Solar in the rain - Page 2 - Fiberglass RV


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Old 03-30-2016, 10:08 PM   #15
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Tim, thanks. Very interesting thread.
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Old 03-30-2016, 10:17 PM   #16
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A few weeks ago we were camped at Cardiff by the Sea at San Elijo State Beach Campground. The weather was warm and gray. Not really any sun visible through the marine layer. Our usual power consumption for the day and evening leaves our battery at around 88%. (100 amp hour battery). In the mid morning I put out our 2 100 watt Panels feeding into a Morningstar Tristar MPPT controller. The power produced was drastically lower than on a sunny day. Amps in were fluctuating between 1.5 and 4 amps. Our panels are on "kickstands" and placed in un-shaded areas oriented at where the sun would be if we could see it. This system would produce 5+ amps per panel in direct sun.
Nonetheless we got the battery up to 100% by early afternoon. If we would have been discharged to 40% we may not have been able to sustain full charge, but close, since the days are long now.
I'm impressed with the performance of our system, and glad to have experienced some gray days to gather input of what to expect. Solar is amazing!
Russ
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Old 03-31-2016, 11:06 AM   #17
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Thanks, Tim and Gordon, for the info. It isn't light reading, but I get the gist of it. A lot goes on in those expensive little boxes!

Tim, I hope you will keep us posted on your progress. Real world results are very helpful to all of us.


Gordon
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Old 03-31-2016, 11:32 AM   #18
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Quote:
Originally Posted by gordon2 View Post
...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%...
This is exactly how I understand the process with the additional comment that charge controllers don't dump the full amperage into the battery all the way to fully charged. Charging amps drop off, regardless of what is being made by the panel or converter/charger, as you approach fully charged. Which contributes to why it generally takes longer to recharge than to drain. Getting the last 10-15% into the battery seems to take forever.


From a Xantrex white paper on battery charging:


The first stage in the charging process - bulk – is a constant current mode that replaces 80% of the battery’s capacity very quickly. The charger applies its maximum output current, or as much as the battery will take, while the battery voltage rises (see Figure 1). When the battery voltage reaches a predetermined level, the absorption voltage, operation switches to the next stage.

The second stage – absorption – is a constant voltage mode and replaces the remaining 20% capacity. The charger voltage is held steady while the current falls as the battery approaches full charge.

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Old 04-01-2016, 01:47 PM   #19
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First, let apologize for this whole thread. I initially posted due to my surprise that contrary to what I had been led to believe, some not insignificant solar charging can still happen during rainy or overcast days. In subsequent posts I went on to describe what I thought I was seeing each day. Trouble was, my Tracer meter (as I feared) was misleading me, if not outright lying. To back up a little, I lost the percentage of charge function on my Bogart Trimetric meter when I disconnected the positive lead from the battery to connect the solar charge controller. Nothing against the Trimetric, that is how it works and they say so in the instructions.

So during much of this sorry episode I had to (or at least did) rely on the controller’s (Tracer) meter for percentage of charge information. Both meters (Tracer and Trimetric) would show the same instantaneous, real-time charge information (volts and amps) so I had no reason to doubt the Tracer meter for percentage of charge or State Of Charge (SOC) data. Before I disconnected the power the Trimetric indicated a 44% SOC. Yes I know that is bad and I don’t like letting the batteries get that low but in the interest of “science” I let it go.

Well, yesterday (Thursday, day 5 of the test) morning I go down and look at things before I leave for work, the Tracer shows 13.1 volts on the batteries and a 69% SOC. The Trimetric showed 13.2 volts and no SOC (yet). Note that this was not charging voltage but condition of battery voltage. Those numbers rolled around in my head yesterday and I came to a conclusion. With that much voltage (13+) showing on a 12V nominal battery bank there must be a higher SOC than I was seeing. When I got home last night my supposition was proven correct.

Last night the Tracer still showed 13.1V but was up only a whole dadgum 1% to 70% SOC. Hummmm? Stepping in the trailer I started pushing buttons on the Trimetric and saw about the same volt reading but the SOC had woken up sometime during the day and was showing 100%! This is how the Trimetric works; it has to “see” a full charge on the batteries before it knows what full is. I think it actually can refine and get a more accurate SOC as it sees a series of discharge/charge cycles over time but that math is above my pay grade.

To sum, it is hard to do real science when your instruments are misleading you. Or perhaps the basis of real knowledge and wisdom is to question initial results? Or to at least question anything you read on the internet? Again, that philosophical discussion is above my pay grade. In any event I am pleased with the eventual result, batteries (apparently) fully charged with “free” power. I suspect that they were very close to fully charged Thursday morning, which would have been after two very sorry charging days (rain and overcast) and three more good (sunny) days, even with the panels poorly oriented and laying on the ground*. Next step is actual boondocking/dry camping with the panels. That will be a far better test starting with fully charged batteries and actually using power during our usual camping routine.


*I don't know what it was about the solar panels laying on the ground but they apparently attract cats. I would come home to find cat foot prints on the panels some days. One day there was loose fur on a panel, like a cat sat there and groomed themselves while on the panel and maybe static made it cling? One morning after putting the cat out of the house and going down to look at things I turned around to see her (the cat) dancing on a panel and chasing her tail in a circle. I hollered "GET OFF THAT PANEL" and she ran. Dang, no telling how that messed with my experiment and how much solar charging I lost with a dadgum cat blocking my panels.
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Old 04-01-2016, 02:48 PM   #20
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It's like it was a CAT a lytic converter
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Old 04-01-2016, 06:12 PM   #21
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Tim,

See? There's another reason to mount your panels up on the roof! Cats, dogs, small children, feral pigs, etc., they all love solar panels.

Seriously, I read that even a small shadow like a flag pole will drastically reduce your output.


Great story! Thanks for sharing that.

Gordon
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Old 04-01-2016, 06:29 PM   #22
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Tim,
Certainly no need to apologize. Very easy to be misled by our instruments. Looking forward to your dry-camping test results.
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Old 04-01-2016, 06:49 PM   #23
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Originally Posted by redbarron55 View Post
It's like it was a CAT a lytic converter
Beautiful....coffee came out my nose, on reading this. Great thread, so happy seeing how fascinating this subject has become. Sort of gives me a kick, learning about solar, the way computers did it for me, in the early 90's.
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Old 04-01-2016, 10:46 PM   #24
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Oh wow. Well, if it's a cool day, a cat will often seek out a warm spot to lie down. Black solar panels would be warm! I suggest propping your panel at enough of an angle to discourage animals, and you'll probably have a better angle on the sun at the same time.
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Old 04-02-2016, 09:22 AM   #25
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To wrap things up and in the interest of full disclosure I report that this morning the Tracer finally showed 98-100% SOC (it jumps back and forth between the two readings). To be fair, the Tracer is a $35 meter and the Trimetric a $175+ setup with the shunt. Both appear to work fine and are accurate for instant readings of charging.


I installed the Trimetric with the intent of installing the 30 amp Bogart controller at some point if I wanted to add a third panel (300 watts total). If two panels do what I need I may put off that purchase and just keep on with the 20 amp Tracer controller.
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Old 04-02-2016, 10:19 AM   #26
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I was interested to read you have a MPPT controller verses a PWM one. I am just about to upgrade my solar controller for this season and was planning to get the PWM one as it is supposed to help batteries last longer among other things. It also happens to usually be slightly cheaper. I'm curious to know why you preferred the MPPT controller. What advantages did you see?
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Old 04-02-2016, 07:16 PM   #27
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Originally Posted by ckayaker View Post
I was interested to read you have a MPPT controller verses a PWM one. I am just about to upgrade my solar controller for this season and was planning to get the PWM one as it is supposed to help batteries last longer among other things. It also happens to usually be slightly cheaper. I'm curious to know why you preferred the MPPT controller. What advantages did you see?
It has actually been quite a while since I bought this setup. I got a little ahead of myself buying stuff before being ready to use it. Seems like the MPPT should more efficiently use the power from the panels. Bogart seems to think MPPT is not worthwhile and PWM is fine.
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Old 04-02-2016, 07:49 PM   #28
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The way I understand it, a PWM controller will use its pulsing ability to reduce the solar panel's voltage output to the voltage desired for charging the battery; if the voltage is being stepped down from, say, 17V to 14V the potential of those 3 extra volts is wasted. MPPT controllers can convert most of that extra voltage into extra current (I'm over-simplifying somewhat) to hasten charging a little bit.

I've read that although MPPT will squeeze out this little bit extra charging current, the MPPT controller will also have a little more loss because it uses a bit more energy in order to function than a PWM controller would use. The general feeling is that for small solar systems there's no net advantage to MPPT, but with 400W-500W or larger systems the MPPT should definitely come out ahead.
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