Israel utilizes solar ponds to produce ‘green’ energy. In a solar pond, the Sun’

Question

Israel utilizes solar ponds to produce ‘green’ energy. In a solar pond, the Sun’s energy is concentrated near the bottom of a salty pond. With the proper layering of salt in the water, convection is prevented. As a result, the top layer of water remains at surface temperatures of 20 to 30oC, depending on the season, while heat is concentrated in the salty layer of water at the bottom, where temperatures of 70 to 90oC are reached.

This heat can then be extracted through some processes.

1. Can you guess the maximum efficiency with which useful mechanical work can be extracted from this pond during the cool season and the hot season? Show your work.

Explanation / Answer

in cool season,

Tc = 20 C = 20 + 273 = 293 k

Th = 30 C = 30 + 273 = 303 k

so, maximum effiecnty, e = 1 - Tc/Th

= 1 - 293/303

= 0.033 or 3.3%

in hot season,

Tc = 70 C = 70 + 273 = 343 k

Th = 90 C = 90 + 273 = 363 k

so, maximum effiecnty, e = 1 - Tc/Th

= 1 - 343/363

= 0.055 or 5.5%

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