An offshore OTEC facility operates with a warm reservoir temperature of $22 ^ { \circ } \mathrm { C }$ and a cold reservoir temperature of $5 ^ { \circ } \mathrm { C }$.
(a) If $65 \%$ of the output power is required for operation of the facility (e.g., primarily water pumps), what is the net efficiency?
(b) In order to transport the electricity that has been generated to land, hydrogen is used as an energy storage mechanism. Hydrogen is produced by the electrolysis of water and is converted back to electricity using a fuel cell, with an overall efficiency of $40 \%$ (see Section 20.9). What is the net overall efficiency, and how does this compare with, for example, wind or solar photovoltaics?

Question

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The Answer is

ext { (a) For the temperatures } T _ { h } = 22 ^ { \circ } \mathrm { C } = 295 \mathrm {~K} ext { and } T _ { c } = 5 ^ { \circ } \mathrm { C } = 278 \mathrm {~K} ext { the Carnot }

efficiency is

\eta _ { ext {Carnot } } = 100 imes ( 295 \mathrm {~K} - 278 \mathrm {~K} ) / ( 2 imes 295 \mathrm {~K} ) = 2.88 \%

If

65 \%

of the output power is required for operation then the net efficiency is

( 0.35 ) imes ( 2.88 \% ) = 1.0 \%

(b) The net efficiency after transporting the energy to shore is

( 0.4 ) imes ( 1.0 \% ) = 0.4 \%

This may be compared to typical efficiencies for other renewable technologies such as photovoltaics

( \sim 15 \% )

and wind

( \sim 40 \% )

. OTEC is significantly less efficient that these other technologies.

An Offshore OTEC Facility Operates with a Warm Reservoir Temperature 22∘C22 ^ { \circ } \mathrm { C }22∘C

An Offshore OTEC Facility Operates with a Warm Reservoir Temperature $22 ^ { \circ } \mathrm { C }$