Lecture 5 Review

The subject of lecture 5 was Ocean Energy. The ocean has a great potential for energy extraction, as it is very energy dense. The earth's surface is 70% water, so the amount of solar energy incident on the ocean is much larger than on land, and is equivalent to 250 billion barrels of oil per day (3000 times larger than the current output of oil). Conservative estimates predict that up to 25% of the world's energy needs could come from the ocean, so they are definitely a renewable energy source that deserves attention.

There are four main ways of extracting energy from the Ocean, from wave energy, tidal energy, current energy and thermal energy. We learnt that the typical amount of energy that can be extracted from a meter of wave crest is about 10 times higher that the energy in a square meter of wind because water density is much higher than the air (areas of the world oceans have upwards of 90 kW/m). However the vast majority of this energy doesn't reach our coasts as it dissipates through wave breaking and interaction with the seabed. Hence the most energy profitable areas are offshore, before this interaction can take place.

In terms of wave energy extraction there are 5 options that we looked at: - Oscillating Water Column, Overtopping, Surge, Attenuator and Point Absorber. Examples were given of each, and Pelamis (attenuator) was highlighted as the only commercially active Wave Energy Converter. We also looked at several of Resolute Marine's concepts, which were all point absorbers. Another advantage of wave energy is that it's levels are in synch with seasonal energy demand in the US - the waves get larger as the heating energy demand increases in the winter.

Tidal energy is only economically viable at about 20 sites around the world, due to the need for large tidal variations combined with specific geographical requirements. It's maximum potential contribution to the US energy need is between 1-2%, and it is only generating power for 35% of the day. However it's predictability means that this can be planned for, and still utilized effectively.

The development of wave energy is currentl
y at the point as wind energy was 25 years ago. Now wind energy has converged on one design, and more and more commercial wind farms are being built. The process for wave energy should be swifter, given the lessons that have been learnt from wind. So ocean energy has a vast potential that hopefully we can start using soon.

Hosted by Professor Dick K.P. Yue