The Good, the Bad, and the Ugly: Classifying SunPower solar cells

If you see me at a trade show and notice that the company shirt I’m wearing does not fit too well around the collar, it is probably because it was bought at low cost from an outlet store by the embroiderer. The label suggests that this shirt is from a highly respected manufacturer and is of high quality, which is all true up to a point, but somehow the buttons and button-holes were mis-aligned during assembly, and so this item was sold off as a “second” or reject item in the manufacturer's outlet store.

Well, guess what? Somewhere out there is an outlet store for low grade, off-spec, SunPower® solar cells.

During manufacture, after solar cells have been tested electrically they are sorted into different “Bins” dependent on how they performed. Some will be over achievers and be put aside for research purposes, while others will simply fail miserably and be destroyed. Those remaining are the Good, the Bad, and the Ugly cells; Good being “Prime”, Bad being “Off-Spec”, while the Ugly cells will have visual or cosmetic defects.

The Prime cells are further graded into High, Premium, and Ultra performance categories, while the Off-Spec cells are

given different Bin designations based on their particular flaws, i.e. low power, failing certain electrical tests, etc. Off-Spec cells with performance flaws and weaknesses will look identical to the Prime cells, even though their level of performance will be very different in real-life working conditions. In general, Off-Spec cells perform poorly in low/poor light conditions compared to Prime cells, mainly due to low shunt resistance and recombination defects.

For a solar panel manufacturer wanting to benefit from the marketing benefits and name-recognition to be gained by using SunPower®cells, there are two options; Prime cells or Off-Spec cells. Both cells will look absolutely identical, and will perform fairly similarly in good/perfect conditions, but the low grade Off-Spec cells will cost the solar panel manufacturer less than 1/6th of the price of Prime cells.

To put that into perspective, a high quality solar panel manufacturer like Solara that uses genuine, high grade, Prime SunPower®cells will be investing over $150 just for the cells required for a 100 watt panel, where a low cost panel producer will pay only $24 or less for the low grade Off-Spec versions.

Hopefully the above will illustrates that this is one case where you do indeed get what you pay for. If you want the most power from a marine solar system over the course of an entire solar day, on both good and bad solar days, then you need to purchase panels manufactured with genuine, high grade SunPower®cells. The initial financial outlay may well be quite considerable, but you may be able to recoup 30% of all your solar expenses as a Federal Tax Credit (contact Coastal Climate Control for details).As we say at Coastal: Do it once - Do it right!