Contribution by Ian Rogers
Congratulations on your approach to remote area power generation from axial flow turbines (Masters et al., 2022).
You have not mentioned mechanical damage to the blades or support cables by floating debris. With rivers over 4 m deep, both surface and river-bottom debris seem likely and serious damage to the blades and the cables and pontoon could occur.
Upstream cable-stayed screens may help, but a lot of experimenting could be needed to prove the system viability. It would be difficult to construct screens to be self-cleaning, although some sort of angled screen could perhaps throw off surplus debris to one or both sides of the turbine.
Authors’ reply
We are pleased to reply to this question. The question of using a screen for turbines in open water has been under discussion since the deployment of the first marine current turbine device in Loch Linnie in 1993. The majority of devices deployed have been open, without a screen. Most of them have been deployed in tidal channels, with a few in large rivers. Floating devices have a clearance between the tip and the surface to avoid collision and reduce the potential for cavitation. This will put the majority of debris either above or below the rotor.
One problem with a screen would be the additional loading on moorings due to the build-up of material. The developer would have to take into account the potentially large area and hence the moorings would become oversized and expensive.
Due to the large torque applied to the rotor in operation, many blade designs are stronger and stiffer than an equivalent wind turbine. This means they are resistant to small impacts. In the event of large impacts, then a system would need to be employed to replace blades after damage. Experience from the field will help to establish the extent of the potential problem.
