New Solar Install

[oldjohnt]

Jack,

 

Thanks for your inputs, I certainly agree with a "whole system" approach with respect to most all sorts of electrical designs and installations. You cant just look at a single solar panel or charge controller and make a decision. In my relatively small system with say four 100 Watt 12 volt panels, my most preferred choices would be wire them all in series for 48 volts (not as high as a 100+ volt system) or perhaps two in parallel (12 volts) in series with another two in parallel for 24 volts down to the controller. In order to reduce voltage drop (subject to cable size and length) from the rooftop panels to the charge controller, I planned to operate at 48 volts UNLESS as you mentioned the controllers efficiency curves are SIGNIFICANTLY improved at 24 versus 48 volt operation or shadowing becomes a problem. Although long retired from engineering, I still enjoy this "sparky" chat.

 

Thanks again everyone

 

John T

[Jack Mayer]

Jack,

Do you still recommend John Palmer in Lake City, FL.?

Yes I do.

[Jack Mayer]

John, in your case with 12-volt nominal panels it would be fine to run them series/parallel. Otherwise you will not get any significant benefit from an MPPT controller. You just have to be aware that you will kill the entire string if you shade any one panel at all.

[oldjohnt]

Hey Jack "Otherwise you will not get any significant benefit from an MPPT controller"

 

That's EXACTLY what the Tech Support gents told me when I called about my Solar Charge Controller (operating at 12 versus 24 volts). They, like you, indicated otherwise my controller wouldn't be utilizing its full MPPT capability. My installation (only a 29 footer mind you) will be flat roof with all four panels similar oriented (none right behind an AC unit ) so hopefully shading wont be too much of a problem. I still see my best two choices as series/parallel at 24 volts or all four in series at 48, but the potential shading problem would perhaps favor series/parallel at 24 (but at 48 there's less voltage drop given the same cable). Gonna have to sleep on it lol

 

John T

[Jack Mayer]

John, since you are probably maxing out your panel real estate I'd probably do everything serial. And you don't have "24" volts....you have 2*Vmp, which is likely close to 35/36 volts if you run a two panel string.

[wa_desert_rat]

The reason I went to series/parallel is that I had two 24vdc (nominal) panels at 8-amps each and two 12vdc (nominal) at 4-amps each. I could not put the 12vdc panels in series with the 24vdc panels because my current would be limited to 4-amps. So I put the two 12vdc panels in parallel to give me 12vdc at 8-amps and then put that in series with the 2 24vdc panels. So all the voltages added and the current stays at 8-amps.

 

WDR

[Mariner]

Yes I do.

 

 

 

Jack,

FYI, John Palmer is now outside Mayo, FL. Talked with him yesterday. An interesting character.

[Jack Mayer]

 

 

 

Jack,

FYI, John Palmer is now outside Mayo, FL. Talked with him yesterday. An interesting character.

Yes, he is outside Mayo. I was just there for two months. And to say John is "interesting" is likely an understatement.

[Mariner]

Yes, he is outside Mayo. I was just there for two months. And to say John is "interesting" is likely an understatement.

 

Jack,

Did you stay on his property, or that campground near him??

[Jack Mayer]

 

Jack,

Did you stay on his property, or that campground near him??

I stayed next door at Suwannee River Rendezvous. Nice big rig sites. However, I was not having work done on my rig. If you are having John do work you will want to be on his property. He has at least one 30 amp hookup, and if you want to boondock he does have water and a dump to do that.

[yourpcgeek49]

Reviving this topic - I am looking for some additional advice ---

 

I am finally ready to purchase & install my solar panels - but I have another concern/question for those with more experience:

 

I am planning to get nominal 24 volt (60 cell) panels, mounting three on the roof. I would "like" to mount two side-by-side lengthwise near the front of the trailer. However these panels are just under 65" long, and the space from the bedroom vent to the front seam (where the front cap attaches) is just 65". So I'm concerned about the possibility that the air flow might rip these off the top of the trailer when we are driving. (This is an EPDM rubber roof, so they will be screwed into the roof, but still.....)

 

I have room to put only one up front, cross-wise and much further back (18 - 20" from the front seam), but that will mean longer cables as the others will each be installed further back on the roof.

 

Anyone have any experience, or thoughts, on the best location?

[reed and elaine]

 

Attached is photo of top of our rig: 6 x 235 W panels. Two of the panels are quite close to the front of the 5th wheel. We have had these on for two years and perhaps 10,000 miles of travel. We have had no problems with them being that close to the "slip stream".

 

If you put them in series for 72 V to controller, you will require a lot smaller controller, smaller cabling and will encounter less power loss. A controller such as a TriStar MPPT-45 will change voltage from 72 V to 12 V, or whatever is the voltage of your battery suite.

 

As Jack noted, you have to be circumspect in setting your rig. Make sure that you will not be differential shading: i.e. a limb, tree, or other protuberance that will put part of your panel suite in shade and not the rest. Have set up in a clearing in the woods numerous times where a single tree had some of the panels in shade for part of the day and then the others the latter part of the day.

 

Reed and Elaine

[Yarome]

Reviving this topic - I am looking for some additional advice ---

 

I am finally ready to purchase & install my solar panels - but I have another concern/question for those with more experience:

 

I am planning to get nominal 24 volt (60 cell) panels, mounting three on the roof. I would "like" to mount two side-by-side lengthwise near the front of the trailer. However these panels are just under 65" long, and the space from the bedroom vent to the front seam (where the front cap attaches) is just 65". So I'm concerned about the possibility that the air flow might rip these off the top of the trailer when we are driving. (This is an EPDM rubber roof, so they will be screwed into the roof, but still.....)

 

I have room to put only one up front, cross-wise and much further back (18 - 20" from the front seam), but that will mean longer cables as the others will each be installed further back on the roof.

 

Anyone have any experience, or thoughts, on the best location?

 

Screwed and lapped well I can't think of any reason why not, mechanically. I assume you'll have them raised 1 1/4" or so? That thin of a frame edge shouldn't catch much. Too low to the roof and I might be concerned about turbulance under the panel. If that's your best option then start slow and see what you get. Worst case you could always attach an air ramp from your rigs roof to the leading edge of your panel frame.

 

Honestly.. my main concern with what you described would be the bedroom vent. Running that close to could present a shadowing issue and kill the panel. If there were any concern of that at all then I would choose option B! Minimal line loss (I don't even know how far of a run your talking about to hit the c-box and down to the controller) is trumped by any possibility of roof obstuctions in my book.

[Yarome]

If you put them in series for 72 V to controller, you will require a lot smaller controller, smaller cabling and will encounter less power loss. A controller such as a TriStar MPPT-45 will change voltage from 72 V to 12 V, or whatever is the voltage of your battery suite.

 

Too bad there isn't 1 more panel. Kind of mismatched distances that would be a good candidate for a series/parallel array. I probably wouldn't chance a single array.. Hmmmm wish I could find a picture of their roof.. would make life a whole lot easier.

[Daveh]

Raises a question, how much of a concern are line distances generally in a parallel array. You could equalize them by just going with the longest needed length for every line even where not needed but is that kind of equivalence necessary. I don't remember any discussion of that specific issue.

 

I don't have an answer for you pcgeek. I am also interested in the responses to your question.

[Yarome]

Raises a question, how much of a concern are line distances generally in a parallel array. You could equalize them by just going with the longest needed length for every line even where not needed but is that kind of equivalence necessary. I don't remember any discussion of that specific issue.

 

 

In just a basic parallel config with all panels identical and oriented in the direction then it's easiest to just think of them as multiple batteries... so yes.. your parallel connections should be of equal length. When it's not all nice a pretty, there are multiple strategies.. one being to sometimes use a litle longer line even though it may not be needed.

 

You can also orient them in relation to where a c-box can be mounted and make my connection at the box rather than from panel to panel. It takes a bit of planning, but it "can" help to keep your runs as short as possible. Of course, you also need to take into account the run from your c-box to the controller and which, overall, is going to be the most beneficial.

 

If it's doable, I will almost always try to split panels into series arrays and then parallel the arrays. Sometimes that means that it is more efficient to puchase 4 - 100watt panels over 3 - 135s. Even if it might be just a tad more expensive.

[yourpcgeek49]

Thanks for the quick responses everyone!!!

Ours is a 38' 5th wheel, so there is a lot of roof. (This is taken from the REAR of the roof.(

 

Here is the Front of the roof:

 

 

 

Here is my planned layout (if the front position is feasible). It keeps all three panels close together where (hopefully) we can arrange for them to all be in the sun. I am planning a 4th panel that I can ground mount & move around if needed. It could also be mounted on the roof later if I decided to do that.

 

I realize that I may have a problem with shading from the TV antenna, and can move the 3rd panel to the 4th position if needed.....

 

But my real concern was wind problems with the front panels. If several of ;you have done something similar without issue, that would be really great news!

[reed and elaine]

You have room for 8 panels. Agree with Yarome to go with the four panels: two series of two (48 V) and then parallel to controller at 48 V.

 

We noted in post #37 that we have two panels at front of rig and have had no problems with slipstream in perhaps 10,000 miles of travel. Have run into low branches when boondocking and still no problems

 

Reed and Elaine

[Yarome]

The pictures and diagrams are very helpful, however, the front would be my last choice. Still not a favorite, but the better of two evils I would mount two lengthwise as far to the rear as possible and to the left and right edges... leaveing a bit of a buffer so a branch or whatnot sliding down the top edge wouldn't snag on them and so as not to interfere with any repairs that may need to be made along the edge seams.

 

However! If I needed that extra space out to the edge to clear more of the A/C shrouds shadow I would take it. Probably use handled bolts in a two piece mounting bracket so they would be easily movable for any repair work on the seams.

 

I would run a check on the air conditioner shrouds shadow profile, but if that checks I would move to your third where you currently have #4. #4 opposite #3 balanced between the skylight and middle vent and again on the edge as far as possible.

 

The C-Box would take some investigation on where to go down, but I would try to get equidistant between panels #2 and #3 along side the air conditioner shroud, but not so close to interfere with acess to the A/C. That would be my "sweet spot", but it's not always practical. You can see where that puts you in the best spot to access all 4 panels (4's not there yet.. I know) as centrally as possible.

 

Now your asking "why" after all of your careful measuring. Sorry. Here is my thinking:

 

1. If it's the only area you have available, that's one thing, but let's face it.. it's not really an "ideal" location riding the front edge. Like you mention, there is a potential wind issue, but if you happen to pass under something a little low (tree branch) it will more than likely catch, tear up the mounts doing damage to your roof, then take out your vent cover.

 

2. Speaking of vent covers.. 1, 2, and 3, are all butting vent lids which have a small rise over the panel height. Watch you get is two fold. Any debris falling on a vent lid will undoubtely slide down onto one of the three. That's minor because it's just as likely for debris to fall directly onto a panel, but with no obstruction (a vent lid along the edge of your panel) it's likely to blow off your panel rather than get stuck on the vent. Butted that closely, you also limit access to repair seals around the vents... as well as rule out any possibility of adding vent covers in the future. The big one really though is if you open your vents your lid will shadow a panel in almost every direction.

 

3. The antenna. That ones self explanatory right. Without moving it your almost gauranteed it will be shadowing at least one panel or other.

 

4. The 4 locations in the rear offer the largest areas of continuous exposure in sequential order. Roof obstuctions we don't have much control over just like the areas of greatest exposure. We DO have some amount of control in our wiring and connection points to help minimize voltage loss, so with the size of your panels it doesn't leave many option, and in this case I would opt to take exposure over voltage loss. After all.. voltage loss is a non issue if the panels are not producing, right?

 

My 2 cents anyway.

[Yarome]

You have room for 8 panels.

 

Reed's right.. you CAN fit 8, but I would still start from the back and leave the less desirable location for later additions. If that's a real possibility then you could move the C-box up between #3 and #4 in the middle if you are worried about holes through your roof, but personally, if it was my rig I would keep it where it is, add the additional 4 panels in one shot and mount a second C-box. You could run them as 2-4 panel arrays if your hardware can handle that, or 4 - 2 panel arrays. Either way than can be run down and combined later at your controller.

[yourpcgeek49]

Thanks to all. I'm moving them to the back, putting all four on the roof, and running two pairs serial and parallel. You all are the best!

[reed and elaine]

Agree with Yarome that panels to the rear do mitigate some problems with running into trees - but we do bang into twigs and branches when backing into spots under trees (no solar then and have to exist off battery bank for 5 or more days).

 

We did not place panels at the rear of our rig since they would have been shadowed by the a/c unit.

 

Reed and Elaine

[Daveh]

new solar panels small.jpg

Attached is photo of top of our rig: 6 x 235 W panels. Two of the panels are quite close to the front of the 5th wheel. We have had these on for two years and perhaps 10,000 miles of travel. We have had no problems with them being that close to the "slip stream".

 

If you put them in series for 72 V to controller, you will require a lot smaller controller, smaller cabling and will encounter less power loss. A controller such as a TriStar MPPT-45 will change voltage from 72 V to 12 V, or whatever is the voltage of your battery suite.

 

As Jack noted, you have to be circumspect in setting your rig. Make sure that you will not be differential shading: i.e. a limb, tree, or other protuberance that will put part of your panel suite in shade and not the rest. Have set up in a clearing in the woods numerous times where a single tree had some of the panels in shade for part of the day and then the others the latter part of the day.

 

Reed and Elaine

 

 

Could someone please refresh me on calculating solar controller size when wiring panels in parallel vs series. I am planning on using 3 Solar World 285 panels

 

 

Rated power P_r SW285 (v4) Peak power P_mpp 285W Peak power voltage V_mpp 31.3V Peak power current I_mpp 9.20A 0pen circuit voltage V_oc 39.7V Short circuit current I_sc 9.84A Max Series Fuse* 15A

 

[Jack Mayer]

In series you add the voltage and keep the current the same. In parallel the voltage stays the same and you add the current. I cover all of this on my website in detail. Notice that this is the same for batteries? Electric is electric.

 

No matter what, you need to do the following:

 

1) Run the numbers for the Vmp and Imp (as appropriate) for the wire size you wish to use through a voltage drop calculator. That is how you choose the appropriate wire size. No guessing allowed - it is simple physics.

 

2) Make SURE you use the same panels with the same specs if you are doing series parallel.

 

3) run your panel configuration through the controller manufacturers "string calculator" to make sure it meets their requirements.

[Daveh]

Thanks jack. I was getting different results than i expected through the string calculator. I will need to go back through things.