Testing solar products is quite interesting (for those not intimidated by the technical aspects) and is one of the most significant challenges for consumers.
Typical customers often can't give a fair evaluation of a solar panel like they would if they purchased another product.
If they buy a tape measure, they can easily compare it to other tape measures and quickly know whether the manufacturer is producing a quality product.
With solar panels, many manufacturers produce lower-quality panels and sell them as rated much higher than reality.
Sadly, these companies rely on the fact that consumers have no way of testing (or don't desire to test).
One of our concerns is that some customers will come away from their experience thinking, "solar simply doesn't work," which taints the entire industry.
At PowerFilm, we have some different dynamics at play. First, we're making our products in the US (Ames, Iowa).
Second, we produce many products for the US Military, requiring reliable/high-quality products that deliver what is promised.
We also produce custom solar products for industrial applications (for example, GPS-asset tracking solar modules for the trucking industry). So, unlike many of our competitors, we don't repackage low-quality cells and sell them with questionable power ratings.
With that backdrop, let's dive into testing.
Things to know about solar testing & simulation
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Light intensity primarily affects current (which affects power)
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Different types of panels will be impacted differently by increases in temperature
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Shading impacts power output. For example, bird poop, or anything else covering portions of a panel, will affect the overall product's production. If the module's architecture is such that large cells are wired together in series, and one of the cells is shaded, the overall impact will likely be reduced voltage (significant power drop).
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The light spectrum will significantly affect output, and solar technologies respond differently to different sources. This is critical.
To assess a solar panel accurately, consider both sides of the equation.
Each light source is different
The spectrum from each source will vary wildly. For example, a fluorescent bulb's light intensity may look very bright to your eyes.
But when you place a solar panel under it, very little power is produced. The bulb has an inferior representation of sunlight, and the panel responds to specific frequencies of light but not necessarily the frequencies produced by the bulb.
Each PV type responds to a given spectrum differently
This is known as quantum efficiency.
You might think of this as a person's hearing. One person may say, "that loud, high-pitched noise is annoying," and their 80-year-old grandfather (who has lost his high-frequency hearing) would say, "what noise?"
In the same way, different PV types under a simulator require special testing considerations because of frequency differences (QE).
In other words, unless you've managed to reproduce the spectrum of outdoor sunlight perfectly, you can't simply throw different PV types (a-Si, monocrystalline, polycrystalline, CIGS) under a simulator and expect to do an "apples to apples" comparison.
The QE differences in the solar types and the spectral mismatch of your light source will distort your results. Also, your reference cell (the cell in your meter to show you the intensity) must have the same type of PV as the module under test.
The sun's spectrum varies
This is another wrinkle that we must accept.
For example, we noticed a sizable change when testing foldable solar panels for the military for one year.
When we checked the outdoor spectrum, we found that the light had changed. We could correlate that to forest fires in the West that had slightly tinted the spectrum toward the red wavelengths.
We have now built several simulators and battled issues such as temperature stability, light uniformity, and spectrum to perfect our simulator.
Many try to make a simple tester that can accurately compare the various panels found on the market. While that's a great idea, it's tough to execute.
We've tried doing that ourselves with similar LEDs and, in the end, decided that the only way to do it was to design a custom LED system (hand-picking each LED, spending many hours considering spectrum matches, and comparing indoors and outdoors).
The bottom line
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Tackling the subject of testing solar panels to compare units in a market full of misinformation is incredibly difficult. We are here to help.
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There are some hurdles you must overcome when using indoor lights for simulation. We developed our dimmable systems with suitable spectrum matches to simulate outdoor conditions for our PV and uniform temperature control.
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Consider that your reference cell should be the same type as the unit under test. It should be temperature compensated as well.
Are you interested in learning more about our testing procedures or PowerFilm?
Please feel free to contact us or leave a comment below.