Ocean Thermal Energy Conversion a Silver Bullet for Climate Change?
“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||%|
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.
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