For systems that require the collectors to be tilted up rather than mounted flush shading of one row by another must be taken into account. Interrow shading occurs when one bank of collectors is too close to a bank behind it and casts a shadow on that collector bank. Obviously this leads to reduced performance of the shaded bank of collectors. To determine the proper interrow spacing an online calculator may be used or the following method may be employed:
- Collector Tilt Angle (degrees) – ⊖
- Collector Length (inches)
- Solar Elevation Angle (degrees) – Φ
- Azimuth Angle (degrees) – ∑
Step 1: Height Difference – sin[Tilt Angle] * [Collector Length]
Step 2: Solar Elevation Angle – Use the following link – http://solardat.uoregon.edu/SunChartProgram.php and input the site’s zip code and time zone to produce a table similar to this. Choose the solar elevation angle by plotting a horizontal line to the vertical axis through 9 am – 3 pm on the December 21st curve. This will be the worst case during the winter solstice.
Step 3: Azimuth Angle – Using the same chart used for the Solar Elevation Angle plot vertical lines to the horizontal axis through the intersections of 9 am & 3 pm on the December 21st curve. Subtract this angle from 180° to determine the azimuth.
Step 4: Calculate Interrow Spacing: ([Height Difference] / tan[Solar Elevation Angle]) * cos[Azimuth Angle]
The resulting interrow spacing distance is the minimum distance between the rear edge of one bank of collectors and the front edge of another.
Example: SLSG-40 collectors at a 25° tilt are to be installed in Altamonte Springs, FL.
- Collector Tilt Angle: 25°
- Collector Length: 120″
- Solar Elevation & Azimuth Angles: Using the link provided enter 32714 as the zip code and select UTC – 5h (EST) as the time zone. Leave all other options as their default setting and click ‘create chart’.
- Using the resulting chart plot the appropriate horizontal and vertical lines corresponding with 9 am – 3 pm on December 21st. The resulting Solar Elevation Angle is determined to be ~23° and the Azimuth is 45°.
- Calculate the Height Difference: sin(25°) * 120″ = 51″
- Calculate the Interrow Spacing: ( / tan) * cos(45) = 85″