PV module procurement: Common mistakes made and issues to consider

solar PV panel common mistakes

As part of our 2021 Solar PV Modules Buyer’s Guide, we asked solar PV panel manufacturers what they considered to be common mistakes made in the procurement process by solar installers and EPCs. Here is what they had to say.

Peak power vs. production

One of the factors that is often overlooked is the concept of Peak Power (Wp) versus Energy Production (KWh/KWp). The most powerful panel for an application may or may not provide the most energy over the lifetime of the installation.

“Pay attention to the modeled energy yield over the lifetime of the array, as well as the warranted power,” says George McClellan, Technical Sales with REC Americas. “Ensure that the array power electronics are a good fit with the specified module to safeguard against excessive clipping. Be able to discuss the cost/benefit analysis of the cost of power electronics compared to the loss of KWh due to clipping. In most cases the amount of energy lost is negligible, but the system owner deserves a solid explanation.”

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Module size versus module power plays into this. Module x and y dimensions have been moving around lately. Some manufacturers are increasing their module power by increasing cell and module size. A smaller form factor for the same power provides a higher module efficiency and a higher module power density (W/M2). A greater power density will allow for more modules (and more Wp) per rooftop, or a decreased footprint (fewer modules to install) for the same amount of Wp.

Going for biggest DC capacity

Though defined first and foremost by their capacity, higher module capacity doesn’t necessarily translate to a more efficient system, or even a longer-term yield. Often overlooked in the residential sales process, but vitally important to the efficiency and long-term reliability of a solar module are its cells, says Brian Lynch, head of solar business development, LG Business Solutions. “Another important point to consider is multi busbar, or back contact modules, which are less susceptible to greater power loss if exposed to micro-cracking.”


Because of growth in the industry, there are many small manufacturers popping up. Low prices can obviously look like a good deal to you and your customers, but the quality of the energy production and credibility of the manufacturer must be factored in.

“Because solar panels have a long lifespan, solar manufacturers are eager to offer product and labor warranties that will entice customers and installers alike, but new manufacturers lack the credibility necessary to make bold warranty claims,” says Mukesh Sethi, Director, Solar and Energy Storage, Panasonic Life Solutions. “If a manufacturer offers a 25-year warranty but goes out of business in five years, the customer is left with a broken solar system and no manufacturer to provide resolution.”

On that note – be sure to read and understand the module warranty. It is typically one or two pages long and can help you understand what is covered and what is not covered.

“Understand the effect of high failure rates,” McClellan says. “Even if a module manufacturer covers all of your costs for an accepted claim (many do now), warranty replacement is not a profit center. You need to be out selling or installing modules, not chasing down failed modules and talking to disappointed customers. The best module warranty out there is one you don’t have to use.”

In utility- and C&I-scale PV project selection, EPCs often chase the lowest $/W as their first goal, all other factors getting lower priority. But that can be a false economy if the lowest cost supplier supplies low quality products creating reliability issues, can’t deliver on time, delivers defective modules or doesn’t have the necessary local support staff to address problems promptly. CAPEX optimization becomes the enemy of the OPEX team.

“Benefits of buying from a proven Tier 1 supplier allow for a streamlined component procurement along with optimization of integration and interconnection,” says Gautam Ghose, senior product marketing manager at Trina Solar. “The right mix of modules, inverters and racking can greatly increase energy production. The sustained dependability of the module manufacturer and their continued support of the power and product warranties through the appointed project terms is also a significant factor that some installation customers forget to correctly weigh in their supplier selections.”

The real price of a module is actually the upfront price and the price to operate and maintain over 25 years.

Tier 1 is not bankability

Highly bankable suppliers will allow for easier and quicker financing of projects and makes the third party IE analysis and approval a breeze. But don’t assume that every Tier 1 supplier is bankable. While modules look similar, their construction and the companies who back them are different.

“The BNEF T1 list is helpful for eliminating new and startup module suppliers, however, it is hardly a good barometer for bankability, as the criteria only seeks suppliers appearing in six projects using non-recourse debt financing in the past two years,” says Jeff Juger, director of business development with JinkoSolar. “This speaks nothing about execution, product quality, or company financials.”

The industry is brimming with examples of suppliers who change power classes at the last second, alter deal terms, or fail to deliver altogether. Being sure of the backsheet, for example, is important. In a 2020 field study of 9 million modules, DuPont Tedlar had almost negligible defects, whereas PA, PET, and PVDF-based backsheets failed at rates from 20-90% by years 6-10 after installation. Backsheet defects like cracking and delamination eventually permit outside contaminants like water to seep into and destroy the modules. This means truck rolls to service and replace defective modules adds to the overall lifetime cost of ownership.

In the end, while price and wattage are both important, the best installers evaluate the specific needs of the customer and the overall value proposition, which Silfab Solar’s Lorraine Hoefler says includes a mix of:

  • who the manufacturer is, (history & focus on solar innovation)
  • the BOM used,
  • quality & testing done to support the quality claims,
  • the manufacturing process,
  • density of the module,
  • efficiency,
  • warranty,
  • customer service,
  • aesthetics, and
  • cost

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