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Solar Panel Delima


dewilso

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I had 9x 100W Grape panels, built my combiner box for 4 strings, planned to do 3 panels in parallel x3, with one spare input available for an additional string of 3 panels. Now I've come up with one additional panel. Should I do 2 strings of 2 panels & 2 strings of 3 panels, OR, as original plan 3 strings of 3 panels, and just add the last as a single. Does it make any difference?

 

My combiner box inputs are by 4x MC4 connections so it is what it is and that's not changing.

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Should I do 2 strings of 2 panels & 2 strings of 3 panels, OR, as original plan 3 strings of 3 panels, and just add the last as a single. Does it make any difference?

 

 

3 of 3, 2 of 4 or 5 of 2 depending on your target voltage, controller and real estate. Yes.. it matters. To get the best performance you'll want all of your arrays balanced and wiring of equal lengths. Personally.. I would do 3 of 3 or even 2 of 4 to get the highest current pushin the juice down the line. Your real estate and controller will really determine which would be optimal for your particular rig/equipment.

 

I would hold off on the single panel until he gets a buddy. ;)

 

On edit: Just to clarify... wired in equal lengths, although, your series connections and parallel connections may be of different lengths. KWIM?

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I had 9x 100W Grape panels, built my combiner box for 4 strings, planned to do 3 panels in parallel x3, with one spare input available for an additional string of 3 panels. Now I've come up with one additional panel. Should I do 2 strings of 2 panels & 2 strings of 3 panels, OR, as original plan 3 strings of 3 panels, and just add the last as a single. Does it make any difference?

 

My combiner box inputs are by 4x MC4 connections so it is what it is and that's not changing.

Unless I am sadly mistaken, all your groups of panels must be at the same total voltage when they reach the combiner box. You can't add the last panel as a single as its voltage, at the combiner box, will not be the same as the groups of panels wired in series.

 

Also all panels in the series string must be of the same wattage or current output, I don't remember the exact details.

 

You may want to do more research. I'm running off of old memory here and don't have a link which I can point to with a lot of details.

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Its your money to do as you please, but from my engineering perspective if I already had nine 100 watt panels in a balanced configuration, I wouldn't muddy the waters trying to add one more 100 watt panel, since for one thing it adds such little more power so is it worth the hassle???? but more importantly, I do NOT like any possibility of imbalance in the entire system that one more panel wired different then the other nine could potentially create ITS NOT WORTH THE RISK IN TOTAL EFFICIENCY IN MY OPINION........

 

As I'm sure you're already aware, when combining panels its best if they are identical in rating and voltage and age and specs.

 

When you add in series the voltage increases but the current you have to send down to your controller is less thereby reducing possible voltage drop (subject to wire size and length) HOWEVER if there's any possibility of "shading" the shaded panel reduces output.

 

When you combine in parallel voltage stays but current down to the controller increases (wire size and voltage drop issues), yet shading is less of a problem.

 

Sooooooooooo engineering speaking I like your 3 x 3 x 3 configuration PROVIDED your controller accepts the voltage and current, but regardless how its wired, I'm NOT a fan of scabbing on one additional out of balance odd ball panel UNLESS you reconfigure such that each leg is identical, and with ten panels that's harder then eight or nine lol. I'm NOT saying one more panel tossed in parallel with another leg of three identical panels all the same rating and specs wouldn't add yes 100 more watts, I'm ONLY saying when you consider potential imbalance and benefits gained, why mess with it??????????

 

In "theory" if you had three in parallel adding one more adds current in that leg and it will "work" so if you hang the tenth panel in parallel in one of your 3 x 3 legs that shouldn't cause any major issues (subject to wiring and balance) even if its NOT my first choice of operation. With a total of ten panels Id prefer 5 x 2 subject to controller capacity, but if you're itching to add that tenth panel and if its identical and its position is compatible with no shading issues GO FOR IT. I cant argue more solar isn't better solar and a fourth parallel panel with one group of your other three will add current in that group !!!!!!!!!!! BUT I STILL WOULDNT MESS WITH JUST ONE MORE PANEL in your balanced 3 x 3 x 3 arrangement.

 

PS if you're running 900 watts, (subject to wiring, how much series, how much parallel, how much series/parallel) at 12 volts nominal (higher Vmp) that could (subject to panels, voltage and sunlight) be around 75 max amps. I trust you have adequate wiring from up top down to an adequate charge controller?? I don't know your panel voltage or for sure your wiring configuration, so thought I should just throw that out for good measure.

 

John T Long retired Electrical Engineer and NOT any solar expert, do what they suggest not me, I could be wrong as rain.

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With your orphan panel... one other point to consider is if you are using an MPPT controller or not. Controllers may be "smart" these days but they are not "genius's". With an orphan panel/array the current variance can confuse the MPPT function.. negating any benefit.

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With your orphan panel... one other point to consider is if you are using an MPPT controller or not. Controllers may be "smart" these days but they are not "genius's". With an orphan panel/array the current variance can confuse the MPPT function.. negating any benefit.

Would that be a current variance or voltage variance? The single panel would be at a lower voltage that the ones which are in matched 2 or 3 panels in series going to the same combiner box. Current is going to vary from the solar panels to the combiner box depending on shading anyways.

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Response & clarification. I'm using the panels I'm using because I got a deal..$0.83 per watt delivered to my door in Livingston, and the smaller panels give me flexibility in mounting locations, AND I had a Morningstar TS-60 controller already. All of the panels will be connected in parallel with MC4's, which I also have laying around.

 

Thanks for the responses.

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Would that be a current variance or voltage variance?

 

I was trying to keep it simple... largely yes.. Al is correct.. more "voltage" over "current", but most accurately is the phase variance the controller will be trying to interpret. IOW.. MPPT controllers like it "clean & simple" in order to be of any benefit over a standard controller.

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I'm using the panels I'm using because I got a deal..$0.83 per watt delivered to my door in Livingston

 

I had a Morningstar TS-60 controller already. All of the panels will be connected in parallel with MC4's,

 

No harm there! A $'s a $. That's quite a good deal on GS panels.. even on poly's.

 

Since you mentioned a 'straight' TS-60 I'm assuming it's a PWM? It would still handle 48vdc nicely if you elected to go with a serial/parallel setup. It's your install, but there are distinct advantages with a mixed array. Shorter serial wire runs within each array (= efficiency)... improved efficiency to your c-boxes and downleg to your controller. It's probably not practical to go with 2 - 400watt arrays, but your original 3 x 3 plan sounds. . real estate permitting.. the most promising option I would pursue.

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So far I like the 235 watt, 24 nominal volt, 39" x 64" panels I bought from the local Amish for 90 cents per watt cash and carry away. I'm running two in parallel with equal length wires all well balanced and a temperature compensated 'Smart" MPPT Solar Charge Controller. Gotta love our Solar

 

John T

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