For many centuries, people have tried to harness the power of wind to make everyday life easier and processes more efficient. The first constructions were called windmills and used for pumping water or grinding corn. In the 19th century, windmills were replaced by fossil fuel engines and a distributed power network. In the second half of the 20th century, a greater insight into aerodynamics and advanced materials, particularly polymers, had a favourable influence on establishing wind power as an efficient as well as green method of energy production establishing wind power as an efficient as well as green method of energy production.
There are several types of wind turbines, which are determined by the orientation of the shaft and rotational axis: A turbine with a shaft mounted horizontally parallel to the ground is known as a horizontal axis wind turbine or (HAWT). A vertical axis wind turbine (VAWT) has its shaft normal to the ground. The main problem with VAWT is that such turbines have a low tip speed ratio, and it is difficult to control rotor speed. Difficulties in the starting of vertical turbines have further hindered their development. However, the VAWT requires no additional mechanism to face the wind and heavy generator equipment can be mounted on the ground, thus reducing tower loads.
Now (2022), scientists at Sandia National Laboratories have come up with a new construction for offshore wind turbines: instead of a tall tower with blades at the top, they designed a towerless turbine with blades pulled taut like a bow for offshore applications.
However, floating offshore wind turbines entail a whole set of challenges, mainly because it is very expensive to support the wind turbines and to maintain them when they are out at sea. Therefore, the scientists aim to optimise the design of floating wind turbines, platforms and control systems to maximize power output while minimizing costs.
For traditional, horizontal-axis wind turbines, the blades can rotate away from intense, damaging winds. The vertical-axis wind blade, on the other hand, catches the wind from every direction. The Sandia scientists took this design and replaced the central vertical tower with taut guy wires. The wires could be shortened or lengthened to adjust for changing wind conditions in order to maximise energy capture while controlling strain. Moreover, replacing the shaft with wires had a beneficial effect on the weight of the turbine, allowing the floating platform to be even smaller and less expensive.
The scientists built upon earlier work of Sandia engineers to develop the vertical-axis wind turbine design tool. The team worked on integrating physics algorithms while also improving the accuracy and speed of the algorithms. Moreover, they tried to validate the design tool using data from a land-based, 34-meter-diameter, vertical-axis wind turbine built by Sandia in the ‘80s. The reason for validating the design tool was that this could eventually be used to certify vertical-axis wind turbine designs to the pertinent design standards.
Having performed this task, the team can set out to design the floating, vertical-axis wind turbine system. The design tool can be used to model and optimise any vertical-axis wind turbine, whether it has a traditional tower or taut guy wires. The team is employing a process called control co-design to find the most cost-effective floating vertical-axis wind turbine system design and control.
For many years, scientists have tried to come up with new wind blade designs to improve harnessing wind energy. In 2019, scientists invented a new design for wind turbine blade which could do without the spars system and used a segmented Aerodynamic Frame as a support structure. The frame supported the open slats that capture the wind and decreased the weight by 2/3rds when compared to the size and power ratio of an equivalent blade. The new blade also increased performance because of its reduced weight to rotational power ratio. It could be built and transported in smaller sections than commercial blades which creates major issues in form, function and transportation. Maintenance was also reduced and made easier with replaceable slats after onsite visual inspections, whereas internal inspections were no longer needed. The design did not employ internal spars to support the body but replaceable slats which were much easier to inspect on this new blade design.
Image: Wind Blade Designs
In 2021, scientists designed a wind turbine consisting of a turbine generator, rotating mast and a bedplate as the foundation of the turbine, and three vertical airfoils positioned parallel forming a diffuser. Two of these foils were side airfoils and the third one, which was positioned in an equal distance between the side airfoils, was the central airfoil. Also, three vertical airfoils had cross-section diminishing upwardly and the central airfoil comprised in its leeward area a mounted turbine generator which was suitable for one or more rotors which could be connected to one or more electric generators. The said turbine generator is positioned inside the central airfoil. The central airfoil in its cross-section had the shape of biconvex airfoil section preferably drop-shaped.
Image: Wind turbine in perspective view from the windward side
There are several advantages to using a vertical design with bow-shaped blades: The design would enable a massive generator which creates electricity from spinning blades to be located closer to the water. This would make the turbine less top-heavy and reduce the size and cost of the floating platform. Since much of the offshore wind around the globe is harnessed in deep waters, you would need to build rigid support structures to support the wind turbines which is expensive. Wind turbines floating above the sea floor could play an important role in diversifying the sources of renewable energy and improving the stability of the grid and help countries get closer to achieving their net-zero emission goals.
With the help of their new specialized software, the team hopes to have an optimised floating, vertical-axis wind turbine system design by the end of the year. The software they developed combines different capabilities, including modeling the aerodynamics and structural dynamics of vertical-axis wind turbines as well as hydrodynamics, and enables them to create a turbine design capable of accommodating different climatic conditions.