The Potential Effect of Wave Energy Converters on Surfing Waves - Steve CHALLINOR

International Symposium on the Protection of Waves

Impacts of Wave Energy Projects on Surfing Waves

Steve Challinor on behalf of Surfers Against Sewage

What are Wave Farms?

• Arrays of wave energy converter devices (WECs)

• Many types of WECs under development• WECs generate electricity by harnessing

power from waves• Located in shallow (seabed-mounted WECs)

and deep water (floating WECs)

Floating WECs

Examples: Pelamis (attenuator) and Powerbuoy (point absorber)

Seabed-mounted WECs

Example: Oyster (oscillating wave surge converter)

How do WECs affect Waves?

WECs change wave characteristics by:• Absorbing wave energy – reduces wave

energy and wave height• Interfering with wave energy (reflecting and

blocking waves) – changes wave height and wave direction

• Changes to waves can cause changes to shoreline bathymetry, particularly at breaks with mobile sediment (e.g. sand bars)

Evidence of Impacts

• Very few WECs deployed, so no evidence from direct measurements

• Most evidence gained from numerical modeling / computer simulations

• Examples from Cornwall, SW England and Orkney Islands, Scotland

• Evidence = threats to surfing waves?

Example 1: Cornwall, SW England

• ‘Wave Hub’ - proving facility for prototype WECs• 8km2 sea area (4km x 2km)• Floating WECs = 20+km offshore • 20MW generating capacity (1MW = 400 houses)

Halcrow (2006) study

‘Typical layout’ of floating WECs comprising:• 1 x Wave Dragon WEC• 2 x Fred Olsen FO3 WECs• 30 x Powerbuoy WECs• 6 Pelamis WECs

2 wave scenarios: • small summer waves (Hs 1m, Tp 7s) • large autumn waves (Hs 4m, Tp 16s)

Wave Hub Array

2 x Fred Olsen FO3 WECs

1 x Wave Dragon WEC6 x Pelamis WECs

30 x Powerbuoy WECs

Small Summer Waves (Hs 1m, Tp 7s)

Wave height immediately behind WECs reduced by >20%

Wave height at shore reduced by 9-11%

Large Autumn Waves (Hs 4m, Tp 16s)

Wave height immediately behind WECs reduced by >20%

Wave height at shore reduced by 3-5%

Different WECs = Different Effects

1 x Wave Dragon WEC

2 x Fred Olsen FO3 WECs

30 x Powerbuoy WECs

6 x Pelamis WECs

Example 2: Orkney Islands, Scotland

• Part of the ‘Pentland Firth’ licensing area for wave farms and tidal farms

• Up to 1,600MW generating capacity

Orkney Islands

Thurso

Venugopal and Smith (2007)

• Site off mainland Orkney

• Seabed-mounted WECs = 2km offshore

• 1 layout scenario of 5 WECs

• 1 wave scenario (Hs = 4m, Tp = 10s)

Porosity Scenarios

• Porosity = % wave energy transmission through WEC

• Wave energy lost to absorption and reflection

• Porosities = 0%, 50%, 60%, 70%, 80% and 90%

5 WECs in line

Downstream wave climate

Wave Height Changes

Wave height reduced from 13% (90% porosity) to 67% (50% porosity) immediately behind WECs

Porosities 0% to 90%

Wave height reduced by >20% 1000m behind WECs

Wave height increased in front of WECs due to wave reflection Wave height

reduced by c.10% 500m behind WECs

Results

• For all porosities wave height and wave energy are always reduced downstream of WECs

• This could affect sedimentation processes and wave climate near the shore

• Lower porosity = lower energy absorption + higher energy reflection = lower wave transmission = more impact on wave height

• Potential for second row of WECs behind first row

Threats to Surfing Waves?

PMSS (2010) study:• Present = 20MW

(Wave Hub) • Future = 1200MW

Threats to Surfing Waves?

West Cornwall

Threats to Surfing Waves?

North Cornwall

Threats to Surfing Waves?

Marwick Bay, Orkney

Threats to Surfing Waves?

Marwick Bay, Orkney Various reef breaks

c.500m

10MW array

2MW array

Conclusions

Studies suggest:• Wave farms pose a threat to surfing waves• Threat related to wave farm characteristics • Different WECs = different effects on waves• Seabed mounted WECs = shallower water / closer to shore = greater threat?• Floating WECs = deeper water / further offshore = smaller threat?

More Info – SAS Reports

• Climate change issues: Climate Change – A Surfer’s Perspective• Wave farms and WECs: The WAR Report – Waves Are Resources• Impacts on surfing waves: Guidance on Environmental Impact Assessment of Offshore Renewable Energy Development on Surfing Resources and Recreation

More Info – Cited Studies

• Halcrow (2006). Wave Hub. Development and design phase. Coastal processes study report. South West of England Regional Development Agency, June 2006.• Venugopal, V and Smith, G. (2007). Wave climate investigation for an array of wave power devices. Proceedings of the 7th European Wave and Tidal Energy Conference, Porto, Portugal, 2007.• PMSS (2010) Offshore Renewables Resource Assessment and Development (ORRAD) Project – Technical Report. Report prepared for South West Regional Development Agency.