Strut-channel Panel Rack

There are times when the best location for solar pool heating panels is not a roof but a rack whether its on the ground, on another surface, or even just to get some pitch on a shallow-pitched or flat roof. This could be due to lack of available roof space or poor orientation, concern about roof leaks, distance from pool equipment, etc., all of which make building a rack on a better option.

Up until last year, we would recommend the use of the all aluminum GroundPro rack listed on the following pages.  Unfortunately for us and our dealers, this rack was discontinued by the manufacturer, not because it wasn't a popular and terrific product, but because demand for it was seasonal and the manufacturer couldn't afford to keep the required floor space for this inventory when their PV rack business was booming.  They had to make room somewhere and the GroundPro just lost out.  It is an excellent product and one that some other manufacturer, possibly even FAFCO, will more than likely take on in the near future.

In the meantime, we have designed a simple, strong, and durable rack structure that will more than satisfy this void in the pool panel rack market.  Sure you can always build a rack out of wood, but woods has one critical weakness...it might not last as long as the panels themselves.  Durability is our concern.  If you want to build a wood rack, we included a schematic that is adequate in strength on the following page.  However, we highly suggest that you consider a more durable alternative made from steel strut-channel.  The following rack is designed for anyone to build, dealer or pool owner.   It is a quality rack structure from components available in your local area.  We want to make it easy for you to install a solar pool heating system.  If you have difficulty finding any components, contact us or your dealer so we can help you find them.

What is strut-channel?

Strut-channel is a steel channel specifically design for structural uses and common in both the plumbing and electrical industries.   We recommend that the strut itself be either galvanized or better yet, chromate-coated (a gold-colored coating that makes the strut extremely durable even in such corrosive salt environments as Hawaii).  The channel can be interconnected with adjoining connector plates and "strut nuts" to secure almost anything virtually permanently.  From our lengthy experience using it in Hawaii and elsewhere, we feel confident in its ability to withstand the test of time in any geographic location.  However, another positive benefit of this material is that it is literally available anywhere.  It goes by the names "Super-strut", "Power-strut", "Uni-strut" and others and all are interchangeable and compatible.  It can be found at any Home Depot, Lowe's, electrical suppliers, etc.  It comes in many sizes and lengths but the most common sizes available at these locations are 1-5/8" x 1-5/8" x 10' and 13/16" x 1-5/8" x 10' and so these are the members we will use out of convenience.  Either can be easily cut with a hacksaw, sawzall, or miter saw using metal abrasive disk.

13/16" x 1-5/8" chromate "gold" strut-channel	13/16" strut-channel with 1/2" slots (recommended)	Different types of strut nuts with 1/4" threads
Strut nuts attached to strut	Strut connector plate bolting two channels together

Building a strut channel rack

1. Rack location and layout
2. Building galvanized "sub-rack"
3. Securing angled 1-5/8" x 1-5/8" channel to sub-rack
4. Connecting 13/16" horizontal channels
5. Securing corrugated sheets to rack
6. Securing panels to rack

The following pictures are of a three panel sample rack at our Oregon warehouse.  Most racks would be built to accommodate 6-12 panels depending on geographic location and pool surface area.  Click here on the rack table to get components necessary to build racks of different sizes.  Remember to click on thumbnail photos for larger view.

1. Rack location and layout

• It is first necessary to determine where the rack will be located.  Racks can be built on level or pitched ground.  Face the panels to the south or SW for ideal solar collection.  You want the rack location to be free from shade from at least 10am to 4pm daily whenever solar heat is needed.  Generally, 4x12' solar panels are used on rack installation because space is usually not an issue and 12' panels save time.  Once the number of panels is determined based on the pool size, the rack space can be readily determined.  Figure 53" per panel for the side-to-side rack  width and 11' or so for the pitched panel length.  If possible, leave walking space around the rack to access panels as needed.  Put stakes at the corners of your rack area and run a string around the perimeter using a string level if you want the panels to be square and level.
• We recommend that the ground underneath the rack be cleared of vegetation so it doesn't grow up to shade the panels later on.  Use weed control fabric or plastic over the dirt and then cover with gravel or crushed rock.  There is some benefit putting white rock in front of rack to reflect additional solar radiation onto panels, especially during early and late part of the summer season. 

2.  Building galvanized sub-rack

• The sub-rack is built from 1-1/4" galvanized pipe, sch. 40, or "rigid" conduit, again, available anywhere .  It consist of short vertical post in the front spaced every 8-10' (max.) to span the required width of the rack.  There are longer vertical posts in the back (9' to 9-1/2' behind the front posts for 12' panels) the height of which will determine the pitch of the rack.  It is usually easiest to use one 10' length of pipe to make both the front and back post (2-1/2' to 3' for the front and the remaining 7' to 7-1/2' for the  back). 
• All posts should be cemented into the ground at least 18-24".  The posts will then be 12-18" out of the ground in front and 5' to 5-1/2' in back.  This give roughly a 20^o pitch which works well with summer heating.  Pitch should be somewhere at latitude less 15^o for summer use and latitude plus 15^o for winter (Hawaii). 

Front posts 9' apart, 18" out of ground in cement	Longer back posts also 9' apart secure in cement	Sample three panel rack layout showing front and back posts

• Once the cement around the vertical posts sets-up, it is time to put a horizontal member over them.  The length of this horizontal member is relative to the number of panels.  The recommended minimum length of this pipe is # of panels x 53" minus 4'.  Example: 6 panels x 53" = 318" divided by 12 is 26' - 4' = 22.5' or 23'.  These pipes are typically 10' long, threaded on both ends and readily connected together using a threaded coupling'. 
• They are connected to the vertical posts using an special aluminum tee with set screws.  Dealers can purchase these through us or Grainger Supply.

 

Aluminum tee holding horizontal pipe to vertical post	Close-up of tee with three set-screws	Pipe termination with threaded coupling to add on to if needed
Galvanized sub-rack for three panels	Another view of sub-rack

3.  Securing angled 1-5/8" x 1-5/8" channel to sub-rack

• Now that the galvanized sub-rack is complete, you can connect the angled strut to it using U-bolts.  Remember, for 12' panels this member needs to be 12.5' long.  Since most strut is going to be 10' long, it will be necessary to add 2.5' by using a strut connector plate and 1 or 1.5" x 3/8" bolts.  These can be galvanized or stainless.  Be sure to use washers and lock washers or lock nuts. 
• U-bolts come in a variety of lengths.  They must fit inside the strut and not extend above the top of the channel itself.  Stainless steel U-bolts seem to be a little short than standard bolts are probably a good idea anyway.
• Since these members are to be located in the middle of the panel, connect the angled strut at 53" on center.  For odd-numbered panels start at the center of the horizontal pipes of the sub-rack and work out; for even-numbered panels start at he center and start 26.5" on both sides.

 

Underside of strut showing connector plate with bolts	Upper side of strut view	With odd-number panels start in the middle of the sub-rack
U-bolt secures strut to horizontal pipe of sub-rack	U-bolt around pipe	Another view of U-bolt
Be sure U-bolt is shorter than top of strut. Use washers and lock nuts.	Install all angled member 52" on center.	Three angled struts installed for three panels

4.  Connecting 13/16" horizontal channels

• Once the angled members are installed and securely tightened, start installing the 13/16" strut to them.  Use the strut connector plates and bolts to connect 10' section together as with the larger strut.
• The top and bottom horizontal strut should be inside the headers of the 12' panel or 136" from both outside edges centered on the angled strut (or 7" in from the edge).  Secure the 13/16" strut to the angled strut using 3/8" strut nuts and 1 or 1-1/2" bolts with lock washers.  Install the next two channels 2' inside and the fifth one one in the middle.  These will be used to secure the panel strapping.
• This completes the actual rack installation.

Strut nut inside angled strut member	Horizontal strut secured to angled strut	Side view showing strut nut locked into angled strut
Another view of strut nut holding horizontal strut to angled strut	Connector plate holding two horizontal struts together	Upper and lower horizontal strut installed
Side view of upper channel	Rack with all horizontal channel attached	Underside of completed rack

5.  Securing corrugated sheets to rack

• Once the rack is built and before the panels themselves are attached, we recommend the use of corrugated sheets under the panels to offer more long-term support.  Over time and especially during stagnation periods, plastic panels will conform to the surface they are mounted to.  They will tend to sage between the 24" and wider gaps between the horizontal strut.  To keep a clean, tight appearance and avoid these issues, lay inexpensive corrugated fiberglass, or polycarbonate sheets under the panels.  Avoid using PVC sheets since they will readily deform with warmer ambient air temperatures plus the weight of the panels with water. 
• Corrugated sheets are available at any hardware or building supply such as Home Depot, Lowe's, etc.  They typically come 8,10, or 12' long and  26"  wide so you will need two per panel overlapped to get the recommended 45-46" in width to fit just inside the panel width.  Their overall  length should be trimmed to fit inside the panel header, about 136" for 12' panels.  Keep this corrugated material out of UV radiation if not rated for such exposure.  These sheet will also minimize convection cooling off the back-side of the panels if any wind blows from that direction.  Convection cooling can reduce the performance of the solar panels. 
• Lay two overlapped sheets over, and center above, one of the angled strut, attach them to the rack in two place using 1/4" strut nuts and 1" SS bolts with fender washers to keep them from sliding out from under the panels.  The panels "belly-band" strapping will secure them otherwise. 
• Simply drill a hole through the sheet where the nut is located on the lower outer corner of the two overlapping sheets.  Don't tighten just yet because it may be necessary to shift the sheets around somewhat to fit neatly inside the panel edges. 
• It is probably easiest to install the first panel now on these sheets and then install the remaining corrugated sheets under the panels as you go.  Go to section #6 to learn the panel installation procedure.

 

Label on corrugated sheet	Two sheets overlapped	Sheets laying on the rack
1/4" bolt with fender washer holding sheet to rack

6. Securing panels to rack

• The following panel installation procedure is in more detail in the "System Installation" section of this site.
• Lay a panel on the first set of corrugated sheets. 
• Slide a ST bracket onto the upper header of the panel.  Center it on the header and secure to the angled strut with a 1/4" strut nut, 1/4" x 1" SS bolt and a lock washer.  This bracket is the only thing holding the weight of the panel, which will be about 70 lbs. with water.  It is very important to tightly secure this bracket to the rack.  Now you can secure the next set of corrugated sheets for the next panel.
• Slide rubber couplers onto all four corners of the panel. 
• Use #40 SS band clamps to tighten the rubber coupler onto the header.  Notice that the "spin-weld" at the end of each header acts as a barbed-end.  This creates a bulge on the rubber coupler.  Put the clamp on the panel side of this bulge.  Tighten securely but don't over-tighten or the clamp will strip.  Slide an open second clamp onto each coupler, slide an ST bracket onto the upper header of the next panel, and slide this panel header into the coupler on each side of this panel.  Tighten the clamps as before. 
• Do this sequence of corrugation first then panel, and so on until all panels and together and secured with their ST bracket to the rack. 
• Square panels to the rack and the corrugated sheets under the panels.  Tighten all bolts.  You don't need to put too much pressure on the bolt holding the corrugated sheets since they are just to keep them from sliding out.   

Lay panel on corrugated sheets from center of rack	Secure upper header of panel to angled strut using ST bracket	Side-view of ST bracket

• Connect the base of the tie-down cleat on the ends of and in between each panel on the horizontal strut two feet up from the bottom header and two feet down from the top header and the center strut.
• Tie a single knot on the end of the Dacron strap leaving 6-8" of strap excess on each end of the bank. 
• Lay a strap in groove of the tie-down base and hand-tighten the caps as you go putting moderate tension on the strap each time.  At the end of the bank, cut the strap again tying a knot at the loose end.  Do this for the other two straps.  If you need to add onto the strap, tie two together.
• The rack should be strong enough to stand on but it would be better to stand on the horizontal sub-rack pipe instead of the horizontal strut.  Be careful with panel edge when you do this.  Reach the upper cleats from a ladder over the top header.

Tie-down base connected to horizontal strut with strut nut and SS bolt	Tie-down base between panels	Tie-down bases between panels
Tie-down base with cap and strap. Note knot is strap.	Tie-down between panels with cap and strap.	Other end of strap.

• The panels are now secure to the rack. 
• If this rack is in a wind area, it may be necessary to secure the bottom header more firmly.  If so, you can run another strap along the bottom horizontal strut.  This will keep the header from lifting.
• Finally, you can install the panel termination fittings:
• Put coupler on all remaining corners if you haven't already done so.
• You want to feed the panels to the bottom header at the farthest corner.  Install a CPVC female adapter here.
• Put the other female adapter on the opposite, upper corner.
• Install the vacuum relief valve (the end cap-looking thing with two hole in it) on the other upper corner.
• Install the end cap on the remaining lower corner.
• The panels are now installed and ready for piping to and from the pool equipment area.

CPVC female adapter on lower left end of panel bank.	The other female adapter in upper, opposite corner	Vacuum relief valve in other upper header - not used in Hawaii
End cap in lower left corner	Completed panel installation.