Wind energy applications — the promising road forward
Monday, June 30, 2014
Wind energy continues to provide major growth opportunities for plastic composites — the industry will reach $4 billion by the end of 2014. The adoption of larger-scale turbines and the expansion of offshore installations that call for stiffer and lighter blades are important to the use of lightweight, strength-to-weight plastic composites.
As blades get longer and narrower, it becomes increasingly challenging to build in sufficient strength and stiffness to protect against blade deflection under load. Low-weight, high-performance blades that can be transported in two sections and combined locally will reduce the cost of logistics and enable onshore wind farms to be equipped with larger, more profitable rotors.
Look at some emerging wind energy application developments, the biggest trend in the future appears to be vertical.
We'll start with vertical-axis urban wind power. A full-scale vertical-axis wind turbine (VAWT) under development by McCamley Ltd. targets urban applications. The flat-pack fiberglass composite turbine requires no supporting mast and can be retrofitted to any roof. A full-scale prototype is being tested at Keele University Science Business Park in North Staffordshire, England.
The composite material construction accommodates the double curvature stator design and provides a lightweight, stiff, multiload path design that reduces shipping costs, assembly requirements and roof structural issues. Unlike horizontal-axis wind turbines (HAWT), which rely on steady wind speed, McCamley Ltd.'s VAWTs can cope with the turbulent and variable wind speeds often found in urban environments.
McCamley Ltd.'s VAWT includes the following features:
- No input from the electric grid is required to start this turbine, which self-starts at wind speeds as low as 1.8 m/s. Also no shutdown speed is needed as the turbine can continue to operate in storm-force winds.
- The absence of down-force from sweeping blades significantly decreases noise and ground vibrations and makes it less likely to impact wildlife.
- Its Lightweight design incorporates multilegs to help reduce building structural requirements.
- Blades are encased in a stator, which affords extra protection.
- It is designed to be aesthetically pleasing.
Moving offshore, new floating wind projects are under development. INFLOW (INdustrialization setup of a FLoating Offshore Wind turbine) is a consortium of 10 partners led by Technip looking to optimize VAWT prototypes and manage all aspects of transition to a feasible industrialization stage.
The project, which will run for four years, is sponsored by the European Commission's Seventh Framework Programme. The main role of the project will be to demonstrate the cost competitiveness of the solution and to bridge the gap in between the development and industrialization phases of the technology. Longer term, the goal is to set up an offshore wind farm composed of 13 turbines with a total capacity of 26 megawatts.
The project will rely on results from the first deep offshore wind turbine prototype of the Vertiwind project. The Vertiwind prototype — a 2 MW floating VAWT — resulted from a joint venture between Technip and Nénuphar. The prototype is a three-column semisubmersible featuring a 50-meter diameter Darrieus-type rotor consisting of three 70-meter blades, angled at 120 degrees, attached to a pole at the center of the floater.
The "air gap" (distance between the rotor and the sea) is 25 meters and the "omnidirectional" direct-drive turbine can harness wind from any direction. The prototype blade is based on a "monobloc" design composite blade technology developed by Nénuphar.
INFLOW offshore wind turbine layout (left) and turbine blade cross section (right).
Offshore wind energy is also extending the breadth of wind-generated power. Land-based wind farms are limited by their impacts on the landscape, large seasonal wind variability and fewer places available for construction. Winds over the ocean are more reliable, attain higher speeds and are less turbulent than winds over land — and no landforms block accessibility of the wind over the ocean.
Even though offshore winds generally offer a better wind resource, installing and operating turbines in harsh ocean environments is challenging. Initial costs for offshore wind energy is high because of the challenges of transporting materials to remote locations and installing them underwater, as well as constructing the foundations so that they can sustain the harsh, often unpredictable, conditions beneath the waves.
Closing the loop analysis-wise, high offshore installation costs in turn are pushing development of supersized turbines to achieve economies of scale. Thus floating wind turbines are an attractive option for offshore installations.
Finally, let's briefly review compact HAWT/VAWT application technology advances. Although multimegawatt wind turbines dominate the wind energy landscape, there is significant effort to develop smaller turbines with output well under 1 MW. The small kilowatt capacity turbines are within the economic range of small businesses, farmers and homeowners.
"PIQO" compact micro-HAWT.
"PIQO" compact micro-HAWTs are being marketed to industrial facilities, high-rise buildings and private homes. EverkinetiQ International developed the PIQO Series of small turbines in collaboration with Pekago, Albis and BASF that are intended to provide locally-generated energy.
Plastic material-wise, a 15 percent glass fiber-reinforced ASA (acrylic ester styrene acrylonitrile) is used for the turbine rotor and unfilled ASA for the 1.5-meter diameter frame. Dutch injection molder Pekago is producing the micro wind turbine parts. ASA offers good resistance to weathering, ultraviolet light radiation and aging. The PIQO wind turbines are rugged and compact, and they generate little noise.
A small multivane magnetic levitation-based VAWT is also being commercialized by Enviro-Energies Holdings. The turbine components are molded from polyethylene terephthalate (PET)/glass sandwich composites formed in a low-pressure compression molding process.
The sandwich composite developed by Allied Composite Technologies (ACT) features a fibrous core of commingled, 2-3 inch chopped glass and PET fibers. The PET fibers melt and fuse the core and skins during lamination, eliminating the need for adhesives.
Thin skins, of bidirectional glass and post-consumer PET resin, are produced in a unique heat-fusion process just prior to lamination by ACT's manufacturing partner, Inline Fiberglass Ltd. PET was selected for its high thermal stability and stiffness.
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