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Interesting Engineering
January 26, 2014

The ocean wave power is one of the most underestimated energy sources nowadays. It has the advantage of being more predictable than winds and could be used 24 hours a day, which could not be said for the solar energy harvesting. There are several projects around the world regarding wave energy, but the potential of this phenomenon is neglected at all.
It is calculated that the current technology could provide between 140 and 750 TWh per year worldwide. The most proper waves for energy harvesting have latitude angle between 40 and 60 degrees. These waves are widely spread around the world. It is obvious that it could play significant role in the electricity production in predictable future.

Significant disadvantage of such technology is its cost. It is estimated that the cost per MWh is higher than 1.5 times the cost of electricity from wind farms and roughly 3 times than the energy from coal power plants. Main reason for these costs is that the technology is still on development level but is expected that further improvements will decrease that cost.

Most researches are focused on the so called WEC devices (wave energy convertor). Each WEC generates electricity in few general steps:

• Absorbing ocean wave mechanical power by utilizing a kind of energy capturing mechanism.
• Forwarding generated power to a generator via transmission mechanism.
• Controlling the power output by arranging rows of similar WECs, using electronic modules or combination of both.

There are several categories of WECs at present:

Oscillating water columns (OWCs). Their main component is a partially submerged reservoir that has water column, formed by the ocean wave ingression, and a column of trapped air. Electricity is generated by the expansion and contraction of the air column, which powers a turbine mounted atop of it. The ocean waves change water level inside the tank, which causes changes in the size of the air column mentioned above. Examples: Islay is a Scottish island around which is deployed the LIMPET power plant. Its capacity is 500 KW. Oceanlinx Port MacDonnell project is expected to be deployed near the shores of South Australia.

Overtopping devices. This type includes power generating units that consist of a central chamber. Waves fill this chamber after which the water is released back to the sea via hydroelectric turbines. Good example is the Wave Dragon deployed near Denmark shores. This commercial platform is a result of research made by deploying smaller prototype of Wave Dragon in 2003.

Attenuator devices. These are long caterpillar-like devices positioned in front of the incoming waves. Such device generates power while the segments flex and along with the wave passing, the mechanical flexing generates energy which is turned into electricity. Pelamis is such device developed by a Scottish company with the same name Pelamis Wave Power, which has been deployed in several locations in Great Britain and Portugal.

Point absorbers. These units oscillate and absorb energy from waves that may come from any direction. They have small sizes which is the reason they produce relatively small amounts of energy. PowerBuoy is a popular example of this WEC type. It is developed by Ocean Power Technologies, a company presented in Australia, USA and UK.


Wave Dragon


PowerBuoy


Pelamis


LIMPET

Although not utilizing ocean waves for producing energy, it’s worthy to mention the PROCODAC project – it is a device that harvests energy from below the sea surface. The device consists of 3 stainless steel buoys located on each corner of an equilateral triangle. They support the fourth buoy on which is located the generator attached to a propeller at the rear end.


PROCODAC


source....

To me it seems the key is diversity.... and living lives commensurate with reasonable local power resources.

Originally Posted by BajaGringo

...Overtopping devices. This type includes power generating units that consist of a central chamber. Waves fill this chamber after which the water is released back to the sea via hydroelectric turbines...

This approach sounds the most promising, but with one major modification: make it tidal, instead of relying on some piddly, intermittent surface chop.

Let the moon's gravitational field do the heavy lifting, in other words.

Quick armchair calc : 1 square mile(5,280' ² @ 1' deep) = 27.9 million ft³ x 7.5 gallons per ft³ = 209.1 million gallons @ 8 lbs/gallon = 1.673 billion foot-pounds of energy available/foot of tide/square mile.

We could get anywhere from 7-8 times that at the most extreme Spring tides(twice a month here), and as little as maybe only 3x at Neap tides.

A big advantage is the water drains through the turbines at the desired rate of power generation, just like a dam.

Originally Posted by Marty Cortez

This approach sounds the most promising, but with one major modification: make it tidal, instead of relying on some piddly, intermittent surface chop.

Let the moon's gravitational field do the heavy lifting, in other words.

Quick armchair calc : 1 square mile(5,280' ² @ 1' deep) = 27.9 million ft³ x 7.5 gallons per ft³ = 209.1 million gallons @ 8 lbs/gallon = 1.673 billion foot-pounds of energy available/foot of tide/square mile.

We could get anywhere from 7-8 times that at the most extreme Spring tides(twice a month here), and as little as maybe only 3x at Neap tides.

A big advantage is the water drains through the turbines at the desired rate of power generation, just like a dam.

I have long thought the very exact same thing amigo. And it's 24/7 energy production...

Originally Posted by BajaGringo

I have long thought the very exact same thing amigo. And it's 24/7 energy production...

Seeing that there is approximately 0.433527501928 psi in 1 foot of head pressure.

and the basic calculation for Kilo watts is: (kW) = HEAD (feet) x FLOW (cfs) / 11.81

That is A LOT of Kilowatts, we now talking Mega watts.

There are other factors that are not taken into account i.e. losses due to cable resistance, equipment efficiency and so on but still not bad.

I guess the biggest problem is cost per kilowatt to construct and to maintain.

I guess break walls for Marinas or areas where people want to protect the shore line from degrading could incorporate this in it construction, they are probably 50% of the way there in cost.

Man it has been a long time since I played with this stuff, thanks I enjoyed the Brain Work.