What the Three Little Pigs taught us about roof top PV

Since the early 1800's people have been telling the tale of the Three Little Pigs to illustrate the importance of building something right, with inherent strength, for ultimate safety and protection. The house of straw and the house of sticks couldn't stand up to the attack of the big bad wolf, but the strong house of bricks stood.

Another classic is the biblical parable of the two builders. The first man built his house carefully on a solid foundation of rock. When the floods and rain came, and the wind blew, the house stood. The second man built his house quickly without digging the foundation deep to solid rock. When the storms came, the house fell.

So what do we learn from these stories as it relates to rooftop PV systems? Build it strong, and understand the foundation. In the case of rooftop mounting systems, the foundation is the existing roof framing. And this is the first place people seem to blow it. In order to build a proper rooftop photovoltaic mounting system analogous to the brick house on a foundation of rock, the racking needs to be strong and firmly mounted to the structural members in the roof. But what we're seeing in the industry is a widespread lack of understanding in terms of roofing and building structures, leading to many rooftops getting the straw and stick house built on sand variety of PV systems. An example of this "straw house" method of putting solar on commercial rooftops is the very common ballasted systems. Ballasted PV systems are the most prevalent in the industry. Ironically, most people don't know that they are potentially harmful to the roof. In fact, the NRCA (National Roofing Contractors Association) recently published "Guidelines for Roof-mounted Photovoltaic System Installations", in which they specifically state they do not recommend using ballasted PV systems. For more of my views about ballasted systems, please see The Roof Penetration Myth blog post.

"The NRCA (National Roofing Contractors Association)....specifically state they do NOT recommend using ballasted PV systems"

As the commercial rooftop solar industry matures over the next few years, we will see the engineering community become a very big part of it. I know it is a challenge when there are no engineering dollars allocated on the front end (believe me, I know), but that is where we will also see certain companies mature and others fade away. Good companies will learn to work with the engineering community, develop internal tools for estimating, and learn to sell the customer on the benefits of paying for engineering up front when possible. Other companies (and there are a lot of them out there right now) will gloss over some very critical aspects of projects and get burned badly. Many will disappear like the house built on sand.