Ocean Power -Waves and tides

Dr David Griffin

Research Scientist (Oceanography)

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Wave power – the basics

• When the wave height is 5m the energy flux is about 150kW/m.• Tasmania’s average usage is 1200MW• 1200MW ÷ 150kW/m = 8km• waves west of Tasmania are 5m only 10% of the time (and

that’s in winter)

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Wave heights west of Tasmania

• most of the time, the wave height is between 2m and 4m:

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Wave energy flux west of Tasmania

• mostly 30-100kW/m, depending on season• 1200MW ÷ 40kW/m = 30km

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Capture fraction, efficiency

• Wave devices do not capture all the incident energy• (You wouldn’t want them to)• Not all the energy they capture can be converted into electricity• let’s assume just 10% of the incident wave energy flux is turned

into electricity• 1200MW ÷ 4kW/m = 300km• = the length of the west coast

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CETO

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bioWAVE

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Pelamis

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Wave power - conclusion

• If we really wanted to, we could power Tasmania using 10% of the wave energy incident on the west coast.

• that would be ~1000 devices, ie 3 per km on average – a massive project

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Tidal currents – 2m/s in Banks Strait

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SeaGen – 16m dia x 2, 1.2MW at 2.4m/s

• Power (W/m²) = ½ ρν³• 2.4m/s → 6.9kW/m²• 400m² → 2.8MW• 40% efficiency → 1.2MW• Banks Strait peaks at 2.6m/s• → ~200kW average• 6km line of 30 SeaGens → 6MW• insignificant for Tasmania• significant for Flinders Island

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Australian company - BioPower

• bioSTREAM

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Ocean circulation

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Median energy flux of ocean currents

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Currents near Tasmania are weaker than up north

• If anywhere, off Brisbane is where it might be worth exploiting the East Australian Current. Median speed = 0.9m/s

• 0.35kW/m² → 60m dia for 1MW

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Conclusions

• For Tasmania, the only significant marine source of renewable energy is the waves off the west coast

• Environmental impact and multiple-use conflicts are probably not show-stoppers

• engineering and economics are more serious concerns• but west Tasmania is as promising a location as anywhere in

the world

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Thankyou

• Mark Hemer (CSIRO) – high resolution wave climatology• John Andrewartha (CSIRO) – tidal currents• Stuart Gibson - photo of Ross Clarke-Jones surfing Pedra

Branca