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Monday, February 12, 2018

WILL THE OCEAN SOMEDAY BE A VIABLE ENERGY SOURCE?

Marine renewable energy can easily satisfy the needs of humanity into the long distance future.  It all depends on how optimistic you want to get on your speculations.

There are several Department of Energy Marine Renewable Energy Centers, one in Hawaii involved with wave energy, primarily, and also in the development of ocean thermal energy conversion (OTEC).  We have several test sites.

While sizable, the following table indicates that, realistically, marine energy sources can only be an important contributor to world power needs:
Global potential
FormAnnual
generation
Tidal energy>300 TWh
Marine current power>800 TWh
Osmotic power Salinity gradient2,000 TWh
Ocean thermal energy Thermal gradient10,000 TWh
Wave energy8,000–80,000 TWh
Source: IEA-OES, Annual Report 2007[3]
How much energy is utilized annually around the world?


While there are a lot of waves, don't count on them for much contribution into the future.  Ocean Thermal Energy Conversion (OTEC) can become significant, but only in the open ocean.  Then what do you do with the electricity?  Thus, to come tomorrow, the Blue Revolution.


The problem with ocean energy is the ocean.  It gets violent and uncontrollable.  The salinity screws up everything.  It is expensive and challenging to operate in that environment.

Take wind power, for example.  Wind turbines on solid land can produce electricity for a third the cost of generation offshore.  Here is a calculation indicating the 6 cents/kWh and 18 cents/kWh difference.  Sure, this was done by a student, but this was at Stanford.  However, if you want something recent from the American Wind Energy Association, check out this comparison:
Yes, very difficult to read, but what that above graphic shows is that wind provides the lowest cost production option, ranging from 3 cents/kWh to 6 cents/kWh on land, but up to 11 cents/kWh offshore.  A surprise is that those residential rooftop photovoltaic systems you see everywhere now show a range from 18.7 cents/kWh to 31.9 cents/kWh.  The average cost of electricity in the USA is approximately 11 cents/kWh. 

In any case, as the above came from a wind energy advocacy group, let me show one from Greentech Media, which should be impartial:

The average for onshore wind energy is 8.7 cents/kWh, with 22.2 cents/kWh for offshore and 14.4 cent/kWh for solar PV.  However, that solar figure is skewed by utility scale PV, which, according to Forbes, is just about half the cost of those rooftop installations.  You ask, why are those different sources so different?  That is the nature of energy production summaries.  It largely depends on who does it.

The whole point is that it is difficult to do anything in the open ocean.  Secondly, most ocean energy sources pretty much depend on natural conditions.  If you can find a good site, such as for tidal power, ideally suited to store and release seawater with large tidal fluctuations (2 feet is typical, but up to 38 feet can be found in special locations), do it.  Similarly, if the wavepower system can naturally be protected, without building expensive reinforcements, that would be attractive.  But there are only a few sites where this can be possible.  Most wave power experiments occur on the open ocean and storms have a tendency of wiping out those facilities.  This one in Norway was well-protected, but still destroyed.  While the Swedish Sotenas 10 megawatt wave power project (left) shows potential, all other efforts have either been decommissioned or remain as proposals.

Back to tidal power, here are two examples of success:

  • Rance Tidal Power Station, along the Rance River in Brittany, France, has a 28 ft tidal range, operating since 1966, enjoying more than half a century of producing electricity for around 15 cents/kWh.  How long ago was that?  Charles de Gaulle inaugurated the plant.  The capacity factor is only 28%.  Yet, the question is, why did it take so long to get #2?
  • Sihwa Lake Tidal Power Station, South Korea, the world's largest at 254 MW, has been operating since 2012.  The tidal range here is 18 feet.  If you have landed at Incheon International Airport, you have seen these enormous tidal fluctuations.
    The Edinburgh-based Atlantis Resources hopes the project will eventually have 269 turbines and provide enough electricity to power 175,000 homes.
  • Scotland has entered the scene with the launching of the first turbine for the MeyGen Tidal Stream Project in the Pentland Firth outside of Inverness in the Scottish Highlands.  The turbine, which measures 49 feet across, will be the first of four to generate a total of four MW, and will of course be placed underwater.  The hope someday is an ocean farm of 269 turbines for a capacity of 400 MW.
  • Want more?  Read TidalEnergyToday.
There is also Osmotic Power or Salinity Gradient, a concept that attempts to extract energy from the difference in the salt concentration between seawater and river water.  The key is development of a permeable membrane.  A modified polyethylene plastic seems promising, as might be a method based on electric double-layer capacitor technology.  As I'm no doubt losing you, let me stop here with a comment that no major effort is today ongoing.

Marine current power can be obtained by capturing the energy from the flow of marine currents, which are more predictable than our winds and sunlight.  According to the U.S. Department of Energy, a 2006 report estimates just capturing one-thousandth of the Gulf Stream would supply 35% of Florida needs.  Here is one summary.

All of those above ocean energy pathways only produce electricity, as do our winds and the sun.  However, there is another marine option, ocean thermal energy conversion (OTEC) that has potential for electricity, biofuels, hydrogen, next generation fisheries, marine biomass plantations, other bioproducts, Disney at Sea and platforms for future countries, with the promise of enhancing our environment.  The Blue Revolution embraces all of them, my posting tomorrow.
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Tropical Cyclone Gita fooled me.  Started as a standard weak cyclonic storm heading east, then began making a U-turn, strengthened and devastated Tonga with winds up to 145 MPH:


Gita is now at 140 MPH, but should weaken and move mostly just south of Fiji:


However, just a slight movement north, and Fiji could also be in big trouble.

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