The azimuth (Y) of the solar collector, that is, the installation orientation of the solar collector. For the Northern Hemisphere, γ=0° when facing due south, γ<0° when east, and γ>0° when west. Studies have shown that in the middle and high latitudes of the northern hemisphere, most of the time of the year, the southward slope has the most astronomical radiation. Therefore, the solar collectors in the northern hemisphere should generally be arranged southward, that is, facing the equator. The “Technical Specifications for the Application of Solar Water Heater Systems in Civil Buildings” (GB50365-2005) proposes that the collector should be set in the south, or within a range of 30° from south to east and west. The best installation orientation of the collector should be facing due south or due south west. If limited by conditions, the allowable range of deviation should be within 15° due south. The National Research Center for Residential and Residential Environment Engineering Technology believes that “solar collectors should be placed facing due south, or within a 40° orientation range from south to east and west to west”. It can be seen that the change of the collector within a certain angle range from the south is acceptable.

According to the typical meteorological solar radiation parameters of a certain area in southern China, the inclination of the solar collector is set to 30° and 60°, and the azimuth angle varies from 0° to 90°, and the change in the amount of received solar radiation on the inclined surface under different azimuth angles is calculated. The monthly average direct solar radiation (H_bH) and the monthly average daily scattered radiation (H_dH) on the horizontal surface are known. According to the calculation formula of the direct radiation factor Rb deduced by Klein and the scattered radiation factor Rd deduced by Liu-Jordan, the solar radiation amount of the horizontal plane is converted to obtain the solar radiation amount (H_β) of the inclined surface:

H_β=H_bHR_b+H_dHR_d

After calculation, the relationship between the azimuth angle of the collector and the annual daily average radiation and the monthly average daily radiation is obtained. It can be seen from Figure 1 that in the two installations with inclination, when the azimuth angle is 0°, the radiation amount is the largest. With the increase of the absolute value of the azimuth angle (that is, the deviation from the due south direction), the amount of solar radiation H_β received on the inclined surface gradually decreases, but the decrease is not large. When the inclination angle is 30°, and the azimuth angle is from 0° to 20° (0° to -20°), the average daily radiation is only reduced by less than 2%, which is basically negligible.

When the inclination angle is 30°, Figure 2(the inclination angle is 30° and the azimuth angle is 0~30°) shows the relationship between the monthly average daily radiation H and the azimuth angle y in January, May and August, respectively. It can be seen from the figure that the azimuth angle has a great influence on the amount of solar radiation received by the inclined surface in winter (January), and the attenuation of the radiation amount with the increase of the absolute value of the azimuth angle is larger than that in summer. This is because the sunshine time in winter is shorter than that in summer, and the main solar radiation is concentrated around noon. If the orientation of the collector deviates from due south, the amount of direct radiation obtained will decrease more than in summer. For solar water heating systems used in winter, the collector should be oriented towards the south as far as possible to reduce the azimuth angle.

The three curves in Figure 3 represent the relationship between the azimuth angle of the solar collector installation and the annual average daily solar radiation received in the three regions of Harbin (Φ=40.75°), Hangzhou (Φ=30.23°) and Guangzhou (Φ=23.17°). It can be seen from the figure that when facing the equator (γ=0°), the daily average solar radiation received by the inclined surface is the largest, and as the absolute value increases, the solar radiation received by the inclined surface gradually decreases. However, the magnitude of reduction is related to latitude, and the magnitude of reduction in low latitude regions is smaller than that in higher latitude regions. The azimuth angle γ also varies from 0° to 90°, and the daily average solar radiation H received by the inclined surface in Guangzhou area. It has dropped by 9%, Hangzhou has dropped by 26%, and Harbin has dropped the most, reaching 49%. Therefore, attention should also be paid to reducing the azimuth angle as much as possible in high latitudes.