Solar in the rain

[Timber Wolf]

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.

[Timber Wolf]

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.

[jon carpenter]

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

[Marv]

Originally Posted by Timber Wolf

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.

[Timber Wolf]

Originally Posted by Marv

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).

[Gordon in Idaho]

The Sun Will Provide!

Gordon

[Larry,C]

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!

[Mike Magee]

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.

[Timber Wolf]

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.

[Mike Magee]

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.

[Timber Wolf]

Originally Posted by Mike Magee

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.

[Gordon in Idaho]

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

[Timber Wolf]

Originally Posted by Gordon in Idaho

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

[gordon2]

Originally Posted by Gordon in Idaho

...

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.

[Marv]

Tim, thanks. Very interesting thread.

[ruscal]

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

[Gordon in Idaho]

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

[Steve L.]

Originally Posted by gordon2

...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.

[Timber Wolf]

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.

[redbarron55]

It's like it was a CAT a lytic converter