26 August 2011

Solar: What's That Up on My Roof?

Our solar installation is underway. (We were moved up in the schedule because another customer neglected to get approval from their homeowners' association. We're so glad we don't have to deal with that. Texas just passed a law that prohibits homeowners' associations from refusing to allow reasonably installed systems, but HOAs can still require owners to jump through a bunch of hoops to get the association's blessing.)

I was really, really happy to see that our installers "tie on" when they're up on the roof -- meaning that they use rock climbing harnesses and rope tied to a fixed object (in this case their truck on the other side of the house) so they don't fall off.



Before construction started in the fall of 2009, we met with our builder (R) and our lawyer to get the legal green light to proceed, and our lawyer actually asked if R if his roofing subcontractor has their guys tie on. Workers have been seriously injured and even died in falls from roofs, but unfortunately, tying on still hasn't become a part of roofing culture, and (adept as they are...really, it's amazing) roofers continue to put themselves at risk every day.

Tying on not only makes our solar job about a million times safer (and gives me a huge amount of peace of mind), but it also allows the workers to work more confidently on a fairly steep, very slick surface.



The first two work days were all about attaching the brackets that would hold the panels. These C-shaped clamps attach to the standing seams of the roof, and the L-shaped brackets attach to the clamps:



They ended up using larger clamps, and I didn't get close-ups of them, but you get the idea. Once the L-brackets are in place, these rails are attached to hold the panels:



By the end of the first day, the clamps, brackets, and rails were installed on the left part of the roof (which will hold 12 panels):



The crew got a lot done that first day because it was overcast. The irony of the solar business? On sunny summer days, it can get too hot to work. Even with the clouds, by about 2 p.m. the metal roof was too hot to touch, so they work fairly short days (although they make the most of the time they have by starting pretty much the minute the sun comes up).

The second day was more of the same, except that they held off putting the rails in place on the right part of the roof (15 panels):



Day three, when the last of the rails were installed, was where things started to get interesting.



But let's back up for a brief lesson in solar power, Idiot's Guide-style (because, honestly, that's all I'm capable of).

Solar panels generate power in direct current (D.C.), but we need to convert it to alternating current (A.C.) to use in the house or send into "the grid." All solar systems include one or more inverters between the panels and the electric meter, which change D.C. to A.C. Many systems have a single inverter near the meter, but another option is to use "micro inverters" at each panel. The advantage of micro inverters hinges on the way shade affects today's solar systems. With a single inverter, shade on one small part of an array (the whole series of panels on a roof) dramatically reduces the energy production from that array. With micro inverters, each panel generates power completely separately, so if one panel of 27 were shaded, we would lose only one twenty-seventh of our maximum production. Since we have trees on either side of our house (in each of our next door neighbors' yards) that shade the right part of the array early in the morning and the left part late in the afternoon/evening, we chose to go with micro inverters to maximize our production.



Those six boxes are micro inverters. Each one will be attached to a panel and will do that D.C.-to-A.C. conversion magic right up there on the roof. You know, once the panels are up and running.

More soon.

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