Power Plant Engineering

NON-CONVENTIONAL ENERGY RESOURCES AND UTILISATION 113

The Lh are hours per day (average of the month)

Lm are maximum day hours in the month.

a, b are Angstrom’s constants.

Angle of declination δ, from above Eqn.

δ = 23.45 sin

360

(284 )

365

+n



For April 15, n is calculated as :

Jan. Feb. March April = n

31+ 28+ 31 + 15 = 105

= 23.45 sin

360

(389)

365





= 23.45 sin 383.67 = 23.45 × 0.4 = 9.41°

From above Eqn. sunshine hour angle ωs

ωs = cos–1 (– tan φ. tan δ)

= cos–1 (– tan 22°. tan 9.41°)

= cos–1 (0.40 × 0.61) = cos–1 (0.064)

= 86.33°

ωs is converted from degrees to radians. 180° = π radians

86.33° =

86.33

180

× π = 1.507 rad

Maximum length Lm =

2

15

× 86.33° hours = 11.51 hours

Lh = 10 hours (given). Now Ho as

Ho =

24

π Isc^

1 0.033 cos^360. sin. sin

365

+ω

−ω

+×ωφδ



∫

s

s

n s + cos φ. cos δ. cos ωs)

Substituting above calculated values, we get

= 37210 [1 + 0.033 cos (360/365) × 105] × (1.507 sin 22°. sin 9.41 + cos 22°. cos 9.41. sin 86.3)

= 37210 [1 + 0.033 × (– 0.23) × 1.507 × 0.375 × 0.16 + 0.93 × 0.987 × 0.998]

= 37210 [1.0076 × (0.09 + 0.916)]

H 0 = 37210(1.09) = 40559 kJ/m^2 day

Hg = Ho

h

m

L

ab

L



+ 



= 40559 [0.28 + 0.48 (10/11.51)]

= 40559 × 0.697 = 28270 kJ/m day

Average global radiation per day in April = 28270 kg/m^2 day.