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!
The recent windstorm in Pasadena did widespread damage - including to some improperly designed or installed solar power systems. Two of those systems came to our attention as we were asked to step in and make them right. We are pleased to report that the final score is now in: Run on Sun 2, Windstorm 0!
We already discussed the first of these solar repair projects; today’s story is the first installment of a three-part series about our work on the second, and it has a bit of history so we will start there.
In 2008, Run on Sun had a contract with our local utility, Pasadena Water & Power, to go out to some of the existing solar power systems throughout the city and assess their performance. We had developed a methodology that incorporated the temperature of the solar panels, the actual amount of solar radiation present in the plane of the panels and actual voltage and current measurements to determine what percentage of the predicted system output was actually being realized. It was a great project for us (and for PWP) as it not only gave us lots of opportunities to learn from the glaring errors others had made in putting together solar power systems, but it also let us speak with dozens of system owners who, without exception, were passionate about having gone solar.
Which brought us to the home of Mrs. C. Her solar power system had been designed and installed by her late husband back in 2001. From the ground it looked solid enough:
We found out from Mrs. C that her system had gone through two inverters already - the now infamous Xantrex GT 3.0 model - and that the entire array had to be removed once to repair roof leaks. Still, Mrs. C was very proud of her system which had been designed and originally built by her late husband. Our testing from the ground showed that the system was operating normally for its age and Mrs. C was greatly relieved to learn that since the last solar company that had worked on the system - replacing the second failed inverter in 2004 - had since gone out of business. We left her with a copy of our assessment and said goodbye.
Fast forward three years to the week following the windstorm when I received a phone call from Mrs. C, telling me that her system had been damaged during the storm. I asked her if her panels were still on the roof and she said they were, but that they had “come loose from their moorings” and could I please come out to take a look. I agreed to do so - and was simply shocked by what I found:
The solar panels that in 2008 had appeared to be so securely fastened to their “moorings” had been ripped loose and scattered across the racking.
As the wind came from the northeast, it had peeled the panels away from the railing (which was still firmly in place) and left the panels in a twisted heap of broken glass, silicon and metal.
As with our other windstorm damaged system, it is extremely fortunate that this damage occurred at night when no power was being generated.
That this system was totally destroyed was beyond dispute. But how exactly had it failed? The framework that was assembled to hold the panels in place - an unwarranted, yet not uncommon, mixture of unistrut and Unirac rails on Unirac standoffs - was still firmly anchored to the roof. So why had the panels torn free? When properly assembled, the Unirac rails are engineered to withstand wind speeds well beyond what was measured in Pasadena that night - so why had this gone so badly south (literally)?
In our next installment we will find the answer to that question and also learn a little bit about how two different solar companies approached working with the insurance company to resolve this claim. (It is a cautionary tale, to say the least.) Finally, we will conclude this series with a happy ending - complete with interviews and a cool time-lapse view of the new system being installed thanks to the support of Unirac. Stay tuned!