Energy From the Oceans

Ocean Thermal Electric Conversion

Instead we are doing this Large Scale NONSENSE:

and this

At some level, it seems fundamentaly insane to blow up the earth to get resources ...

Why not try something different?

This technology in fact is a "global solution" and represents a chance for the world to collaborate on various infrastructure and production facilities. Such cooperation is required because:

• No one owns the world's oceans
• The capital cost of harvesting this energy is enormous estimates range from $4 to $10 a watt.

But the potential yield is also enormous:

On an average day, 60 million square kilometers (23 million square miles) of tropical seas absorb an amount of solar radiation equal in heat content to about 250 billion barrels of oil.

We use 85 million barrels a day 3000 times less than this absorbed energy. Hmmm, seems like a solution.

The mechanism of electricity generation is based on simple principles of thermodynamics that allow the ocean to be characterized as a giant heat engine.

Physics of Heat Engines:

• efficiency = work done/energy input
• it can be shown that this is equivalent to
  efficiency (in %) = 1 - T1/T2 ; T1 < T2

  T is measured in Kelvins

• Any two reservoirs with different temperatures T1 and T2 can produce energy.

  Examples:

  • Geothermal example: 200C reservoir couple to surface water (20C)
    eff = 1 - (293/473) = 38%

  • Solar Thermal Molten Salts/Water at Air Temperature combination:
    eff = 1 -(300/1000) = 70%
  
  
  
  Thermodynamic Constraints:
  • Systems are in equilibrium when they are at the same temperature

  • energy is conserved within a closed system

  • it is not possible to extract heat energy from a reservoir and perform work without transferring heat to a reservoir of lower temperature. In other words, all thermodynamic systems must tend towards equilibrium. Some energy goes towards performing work and some is lost as waste heat.

  To get the highest efficiency one wants to maximize the difference between T1 and T2 but in most natural environments nature doesn't really do this.

  For example, here is the situation for OTEC:

  • Surface Ocean temperature is 25 degrees C (298K)

  • At 500-700 meters depth the temperature is 5 degrees C (278K)

  • Efficiency = 1 - 278/298 = .067 (6.7%)

  Basic principle is that heat difference is used to condense a steam into a liquid then return it to be reheated. But we would need a working fluid that liquifies at a temperature of about 25 C. Ammonia!

  And there is plenty of ammonia (NH₃) to use as the working fluid.

  Energy extracted comes from the cooling of the warmer water this is transferred to the ammonia which does the actual work of turning the turbine (as ammonia steam)

  Energy extracted is directly proportional to the volume of water and the temperature it drops.

  Principal energy loss is when the warmer water meets the cooler water in the condenser.

  Does this mean OTEC is silly due to low efficiency hell no because the potential stored energy is gigantic in the ocean.

  Qualitative energy math:

  low efficiency * semi-infinite resource = shitload of output

  (note that the sun is a power plant operatin at 0.7% efficiency)

  To compensate for low efficiency, OTEC plants need to move a huge volume of water. This is the technical/engineering challenge. You need to net export electricity rather than spending more electricity to just run the pumps!

  
  
  
  Conceptual OTEC Turbine Design:

  

  

  

  
  Scale is that a 50-m diameter foot print yields a 100 MW facility

  

  Total available power in tropical waters. This is difficult to really properly estimate.

  • one conservative study suggests 0.2 MW available per square km with out any environmental damage (due to changed heat structure balance or large water discharges) Total yield is then 12 TW (enough electricity for the whole planet)

  • However, studies by Avery ( a real optimist ) suggest that "mobile" floating islands that move at 1/2 mile per hour could harvest OTEC at the rate of 5MW per square km (25 times higher than previous estimate). Floating barges would migrate (slowly) from anchor point to anchor point.

  

  How about some artificial floating islands with solar cells and windmills overlaying the OTEC infrastructre. Why the hell not?

  

  Regardless of the overall yield, we must first construct our unit plants.

  

  Some Engineering:

  • Ideal 8% efficiency achived between 26 C and 4 C water
  • OTEC plants will transfer heat in an irreversible manner so the operating efficiency will be closer to 4%

  • To export 1 MW of electricity requires:
    • 4 cubic meters per second of warm water "joined" with 2 cubic meters per second of cold water with a temperature difference of 20C.

  Scaling this to a 100 MW plant:

  • 400 cubic meters per second of 26 degree water "joining" with 200 cubic meters per second of 4 degree water

  • warm water flow requires a pipe diameter of 16 meters extending to a depth of 20 M

  • cold water flows/pumped through an 11 meter diameter pipe extending to depths of 1000 M (this is an engineering/materials challange)

  • Mixed water return requires 20 m pipe. Mixed water about 6 degrees higher and needs to be discharged to a depth of 60-100m.

  So, large pipe/pump infrastructure is needed!

• Possible Additional Benefits:

  Can be done ON shore (much easier engineering)

  

  • can also serve as a desalinization facility

  • Can produce mineral rich salts.

  • Spraying back of deep seawater onto the sea surface may help cultivate richer fishing grounds as nutrients are brought up.

  • Can produce Hydrogen! Rate is approximately 1.3 kg per hour per 1MW of net electricity generation.

  • Large scale employment from building the infrastructure:
    

  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.

  • Maximum real world operating efficiency is 4%

  • 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 Gigawatts

  Some other OTEC resources:

• One comprehensive study for small scale development

• More on OTEC