Ocean renewable energy - resources & impacts

1. Ocean renewable energy –
resource & impacts
Simon Neill*, Matt Lewis, Peter Robins
School of Ocean Sciences,
Bangor University, UK
*s.p.neill@bangor.ac.uk
DrSPNeill

2. Outline
• Tidal energy potential
• Sediments & tidal energy sites
• Near-field impacts
• Headlands/sand banks
• Far-field impacts

3. 3

4. 3D model of the Irish Sea:
resolution 1/240° x
1/404° ~278m
10 depth levels
Peak current
speed (m/s)
Lewis et al. (2015)

5. Co-tidal chart
5
• Co-tidal lines join locations which
are in phase (i.e. HW occurs at the
same time)
• Co-amplitude lines join locations
that have the same tidal amplitude
(which is half of the tidal range)
M2
Neill & Scourse (2010)

6. Bristol
Channel
Skerries
Pembrokeshire
𝑃𝑃
𝐴𝐴
=
1
2
𝜌𝜌𝑈𝑈3
𝐶𝐶𝑝𝑝

7. Impact of energy extraction on bed shear
stress/sediment transport
• Bed shear stress is a function
of U2.
• Small changes in the tidal
currents could lead to large
changes in the corresponding
bed shear stress.
• Transport of sediments is
proportional to an even higher
power of velocity than bed
shear stress, e.g. U3. Neill et al.
(2009)
U2
U

8. Mobile sediment in the Pentland Firth
Fairley et al. (2015)

9. Local impacts due to tidal energy
extraction

10. Particle size ranges

11. ‘Rouse profiles’ for a range of sediment grain
sizes
Neill et al. (2017)

12. Neill et al. (2012)

13. Peakcurrentspeed(m/s)

14. Residual sediment transport

15. Change in mean velocity (m/s)

16. Change in mean sediment transport (m2/s)

17. Tidal-stream energy extraction
How do TEC arrays affect:
– Suspended sediment?
– Formation of sand banks?
– Net sediment fluxes?
Is the impact significant relative to natural
intra-seasonal and inter-annual variations?
TEC array simulations:
• Turbines induce drag force on flow
𝐹𝐹𝑥𝑥 = −𝐶𝐶𝑝𝑝
𝑃𝑃
𝜌𝜌𝜌𝜌𝜌𝜌𝜌𝜌
𝑐𝑐𝑐𝑐𝑐𝑐 𝜃𝜃
• TEC array rated power modelled:
• 10, 50, 100, 300, 500 MW
Robins et al. (2014)

19. Conclusions
• Sediment present even in regions of very strong
tidal flow
• Turbines could lead to a local increase in bed
shear stress
– 3D modelling required
• Impact significant for large scale extraction, e.g. >
100 MW
• Impact needs to be assessed against natural
variability
• Validation & tuning of sediment transport and
energy extraction required