Solar Panels & Sandwiches: Quality Matters

By in Manufacturing, Technology
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At Yingli Solar, we make solar panels that are designed, built, and proven to perform. But most top-tier, large-scale solar panel manufacturers – including Yingli – operate very similar production lines. So, what makes one company’s panel better or worse than all the rest?

It might help to think about a solar panel like a sandwich. Almost every deli makes sandwiches in the same way: two slices of bread, cheese, meat, maybe a veggie or two – but you can taste the difference between turkey that’s freshly sliced and turkey that’s been vacuum-sealed.

The same goes for solar panels: it’s all about the ingredients, even if they’re not quite as tasty as those found in sandwiches.

Solar Sandwhich

Think of solar panels’ frames like crusts of bread. They provide panels with their structural integrity and rigidity, just like bread crusts hold together a sandwich that’s loaded up with delicious ingredients.

At Yingli, our frames go through a comprehensive qualification process known as “static and dynamic mechanical load testing.”  That’s a fancy way of saying we bend our modules in every direction, which ensures they can handle double meat and double cheese – that is, the toughest wind, rain, snow, and hail loads.  It’s kind of like when you go to IKEA and look at the cabinet door being opened and closed continuously by a robotic arm in order to assess its reliability.

solar panel testing

As we move from the crusts and onto the center of the bread, durability remains a top priority. That’s why our solar panel sandwich boasts two different ‘slices of bread’ that protect the panel from environmental elements and maintain structural integrity in adverse conditions: who wants soggy white bread that falls apart under the weight of your pastrami or disintegrates in your lunchbox?

The ‘top slice of bread’ in a solar panel is low-iron, high-transmission, anti-reflective coated glass, which protects the panel from inclement weather and boosts performance. Our large-format YGE-U and YGE 72 Cell Series (designed for utility projects) feature extra-thick 4.0mm glass to safeguard against microcracks – just as larger sandwiches require extra-thick bread, larger panels require thicker glass.

While the anti-reflective coating is not critical to a panel’s structural integrity, it increases energy yield by reducing soiling and maximizing the amount of light captured by the solar cells. It’s comparable to spreading a layer of extra-special mustard on your top slice of bread – that mustard just might be the ingredient that elevates your sandwich from “satisfying” to “mind-blowing.” Similarly, AR coating can push a panel’s performance above expectations for energy yield.

The ‘bottom slice of bread’ in our solar panel sandwich is a fluoropolymer-based backsheet, which prevents water, soil, and other materials from entering the panel from the back. Yingli proudly uses backsheets made with DuPont™ Tedlar®, which is known to be one of the world’s toughest polymer-based protectors. NASA even uses it in their rocket ships!

Using an inferior  backsheet is risky and could lead to reduced power output, shorter system lifetimes, panel yellowing, degradation, and even delamination – so ask if your supplier is using a sturdy, fluoropolymer-based material – and make sure they’re not using the solar industry equivalent of Wonderbread™.

After the glass and backsheet, we come to the glue that binds the solar panel together, affixing the solar cells to the panel’s backsheet and glass. There are two layers of this glue, or ethylene vinyl acetate (EVA) – try saying that ten times fast. Let’s just call it cheese for short. Of course, a tasty sandwich might contain any number of cheeses, but it’s best to think of EVA as two thick, sticky slices of brie: one sits beneath the glass and one sits above the backsheet.

Because EVA adheres the solar cells (that’s the meat – we’ll get there next) to the glass and backsheet, heat and humidity resistance are critical. Cheese that melts and slides while you’re sitting down to lunch creates a messy, sub-optimal eating experience. Likewise, EVA that degrades in harsh climates can cause sub-optimal performance. Yingli only uses the highest-quality solar encapsulant, such as Firsteva™. This EVA quickly dissipates heat thanks to its low thermal resistance, which improves panel performance in hot environments and prevents overheating.

Now, we’ve finally reached the heart of the sandwich: the meat, or perhaps a veggie patty depending on your preference. The meat contains the majority of the sandwich’s protein and flavor, and even if every other ingredient is top-of-the-line, meat quality will make or break a sandwich. Like ham, turkey, or pastrami, solar cells are at the heart of every solar panel, as the core component that actually turns sunlight into electricity.

Yingli’s solar cells are among the industry’s highest performing, with multicrystalline solar cell efficiencies up to 18.1%. As the world’s largest solar cell manufacturer, we understand every element that makes up a quality solar cell. For U.S. tariff-compliant product, we have partnered with the industry’s top solar cell suppliers and adopted rigorous inspection and product testing procedures to ensure quality and consistency. These procedures include regular on-site inspections and random third-party and in-house testing of both cells and completed panels. It’s kind of like your local health inspector, but even more intensive.

So there you have it – ingredients make a difference in solar panels AND sandwiches. Now, who’s ready for lunch?

Willy Wang is a Product Manager at Yingli Solar’s PV Testing Lab in San Francisco. 

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