As an estimator, there are several nuances to every solar system that are hard to pin down. That’s where the art of estimating comes into play. These nuances range from wiring best practices to how much a subcontractor will really cost to racking for the specific site to pure mobilization costs. I think that all these numbers can be wrapped into one over-arching factor: SPF. No, not sun tan lotion. Solar Puke Factor.
OK, ok, enough dramatics. What does this really mean? First I’m going to define what it is and then I’ll take you through a few case studies. By the time you’ve read through this, I think you’ll be a believer. Let’s get this term to be an industry standard!
Definition: Solar Puke Factor (SPF)
That feeling you get when you look at a PV system layout. When it’s a nice, clean, rectangular and linear array, you’re looking at a SPF rating of 1, because it feels good and shiny. When it’s incredibly broken up, with few portions of the array actually displaying any sense of cohesiveness, even argued to be aligned and it looks like someone simply puked solar onto the site. Well, the latter example, that’s a SPF rating of 5. Though he claims no credit, it is believed Roger Williams was the originator of the term. It was pressed into regular use and initially perpetuated by Katie Fearon and is something I have used for a good portion of my career.
So how does the SPF impact costs? Easy, the more distributed it is the more labor and some materials go into the system.
EXAMPLE 1: Let’s take a ballasted racking system on a flat roof as an example. If you are in a high wind zone or seismic zone, ballasted systems require some sort of mechanical attachment. When the system has an SPF of 1, those attachments aren’t that frequent. Maybe 1 attachment per 10 modules. Fewer even if allowed. The key here, however, is that attachments have to mechanically connect racking. In the SPF = 5 region, for example, there could be a few groupings of 4 modules, each requiring at least 1, sometimes 2, attachments. As you can see, that immediately moves the attachment ratio from 1:10 to 1:4. And when a roofer has to maintain the warranty on their roof, they will often charge a substantial amount per anchor. They see the anchors as risk, after all. Additionally, your labor force has a substantial number more attachments to install. So, higher SPF = higher costs.
EXAMPLE 2: Anchors are all fine-and-dandy but there are other significant costs due to SPF. Conduit and wire is another great example. On a clean, contained array, the NEC allows wires to be under the array without conduit. That means you can run string wires under the array to the point of exit. When you have strings of 28 the easiest approach is to create arrays in multiples of 28 and then conduit is only required from the edge of the array to the inverter. Or from the edge of the initial 28 module area to the inverter, depending on your QC approach and warranties. But, returning to an example where there might be a few pockets of 4 modules, then the labor force again has to install additional jumpers from array to array, plus the conduit from array to array. That adds up fast. Suddenly your system has 7 times the array conduit because of of how messy it is.
So lets support Katie and Roger’s notion of SPF and start using as an industry term. I think it’s great. Do you?