At Suva ( = 18) at 9 a.m. on 20 May, the irradiance measured on a horizontal

At Suva (φ = −18)   at 9 a.m. on 20 May, the irradiance measured on a horizontal plane was G _h = 1.0MJ/h.m ² .

• Determine the angle ϴ _z   between the beam radiation and the vertical, and hence find the irradiance G ^∗ = (G _b + G _d ) ^∗ measured in the beam direction. (Assume that G _d << G _b ), as might be the case on a clear day.)
• Under the same assumptions as in (a), determine the angle ϴ _c between the beam and a collector of slope 30 ^o facing due North. Hence find the irradiance G _c on the collector.

 Suppose instead that the diffuse radiation G _d is uniform across the sky, and that G _dh = G _th / 2. This is realistic for an overcast day.