comparing 2 panels 110 W vs 120 W

westbranch

OK, 2 PV panels are sized identically, the 120W is 2 cents cheaper per watt, same manufacturer, specs are:

110 W 15.5% efficiency, +- 3% tolerance
Vmp 23.3
Voc 26.8
Imp 4.73
Isc 5.07

120W 16.8% efficient , +- 3% tolerance

Vmp 23.4
Voc 26.9
Imp 5.12
Isc 5.54

I suspect they are all off the same production run and labeled based on the test specs.

As I am going to use MPPT for a 24 V system, I have looked at another brand of 18V 110W panels for comparison.

Outback calculator says Vtoc = 130V and 98V respectively for 4 in series x 3 strings to 3 in series x 4 strings. the 110 is about 1 amp less than the 120 panel in either configuration. really splitting hairs here...

Does anyone see any significant difference between them other than total Watts 1322 / 1431W and a minuscule diff on the Amps?

thanks
Eric.

SolarGeek

Re: comparing 2 panels 110 W vs 120 W

I'm no expert on the behind the scenes story on panels, but it's my understanding the individual cells (not the entire panel) are graded for their current capability as they're manufactured. The cells from the various grades are then used to assemble panels of the same physical size but with slightly different power ratings.

Intel does the same thing with their processors. Within a given family, the ones that test out slower end up being sold as cheaper versions that are clocked at slower speeds. But they all started life on the same wafers of silicon as identical parts. But the nature of semiconductor manufacturing--PC processors or solar cells--is it's an imperfect process. So some test better than others (and some get rejected completely).

The cell matching is important because a few weak cells would drag down the performance of the entire panel. So some manufactures choose to not only match the cells but create different part numbers with different ratings from each grade of cells. They get higher yields and make more money that way.

As I noted in my other recent post, the same Suntech 24 volt panels come in 150, 160, 165, 170 and 180 watt ratings. The only difference is the higher wattage panels are assembled from cells that tested better. So it would seem they sort their cells into 5 categories.

So it comes down to if you need the few extra watts and are willing to pay for it? In the case of the Suntech's from SolarBlvd they're all the same $1.99 per watt. For someone who's constrained by space (say roof area) rather than budget, they probably want to go with the highest output versions to get the most power from their available area. You also have to consider if battery/controller/inverter capacity is a limiting factor as well.