Energy from the Ocean

More promising technology is OTEC (Ocean Thermal Energy Generation). This takes advantage of the fact that the ocean is an enormous 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

• So, in principle any two reservoirs with different temperatures T1 and T2 can produce energy. The IN class demo demonstrated this principle.

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 then their are material problems (containers melt, freeze, etc)

Typical Case:

• Coal-fired burner: T = 825K
• Cooling tower: T = 300 K
• efficiency = 1 - 300/825 = 64%

How this all works:

Exhaust steam is condensed back into liquid thereby decreasing its total volume by a factor of 1000

Therefore the work done by the pump is down by a factor of 1000 compared to if it had to pump steam directly back into the system

Overall efficiency of the above is about 1/3.

a 1000 MW plant therefore requires a 3000 MW Boiler and 2000 MW are given off as waste heat

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