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Mixing Panels - Mono/Poly...140w / 160w

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I have two 140w / 12v Poly panels on my TT running through a Bogart PWM controller. They are in parallel.


I see a good deal on Ebay for 165w / 12v Mono panel that I'd like to add in parallel to the existing.


My controller can handle up to 30 amps which I would be well under.


Is this doable?

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Mono combined with Poly is not an issue as long as their operating voltages are within a few tenths of a volt. Exact operating volts is preferred.
The 12v nominal you mentioned is not enough to go by. The Vmpp is the spec you'll want to look at.


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rb, I'm NOT a Solar Expert, but lets do the math. If I understand your post you have two 140 watt panels in parallel and you want to add another 165 watts still all in parallel right?????????????


If so that's 445 total watts and ifffffffffffffffffffff your panels actually produce 18 volts under load ????? (I cant know that setting here) that's 25 amps and your 30 amp controller will suffice. Of course, if your actual loaded operating voltages were significantly less, the 30 amp may not suffice???? Subject to the length of your wiring from panels to controller and assume 25 max amps, depending on how much voltage drop you can tolerate, that could be 8 Gauge minimum and preferably even bigger wire (Id design for overkill and use bigger wire even where smaller gauge suffices) to your controller.


While the voltages you listed might "work" if I had my druthers Id prefer the output voltages of panels in parallel to be closer then what you posted, as the two will be in competition with the new single BUT I DONT HAVE ANY EXACT DETAILS AND VOLTAGE TOLERANCES HANDY.



Something to consider in series versus parallel configurations.


a) In series, the voltage differences are less crucial (then in your parallel proposal given different voltages) as they are additive, and even if one were 18 volts and the other 19, it wouldn't be so critical.


B) In series, the higher net voltage equals less current flow and less voltage drop (subject to wire size and length) in your wiring down to the controller.



HOW ABOUT USING THE EXISTING TWO IN PARALELL IN SERIES WITH YOUR NEW PANEL??????????????? That way the different voltages isn't so much a worry, nor the poly versus mono, plus you're operating at a higher voltage which means less current you have to carry down!!!!!!!!!!!!!!


Just a thought, no guarantee it will work, see if any solar experts think its a good or badddddddddddddd idea lol


John T NOT a solar expert

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Thanks John......But my solar controller can only accept 12V. If I put the two 12v panels in parallel that would be 12V and in series with the new 12v panel would be 24V total.....No Can Do with my controller.


I'm using 4g wire and my longest run is 20'. Both 12V panels tied together on the roof and one set of 4g wires to the controller...from there 24" to the batteries.


link to the article I wrote about my solar install. http://rvbprecision.com/rv-projects/solar-install-grey-wolf-19rr-toy-hauler.html

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rb, well shucks, I thought I had a solution to your problem. My MPPT solar charge controller works at the higher series configured operating voltages besides 12 only, and I didn't realize yours didn't do likewise. Back when I had a cheaper PWM controller using two 12 volt panels in parallel and wasn't satisfied with the results, the vendor instructed me to wire them in series and performance greatly improved. When placed in parallel I'm just NOT a fan of panels with different operating voltages, but I don't have any exact specifications to tell you just how much difference, if any, is acceptable. What you propose (different panels in parallel) may still "work" at the risk of loosing some efficiency or net energy harvest. I wouldn't be surprised if you asked any of the panel vendors they would say NOOOOOOOOOOOOOOOO you shouldn't mix panels in parallel that aren't exactly the same, but of course they would gladly sell you more of their panels lol


Sorry, I cant tell you with any certainty (based on accurate technical specs and data, not just an opinion) how much difference may be acceptable when placing different panels in parallel.


John T

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Wired the way you propose the lower voltage panel will tend to bring the entire string down to its voltage. That may be acceptable to you. You can work the numbers and see if you are "losing" more than you like. But you will not get the rated watts from the array. However, it is probably close enough that you will be satisfied with overall performance. The cost per watt gained will increase some.

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The Vmpp is the spec you'll want to look at.


Wired the way you propose the lower voltage panel will tend to bring the entire string down to its voltage.


Right on track. It's certainly doable, but your array will only perform at the lowest rated panel in the string. Overall, you'll be generating more juice and there is certainly no reason to balk at a good deal.

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EXACTLY, Yarome and Jack, as we all recognized above, when you place 2 or more panels in PARALLEL the voltage across the + and - BECOMES JUST ONE COMMON VOLTAGE, which is why you could/might indeed loose some energy versus they were in series. The initial higher voltage source (subject to its energy) may provide current to the lower and the lower rob from the higher at time T = 0+ but obviously there's only one common voltage in the end. I think the ONLY way to accurately measure the results would be to have panels in series then in parallel but who's gonna do all that??? and besides your PWM doesn't take over 12 volts. While I prefer NOT to place unequal output panels in parallel, I don't envision permanent harm in trying your plan and even if you don't end up with 140 + 140 + 165 watts, I bet you have a wholeeeeeeeeeee lot more then 280 !!!!!!!!


Let us know where you end up.


NOTE Before making your parallel 3 panel connection, check with true experts and whatever you do, DO NOT try it just because I might, I don't want responsibility if you harm a panel.


PS just as its critical how you connect batteries in parallel, if I was going to wire three panels all in parallel, Id use the exact same cables and gauges and cable length from each panel to the common buss where the 3/6 connections all merge. Of course that's more for when all panels are the same, but Id still do it anyway. See Smartgauge's data.


John T

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HOW ABOUT USING THE EXISTING TWO IN PARALELL IN SERIES WITH YOUR NEW PANEL??????????????? That way the different voltages isn't so much a worry, nor the poly versus mono, plus you're operating at a higher voltage which means less current you have to carry down!!!!!!!!!!!!!!


That would restrict the array's amperage to the lowest amperage panel in the series string.

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Good afternoon Jack and Oldman, I want to be sure I understand your post, so I have three preliminary plus one FINAL question for you both so I can learn more about the physics of Solar Panels, I told you I'm NOT a Solar expert and want to learn, so please help me out here.


FIRST HOWEVER I took your post to indicate the current in my proposed three panel Series/Parallel combination would be limited to the “lowest amp panel in the string” which is 11.66 (140/12) amps. I APOLOGIZE IF I MISUNDERSTOOD YOUR POST…. I thought the current could be much higher IE 18.54 amps (higher then the “lowest panel in string” which is only 11.66 amps at 12 volts) as I explain below




a) If you have a 140 watt capacity 12 volt energy source in PARALLEL with another 140 watt 12 volt energy source, that's 280 watts of power (V x I) at 12 volts right or not ???????????


B) If in SERIES with the total energy above you place a 165 watt 12 volt energy source, there would be 12 + 12 = 24 total volts across the three panel combination right or not?????


c) If the combination of all three above is an energy source of 445 (140 + 140 + 165) watts at 24 volts, and if P = V x I, that would normally (unless different because its solar panels, is it ????) total if all was perfect and 100% efficient in theory 445 Watts/24 Volts = 18.54 amps capacity right or not?????????








NOTE: If you answer YES I would counter that in the two panel PARALLEL connection, thats a 50/50 current divider, so in the three panel Series/Parallel configuration you can still have the 18.54 amps since in the two panel configuration each panel ONLY carries 18.54/2 = 9.27 amps each AND THAT’S LESS THEN THEIR 11.66 AMP CAPACITY


NOTE: CURRENT DEPENDS ON THE LOAD: If a panel is rated at 140 watts and lets use 12 volts (I know that's not Vmpp), at 12 volts in can

deliver 140/12= 11.66 amps at its rating. HOWEVER if you try and load it to more amps then its rating can deliver, voltage will start


NOTE DUH I'm aware of Vmpp and that its higher but I just used 12 and 24 above to simplify things

Also since his PWM Controller is limited to 12 volts, my proposal of using all three panels at 24 volts cant work anyway



John T As I' ve posted many times, I'm sure NOT a Solar Expert (just a too darn long retired and rusty electrical engineer) and am anxious to learn all I can, so please let me know if or how the above combination of the three panels in series/parallel is limited to 11.66 amps which is the "lowest amps in the string" ???? IF THAT’S WHAT YOUR POST INDICATES!!!!! I NEED TO LEARN THIS SOLAR STUFF. I consider a Solar Panel as an energy source just like a battery stores and can deliver energy into a load BUT I MAY BE WRONG AS RAIN and it won’t be the first nor will it be the last time.

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a) correct

B) b ) correct

c) no


In parallel, the panels' amps are additive while the voltage remains the same. In series, the panels' voltage is additive, BUT, the current is not additive, it's the SAME in every part of the circuit. - that's basic DC theory. That means that the panel with the lowest amperage rating dictates how much total amperage is supplied by the string.


An easy way to think of this is to imagine 5 water pumps in series. Each pump adds its pressure to the incoming water, but the volume of water is not increased. And, if you have a little teeny pump with a very small orifice, you get only the amount of water that the smaller pump will allow. Sorta like the 'weakest link' analogy for a chain.

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Good Morning Oldman, thanks for and it’s good to hear your response, this is fun and informative for me at least and maybe were all learning something even at the risk of boring the non sparkies to death lol.


While I'm no solar panel expert I know if you place say two 6 volt batteries in series each rated say 200 CCA, you end up with 12 volts (you are correct voltage adds) BUT STILL ONLY 200 CCA BECAUSE THE AMPS IS NOTTTTTTTTTT ADDITIVE. That's a given which I think most people are aware of and there's no disagreement.


To make a comparison, a battery is an electrochemical energy STORAGE device that stores a finite amount say 200 Amp Hours of energy. A Solar Panel does NOT store energy but directly in real time converts sunlight into electrical energy, instead of storing energy it’s like a constant producing energy source with its energy dependent on the sun. Unlike a battery, it DOES NOT reduce its energy output over time because the storage is depleted, it just keeps constantly producing SOOOOOOOOOOOO if a solar panel can not allow more current to pass through it then its own rating, IT MUST SOMEHOW BE ABLE TO CLAMP OR LIMIT OR RESTRICT CURRENT TO X AMPS AND THATS THE PART ABOUT SOLAR PANELS I DONT UNDERSTAND. Sure I understand how batteries (energy storage device) in series does NOT add the available amperage each can deliver BUT I DONT UNDERSTAND THE PHYSICS OF HOW A SOLAR PANEL LIMITS, RESTRICTS AND CLAMPS CURRENT TO BE NO MORE THEN IT CAN PRODUCE IF STANDING ALONE ??????????????



WE NEED A SOLAR EXPERT TO EXPLAIN THE PHYSICS OF HOW A SOLAR PANEL LIMITS AND RESTRICTS CURRENT FLOW TO NO MORE THEN IT CAN PRODUCE ALONE. I hope someone can explain the panel physics to me, back in my days at Purdue University, we didn't cover solar panels, but did vacuum tubes lol


Back to (even though it cant work with only a 12 volt controller) the original post, the lowest rated panel the OP has is the 140 watt 12 volt which is 11.66 amps. BUT HE HAS TWO OF THOSE IN PARALLEL ACTING AS A 50/50 CURRENT DIVIDER so I believe such could pass 2 x 11.66= 23.32 amps and NOT exceed either panels rated amperage. Therefore with those two in parallel in series with a third new 165 watt panel and now operating at a net 24 volts I STILL DONT SEE THAT COMBINATION AS BEING LIMITED TO THE LOWEST 11.66 AMP PANEL. AGAIN I'm using 12 or 24 for simplicity versus the true Vmpp


A) Maybe its somewhere in between?? 11.66 and the ideal (if there were no current limiting) 18.54 amps ????


B) Maybe its limited to the 165 watt 12 volt panel alone which is 13.75 amps ????












1) I have Four series 100 Watt so called 12 volt panels, and according to their rating, those individual 100 watt panels produce 8.33 amps at

12 volts or 5.88 amps at 17 Vmpp volts

2) The lowest panel in my series string can on its own only produce 100/12 = 8.33 amps (5.88 at Vmpp)

3) I have an MPPT smart 4 stage solar charge controller that accepts higher series voltage configurations

4) On a typical day my MPPT Solar Charge Controller according to an in line analog ammeter plus a digital ammeter, is pumping maybe 20 to

24 or more amps into my 12 volt four battery bank, which is much higher then any of my 8.33 amp panels can produce.





If my series four panel string is limited to what only one panel can produce which is 8.33 amps (more at Vmpp) BUT my MPPT Solar Charge Controller is pumping 20 to 24 amps into my 12 volt battery bank, ITS BECAUSE MY CONTROLLER IS TAKING IN THE TOTAL 400 WATTS OF ENERGY AT 48 SERIES VOLTS AND CONVERTING IT TO AROUND 13/14 VOLTS AT 20 OR MORE AMPS !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! If I measured the current at 48 volts INTO my solar charge controller, it can sure be different then the current at 13/14 volts OUT


8.33 Amps at 48 volts = my 400 total watts INPUT to MPPT, and lets use 24 amps at 13.6 charging volts OUTPUT of my MPPT = 326 Watts OUTPUT that's within efficiency and dependent on sunlight intensity AND THAT WORKS FOR ME AS AN ANSWER AND EXPLANATION



God Bless and thank all, maybe in this discussion we can all learn how a solar panel clamps and limits current to no more amps then it could produce alone. If a person had the set up and equipment it would be fun to place the three proposed panels in series,,,,,,,, and parallel,,,,,,,,,,, and series parallel and measure the energy in all configurations. I'm well aware of how batteries perform in series or parallel, but I just don't know the physics of how a solar panel (NOT an energy storage device but a constant producer) performs grrrrrrrrrrrrrr and I may well just be too darn old to learn lol

John T Tooooooooooo long retired engineer and the old brain cells are fading

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Hi again oldman... You're exactly right "The higher amps are what's going into the battery.. watts are conserved"


In the Solar Charge Controller, or anywhere for that matter, energy is not created or destroyed, only changed in form. If you put 400 Watts INTO the Controller you get almost 400 Watts out (less heat losses) so on the INPUT it could be as high as 400 watts in my situation (48 volts x 8.33 amps given perfect sun conditions) while on the OUTPUT I'm getting something in the neighborhood of around 25 amps at 13.6 charging volts, or 340 Watts, and I could in theory get more if the sun were brighter and directly overhead.




Now if a Solar Panel expert can just explain the physics, electronics and mechanics of how a panel limits and restricts the current through it (when in a series or parallel configuration) to no more then it could alone produce, Id be even a happier camper.


Take care oldman and thanks again


John T

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Without going too "deep".. basically there are multiple factors at play when mixing panel capacities and ratings (we're not really talking wattage here).


1. The electrical component characteristics of a panel. That's going to come most in to play when wiring in series, but will also have a "by-product" affect when wiring in parallel as well. Especially when the voltage is lower in one particular panel.. I guess you could call it a "bleeding" affect on the others more so than really "throttling".


2. To a lesser degree.. the degradation rate (which you generally won't see on the ratings label). Even panels that have, in most respects, nearly matched ratings, the degradation rates may vary. That would also apply to identical panels added to an array at significantly different periods of time/use.


3. Solar controllers can become "confused" when trying to determine the optimal voltage and current to pass. That is especially true with MPPT controllers where you pretty much loose any benefit of having one in the first place. That doesn't mean they won't work. That just means that the current being pushed through to your battery bank will be diminished. In that respect.. "throttling" would seem to fit.


4. Of course.. you could also get into physical construction characteristics. A particular panels ability to dissipate heat, glass quality, etc. and the impact it might have on production within the array.


For those that are interested in reading more, just a cursory search pulled up this article that isn't too bad. It's not that technical. Pretty basic concepts and starts out like you're just figuring out what a solar panel is, but if you skip down a few sections it's not too bad and gives a little more in-depth explanation.

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