Panel Installation, Part 2

The Next Morning

Early the next morning we were off to Nuts & Bolts Supply who could supply us with the proper stainless hardware, then back home to replace those 42 mid-clips and bolts which, as you have guessed by now, required sliding everything off, replacing the bolts, and sliding everything back on. The new wrinkle this time was that over the night moisture had condensed on the rails, in the track, and had frozen. It took some effort to get the old bolts off.

Things started to move pretty smoothly. A neighbor had very kindly loaned us a scissor lift which made the job oh so much easier.  Once we got the first nine panels in place we tested the 'A' string with a voltmeter. The meter read a very pleasing 387 VDC!

Note that it is very important to use a proper torque wrench when tightening the end-clip and mid-clip bolts. Exceeding the recommended torque will easily damage the panels by cracking the tempered glass. It's also critical to avoid damage the back of the panels since it consists of a thin coating over the back of the individual cells and scratching of that coating would be a serious matter.

As each string of 8 panels was completed we tested the output voltage to make sure we were getting the desired output. We finished mounting the panels just as the sun set (and things started to get really cold) and it was not possible to test the final string since there was no longer adequate light.

Putting that last panel up was very satisfying. I tried to give my son a hug, he went on his way, and I cleaned up all of the cardboard from the panels while collecting the serial number stickers for my records.

The next morning, after the sun came up, I went out and measured the voltage of the final 'C' string and double-checked the 'B' and 'A' strings.  'C' and 'A' was fine but 'B' was measuring only 334 VDC, indicating that one panel was not producing. Since I was getting some voltage I concluded that the Tigo Maximizers were properly wired to one another. The problem had to be either a bad connection between one panel's output into its Tigo Maximizer or a Maximizer was flaky.

The best way to identify the problem was by using the Tigo MMU (Maximizer Management Unit). Tigo had already set up my account at their web site so that once I hooked up the MMU to my Internet service I could go to that web site and see how each panel was performing.

There was some confusion on my part, mostly due to inadequate documentation of the MMU and how the Tigo products worked — but this was a brand new product and I had expected some 'bleeding' edge experiences along the way.

The installation manual for the MMU did not explain how to hook up the sensor/gateway cable. The sensor/gateway is a small box that wirelessly communicates with the 24 Tigo Maximizers (LMUs) which we had earlier mounted to the back of each solar module. I dashed off an email to James Bickford at Tigo and very quickly had a Tigo engineer on the phone helping me get things set up.  The engineer also explained that it was not necessary for the solar modules to be connected to an inverter in order to determine how each module was performing.

After some initial miscommunication, I got the sensor/gateway all cabled up, the MMU connected to the home's ethernet, and powered up. By this time the sun was going down and it was futile to see if there was any output coming form the panels.

Panel Installation

We hired a couple of roofers to mount the rails. They did a fine job and the cost was reasonable.

The key when installing the rails is to insure that the L-feet are firmly lagged into the trusses.  Roofers are good at that, though one does end up having a few extra holes in the roof — nicely sealed, of course, or, in roofer-speak, 'gooped'. Chalk-lines helped keep things aligned.

The rails are mounted horizontally so that they will support the solar modules, which are 'portrait' oriented: the longest dimension of the module is vertical. The L-feet are no more than 48" apart.

The weather was starting to get cold. Because the wires from each Tigo Maximizer run between the panels (as shown in the previous post) we put adhesive cable tie holders at strategic locations on each module. It was so cold that evening that the adhesive wouldn't stick so I had to warm up the aluminum frame a bit and slap on the cable tie holder. It took a couple of hours.

A few days later my son and I started mounting panels.  Earlier in the project I was a bit reluctant to scramble around on the roof but the rails made getting around a lot easier. First thing was to slide the mounting bolts and clips into the track of each rail: 42 mid-clips and bolts, 12 end-clips and bolts, and six grounding straps over the rail splices.

We forgot the grounding wire clips! Slide off about half the clips and bolts, slide on the grounding wire clips and slide back on the other clips and bolts.  Ready.

We mounted the first panel. Almost. The end clips went on just fine and held the panel pretty firmly but we were anxious to get the other side of the panel secured. It would not be good if the panel came loose and slid down the roof. That's when we discovered that the 2-1/4" stainless bolts used to secure the mid-clips were too short! Big mistake by Wholesale Solar! We needed 2-1/2" bolts! So it was a mad dash off to the local hardware store and pick up a bag of 50 bolts.

Slide off 42 mid-clips and bolts, six end clips and bolts, the six grounding wire clips, and the six grounding straps.  Replace the mid-clip bolts and slide on 42 mid-clips and bolts, six end clips and bolts, and the six grounding wire clips.  Forgot the six grounding straps.  Slide, rinse, repeat.

We mounted the two panels immediately below the original panel, connecting the Tigo maximizer cables, and called it a day.

During the evening, as I was checking and double-checking everything, I realized that the new 2-1/2" bolts we had installed were galvanized, not stainless steel. This was not good — the galvanized hardware would have a galvanic reaction to the aluminum rails causing the metal to degrade. Sigh.