Solar, worth it in my case?

Almot wrote:
. Once or twice I saw the dark panel dragging the total output close to what one bright panel alone would deliver, if left alone.

That's what I would expect.

I guess we all have different results. I was given dire warnings about panels in series, but, I have not seen that. Of course the output drops, but not to the extent to which I was warned. I guess lots of folks think back to the Christmas light strings in series.

Anyway, it's somewhat moot as my array is rarely shaded, and then only partially by my a/c hood. Unless I wanted to rewire my coach from roof to basement, I had to go series.

2oldman: my 2*24V panels are in series and have 4 bypass diodes each. I didn't do extensive shade testing, but when total voltage dropped from 60 to 30 (which means one panel is out or almost out), the amps dropped a lot. Though with only 2 panels, when one is affected a lot, the amps are expected to drop a lot. Once or twice I saw the dark panel dragging the total output close to what one bright panel alone would deliver, if left alone.

In a little shade testing that I did on a single panel, the output of one panel dropped proportionally to the shaded area, but at some moment the output dropped completely while the shade was between 70% and 80% of panel.

Now when I think about it, if one of 2 panels is affected so much that its "almost out" - say, more than 75% of area is shaded and/or the shade extends over all 4 strings - the total output would drop in half of course.

you might consider some portable panels. I have 200W of portable panels with MPPT controller and 100ft of #10 cord. Lets me get to sun almost anywhere, each panels is easy to carry/store. With this I can generally get to 100% charge early in the afternoon. On the occasions where it is cloudy for a few days, one good day of sun gets us to full charge on 4 T-125's. We have LED lights but do run fans etc and the microwave off inverter when needed. Are careful but not anal about power usage, Last Sept we camped for two weeks using furnace in the am, fans in the afternoon. After two weeks of only a part day in the sun I was down to 75% SOC (25%DOD). Other than runnning the AC we don't need the generator anymore.

upside of portables: put them where you want and park in the shade, easy to orientate for max power,

downsides: they can "walk away", need a place to store them, don't charge when traveling, cost more to start with.

Almot wrote:
"Any panel will generate less power when partially shaded or in low light". Should've limited the "treatise" to this one line perhaps...

:)

Logic would dictate that the only way one panel could be less affected by shade than another would be its efficiency.

Almot wrote:
If your array is made of panels wired in series, and one has dropped to 0.3 of its capacity, then all other panels will also drop to 0.3 of their capacity,

I'm going to have to take issue with this statement. As you're probably aware, my 6-panel array is wired in series. After extensive shade testing, I'm not seeing the kind of degradation you've described.

Bypass diodes in the panels do a very good job of ensuring the entire string is not killed by shade on one panel. Now, if panels do NOT have bypass diodes, then your statement would, in all liklihood, be true.

Well, I knew it was too long post to read :)...

That's why I said somewhere in there: "Any panel will generate less power when partially shaded or in low light". Should've limited the "treatise" to this one line perhaps...

sjturbo wrote:
Can you tell me what the actual difference? Also I am not aware of panels that can be shaded and not have their performance degraded. Anyone?

If Almot's treatise is not definitive, no. I'd have to look it up using my old friend.

sjturbo wrote:
I was aware that grid means the household electric grid but I did not know that there was any difference in the panel itself. Can you tell me what the actual difference? Also I am not aware of panels that can be shaded and not have their performance degraded. Anyone?

As others said, amorphous panels work better in low light or partial shade. The drawback is that they are waay less efficient per sq.ft, like Full Mosey said "require more real estate". So unless you always camp in the shade, I don't think it's worth it.

Crystalline panels are more efficient per sq ft, and mostly you will see this type in solar stores. They can be poly- and monocrystalline. Poly is said to be "somewhat" more efficient in low-light, but I don't think this should be the deciding factor.

"Low light" in case of crystalline panels should not be confused with "partial shade" - the latter is when part of the panel is shaded and the rest is in bright sun, and this is where the layout of the panel is important. I haven't heard of panels distinguished by "grid" and "non-grid". Usually people describe the panel by its nominal voltage (i.e. 12V or 24V), and cells layout i.e. a number of strings of cells and number of diodes between them.

In more details on myth of "considerably" or "completely" degraded production of panels in partial shade. Again, we should distinguish between multi-panel array when some panels are in partial shade, and a single panel when part of this panel is in shade.

Single panel: the higher is the number of diodes, the better it handles partial shade. 2 is considered "not good enough", 4 and more is considered "enough". Though manufacturers, especially no-name Chinese panels that have flooded the market, rarely tell the number of diodes. So I suggest you forget about this. Any panel will generate less power when partially shaded or in low light.

Muti-panel array: let's say one panel in array dropped out of production because it has only few diodes OR because it's almost entirely in the shade. Doesn't matter why - the panel is out or almost out.
A) If your array is made of panels wired to each other in parallel, you will only lose production of this one panel. So if you have 6 panels and one is down to 30% of production, you lose 1/6 of 0.7, or 11% of total production. This peanuts, nothing.
B) If your array is made of panels wired in series, and one has dropped to 0.3 of its capacity, then all other panels will also drop to 0.3 of their capacity, so you lose 70% of total production. Not always, but for simplicity this is how you should think of it. Imagine a series of pipes where one is partially blocked to 0.3 - the entire pipeline capacity drops to 0.3 of initial.

I hope this wasn't too "technical". In case if it was, just remember that when you have many panels with frequent shading on some panels, it's better to wire them in parallel. Not absolutely necessary, but better.

Another thing to remember is that you can never have "too much" solar. Get as much total panel wattage as possible. When you have a lot of total wattage, you may forget about "pitching" (called, btw, tilting). You can increase production by 30-50% by tilting, and you can increase it by adding more panels.

There was a good suggestion to make "dummies" out of cardboard and see how they fit. After you've figured out how many panels and of what wattage you will have, people will tell you what controller you should get. You will find panels dimensions in places like http://www.solarblvd.com. Note that there are 12V nominal and 24V nominal panels - I think for installs 500W and larger, 24V panels would work better, and your 5-er allows at least that much. With flat array (= not tilted), size 600W or larger, in AZ you should be able to live off solar without ever needing a generator, other than when you need airconditioner. A/C is the only thing that solar can't handle. Some people can live off 300-400W in places like this. Depends on whether you're trying to conserve energy or not.

And, - no, this is not the forum where people usually discuss solar. I don't think this is something curved in stone, it's just the way people here got used to it.

Thanks 2oldman! I was aware that grid means the household electric grid but I did not know that there was any difference in the panel itself. Can you tell me what the actual difference? Also I am not aware of panels that can be shaded and not have their performance degraded. Anyone?

Amorphous panels are more productive in shade or low light. However, they use up more roof real estate. Mono has highest power per area covered. See, it gets complicated when you ask questions!

Grid may as well mean MPPT required. It is voltage per panel.

HTH;
John

I didn't mount mine on the roof, but that might happen in the future. Just got into solar this last winter out at Quartzsite and only have 1 140w panel. When I get more panels they might go up on the roof. But IMO there's just to much loss flat on the roof for 1 panel, and due to physical problems I can't get up there to tilt them. So my answer, for now, was to build a mount and mount it on the rear of the TT. That allows me to tilt it to face the sun or disconnect the mount and use it as a stand on the ground. 1- 140w panel will charge my 4 gp24 batteries by around 1-2pm. That allows us to watch sat tv, or whatever, till we go to bed. I still run our EU3000si for 1-1.5 hrs at night before 10pm to top the batteries because I use a CPAP. For charging I use a PD9260 converter.