Page 127 - Solar Power in Building Design The Engineer's Complete Design Resource

INSOLATION 97

Figure 4.3 Solar zenith angle (Z).

solar energy loses 30 percent of its power; as a result on a clear, sunny day the energy
2
received on Earth’s surface is reduced to about 1000 W/m . The net solar energy
received on the surface of Earth is also reduced due to cloudy conditions and is also sub-
ject to the incoming angle of radiation. Figure 4.3 solar zenith angle (Z) and Figure 4.4
depicts solar declination angle.
Solar insolation is calculated as follows:
I = S × cos Z

where S = 1000 W/m 2
Z = (1/cos) × (sin L × sin i + cos L × cos I × cos H)
L = latitude
H = 15°× (time − 12)

Time in the preceding formula is the hour of the day from midnight.

Magnetic Declination As is commonly known, ordinary magnetic compasses do
not normally point to true north. As a matter of fact, over the entire surface of our globe
compasses do point at some angles either east or west of true geographic north. The

Figure 4.4 Solar declination angle in northern hemisphere.