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PostPosted: September 8th, 2017, 5:44 am 
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Btw, my measurements were taken from an MPPT controller which shows Volts and Amps for both input from the panel and output to the battery.

If you can disconnect the solar panel, and have a 10amp multimeter, you can test the panel yourself:

http://www.solar-energy-for-homes.com/h ... meter.html

I recently had a flexible 50W panel that gave up the ghost and started only producing about 0.2A in sunlight. I had to disconnect it because it was dragging down my other good 50W panel.

Kev

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PostPosted: September 8th, 2017, 12:11 pm 
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Just to make things easier (eliminate hard-to-pin-down variables), could you try to do your tests at around noon? Even at noon now the sun is no longer directly overhead, but early September, 6 p.m., and a flat panel is a tough test. A lot of potential power is lost but how much?

(Since my panels at the moment are ground panels, it's easy for me to have them flat, see how many amps are coming in -- with enough demand so that I know they are asked to put out all they can -- and then tilt them and see how much it improves - it's not a small factor.)

There are a number of factors working "against" the stock Chinook system in the best of times, so having the sun as overhead as possible will help the testing by (mostly, since it's not July) eliminating that one.

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PostPosted: September 8th, 2017, 2:45 pm 
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I'll try earlier tomorrow before taking anything apart. it was 3:30pm when I try it today, but there are 1/6 of panel that got shaded. The current was 00.2 according to the read out, with fans and some of the lights on. The voltage was 12.7V.

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PostPosted: September 9th, 2017, 7:22 am 
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Your panel has three long strings of 12 cells each. Each cell puts out about 0.5V at up to 3A (depending on light). The full 36 cells x ~0.5V = 18V.

A shadow fully across a cell turns that cell off. With no current flowing through that cell, the entire string it's in is blocked, and thus the entire string will be bypassed via a diode.

If the shadow is across any full cells on all three strings, the entire panel will have no output. So first off, do not test with any shadows :)

(In the wrong sun orientation, just an open roof vent can severely affect the output.)

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PostPosted: September 9th, 2017, 12:56 pm 
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The Siemens panel is only 15.x volts (one of its downfalls). Okay, that x is just because I'm feeling lazy; let me look up the specs...

Vmp is only 15.9 volts. Modern "12 volt" panels are typically in the 17.5 - 18.9 range, which gives you much more "head pressure" when running a single panel, or multiple panels in parallel (vs. series, where you add voltages).

Originally I figured I'd get new panels, but why not also wire in the original Siemens? Once I saw the specs I had my answer: Putting one much lower voltage panel in parallel with others drags them down; and I couldn't easily use it in a series/pair either. So I just went with modern panels. The good thing is that panels are "dirt cheap" compared to what they used to be. I mean, decent, 100 watt panels for $130 and free shipping on Amazon Prime? That would have seemed like a laughable dream back in the late 90's when these Siemens panels were put on our Chinooks. I can only imagine how much they cost then ($$$).

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PostPosted: September 9th, 2017, 3:25 pm 
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Ah, so Chinook used the Siemens with only 33 cells?

(Really odd number.)

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PostPosted: September 9th, 2017, 4:18 pm 
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Yes, it's 33 cells. One reason it's narrow: Only 3 wide (by 11 long). Here are the specs for the SM50-H, which is ~13" x 48":
Attachment:
Siemens SM50-H specs.png
Siemens SM50-H specs.png [ 77.46 KiB | Viewed 53 times ]


Just for comparison, here are the specs for a sort-of-modern 70 watt skinny panel, the Solarland SLP-070 (formerly -065). This is ~13.5" x 58".
Attachment:
SLP-070 specs.png
SLP-070 specs.png [ 80.02 KiB | Viewed 53 times ]


And for a 100 watt Renogy Eclipse panel (they can be a 32-cell panel vs. a typical 36-cell 100-watter because the cells are more efficient). This is ~20-3/4" x 40-3/4" - very efficient for its size.
Attachment:
Renogy Eclipse panel specs.png
Renogy Eclipse panel specs.png [ 40.93 KiB | Viewed 53 times ]


You can see the Vmp is quite a bit higher on the Eclipse, and nearly as high on the Solarland. This is not as critical if you have a pair in series; but for a single panel or a bunch in parallel, 15.9 volts is kinda low. (But again, 1998 was a loooong time ago, and I'm sure the Siemens panel cost a pretty penny!)

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PostPosted: September 9th, 2017, 8:43 pm 
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I cleaned the panel, and did it in full sun this afternoon. No shadow. It got to 1.4 A on the controller when I turn on all the fans and lights. I guess it is still up to spec consider its age and technology?

When you connect two panels with different voltage (old Siemens with new Eclipse, for example), I think the lower voltage panel will get heat up by the one with higher voltage, and so you will be wasting solar energy, and damage the weaker panel at the same time. This is what the solar contractor told me when he was here to check out my house's roof.

(If any of you want to sell your old Siemens panel, drop me a PM. I am planning to put an extra one up there in series, and get a MPPT controller.)

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PostPosted: September 10th, 2017, 11:00 am 
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I hadn't heard about heating up or ruining; but understood that whichever panel is "lesser" will drag the other(s) down to its level. Not what you want.

But just to be clear, I wasn't suggesting hooking up the Siemens panel with anything else. I think it'd be hard to find any modern panel that would "match" in any way. You could hook up another Chinook panel that someone was discarding, as you mentioned. If it were me I'd just go with new panels, given their incredibly low prices nowadays (but then too, I never had two of the Siemens panels).

The basic idea is that if hooking up in parallel, the voltages need to match (or be within .5 volts or so). So the concept is that if you hooked up the 15.9 Vmp Siemens to a 17.x "modern" panel, you'd be dragging the whole works down, and 15.9 is pretty low - you'd need a real lack of voltage drop to ever get into the absorb stage (14.4 at 77ºF, higher in colder temps). That's the bugaboo of the Siemens in parallel, to my mind (even if two in parallel). If I did want to run two of them, I think I'd make them a series pair with an MPPT controller. Then you'd be inputting closer to 32 volts and have some "headroom."

It does somewhat depend on your use case and goal for the system. Battery maintainer when parked unused? Boondocking? The "trickle" of amps from the Siemens would be decent for maintaining, although I still wonder if it could make absorb stage (necessary to get from 85% to 100% charged) with the lossy stock wiring setup.

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