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Ocean Thermal Energy Conversion a Silver Bullet for Climate Change?

ocean thermal energy converstion“In folklore, a bullet cast from silver is often the only weapon that is effective against a werewolf, witch, or other monsters.” Wikipedia.

In a speech following his Minnesota primary win in 2008, then candidate Obama said, “this was the moment when the rise of the oceans began to slow and our planet began to heal.”

Not only was this assurance an Obama presidency would address the climate problem, it identified the monster – rising oceans – that needed slaying in order that the planet could begin to heal.

So what makes the oceans rise? 

Stefan Rahmstorf points out there are three reasons, thermal expansion of sea water as it warms up, melting of land ice and changes in the amount of water stored on land.

About 90% of overall global warming goes into heating the oceans, and new research confirms this warming and thus the ocean’s thermal expansion has accelerated the past 15 years.

The First Law of Thermodynamics dictates there exists for every system a property called energy and that the change in energy of the system is equal to the difference between the heat added to the system and the work done by the system.

So we have a system, the ocean, accumulating 90% of the heat of global warming, increasing the energy of the system, which excites the water molecules causing an increase in their average separation and thermal expansion.

The only weapons to counteract thermal expansion are to stop adding heat to the oceans, which we cannot do, or convert the heat being added to the system to work, which we can by moving surface heat to the cold reservoir of the deep ocean through a heat engine in a process commonly referred to as ocean thermal energy conversion or OTEC.

Due to the thermodynamic inefficiency of this process, as a consequence of the small temperature difference between the hot and cold reservoirs, about 20 times as much surface heat as energy produced has to be moved to the depths.

This however is also a sea level benefit because at temperatures and pressures at 1000 meters, where OTEC systems typically access the cold reservoir, the coefficient of thermal expansion of water is half what it is at the surface.

Coefficient of Expansion Depth Temperature Pressure Salinity
e x 10 to 6th power M C decibar %
297 0 26 0 3.5
120 1000 4 1000 3.5
136.2 2000 3 2000 3.5
178.4 4000 3 4000 3.5
215.6 6000 3 6000 3.5
240 8000 3 8000 3.5

 

The second cause of sea level rise is the melting of land ice, 99 percent of which exists in Greenland and Antarctica. NASA, tells us the poles are warming faster than the rest of the planet largely as a result of energy in the atmosphere being transported through large weather systems.

Again, this accords with the Second Law of Thermodynamics; heat flows from a hot area to a cold one in an effort to attain equilibrium.

A study by the Niels Bohr Institute tells us we can expect as many as 10 times more storms like Katrina as temperatures rise two degrees above current levels and thus even more heat will be moved to the polls causing more melting. And Cornell researchers point out that the loss of summertime Arctic sea ice due to warming at the polls appears to alter the flow of the jet stream in the Northern Hemisphere creating a blocking pattern like the one that steered Hurricane Sandy west into New York City.

The confluence of more storms made stronger by global warming and sea level rise is a recipe for even greater disasters but again OTEC offers a reprieve. It converts the surface heat that powers tropical storms to mechanical energy and moves many times more of this surface heat to colder, deeper, water.

Essentially it replicates the processes Nature uses to address overheating oceans and in the process removes the surface heat hurricanes thrive on.

Changes in the amount of water stored on land are not addressed by OTEC but as Meatloaf has confirmed, “two out of three ain’t bad“. And the third cause of sea level rise can be addressed advantageously as well as has been suggested here and here.

In order to start healing the planet we have to stop believing silver bullets only exist in folk lore and stop believing those that insist that is the case in order that they can continue to profit from the suffering of others; specifically, and worst of all, their children and grandchildren.

Now that truly is a “grim” tale.

Jim Baird's picture

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Discussions

Jessee McBroom's picture
Jessee McBroom on Mar 28, 2013 3:30 pm GMT

Thanks for the post Jim. I first proposed this method of OREC mitigation back in 2008 in a working group on global warming on the Pickens Plan websir. Dince then a woman I know has obtaqined US Patent on what she describes as  a  Mechanically Produced Thermocline. Essentially the utilization of colder water and differing salinity found at lower depts th cool surface water temperature by pumping deep water to the surface utilizing the pressure at depth to force water to surface where it may be introduced into the Oceanic Conveyors. Simple efficient and effective.

Jessee McBroom's picture
Jessee McBroom on Mar 29, 2013 4:21 pm GMT

They are both heat exchange technology applications. The efficacy would be the primary driver if a preferred technology were to be sought. Your technology has merit as well. The pressure differential is there for the use. Perhaps both should be employed and perhaps in conjunction.

GeorgeYuri Mogiljansky's picture
GeorgeYuri Mogiljansky on Mar 29, 2013 4:16 pm GMT
Roger Faulkner's picture
Roger Faulkner on Mar 29, 2013 9:49 pm GMT

Your table made no sense to me. I assume this should have read 3.5% salt on the right column, not 35% ?? Beyond that, the change was not monotonic, as the text suggested, but shows a minimum value of TCE at ~1000 meters depth. Oh, I see; most of that is due to the temperature change; water is near its maximum density at 4 degrees C. 

Surely you must realize that we cannot affect the thermal statification of the oceans to change sea level rise?

Roger Faulkner's picture
Roger Faulkner on Apr 4, 2013 2:37 pm GMT

I went to the reference you cited. The one degree reduction is a reduction of average surface temperature while the OTC plants are working. It is not cumulative. And the heat does not go away; rather there is some de-stratification due to warm waters mixing with deep waters. Cooling the surface temperatures would potentially take some energy out of hurricanes, but there is no net cooling. Even the electricity harvested all winds up back in the atmosphere. And it could have unintended consequences as the middle layers of the ocean are warmed: this could melt methane hydrates from the continental shelf edges.

I do think OTC is a great technology, and I have in fact been in contact with Robert Varley of Lockheed Martin with some new ideas for the siphon tubes, and for how to generate upwelling without pumps. Cooling the surface of the icean is feasible; cooling the Earth is not.

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