The successful operation of a solar water heating system relies greatly on the proper placement and layout of the collectors in arrays. Arrays must be sized and plumbed correctly to ensure proper, balanced flow, allow for thermal deformation of piping, permit serviceability of the collectors, and keep tilted collectors from shading arrays behind them.

There are several key aspects to keep in mind when designing the collector layout:

  • It is important to keep the flow velocities in all piping at, or below, 5 ft/sec. including the piping integral to the collector absorber plate. This reduces the friction head loss in the system as well as reducing the risk for water hammer.
  • For Solene collectors with 1″ manifolds the following table gives the maximum allowable bank sizes for different collector sizes:
    Maximum Allowable Collector Sizes
    Collector SizeBank Size
    4′ x 6′12 collectors
    4′ x 8′10 collectors
    4′ x 10′8 collectors
  • Some allowance for thermal deformation of piping between collector banks and the supply & return piping needs to be made. Rigid piping changes length with temperature so piping connections should be allowed to flex and should not be completely constrained.
  • Flow balancing through the collector array should be done using a reverse-return method if possible. If this is not possible then another method of flow balancing will need to be included using ball valves or balancing valves.
  • All copper piping should be insulated and covered in a UV-resistant latex coating or jacket.
  • It is good practice to include isolation valves at the collector bank(s) for serviceability reasons. For large systems with multiple banks in an array one bank can be isolated for service while the other banks remain functional.

Direct System Arrays

The diagram below shows a (16) collector array using (2) banks of (8) collectors in a direct system installation. The system is plumbed in parallel in a reverse-return manner for optimal flow balancing. Each bank has isolation valves at the supply & return connection for service and/or flow balancing purposes. Direct systems also feature air vents, pressure relief valves, and freeze valves located on the return side of the collector bank. Drains are also recommended on the lower manifold opposite the supply connection in case a bank must be drained for service.
Array - Direct

Indirect Drainback Arrays

The diagram below shows an indirect drainback collector array similar in layout to the direct system discussed earlier. Since drainback systems are unpressurized the need for air vents, pressure relief valves, and freeze valves is eliminated. It is still good practice to install isolation valves for the same reasons given for the direct system type. Though the design may appear simpler and require less parts it should be noted that the plumbing of the system is more complex requiring all piping to slope a minimum of ¼″ per foot back to the drainback tank.
Array - Indirect Drainback

Indirect Glycol Arrays

The diagram below shows an indirect glycol collector array similar in layout to the indirect drainback system. Indirect glycol systems, like direct systems, are under constant pressure whether the circulator pump is on or not so many of the valves and other equipment required is identical. Notably missing are the freeze valves as indirect glycol systems rely on the propylene glycol HTF to protect against damage caused by freezing fluid.
Array - Indirect Glycol

Interrow Shading

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:
Data Required:

  • 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: ([51] / tan[23]) * cos(45) = 85″
Shading Data Diagram

Shading Data Diagram

Solar Angle Chart - Clean

Solar Angle Chart – Clean

Solar Angle Chart - Marked

Solar Angle Chart – Marked