Solar in the rain - Fiberglass RV


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Old 03-28-2016, 01:51 PM   #1
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Solar in the rain

Went camping a week back and was a little sorry getting the rig put up and plugged in when we got back. We got in kinda late Sunday and had to be back to work/school Monday morning so the trailer sat behind the house still connected to the truck awaiting bed stripping and fridge unloading. I was in and out of the trailer and fridge a little Monday through Thursday in the evenings until I finally got the trailer backed under the Scamport and the truck disconnected. As the fridge (Truckfridge TF130) had been running for several days just off the batteries (two 6V 220 AH) they were down to 44%. Instead of plugging in I figured this would be a great time to hook up my solar stuff and see what it would do in a sho-nuff charging situation.

I had turned off the fridge Thursday and Friday when I got home from work I hooked up the Renogy (Tracer) 20 amp MPPT controller, remote meter, and two 100 watt panels with appropriate wires and fusing. The panels are on 25’ #12 wires and just laying out in the yard on the grass as far as I could get them away from the Scamport. At noon and all afternoon the panels are unshaded but the Scamport and tree canopy block things a little till noon. As luck would have it, it rained all day (and I do mean an all day, good soaking rain) Saturday and Sunday. The results were interesting nonetheless. I would go down (in the rain) and check the meter periodically both days and was a little surprised to see that some minimal charging was actually going on. It might only be .10 (point-tenth), .20, or .30 (wee!) of an amp but it was doing something. On Sunday at one point it was less cloudy and even in a pretty good down pour the meter was showing charging of .70 amp (we are charging now!).

If the meter is to be believed, and I am not sure it is, I got back 5 to 6% of the battery bank’s capacity just in that two poor days of charging (with no loads except minimal parasitic). It will be interesting to see how things did today as it is a pretty nice day. This morning I did shift the panels over a couple of feet to shade some different grass but other than that there is no change in the setup. Will report more later.
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Old 03-28-2016, 08:07 PM   #2
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Got home late tonight around 7:30 and the panels were in full shade so were not doing much. However the meter showed that the batteries had gained another 6-7% of capacity. So, the take-away is that two rainy days equals one sunny day, at least this time of year. I was not expecting that.
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Old 03-29-2016, 01:31 PM   #3
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Tim,
I have been thinking about purchasing a solar unit to supplement our battery when we boondock. I wasn't sure how well it would work in the shade and/or the rain. Think you answered my dilemma. I feel more confident now about it. Good information provided.
thanks....jon
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Old 03-29-2016, 02:04 PM   #4
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However the meter showed that the batteries had gained another 6-7% of capacity. So, the take-away is that two rainy days equals one sunny day, at least this time of year.
Hi Tim,
I'm not sure I understand. Are you saying that on a sunny day you expect to gain about 14 percent of capacity? I would have thought that 200 watts with MPPT would give much better performance. I have seen reports like "the batteries were full by noon." Your batteries were pretty far down and it is barely spring season, but at that rate it will take a few days to recover from that one episode.
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Old 03-29-2016, 03:34 PM   #5
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Hi Tim,
I'm not sure I understand. Are you saying that on a sunny day you expect to gain about 14 percent of capacity? I would have thought that 200 watts with MPPT would give much better performance. I have seen reports like "the batteries were full by noon." Your batteries were pretty far down and it is barely spring season, but at that rate it will take a few days to recover from that one episode.
The batteries charged about as much (actually a little more) in one sunny day as two rainy days. It was not clear that I was surprised that a rainy day apparently charged at 50% the rate of a sunny day. In other words, I got more charging on a sorry (rainy/overcast) day then I had previously thought/been led to believe was possible.

I think those people saying they were charged by noon were not nearly as far down as I was and probably had a much better panel situation (orientation/shading). Note that I let things go five days before I shut the fridge off and even started doing any charging. Not a situation I would ever willingly get into if actually camping and depending on 12V power. My panels laying on the ground in a poor orientation are far less than ideal as well. My current test is little more than "this is what happens in this situation" which may not be very applicable to another situation but I am finding it enlightening (pun intended).
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Old 03-29-2016, 05:52 PM   #6
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The Sun Will Provide!

Gordon
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Old 03-29-2016, 08:33 PM   #7
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It never seises to amaze me how much charge I get on cloudy, rainy days and shady campsites. I actually look forward to rainy days to rinse off the panels. I really don't like to see my batteries lower than 80% though. Some say I am over paneled but I don't use a converter and I like to use electricity. We just got back from 12 weeks on the road with more than 50% of the time boon docking and only once did the meter show less than 80%. I love solar power!
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Old 03-29-2016, 08:38 PM   #8
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I would have expected you to gain back about 1/3 of your battery charge in one sunny day. It should have been picking up about 8A/hour at mid-day, I think.
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Old 03-30-2016, 12:22 PM   #9
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I think the meter is lying to me or at least messing with me. Last night I looked after another sunny day and it showed a gain of 9-10% capacity. I looked again this morning before leaving for work and it showed a 12% LOSS from last night! With nothing on in the trailer this has to be bogus. I should mention this is the Tracer meter for the controller. I have an expensive Trimetric in the trailer also but it lost the charge percentage function when I disconnected the battery to hook up the solar stuff the other day. The Trimetric has to go through a "full" cycle to tell what the charge percentage is after that. So, I don't really know much about the current state of my batteries. I do know something (charging) is going on though. I will give it until the weekend and hit it with the PD Charge Wizard.
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Old 03-30-2016, 05:41 PM   #10
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Did your panel come with a diode built in, to prevent backward flow of current? If not, it could actually leach power from the battery at night.
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Old 03-30-2016, 07:07 PM   #11
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Did your panel come with a diode built in, to prevent backward flow of current? If not, it could actually leach power from the battery at night.
I think I saw on either the panel or controller info that it prevented that. It showed another good day of charging but I don't really know what is going on. I will do better next time with the Trimetric fully up I should know more about what is going on. I am planning a two or three night boondocking trip soon and that will be a better test with starting fully charged and charging as we go.
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Old 03-30-2016, 08:20 PM   #12
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Assuming the diodes are present, how are the batteries? You might try disconnecting the battery bank at dark, testing with a voltmeter, and testing again in the morning. I don't know about your meter, perhaps it's reading a float charge, and then the voltage drops overnight? In order to properly test a battery's voltage, it must be idle for a few hours, nothing in or out.

I'm not an expert on this, but maybe a little experimenting with this might provide some answers.

I'd like to know how a meter like the trimetic can read percentage of charge. Anybody know?

Good Luck

Gordon
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Old 03-30-2016, 09:04 PM   #13
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I'd like to know how a meter like the trimetic can read percentage of charge. Anybody know?
Here is a link to the FAQs on the Trimetric:Frequently Answered Questions - Bogart Engineering
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Old 03-30-2016, 09:10 PM   #14
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...

I'd like to know how a meter like the trimetic can read percentage of charge. Anybody know?

...
Well, overly simplified, starting from a fully charged battery, it counts the electrons going into the battery and also the number coming out of the battery (or the amps I should say). Take 10 amps out, then put 10 amps back in (plus typically 10% more to account for charging inefficiencies), and its back to 100%

They have a lot of documentation that is really worth the read even if you don't buy their meter (or solar charger). See section 6.2 of the manual for the specifc answer to your question.

I have to wonder if the voltage is getting high enough in the rain to get the battery charged. In rain type situations, I have seen the TriMetric show that the solar is charging but when it gets close to charged, the percentage increases more slowly.
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