My Newbie Solar Mistake

Actually, it wasn't totally my fault. I just didn't know any better.

I bought a Renogy Eclipse 200 Watt suitcase last year w/Voyager 20A PWM controller. I had some solar cash burning my pocket.

I should have studied more.

Recently, I finally had time to study and play with the system. It is an attractive package, albeit, not the most efficient use of two 100 Watt panels - at least not the way Renogy designed them. I have learned that now.

Take the panels out of the suitcase, point them at the sun and, sure enough, they will pump a respectable amount of amps into you battery bank. I have seen 10 amps in full sun and a battery that needed that much. That's the selling point. But could be so much better if they only were truly two 100 Watt 12 volt panels as advertised. They are not! I wish I would have educated myself before I spent over $500.00 for 6 volt panels!

OK, here's the deal.

I wanted options.

One option was just as shipped. PWM controller on panels and short 10 AWG run to battery bank. That works. One would assume the two panels were connected parallel to controller and short run to battery bank. Longer run, heavier gauge wire.

Option two, which I like better is controller closer to battery bank and take advantage of higher output voltage of series connected 100 watt 12 volt panels to use smaller gauge extension from panels to controller. Would swap out PVM controller w/MPPT controller. Easy to do with any two 100 watt panels. I know now that this is solar 101. Problem is...you can't do this with expensive Renogy 200 watt solar suitcase because it is made with 50 watt 6 volt panels in parallel/series. Sounds weird, doesn't it? That's what I thought!!

First clue should have been label on one of the panels. See below. Label still doesn't make sense to me. Renogy offers no explanation so far.

Second clue was what sure looks like series connection between panels. This was a mystery. 2 100 Watt panels which look to be hooked in series, but deliver ~20v open circuit voltage. That didn't make sense. I opened the PV junction box thinking maybe there was some kind of shunting going on to make parallel connection. Nope. Straight series and voltage output at each junction box measured ~10 volts! 32 cell, 100 watt 6 volt panels. Seems very, very, strange!!

I went back and read the advertising literature - "Two 100 watt Eclipse panels" Hmmmm, would you say two 50 watt 6 volt panels wired in parallel = "100 Watt Eclipse panel" I wouldn't. I guess lawyers would.

It seems now that Renogy has changed the design and is using two 100 watt 12v Eclipse panels. I wonder how many were shipped like the one I got.

Besides the deceptive advertising and the circuit disadvantage of two 6 volt panels in series, if one panel breaks, the system is useless.

If you have purchased a 200 Watt Eclipse Monocrystalline Solar Suitcase w/o Controller: RNG-KIT-STCS200MB-NC-BC, please check the sticker(s) on the back and let me know.

If you think I'm making too much out of this let me know. I'm just bummed that I didn't get what I thought I was getting and pissed at myself for not knowing!!

fred

The panel dimension on the label does not match the actual panel dimension?

Mi biggest beef is that any educated buyer would assume they were buying two 100 Watt 12v panels with all the inherent options. I wasn't educated and that's my fault. I think Renogy took advantage of that.

Three questions:

1. Did you purchase direct from Renogy or from a 3rd party seller (such as Amazon)?

2. If you purchased direct from Renogy, have you contacted Renogy about this?

3. If you purchased from a 3rd party seller, have you contacted the seller about this? 

Here is a picture of the sticker on my 100W unit:

The two panels in mine are square. The picture of yours looks like they are taller rectangles.  Each panel on mine is a 4x4 matrix of cells. From the Renogy site, the 200W kit each panel has a 4x8 matrix of cells. On mine, there is one label. On Renogy's site, the picture they show of the back side of the suitcase shows a label on each panel. I can't enlarge it enough to read what is on the labels though.

One thing that indicates that it is not a 100W unit is that you have already seen greater than 6A output. The short circuit output of mine is 6.1A with 5.68A optimum output current. I'm pretty sure that the sticker in your picture indicates the current output for one of the panels, not both panels.

Is the output of the PWM controller 12V? If so, then you did get what you paid for as did I. Why it would be labeled that way is up to Renogy to explain. You are getting the watts you paid for.

These are the specifications I found on Amazon for the panel:

As I said, that is a question for Renogy to answer. I have not measured the output of my panels so I would not be able to say whether they are 6V or 12V. What you purchased is a "200 Watt Eclipse Monocrystaline Solar Suitcase. I do not see anywhere in the description that shows that each panel is 12V. If, as you state, each panel is 6V, then wired in series would give you 12V. It is possible that the two panels in my 100W Eclipse solar suitcase are also 6V in series to deliver the rated 12V, 100A. However, the most likely explanation is that somehow, the wrong label was placed on the back of your panels. The fact that the panels you received match the dimensions that I posted and not the dimensions on the label in your picture are another indicator that the wrong label was pasted on the back of your panel.

Edit: See pages 14 and 17 in your manual for the correct specifications.

I'm not sure. Since I have the solar suitcase, it would make no sense to separate them for use. I'm not a solar engineer though, so I don't have the answers to some of these questions. If it were two separate panels, I could see your point. In that case, they would be connected in parallel. The suitcase is made to be used as a suitcase, so connection in series is not an issue. The panels are not meant to be used separately. That is purely my opinion though. To get the full answer, you would need have someone much more knowledgeable and/or get it from Renogy.

Victron has a pretty good white paper on PWM vs. MPPT.

http://www.victronenergy.com/upload/documents/White-paper-Which-solar-charge-controller-PWM-or-MPPT.pdf - http://www.victronenergy.com/upload/documents/White-paper-Which-solar-charge-controller-PWM-or-MPPT.pdf

I am adding a 100W panel to TV roof rack which will pump a few more amps to battery bank while under way and easily be deployed in campground. No reason not to have multiple controllers feeding battery bank as far as I can tell.

fwunder, Have you disconnected one panel and tested? Getting 10amps would be too much for two 6v panels to achieve. 

I'm not sure I follow. I did test voltage @ both PV junction box @ 9.75v with panels disconnected.

And, your two modules certainly appear to be connected in series, so that would imply that the modules are 6V nominal. Voc (open circuit voltge) of the cells should be around 0.6V so your 10V per module measurement would imply that there is a 16S by 2P  series/parallel cell configuration internal to the modules. 

Can you take  a photo of the front of one of the modules and post it? It should be possible to trace the internal cell connections if the resolution is good enough.

Originally posted by offgrid They feel that parallel cell connections help mitigate shading issues (they can)?

What meant by "they can." or "they can?"? The sentence is a bit ambiguous. Please clarify how that works. I have the 100W setup, so mine is 32 cells. 32x3=96 watts, which rounds to 100. I am guessing from what you wrote that my modules are also 6V nominal and the two panels connected in series would make the kit 12V. Am I correct in my understanding?

This was whole whole point of me bringing this up in the first place. Thank you.

Yes I was deliberately vague about how paralleling cells can reduce shading impacts, because its a little complicated. What happens is that if you have a long string of cells in series, shading one cell can block current flow through all the other cells in that string. So, imagine a leaf that covers one cell, that can take out the whole module, or more than one module in a higher voltage system. That's what bypass diodes are for (the devices in the photos of the module jboxes). They allow current to bypass around shaded cells or groups of cells. 

By placing the cells in parallel you reduce the impact of shading individual cells, because the cells can share current between them. This works especially well if the parallel cells aren't directly next to each other so it becomes less likely to shade both of them at once. There are drawbacks too, the currents are higher so the bypass diodes (the devices in the photos of the module junction boxes) have to be larger. 

That's probably enough solar 202 (you already passed 101!) unless you really want more. Sorry you can't do the MPPT controller and use a lighter gauge wire. But, at least you are getting a reasonable output from your system. To answer your original question personally don't use Renogy stuff because I think its overpriced for what you get. If the size works for you, the best deals in solar are going to be standard 60 or 72  6 inch cell residential or industrial modules. with an MPPT to take that down to 12V. Often those can be had from CL or Ebay for less than 50 cents a watt. 

Back to my suitcase...It's really not all bad news. These panels really do perform.

Thanks for the education! Still learning!

Sorry about not being able to convert to an MPPT for those modules, but maybe you'll make up for it a bit when're camping in partial shade someday.