Question

Calculate the exergy efficiency of a CSP plant, which has a receiver at 900 K with a solar
absorptivity of 0.9. and a concentration factor of 100, when the emissivity for the thermally
emitted radiation is a) 0.9,  b) 0.1.  Take G = 900 W m², T_a = 300 K.

Answer 1

Given that

Temperature of receiver Th = 900 K

solar absorptivity   =  0.9

Concentration factor c = 100

G = 900

T_a = 300 K

Part(a)

thermally emitted radiation = 0.9

We know that

Efficiency of carnot engine

ηc = 1 − Ta/Th

ηc = 1-  (300/900)

ηc = 0.66 or 66.66%

Now efficiency of CSP plant

η =  ηc* ηr ------------------------------(1)

where  ηr = efficiency of receiver of csp plant

ηr = (Qabsorbed -Qlost) / Qincident --------------------------------(2)

where Qincident = solar flux = Qsolar

Qsolar = GcA

Qabsorbed = *G*c*A

Qlost = ATh^4

here = 0.9

= 5.67*10^-8 j.m^-2.s^-1.k^-4

from eq(2)

ηr =  *G*c*A - ATh^4 /  GcA

ηr =   - ( Th^4 / G*c)

ηr = 0.9 - ( 0.9*5.67*10^-8 *900^4) / (900*100)

ηr = 0.527 or 52.7 %

now putting this value in eq (1)

η = ηc*ηr

η = 0.66*0.527

η = 0.35 or 35.8 %

Part(b)

when = 0.1

ηr = 0.9 - (0.1*5.67*10^-8*900^4) /(900*100)

ηr = 0.858 or 85.86 %

η = ηc*ηr

η = 0.66*0.858

η = 0.576 or 57.62 %

Good Luck !!!