Case Study

ESRU Energy Systems Research Unit

University of Strathclyde


Conclusions: Summary


The following conclusions can be drawn from the work carried out during the course of the project and the results attained in the case-study: There are many further intuitive conclusions which one can draw from the nature of this study and the current developing nature of the the marine industry.

• Matching the appropriate technology to the resource is very complex & iterative process
As seen throughout the case study and methodology presented, there are a vast number of interdependent variables to be taken into account. These broadly ranging from initial site selection, technology type, design and power rating, deployment and economic limitations, environmental and SIF limitations are need to be taken into account and balanced.

The velocity distribution is more uniform than expected therefore technology could be deployed at depths closer to the seabed
General limitations as to the proximity within which devices can efficiently capture energy have been specified to range from 25% of LAT to within 5 metres. It was found however that shear and roughness have lesser affect on the flow than previously thought, hence devices extraction mechanisms could be deployed to within 2 meters if the sea/channel bed

• The flow characteristics of a site can not be assumed to be equally bi-directional and therefore uni-directional technology is a feasible option
Typically tidal flow models presume and approximate sinusoidal ebb and flood model. However due to positioning of landmasses, out of phase tidal flows can cause flow regime harmonics and unidirectional flow in some channels.

• Site geometry was generally the limiter in lateral sense, where SIF dictated longitudinal spacing

It is assumed that when technology develops and devices can be deployed in deeper areas (depths >30m), the energy extraction will be substantially increased however our results suggest that SIF will limit that extraction. In our preliminary case study taking into account depth limitations we were achieving SIF’s approaching 9%

Therefore if SIF becomes legislation, the amount of exploitable energy will not increase even though technology to deploy it deeper develops
While larger turbines have the largest power coefficients and power outputs, their blockage effects and hence low packing density & price make the deployment of these devices an inefficient use of space and expensive options due to the associated cabling and managing costs of large tidal farms.

• Better to have lower SIF & higher number of smaller/alternative devices (dependant on technology costs…)

This enables rapid flow rejuvenation, higher average farm flow velocities and higher power outputs.

Case study showed Oscillating Hydrofoils to have low efficiency and low blockage effects balancing overall farm output.
The Oscillating Hydrofoil on average had 40% lower efficiencies the than alternative devices. The device recovers to full stream velocity in 25% the distance in comparison to other technologies. These two combined finds indicate their farm power output is comparable because more devices can be fitted into a lesser area as the design has a minimal blockage effect.

• Velocity recovery distances after energy extraction are much larger than expected
Rejuvenation distances are more so in he scale of kilometres rather than tens or hundreds of meters. Therefore tidal farms will be required to hold considerable marine sites to enable this flow rejuvenation.

• Economic drivers will likely dictate the influence of SIF and levels of adherence
Similar to the development of wind farms, finally economic factors will dictate the levels of industry compliance with SIF and what final device spacing with result

• No clear Market leader.
Individually the horizontal turbines have the highest performance Producing increased power levels than the other devices but when space is limited and the case study shows that there is no clear winners in the different technologies for tidal farms energy capture.

• Hydrodynamics is not equal to Aerodynamics

There are limits to the similarities aerodynamic theory and hydrodynamics and to the extent to which they can be interchanged in marine device development.



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