Solar expectations - panel output seems low - Fiberglass RV


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Old 06-24-2012, 03:52 PM   #1
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Solar expectations - panel output seems low

Got my amsolar GS100 panel wired up today. I'm using a Morningstar ProStar PS-15 for the controller. Everything is working, but I'm disappointed by my early results.

It is supposed to be a 100 watt panel that under ideal conditions could produce 5.7 amps (Ipm rating). Today is a pretty hot and sunny day up here in Wisconsin. I'm getting 1.4 amps max off the panel so far. Measured it with the TriMetric 2025RV, but then just used my meter to measure right off the back of the panel as a sanity check.

The panel is just laying out on the driveway, no shadows, and I've tried angling it at various levels to maximize the power. Out of curiosity I also took a winter scarf and covered up sections of the panel to see how that influences things. Sometimes it seems to halve the power, but other times it has very little impact. Wiring is 22' of 8 gauge umbilical to the charge controller. Then into the bargman trailer connector.

Is this much power loss expected? I figured there would be some degradation, but was expecting to get in the 3-4 amp range under such conditions and I'm barely half of that.

I'm going to chat with amsolar on Monday, but just wondering what other experiences folks have had with solar.
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Old 06-24-2012, 04:03 PM   #2
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I assume that you have the panel connected to a battery. The amount of charge in the battery also determines how much current comes from the panel/charge controller. It the battery is at full or almost full charge that about what you can expect. If the battery was to be run down to near the discharged point your current would be much higher.
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Old 06-24-2012, 04:29 PM   #3
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To follow Byron's comment you could put heavy load on the battery to discharge it and then test it again. Charging current will vary dramaticly with battery's state of charge.

George.
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Old 06-24-2012, 05:13 PM   #4
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John,

Try measuring the short circuit current. Short Circuit current is the highest current the panel can produce. Simply put your meter at it's highest current setting between the two leads of the panel.

Do not, I repeat do not do this with the panel connected to the battery. This test is a test of the panel only.

The test takes just the panel and the highest current range of your meter.

As well, with no load on the panel measure the open circuit voltage. This should be the highest voltage the panel will produce. Do this test on the voltage setting of your meter.

These two readings will give a fair measure of the panel.
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Old 06-24-2012, 06:14 PM   #5
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John,

Try measuring the short circuit current. Short Circuit current is the highest current the panel can produce. Simply put your meter at it's highest current setting between the two leads of the panel.

Do not, I repeat do not do this with the panel connected to the battery. This test is a test of the panel only.

The test takes just the panel and the highest current range of your meter.

As well, with no load on the panel measure the open circuit voltage. This should be the highest voltage the panel will produce. Do this test on the voltage setting of your meter.

These two readings will give a fair measure of the panel.
That would work, 10Amp range or higher.
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Old 06-25-2012, 08:38 PM   #6
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Thanks for the tips!! Today was a completely clear day and I tested the panel at about 1:30pm in prime sunlight.

Open circuit voltage measured = 20.9 volts (Voc rating was 21.2 volts)
Short circuit amps measured = 6.16 amps (Isc rating was 6.10 amps)

So I can clearly conclude that the panel is working just peachy. Big relief as I was not looking forward to trying to package that up and return it.

The TriMetric 2025RV indicated the battery was at 84% when I tried the charging test yesterday where it was only drawing 1.4 amps.

I think my next couple of simple tests are:
a) drain the battery down to 60% or more and give it a test then
b) try eliminating the bargman wiring and go straight off the controller to the battery
c) eliminate the umbilical and just try panel to the controller to the battery (maybe my splicing attempts aren't that great after all)

I suspect that (b) may be adding a good 20' or more of 10 or 12 gauge copper wiring as the trailer umbilical goes all the way to the distribution panel in the back of the scamp and then separate wires are run back out to the battery (vs. splitting off the battery supply immediately once it enters the front scamp closet). Access is really hard to see in there so I can't discern which of those it is, but this is a really simple test.
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Old 06-25-2012, 09:43 PM   #7
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Wiring...
I go straight from the controller to the battery and leave the rest of wiring alone. I'm using AWG 12 because that's what I bought to run my Ham radio and am using some the same wire. Very seldom will you be charging with the full 6 amps.
You don't need to use the "out put" or "load" connections on the controller.
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Old 06-25-2012, 09:56 PM   #8
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Wiring...
You don't need to use the "out put" or "load" connections on the controller.
I agree, all my 12VDC load connects directly to the battery. I don't know if connecting a load to solar charge controller "out put" or "load" would still be usable at night.
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Old 06-25-2012, 11:13 PM   #9
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I agree, all my 12VDC load connects directly to the battery. I don't know if connecting a load to solar charge controller "out put" or "load" would still be usable at night.
George.
I think the only reason for using that out put is so the little LED can tell you that your battery is low.
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Old 06-26-2012, 01:14 AM   #10
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I think the only reason for using that out put is so the little LED can tell you that your battery is low.

Which is the whole reason for having a monitoring system in the first place. I am connecting my trailer to the load terminals so I can get accurate feedback on how much power I have used and how much I have left.
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Old 06-26-2012, 10:03 AM   #11
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Which is the whole reason for having a monitoring system in the first place. I am connecting my trailer to the load terminals so I can get accurate feedback on how much power I have used and how much I have left.
That's your choice. I'm only pointing out that it's not necessary to use the "load" output. The most important thing is how well the charge controller charges and maintains the charge on your battery. The rest is "bells and whistles". If like "bells and whistles" and want to pay the price for them, there's no problem. Sales people will always try to tell you, you need the "bells and whistles" when you don't really.
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Old 06-26-2012, 10:59 AM   #12
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I agree, all my 12VDC load connects directly to the battery. I don't know if connecting a load to solar charge controller "out put" or "load" would still be usable at night.
George.
I need to correct myself regarding night usefulness of a “Load” output on a solar charge controller. I thought, it was just voltage controlled solar panels output not a battery output. Somehow I failed to realize usefulness of powering a trailer via solar charge controller.

These controllers are usually 10-15 amp range with small terminals which is perhaps insufficient to meet peak DC power consumption between lights, furnace, TV/notebook and water pump. If a trailer is only equipped with LED lights than even portable 5-10W solar panel (a car dashboard one like) should suffice.

Monitoring a battery via current>mV shunt at the battery with monitor such as Link10 or Trimetric is a safer route.

George.
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Old 06-26-2012, 02:04 PM   #13
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A system monitor like the trimetric is great and the best for larger systems. BUT a trimetric is relatively expensive. A 30 amp controller with a digital load monitoring readout is very cost effective and should be sufficient for single battery/panel systems.
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Old 06-26-2012, 02:17 PM   #14
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A system monitor like the trimetric is great and the best for larger systems. BUT a trimetric is relatively expensive. A 30 amp controller with a digital load monitoring readout is very cost effective and should be sufficient for single battery/panel systems.
I agree, the world is full of tradeoffs, cost is a big one.

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