outside of the blade - air pressure of 1 bar/14.5 psi vs. “Cramming” more material into the blade meant designing a shorter blade (9m/29.5 ft) than would be required for a wind turbine of the same 1-MW capacity (30m/100 ft rotor diameter). “We must design the blade to accommodate the reduction in strength,” he notes, “so that the blade at the end of life is still strong enough.” Further, he notes that the composite materials used in the blade have a natural tendency to absorb water, which over time can compromise the strength of the blade. “We have to cram a lot more material into the blade to make it structurally viable,” Royle quips. The difference - about a factor of 800 - represents a substantial physical load for a blade, thus it must be more stout to provide continuous service. By comparison, the air, depending on pressure and temperature, ranges from about 1.1 to 1.4 kg/m 3. One of the biggest differences, of course, is water density, which is about 1,025 kg/m 3. ANDRITZ HYDRO Hammerfest had designed, built and tested a smaller predecessor, the HS300 (rated at 300 kW), in waters off the coast of Norway and was looking to scale up that design as the next step in its progression to a 10-MW tidal turbine farm in the Sound of Islay off the west coast of Scotland.
Gurit (Newport, Isle of Wight, U.K.) faced this multifaceted challenge when it was approached by ANDRITZ HYDRO Hammerfest (Hammerfest, Norway) to develop composite blades for the company’s newest tidal turbine, the HS1000, a 1-MW system destined for placement in waters controlled by the European Marine Energy Centre (EMEC), located near the Orkney Islands off the northern coast of Scotland. And the presence of sea creatures - many much larger than the birds that sometimes collide with wind blades - and a variety of underwater plant life, boats and other marine craft present many more potential hazards than wind blades are likely to encounter. Water temperature and, especially, pressure, density and turbulence require much greater strength and durability. When the composite structure of a turbine is to function fully submerged in saltwater for a long period of time, the blade’s designer must consider a host of differentiating factors: While a wind blade has to withstand occasional rain or snow, a tidal turbine blade must handle continuous submersion in highly corrosive saltwater.
Tidal blade series#
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