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Thursday, June 13, 2013

IS OTEC THE MOST PROMISING FUTURE SUSTAINABLE ENERGY OPTION?

Jim Baird referred me to his posting today in The Energy Collective on the promise of Ocean Thermal Energy Conversion (OTEC).  I've been saying most of this for forty years or so, so it's nice to gain some respected company.  Let me summarize some of his  highlights:

1.  First he cites Wikipedia and provides the most optimistic assessment of proven fossil fuel reserves in years (at current use):

  • coal:            417
  • oil:                43
  • natural gas   167 


2.  Then, quoted is Eric Davidson, president of Woods Hole Research Center:

If we burn all known reserves of coal, oil and natural gas, we will warm the earth by more than ten degrees F, creating a world unfit for civilization...

Of course, sea levels would rise by 69 feet (but this will take many hundreds, if not thousands of years) and trillions of coastal infrastructure will be lost.

Baird uses USEIA info from 2006, but if you just look in the column to the right, presented is the energy consumption in real time, and the data really have not changed that much, for he indicates that fossil fuels account for 87% (it is now 88%) and the total terawatts being consumed as 15.71 (now 15.93), so let's just use 16 TW as the power continuously being used by humanity today.

Martin Hoffert estimates we will be using 30 TW by 2050, and we will just about be out of oil at current usage.  The International Energy Agency forecasted an investment of $8 trillion by the oil industry to maintain current production until 2038.  But why would an investor spend so much money of a commodity that would be soon to disappear.  Then there will be those scary global warming implications.

Forget fusion for a long time.  Even with Fukushima, if we are forced to expand nuclear by a factor of five, that would only be around 5 TW, and fission is so inefficient that 10 TW of heat would be added towards global warming.  Delete nuclear for now.

How much renewable energy do we have available?  Where can we find 14 TW?

  hydroelectricity: we're close to tapped out, and consider the NIMBY (not in my backyard) and environmental issues

  geothermal energy:  a maximum of 2 TW might be possible

  biomass:  there are too many food and water shortage problems for now

  tidal energy:  0.12 TW

  wavepower:  3.7 TW (hugely optimistic)

  OTEC:  25 TW

Thus, OTEC is the only of the above options with any kind of chance for making a real contribution.  The especial advantage of OTEC is the cornucopia of co-products, not only electricity.  Termed the Blue Revolution, here is part of my message today to Joe Quirk, who is (has completed?) writing a book for the Seasteading Institute on this subject:

So, as you say, this upwelled fluid from OTEC is like free fertilizer for marine bio-growth.  Add the fact that this deep ocean fluid is essentially pathogen free, and you eliminate yet another problem land aquaculture faces.  Even more attractive is the fact you also have free irrigation, and, as presently conformed, free space.  And that's not all, folks!  Under controlled conditions (we might need to add some iron), some of us think we can suck up carbon dioxide from the atmosphere to remediate global warming.  Finally, these productive floating platforms will someday be placed at the equator to maximize the warm temperature, and guess what?  No hurricane has ever gone through the equator.  There is a safe region around the equator with no major storms.


I have published several articles in the Huffington Post on this subject, a typical one being Blue Revolution.

The above analysis is in terms of power, which is energy divided by time, for the first question you might ask is why weren't solar and wind options mentioned.  Keep in mind that solar and wind energies are intermittent, while much of the above is baseload.  Some useful conversions for energy are: 

  one BTU equals about 1000 joules

  one quadrillion BTU equals one Quad (Q) equals about about 1 exajoule (EJ)

Many engineering references use EJ, so isn't it convenient that one EJ equals about one Q?  One Q represents five times the amount of energy of the Tsar Bomba (largest hydrogen bomb exploded).   



Note that the Atomic Bomb over Hiroshima was only around 15 kiloton, while the Tsar Hydrogen Bomba was 50,000 KT.  


The above drawing shows that the incoming solar radiation is 174 Petawatts (10 followed by 14 zeros watts, or a thousand times a Terawatt), and 89 PWs are absorbed by Planet Earth.  That's power.  Regarding energy, almost 4 million Qs of sunlight impact our Earth each year.  Basically, one hour of sunlight equals the energy used by civilization in one year.  In one year the solar energy reaching our surface is equal to all the energy to ever be obtained from coal, oil, natural gas and mined-uranium.  The total wind energy available is in the range of two thousand Q/year.  Photosynthesis is responsible for three thousand Q/year.  The maximum potential of biomass is perhaps 300 Q/year.  A rough rule of thumb is that humanity uses 500 Q or 500 EJ per year.  These units kind of get to you, but this is the life of a solar engineer.

Our kind (Homo sapiens) began to evolve perhaps 200,000 years ago.  Planet Earth has another five billion years before our Sun becomes a Red Giant and consumes us.  At current usage, all the fossil fuels and uranium will run out within a millennium, and perhaps less than a century under bad case scenarios.  The future of Humanity on Planet Earth will clearly be a delicate balance of population, lifestyle and renewable resources.  We overcame the Cold War where a nuclear winter was a button push away.  If we survive global warming, I have long predicted that a sustainable population living at least at the level of an American lifestyle will not be 7 billion, but something closer to one billion.

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