Energy from the Ocean

Review of OTEC (Ocean Thermal Energy Conversion)

• Thermal gradients of greater than 22 C can be exploited and used as a heat engine

• Energy is derived from cooling warm surface water to the temperature of the water at approximately 500-1000 feet depth.

• The maximum surface temperature of ocean water is 25 C and its minimum value is of course 0 C

• efficiency is then 1 -(273+0)/(273+25) = 1 - 273/298 = 7%

• Energy is derived from the cooling water via transfer to a working fluid such as ammonia which when mixed with warm water vaporizes to steam and powers a turbine

• Ammonia returns (condenses) to liquid when mixed with cooler water at depth and then the cycle repeats itself

• Since the volume of water in the oceans is huge, the capacity in just the Gulf Coast Waters alone is several 10's of Giga

  More on OTEC

  Hawaii Facility

  Ocean Power also comes in 2 other forms:

  • Tidal Energy
  • Current Flow Energy

  The ocean is a huge reservoir for storing the energy of the sun that is incident on the earth. How huge is huge?

  Incident flux on ocean surface area is 10^17 Watts or 0.1 Billion Billion Watts (its a large number)

  The oceans are a huge heat engine. Temperature differences, caused by differences in insolation both in latitude and in depth.

  • Equatorial waters warmer than higher latitude waters
  • surface layers warmer than deeper layers
  • This sets up an enormous circulation network
  • 

  Major currents are shaped by:
  • Temperature differences (driven mostly by tilt of earth's axis)
  • Prevailing wind patterns interacting with the surface waters (again driven mostly by tilt of earth's axis)
  • the rotation of the earth --> the Coriolis Force
  • shorelines of continental masses

  Tapping the Current for Energy:

  • Gulf current has 1000 times the flow of the Mississippi River(!)
  • Current averages about 5 mph
  • Density of water is higher as well
  • Its always there - no intermittency problem --> no need for energy storage
  • Build Turbines for underwater use
  • Anchor a foundation to the ocean floor
  • hundreds of miles long rigged with turbines
  • cables on ocean floor to shore deliver the electricity

  • An engineering challenge but there are few bad side effects from producing energy this way
  • Obviously the capital costs are huge in this case but this does represent a Large Scale Solution

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