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In the first installment of this series, we looked at the solar system of Mrs. C which had been entirely destroyed in Pasadena’s terrible windstorm. Given that the racking itself was still securely attached to the roof, the critical question was: Why had this system failed?
As we began to dismantle the now scrap system, we examined the panels, the railing and the bolts that had held the system together. This array had been crafted out of a hybrid combination of unistrut steel parts - that created a 26° tilt - with Unirac rails and clamps. The array was on a flat roof on the northern section of the house - which meant that it was completely exposed to the full force of the wind with no other part of the roof to interfere with the flow. Under such circumstances, any mistake in the installation would be put to a very extreme test.
Our examination revealed that the forces on the panels had been so intense that the railing itself had failed.
This is how an end-clamp normally appears when holding a panel to the rail. You can see how the edge of the clamp grips the panel, the base of the clamp rests on the rail, and the bolt coming up from the rail is tightened down to hold the panel securely.
The portion of the clamp at the bottom right of the picture was supposed to grip the side of the panel but now it is gripping nothing.
Let’s take a closer look at this point of failure:
The t-bolt is made of stainless steel, whereas the rail in which it sits is aluminum. Under the extreme forces that occurred that night, the uplift from the panels caused the t-bolt to chew its way completely through the rail! You can also see how the bottom of the end-clamp had started to deface the top of the rail, as well as the scratch marks created by the solar panel (to the right of the rail failure.)
That answered the question of what had failed, but it didn’t answer the question of why. After all, when properly installed, that rail combination is designed to withstand forces far beyond what were experienced that night. In the days following the windstorm, Run on Sun inspected all of our projects that used this same combination of bolts and rails and none of them showed the slightest sign of failure. So why was this installation different?
We brought this system failure to the attention of Unirac and Pasadena Water and Power. We wanted Unirac’s sense of why this had failed and we wanted PWP to encourage its solar customers to have their systems inspected for possible signs of unexpected wear.
We got a great response from Unirac, who took this issue very seriously and helped us diagnose what had ultimately caused the failure. One possibility was that the last person that worked on those panels might have over-torqued the bolts. Unirac provides specific torque settings for the clamps used to hold the panels to the rails. Those setting have been tested to assure the maximum strength without running the risk of damaging the parts. But not all installers use a torque wrench when they are tightening their panels to the rails. Without a torque wrench, an installer has to tighten by feel alone, and a careless - or harried - installer could easily over-tighten the bolts which could weaken the rail and lead to a possible failure. Did that happen here? We will never know.
And yet, a different culprit ultimately emerged which almost certainly played a major role in the failure of this system. Indeed, it was right in front of us all along (you can see it if you look closely at the first picture in this post), but we didn’t notice it until we were starting to take the damaged panels off the roof.
Did you figure it out? Take a look at this photo:
Right there in the middle of the photo is a nut on the end of a bolt - these two panels were bolted together! Indeed, the installer had bolted all of the panels together into pairs. Why was that done? No idea - but the impact of that decision was profound. Now each panel - as “seen” by the rails - was twice as wide as normal. For each row of 10 panels, the number of mid-clamps available to resist the uplift force dropped from 18 (two each in the nine gaps between panels) to just 8. As the wind force increased to historic proportions, the loading simply exceeded the down-force that those 8 mid-clamps could provide. The result was a smashed solar power system with panels flung across the roof.
We were pleased to have discerned why Mrs. C’s system had failed and she was eager to get it replaced. She contacted her insurance company which contacted us and asked us to provide an estimate to repair the system. Given that there was lots of old gear to be removed and hauled away, in addition to installing what was pretty much an entirely new replacement system on a tilt-up rack, we gave them what we considered a fair bid that worked out to ~ $7/Watt. Not surprisingly, the insurance company informed us that since the amount was so large, they would need to get a second bid. Which they did - and that bid came back $11,000 more than ours! What’s more, they charged $250 just to provide the bid!
Mind you, we proposed using Sanyo panels and Enphase micro-inverters for this project - which is the absolute top-of-the line gear that we could have chosen. So how on earth does a competitor look at the same project and propose a system price nearly twice what we did? One can only assume that they saw that an insurance company would be paying for this and so they decided to go for a jackpot. To which we have just one response: PATHETIC!
Happily, the insurance company stepped up to the plate and Mrs. C awarded us the contract to “repair” her system. The folks from Unirac chipped in and agreed to provide the replacement racking for the project. In the final installment in this series, we will tell you about how that system came together and we will even have a totally cool video to share. Stay tuned!
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