I bought a pair of $1/watt W Solar 45W monocrystalline panels from Solar Blvd which arrived today. First thing I noticed was there were 40 cells on the panel, not 36 like usual for a '12V' panel, but the open circuit voltage was not 4 cells higher.Took it outside to do some measurements and when checking shading performance I was VERY surprised to not see the amps drop when I shaded one cell, then another, then another.Hmm, I don't see blocking diodes on the cells. Blocking some of the other cells, there was an immediate drop. "What is going on?"Closer inspection showed that though this panel has 40 cells, only 36 are wired up. 4 cells appear to be wired up but are not as seen in the 2nd photo.I guess it was more important to make a square'ish panel vs a rectangular panel even if it meant wasting 11% more cells. Too bad they were not wired up - would have liked to have used that extra voltage for an MPPT controller.Performance wise, Isc and OCV matched the label even at 4:30PST sunlight with the panel facing the sun.Green arrows show cells not wired upGreen arrow shows connector ribbon not extending beyond edge of cell.

Would you have bought it if it were missing four cells? ;)

my guess,it was supposed to be 40cell panel, but something in that row tested badso it was wired and sold as a 45w 36cell paneli know CPU chips get graded, if they don't pass the highest testing levelsthe get marked and sold at the grade they do passa chip that was supposed to be quad core, might be sold as a lower grade duo core

You could always remove it from the frame and wire it up... It might work.

MrWizard wrote:my guess,it was supposed to be 40cell panel, but something in that row tested badso it was wired and sold as a 45w 36cell paneli know CPU chips get graded, if they don't pass the highest testing levelsthe get marked and sold at the grade they do passa chip that was supposed to be quad core, might be sold as a lower grade duo coreI was thinking about CPUs and yield and clock rating as well. Either their spec is only 36 cells and those 4 are available to jumper in to make spec when necessary, or they sell panels with fewer working cells as a different model.Do the cells make power in sunlight similar to the connected ones?If you find they have the full output of their peer cells under various conditions, I don't see any reason not to just Jumper them in, in series, and bump up your panel voltage a couple of volts. If you have MPPT you could even take advantage of the extra watts.What actual model panel is it? What are the specs? Sometimes low watt battery maintainer type panels are intentionally lower voltage because they are designed to run direct attached to a battery bank without a controller. There could be two versions, and the one using all panels has the extra volts to work better with a controller in the middle.Jim

I noticed on the spec. at the website, that the 45W. weighed 20 #. The 40W panel next to it weighed 10 # while only being a inches in L & W shorter.As I would plan on a portable panel being used as a battery maintainer while my RV was in storage for my house and chassis batteries, carrying this to the roof of my RV would be noticeable.Does it really weigh twice as much, 20# vs. 10#.Why would that be for almost the same size panel?

Solar so cheap that cells can be wasted | Good Sam Community

15 Replies

HiTech
Explorer
May 12, 2013
They are disconnected right? Is there much risk to seeing if the unused ones will wire up together and accept solder and wire attachments? I too would be very careful before I would disturb the working cells. It might be near impossible to attach wires to the PV cells. But you have this cool low risk play ground with the unused ones...

Jim (Home brew/ "maker" instigator)
DSchmidt_2000
Explorer
May 12, 2013
bigcitypopo wrote:
Are you gonna wire it up? Connect those other cells?

No way! Again, I don't want to damage the PVA.

The reason for the 45W panels is just something small for car based tent camping and also a small test setup for kids to learn about solar power. Going to either hinge the pair so they can be folded up or just go with one panel.

I have a nice metal 'key lock box' to put a couple of 7AH SLA batts and a PWM controller into it. Can probably fit a small laptop inverter too.
bigcitypopo
Explorer II
May 12, 2013
Are you gonna wire it up? Connect those other cells?
BFL13
Explorer II
May 12, 2013
Mr Wiz, that could be it, but OTOH looking at "my" guy's panels,

100w is 26 x 43 3/8 for $108, and a 50w is 20 x 30 1/2 so two is:
100w at 40 x 61 for $108 ($54 each)

If the roof is broken up with vents etc so there are no big spaces then having several small panels can be needed to make up the wattage.

I see the OP's 45w is 25.35 x 27.3 = 692 sq in while the 50w above is 20 x 30 1/2 = 610 sq in. Those extra cells in the 45 do make it bigger than needed.

Maybe they were a special order that fell through, so they derated them to 12v 45s so they could sell them off.
MrWizard
Moderator
May 12, 2013
portability, roof spacing, PRICE !!!
BFL13
Explorer II
May 12, 2013
The shape may be the deciding factor as the OP suspects.

I see "my" dealer has different shapes of 12v panels. No idea why.
eg, the 100w is 26 x 43 3/8 and the 120w is 26 3/4 x 52. It seems like the higher watts means 26 wide standard by ever longer panels

The 139w is 26 x 58 which continues this trend, BUT

The 150w is 39 x 44 1/2. Maybe they have a five foot limit in this case, no idea.

http://www.windturbine.ca/sun_panels.html

I like that the OP gets Isc, which I have been on about as the "expected amps" for 12v and PWM.

Be interesting to know why to choose two 45w panels for anything though, instead of say one 90w or whatever.
HiTech
Explorer
May 12, 2013
Did you measure their output? I know some panels are really hard to work on. But me, I'd try soldering sufficient sized lead onto one and see how it goes. If they are unused, I don't see a risk.

It's possible they are under spec cells they would have thrown away put in just for cosmetic purposes. If so you want to be sure they can keep up with the others.

I would have a hard time keeping myself from trying to connect the 4 up in series with leads out to measure their performance compared to the others.

Jim
DSchmidt_2000
Explorer
May 11, 2013
It's is wired in series, 36 cells in series.

I an completely convinced that the manufacturer wanted to build a more square'ish panel vs rectangular and put un-wired ones in there because nobody would want to buy a panel with white space in it.

The panel puts out what it is spec'd to do. The non-wired cells look perfect. Same hue/color, no chips or cracks, completely blemish free.

Again, I wish they were connected so MPPT users could take advantage of it, though it would be more of a mismatch when paired with different panels. No way I'm tearing into the PVA to attempt to wire up these extra cells. I don't see how they can be meant to wire in for yield losses either for another cell as the re-routing would be extensive and why do that before the PVA is in when you can just remove and replace a cell easily.

As far as weight goes, what they say online is not exactly what it weighs. I just weighed one at 11.7 lbs. I'm guess SolarBlvd pads the weight up to take care of handling charges, plus they did add heavy edge protection all around plus strapping.

Nice panels - put out what is rated as far as Isc and Voc. I have the inexpensive Chinese 20A MPPT controller on order that JiminDenver has. It'll be my first MPPT controller to dip my feet into. Hoping to take a trip to SolarBlvd one day to pick up one of those screaming 24V panel deals soon.
HiTech
Explorer
May 11, 2013
I was thinking straight serial. .5Vmpp per cell x36 adds up to the 18vmpp listed. Not a typical single cell output with current technology? Other options are 1v per cell and 2v per cell with this count and Vmpp. I can't really think of many more options.

4 parallel strings might make the most sense. 1 spare at the end of each string that could be jumperd in and jumper a bad one out.

Jim
MrWizard
Moderator
May 11, 2013
just noticed it is five cells by eight cells, which to me is a weird arrangement
i wonder how it's wired internally, as cell rows
cells have to be wired in series for voltage, then the series sets/rows wired parallel for amps
neat equal number rows running side by side is the easy neat normal way

36 would normally be four by nine, becasuse six by six would not prouce enough voltage

five by eight makes no sense
must be some cross jumpering and strange 'cell series' connections

but hey the price was right , the output seems correct