3rd Draft, Reader Response

 With the increasing difficulty of finding suitable land for land-based wind turbines, the webpage “Products'' from SeaTwirl (n.d.) introduces the SeaTwirl offshore vertical axis wind turbines (VAWT) as a way to leverage the surface of deep ocean waters to produce clean energy while having economical production and affordable maintenance. Primarily, it utilizes wind to produce energy through the conversion of wind’s kinetic and potential energy to electrical energy. Listing its features, the offshore VAWT has wind blades, an energy converter, a floating turbine body consisting of a buoyancy-providing and ballast portion, and a water movement based braking arrangement. Moving on to their functions, the energy converter converts kinetic and potential energy caught by the VAWT’s wind blades to electrical energy. Next, the wind turbine body is kept afloat with its longitudinal axis generally vertical and upright by its buoyancy-providing portion and ballast portion (Ehrnberg, 2020). Finally, a means of controllably reducing the speed of rotation of the wind turbine is a must to protect the VAWT from the damaging high wind conditions (Ehrnberg, 2020). As a result, the water movement based braking arrangement was made. With these functions and features, SeaTwirl’s offshore VAWT is superior in terms of effective wind utilization and cost to offshore horizontal axis wind turbines (HAWT). 

One such feature would be the SeaTwirl offshore VAWT’s omnidirectional design, it being the reason why the SeaTwirl offshore VAWT is more effective at utilizing offshore wind than HAWTs. Dvorak (2014) states that HAWTs generally need to be facing against the wind in order for the wind blades to rotate. Contrastingly, the blades of a VAWT, in absence of directional orientation, can catch wind regardless of wind direction, resulting in turbulent conditions being ideal (Dvorak, 2014). Moreover, the VAWT has a more advantageous scaling behavior compared to gravitational loads, the square cube law, due to its experience of varying aerodynamic loads (Hand et al., 2021). This indicates that the VAWT is not reliant on alignment against wind direction for wind utilization unlike the HAWT and that it has better scaling behavior against gravitational load than that of the HAWT. In essence, the SeaTwirl offshore VAWT’s wind insensitive design makes it better than offshore HAWTs at utilizing the directionally ever-changing winds present out on the ocean.

Another feature would be the low center of gravity of the SeaTwirl offshore VAWT’s floating body topside which enables the Seatwirl offshore floating VAWT to have lower production cost than offshore HAWTs. It has a low center of gravity because the rotating vertical axis is perpendicular to the water's surface, allowing the heavy drivetrain to be located close to the surface of the water. On the other hand, the offshore HAWT’s rotating horizontal axis is parallel to the water's surface, forcing the heavy drivetrain to be located well above the water surface to prevent collision between its wind blades and the water's surface. Consequently,  a HAWT’s topside possesses “a higher CG, larger aerodynamic load and higher center of pressure than the VAWT, thus, the size of the platform must increase to provide a similar level of performance” (Griffith et al., 2016, p. 7). According to Griffith et al. (2016), when both the offshore HAWT and offshore VAWT have an equal mass of 600 metric tonnes, the VAWT’s spar-buoy needed 48% less steel mass than the HAWT’s spar-buoy and the VAWT’s semi- submersible needed 41% less steel mass than the HAWT’s semi-submersible. This tells us that VAWTs require less material than HAWTs for their floating platforms which are the spar-buoys and semi-submersibles. Overall, the Seatwirl offshore VAWT’s low center of gravity topside enables it to require less material than offshore HAWTs for their spar-buoys and semisubmersibles, thus being cheaper to construct.

Despite these upsides, the wind blades are currently not being recycled or reused. Chen et al. (2019) explains that the composites are hard to recycle due to the “cross-linked thermoset polymers for their matrices, which cannot be re-melted or remoulded” (p. 567). Additionally, much work is required before the realization of commercial production as the current technologies of recycling and reusing FRP waste are insufficient, most still being in the laboratory stage (Chen et al, 2019). As a result, open air storage, landfills and incineration are the conventional methods of disposal. All in all, the inability to remelt or remould wind blades combined with the limited technologies for recycling and reusing FRP waste make the recycling of SeaTwirl VAWT’s wind blades unfeasible.

In conclusion, SeaTwirl's offshore VAWTs are generally not being recycled because of its inability to be remelted or remoulded and its limited recycling and reusing technologies. Despite that, the design of SeaTwirl's offshore VAWT, some features being its omnidirectional design and low center of gravity topside, make it better than offshore HAWTs in terms of wind utilization and cost when leveraging the deep ocean waters to generate clean energy.

SeaTwirl. (n.d.). [Products].

https://seatwirl.com/products/ 

Ehrnberg, D. (2020). FLOATING WIND ENERGY HARVESTING APPARATUS WITH BRAKING ARRANGEMENT, AND A METHOD OF CONTROLLING A ROTATIONAL SPEED OF THE APPARATUS (U.S. Patent No. 10,662,926). U.S. Patent and Trademark Office. https://image-ppubs.uspto.gov/dirsearch-public/print/downloadPdf/10662926 

Dvorak, P. (2014, October 31). “Vertical-axis wind turbines: what makes them better?” Windpower Engineering and Development. https://www.windpowerengineering.com/vertical-axis-wind-turbines/#:~:text=A%20conventional%20HAWT%20must%20first,to%20control%20yaw%20and%20pitch 

Hand, B., Kelly, G., Cashman, A. Aerodynamic design and performance parameters of a lift-type vertical axis wind turbine: A comprehensive review. Renewable and Sustainable Energy Reviews, 139, 1-30. 

https://doi.org/10.1016/j.rser.2020.110699 

Griffith, D., Paquette, J., Barone, M., Goupee, A., Fowler, M. J., Bull, D., Owens, B. (2016). A study of rotor and platform design trade-offs for large-scale floating vertical axis wind turbines. Journal of Physics: Conference Series. 753(10), 1-10. https://doi.org/10.1088/1742-6596/753/10/102003 

Chen, J., Wang, J., Ni A. (2019). Recycling and reuse of composite materials for wind turbine blades: An overview, Journal of Reinforced Plastics and Composites, 38(12), 567-577. https://doi.org/10.1177/0731684419833470