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Solar on Roof -- How You Park-Series vs Parallel ? UPDATE

BFL13
Explorer II
Explorer II
Update 8 March
--------------

Got my second 255w on the roof and went camping where I could check it all out. Solar here in January with such low sun angle is not worth much, but I was able to get some (IMO) interesting measurements.

I have a 255w at the back sloped down a bit and another up front flat. Between I have the three 100s flat. (see photo in profile--wood shows where three 100s are in the middle. New 255 in front of that, old 255 in back by cargo rails driver's side)

The back 255 is on an Eco-Worthy MPPT 20 amper and the front 255 is on a Tracer MPPT 20 amper where the controllers are in parallel on the battery bank. The middle array of three 100s in parallel, is on a PWM Solar30 amper also in parallel on the bank. ( I will add a photo of the roof if that works out)

No solar in the woods at the campground, but went to the library in town. I was parked nose down a bit on the street. Sun was toward the back, favouring the back 255.

I got, back to front:
3.43a, 3.8a, 2.9a. ( total = 10.13) Trimetric said batteries were getting 8.4 amps so load was 10.13-8.4 = 1.19a

I wanted to see what happened if parked more level, so I moved the C to where it might be better. Sun a bit more to the side too. (Also note it was closer to high noon by then, so amps better) This time I got, back to front:
3.86, 4.4a, 5.2a (total = 13.46)

So now the front 255 was doing better. Hmmm, what would all this be like if I had the panels in series all on one giant controller, so amps would depend on the lowest amps panel? Oops?

If I understand it, in the second example, if I only had the two 255s, I would get two 3.86 = 7.72a instead of 3.86 + 5.2= 9.06a as I got with them in parallel.

I then went to a place where it turned out one of the 255s was shaded and I got nothing from it, but got 4.56 and 4.4 from the other two arrays. If they were the usual set-up all in series, and that end of the roof were shaded, what would I have got?

So all in all, I know about the wiring to be saved and don't park in the shade in the first place, but still---I think I am better off as is.

These low amps don't mean much for differences between them, but in summer at full amps that could mean significant amps.

I think maybe there is more to the story about series vs parallel. A typical RV roof is not flat, but part of it slopes down at the back, so it can depend on how you are parked wrt to the sun, which is the "weakest" panel that will set the pace if they are in series.

Never mind the ugly mess, I don't care about it. It works!



BTW a previous owner tossed the air conditioner and put in a fantastic fan, so that is what you see. I don't have rain cover for it, but could if wanted( not needed) Panels cover two skylights (don't care) and part of the fridge vent cover, no problem. Roof is a mess of Eternabond bandages I did, plus Dicor goops as required. ๐Ÿ™‚ It is how it is!
1. 1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
Photo in Profile
2. 1991 Bighorn 9.5ft Truck Camper on 2003 Chev 2500HD 6.0 Gas
See Profile for Electronic set-ups for 1. and 2.
21 REPLIES 21

BFL13
Explorer II
Explorer II
Two months later, sun is higher and the "issue" did not appear this week as in the OP with sun lower. Front and back 255s about the same amps when parked level and towards or away from sun.

Next time with sun even higher should be the final proof, but so far, it seems the OP was a false alarm based on it being January and the angles involved being such a high proportion of the sun angle factor.
1. 1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
Photo in Profile
2. 1991 Bighorn 9.5ft Truck Camper on 2003 Chev 2500HD 6.0 Gas
See Profile for Electronic set-ups for 1. and 2.

BFL13
Explorer II
Explorer II
The OP measurements need to be repeated in a couple of months when the noon sun is higher. I might have jumped to conclusions. We'll see.
1. 1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
Photo in Profile
2. 1991 Bighorn 9.5ft Truck Camper on 2003 Chev 2500HD 6.0 Gas
See Profile for Electronic set-ups for 1. and 2.

ajriding
Explorer
Explorer
So,if you run in series your voltage goes up and amps down relatively.??
You would do as said, run two in series for 24 volt, then another two for 24 and run those parallelโ€ฆ

What do you have to need so much panels?

I have never thought to run a controller for each panel, as one response mentioned, does that do anything other than information? I run my two 100's into one controller and connect at the controller.

CA_Traveler
Explorer III
Explorer III
Thank you, missed those CGs but not the next time!

Love the Campbell River Providential Park.
One night it poured! Got soaking wet checking the kids in their tent who were warm and dry. Another time our daughter was dry on the picnic table under the awning in the pouring rain.

And sunshine the next morning!

Loved the Lady Rose - guessing they don't run her anymore?
2009 Holiday Rambler 42' Scepter with ISL 400 Cummins
750 Watts Solar Morningstar MPPT 60 Controller
2014 Grand Cherokee Overland

Bob

BFL13
Explorer II
Explorer II
CA Traveler wrote:
BFL13,

Hopefully I'll visit your neighborhood again. Where is that CG? And you once posted about a CG with eagles flying around etc, want to share?

We were fortunate to get a tour of the fantastic MARS Water Bomber. And on the same trip a kid was selling wheel barrows full of firewood. ๐Ÿ™‚

You gotta just love British Columbia! ๐Ÿ™‚ :C


This is the campground we like in the summer once it opens in May. It is central for driving around to lots of good places to check out. We use the open field when we go. See map there.

http://campground.qualicumfirstnation.com/north_campground/

From Oct to April we like Rathtrevor provincial park (sites in trees so no solar)

I'll try to post a photo of eagles for you here. They fish in the river. I'm not much of a photographer, but here's one:

1. 1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
Photo in Profile
2. 1991 Bighorn 9.5ft Truck Camper on 2003 Chev 2500HD 6.0 Gas
See Profile for Electronic set-ups for 1. and 2.

CA_Traveler
Explorer III
Explorer III
BFL13,

Hopefully I'll visit your neighborhood again. Where is that CG? And you once posted about a CG with eagles flying around etc, want to share?

We were fortunate to get a tour of the fantastic MARS Water Bomber. And on the same trip a kid was selling wheel barrows full of firewood. ๐Ÿ™‚

You gotta just love British Columbia! ๐Ÿ™‚ :C
2009 Holiday Rambler 42' Scepter with ISL 400 Cummins
750 Watts Solar Morningstar MPPT 60 Controller
2014 Grand Cherokee Overland

Bob

CA_Traveler
Explorer III
Explorer III
My panels come with pigtails and my installation gives easy access to their MC4 connectors. Therefore I could easily check each panel for Voc and Isc and if required bypass a defective panel.

However with a good installation, a 25 year panel warranty and a hands off approach I'm not planning on a roof adventure.

BTW I do get a chuckle and appreciate the OPs twirlers and roof adventures.
2009 Holiday Rambler 42' Scepter with ISL 400 Cummins
750 Watts Solar Morningstar MPPT 60 Controller
2014 Grand Cherokee Overland

Bob

BFL13
Explorer II
Explorer II
I wonder if the large differences in amps per panel wrt to total amps I reported in the OP was more from the sun being so low mid-day.

The minor angle differences of flatness on the roof would be bigger wrt to the sun's angle than if the sun were higher. Perhaps with the sun higher, the amps differences would be less in proportion to the total amps, and become trivial?
1. 1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
Photo in Profile
2. 1991 Bighorn 9.5ft Truck Camper on 2003 Chev 2500HD 6.0 Gas
See Profile for Electronic set-ups for 1. and 2.

CA_Traveler
Explorer III
Explorer III
BFL13 wrote:
Normally, you can't tell how much each panel in an array is providing towards the total array output. After this, I now picture all you folks up there with clamp on ammeters poking at your combiner box inputs to find out! Too bad for those with panels in series and the junction boxes out of reach under the panels ๐Ÿ™‚
I've never had any need to break out the clamp on and the ladder.

I'm more interested in total serial power which is easily checked via watts or amps and volts from inside the rig as desired.
2009 Holiday Rambler 42' Scepter with ISL 400 Cummins
750 Watts Solar Morningstar MPPT 60 Controller
2014 Grand Cherokee Overland

Bob

CA_Traveler
Explorer III
Explorer III
twodownzero wrote:
I'm running 400 watts with an MPPT charge controller. All of my panels are in series now, but I've wondered if I'd be better off with them in 2x2, series/parallel. I believe I would, it'd just take more wiring.
The most shade tolerant configuration is series IF the panels have bypass diodes. Next is parallel. Series/parallel is last since a panel shadow eliminates that series pair (for say a 2x2 array).

Each of my 3x250W series panels have 3 bypass diodes meaning I have 9 panel sections in series. A shadow on one panel section gives me 8/9 of the power. 2 panel sections with a shadow yield 7/9 of the power, etc.

Iโ€™ve posted graphs showing how leafy shadows effect the power output.
2009 Holiday Rambler 42' Scepter with ISL 400 Cummins
750 Watts Solar Morningstar MPPT 60 Controller
2014 Grand Cherokee Overland

Bob

2oldman
Explorer
Explorer
My panels tilt. Easy access to jct box.
"If I'm wearing long pants, I'm too far north" - 2oldman

BFL13
Explorer II
Explorer II
DarkSkySeeker wrote:
How are you measuring the current? Does your charge controller display that? For each batt?


I have three controllers, one for each array as in the OP. Each controller has a display showing the amps it is getting in. The Trimetric monitor shows what the battery bank is getting/accepting out of that total.

The 450AH bank is not split, so all three controllers are in parallel to the one bank. The three are set to the same voltage, so they add their amps.

However, the Tracer does have a two hour time after the batts reach the set voltage, while the others do not have that time limit.

In a long day of solar, after the bank reaches the set absorption voltage and then two more hours, the Tracer will drop to 13.6, so no amps anymore from its 255w panel. By then, the total amps from the other two controllers will likely be more than the bank will accept anyway, so no matter. (Where we use solar, it is ok to stay at Vabs till sundown--no need to reduce to Float during daylight time)

I have this arrangement from using my collection of solar stuff from previous set-ups in previous RVs. If starting from scratch of course you would not do it this way. However, it is from doing it this way that I discovered this OP aspect to the series vs parallel discussion.

Normally, you can't tell how much each panel in an array is providing towards the total array output. After this, I now picture all you folks up there with clamp on ammeters poking at your combiner box inputs to find out! Too bad for those with panels in series and the junction boxes out of reach under the panels ๐Ÿ™‚
1. 1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
Photo in Profile
2. 1991 Bighorn 9.5ft Truck Camper on 2003 Chev 2500HD 6.0 Gas
See Profile for Electronic set-ups for 1. and 2.

pianotuna
Nomad II
Nomad II
The "perfect" panel for RV'ing in the shade would have bypass diodes between each and every cell. Unfortunately the only maker I am aware of that did do that is UniSolar and they have been out of business for a dozen years now.

Since I happen to have them, my system 'punches' above its weight as far as output goes with 256 watts from 4 panels wired in series/parallel for an input of 33 volts. I know BFL13 wants to know my amps at 12 volts--it works out to 17, post controller, if the battery bank is hungry. (voltage circa 15).
Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp-hours of Telcom jars, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

DarkSkySeeker
Explorer
Explorer
How are you measuring the current? Does your charge controller display that? For each batt?
There is something special about camping in an RV.
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