A Pressing Need for Design and Engineering Standards

The solar industry has historically applied its technical resources, research dollars and time to increasing the efficiency, driving down the cost and improving the reliability of modules and inverters. The infrastructure that supports these solar modules, however, has largely been ignored probably because it does not generate any revenue for investors, businesses or homeowners.

I view this as an extremely dangerous position for the industry over the long term; unless we pay as much attention to the proper design and engineering of infrastructure as we do to the modules and inverters themselves, the integrity of entire solar power systems will become compromised, causing potentially serious financial and safety issues.

The solar industry needs to develop design and engineering standards that will help mitigate the risk of structural failure and ensure successful solar installations over the long term. Small structural failures are not publicized and most solar installations to date have been relatively small.

At present there aren’t any unilateral evaluation standards or criteria in place and being enforced, leaving solar projects at risk for a variety of engineering and installation failures. Moreover, the difficulty of applying current “code” to solar structures is that the code has been subject to interpretation for years. Solar infrastructure manufacturers typically employ a single consulting engineer to provide code compliance letters. This leaves the interpretation of these codes to individual engineers, and there’s no guarantee that these individuals even know the hierarchy of codes and standards that they should be applying to solar infrastructure.

The entire product line is then dependent on the knowledge and expertise of a single, individual engineer. Designing solar structure is not like designing a building or bridge. A good example of this is the use of clamps in solar structures.  Clamps are dependent on friction to resist forces. Bridge and building engineers do not typically use friction to hold up a structure. Engineers must read the code and apply their own interpretation to it because the code does not say explicitly, “For solar, do this,” in the same way it says it for bridges and buildings.

For example, while beam strength is a calculation that structural engineers do on a daily basis, important elements such as lateral torsoinal buckling and the beam interaction equations found in the Aluminum Design Manual and AISI are not standard fare for structural engineers who focus on general building design. This means that issued code compliance letters may or may not take all the relevant concerns into consideration, and there’s no way to know whether they do.

A beam can fail in lots of different ways. It can bend, twist, crumple and shear to name a few. Those are called failure modes. There are standard span tables for off-the-shelf beams that take all the different failure modes.  With custom designed beams, those span tables don’t exist. Doing a few quick calculations in combination with published span tables is inadequate for the custom designed beams that are used in the solar industry.

As for physical testing, again there is no established standard for how solar infrastructure manufacturers test their products. Calibrated load cells and computer-controlled hydraulics offer a high degree of accuracy about how an installation will react under extreme weather conditions and there are a few sophisticated manufacturers doing this type of testing.

Unfortunately, it’s far more common for manufacturers to do simple sandbag testing, which is not an accurate testing methodology. With sandbag testing, sand bags are applied to the top of an assembly one at a time, by hand, gradually. Wind gusts do not act like sand bags. Wind loads are applied faster with more jarring force. A good test plan will specify not only how much force is applied, but how quickly and often.  That is why it is nearly impossible to accurately simulate wind loads with sand bags.

Additionally, as module prices continue to drop, many investors and contractors are pushing for lower costs in the underlying solar infrastructure as well. Such pressure has led many solar infrastructure vendors to cut corners — either knowingly or unknowingly — which further reinforces the need to establish new design and engineering standards.

To maximize a solar project’s return on investment (ROI), the system needs to last 20 to 30 years. Given this, proper design and engineering of the solar infrastructure is of paramount importance; an inverter or module failure is usually localized, but structural failure is systemic. In fact, the financial losses from a structural failure may be unrecoverable, even in court.

Right now, it is incumbent upon individual installation companies to critically assess the engineering expertise and knowledge of their chosen solar infrastructure provider. They must proactively take steps to mitigate and manage their projects’ risk. Unfortunately, placing the responsibility on a variety of companies and individuals leaves room for significant gaps in this complex engineering process and is not sustainable over the long term.

While some companies will by nature take the proper steps to ensure a safe and long-lasting installation, without accepted design and engineering standards in place, others will simply cut corners in order to shave costs today with little regard to downstream consequences.

As a rapidly maturing industry, we must formally adopt design and engineering standards that will mitigate the risk of structural failure and help ensure solar installation success over the long term. The stakes are simply too large for us to ignore any longer.

 

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Juan Suarez, Senior Director of Engineering and Program Management, brings over ten years of experience as an award winning general contractor to the Unirac team. At Unirac, Suarez has tripled the company’s patent portfolio in less than two years, and lead the engineering and product development process to achieve ISO 9001 certification. Prior to Unirac, Suarez owned his own construction and development company specializing in green building. Suarez has a Bachelor of Science in Industrial Engineering from New Mexico State University.

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