5.) One renewable energy scheme involves using the temperature between ocean sur

Question

5.) One renewable energy scheme involves using the temperature between ocean surface temperature and subsurface (roughly 1000 feet deep) temperature to power a heat engine for electrical generation.

a) If the surface ocean temperature is 18oC and the temperature 1000 feet below the surface is 5 oC, calculate the ideal (Carnot) efficiency of a heat engine using this temperature difference.

b) Will the actual efficiency of such a system be greater or less than the efficiency you calculated in part a? Why?

Explanation / Answer

(a) Tc = 5oC = 278 K

Th = 18oC = 291 K

Carnot efficiency = 1 - (Tc / Th )

= 1 - (278 / 291)

= 0.0447

= 4.47 %

(b) There is LOTS of sea water! The temperature gradient in the ocean provides an abundant source of energy although the small temperature gradient means the efficiency is very low.

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