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Old 23-11-2014, 06:34   #121
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Re: Solar Panels - Series or Parallel ?

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Originally Posted by zboss View Post
Or you have one controller per panel, as I do. This is neither a series or parallel connection then.



I do, using four Genasun controllers. I have a love/hate relationship with these controllers. Love them because every panel is completely independent, so if one controller or panel goes out, I don't lose the whole system. They are also cheap, I paid just a slight bit more for four controllers over a single ganged controller.

I hate them because they are not adjustable and give you zero feedback on voltages, amps, etc. They are just basic MPPT controllers.
Unfortunately when yous set out to build both a high performance and low cost MPPT, that can be fitted to each panel, and come out less money than a single 40A controller, well somethings gotta give.... For what they are, they are a tremendous value.

Earlier this year I pitted a Genasun GV-10 in a head to head with a Midnite KID & a Rogue MPT-3048. I could not detect any measurable performance differences between the inexpensive Genasun & the much more expensive Midnite KID and the Rogue MPT-3048. I think the Genasun controllers fit the niche Alex intended them for, and do so very well...
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Old 23-11-2014, 09:11   #122
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Re: Solar Panels - Series or Parallel ?

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Re series vs. parallel, here is something to read...
Thanks that's just what I was looking for. It's interesting that they use panels with only 32 cells. I would think you'd get even better performance with the standard 36 cells. But maybe the higher voltage would allow you to use the bypass diodes making series better. so round and round we go. Can't tell you how many times I've changed my mind on this.
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Old 24-11-2014, 21:01   #123
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Re: Solar Panels - Series or Parallel ?

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Unfortunately when yous set out to build both a high performance and low cost MPPT, that can be fitted to each panel, and come out less money than a single 40A controller, well somethings gotta give.... For what they are, they are a tremendous value.

Earlier this year I pitted a Genasun GV-10 in a head to head with a Midnite KID & a Rogue MPT-3048. I could not detect any measurable performance differences between the inexpensive Genasun & the much more expensive Midnite KID and the Rogue MPT-3048. I think the Genasun controllers fit the niche Alex intended them for, and do so very well...
My cost advantage wasn't that good for what I lost. The controllers were $203 each x 4. If I change battery types I have to sell the controllers at a loss because they are not field programmable, or return them for programming... who knows how much that will cost with shipping.

So, I gave up a display, logging, and programming for less than $50. All features that are worth a lot more than $50 individually.

I gained completely redundant solar, which is great.
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Old 24-11-2014, 23:48   #124
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Re: Solar Panels - Series or Parallel ?

As I amliving on a new boat (new to me anyway) I added a new house battery and controller I got off ebay. I was surprised to see the result. I have used a sepperate cheap MOST controller for each battery group. I use a selector switch for switching between house batteries. Each system is now a stand alone unit. I shorted a unit out and for $10 I used my spare. I can't make these for the price they sell them for. I have put the controller near battery, instead of mounted on the controller. Works well. Ample power...However, I am not running a fridge yet.
The cable ties worked for keeping birds off. I have moved now so I have taken them off.
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Old 25-11-2014, 09:27   #125
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Re: Solar Panels - Series or Parallel ?

Hello,

Most of the information in this message is contained in a PDF file that was attached to a previous post by me. I will refer to the parallel/series wiring of solar panels in the context of the instalattion that I performed in my sailing boat about 7 months ago.

I used three panels in series. They can produce a maximum voltage (see the table in the other post) of 3 x 23.94 = 71.82 volts. Most MPPT regulators do not admit such a high voltage input. Fortunately the controller that I have used (TR-2210RN) allows an input voltage of 100 volts. By connecting panels in series the current is smaller than it would be if they were in parallel and the section of electrical cables connecting the panels to the controller may be smaller. In my case I used a section of 4 mm2. The distance of the panels to the batteries was about 7 meters. So I have a total cable length of 14 meters. The section of the cable is critical, since the voltage drop along the cable will be responsible for a loss of power. If the panels were connected in parallel we could use a MPPT controller with a lower input voltage (less expensive). In that case, the current would be 3 times higher and, for the same loss of power, I would need to increase the cable size from 4 mm2 to 12 mm2. That would be more expensive and, moreover, would make the job of inserting the cable through the 1 inch stainless steel tube of my bimini into a very difficult task. The controller cable to the batteries carries a larger current, but it has very short lenght. I used a cable with a 10 mm2 section. I used a 30 A fuse in the positive cable near the battery.

I really think that my choice of a serial connection is fine. I leave here my reasoning and I hope I am not mistaken in my calculations. I hope this post will be useful to clarify some aspects of solar panel wiring. In the following picture it is shown the I-V curve for the 75 W solar panel that I am using.



I point out 4 possible operating points along the curve. Point A is the point of operation when there is no load connected to the panel (open circuit). The electric current will be zero and the voltage 23.9 V. Obviously, the power to the load is zero. Point B refers to the case of an electronic device (MPPT controller) as the load to the solar panel. The voltage is 19.4 V, the current is 3.8 A and the power supplied to the controller is 73.7 W. Point C is the operating point if we connect the panel directly to the battery (or if you use a non-MPPT controller). The voltage supplied by the panel will be imposed by the battery where we assumed a normal battery voltage of 12.8 V. Using the curve, I believe that the current is about 4 A, which means that the power supplied by the panel is 51.2 W. These two numbers, 73.7 and 51.2 show the improvement when using the MPPT controller.

Before comparing the series to parallel wiring, let me consider the cable connecting the panels to the controller. In my case the distance between the panels and the controller is about 7 meters long. I used a photovoltaic cable with a cross section of 4mm2. This is a very flexible cable, well protected from the environment, and with a total outer diameter of 6 mm. If we evaluate the ohmic resistance of a copper wire with a length of 14 m and a section of 4 mm2 we will get 60 mili-ohms. I will use this value to estimate the power loss along this critical cable. Later I will discuss the effect of shading on the panels and I will disagree with the opinion that parallel wiring offers significant advantages over the serial wiring.

Taking all of the three panels as a single identity (... Thevenin ...) the I-V curve of the set is very similar to that of the first image in the case of a single panel. We only need to change the numbers as labels. Assuming that the panels are used with an MPPT controller, I only comment about point B (the point of maximum power transfer). In the parallel case, the output voltage would be 19.4 V, but the output current would be 11.4 A. In the series case, the output voltage would be 58.2 V and the output current would remain 3.8 A. Note that, in the case of series wiring, the MPPT controller must support an input voltage of about 60 V. Not all controllers on the market support this "superior" voltage.



The voltage drop across a resistor R carrying a current I is R x I. In the case of the parallel connection (I = 11.4 A) the voltage drop is about 0.68 V. Since the voltage available at the panel is 19.4 V, the voltage drop means a loss of power of 3.5%. In Watts, the power loss is 7.8 W. For the series connection, the voltage drop is 0.23 V. However, the voltage available on the panel is 58.2 V, which means a loss of 0.4% or 0.87 W in terms of watts.

Following is my view of shading on solar panels. I will assume a panel with 30 cells capable of supplying the 12V 5A. I am going to refer to 3 images. The first image (Fig 1.A) represents the panel in normal operation. There are zonal protection shunt diodes (bypass diodes), as shown in the image. The diodes are reverse biased and do not consume any power. Suppose now that the panel is shaded as shown in the next image (Fig. 1.B).



The shaded cells can be considered as open circuits. The panel continues to operate but with a lower output voltage of 7.4 V. If this panel is connected in series with other panels, there will be no problem. By contrast, we do not want to connect this panel in parallel with other 12V panels. In Fig.2, I represent the mounting of the panels in series. One panel is shaded, so that the total output voltage is 31.4 V instead of 36 V.





In Fig.3, I represent what I would use if I had to connect the panels in parallel. I'm not entirely sure if I'm correct. First, I would use 3 external diodes. Electrical engineers do not like voltage sources connected in parallel. By contrast, the current sources should be connected in parallel. The question is: should we consider the panel as a voltage or current source? or as a "mixed" source? I will not try to answer. External diodes consume 3 W power which is not good. And the shadded panel is completely off. It does not contribute to any current to the load. Instead of 15 A flowing into the load we will only have 10 A as if only had 2 panels.

Regards, Vladis
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Old 25-11-2014, 09:59   #126
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Re: Solar Panels - Series or Parallel ?

Thanks for a very detailed post Vladis.

However the mathematical modelling of shadowing on series/parallel connection is very complex.

You have considered the case where the shadow only falls on on a group of cells within the bypass diode of one panel. This is a very unique case that favours series connection.

To correctly model the system we need to consider a multitude of possible shadow options. Shadows that fall across multiple bypass diodes and multiple panels, as would occur in real life. The maths becomes very complex and is beyond my ability, but it would be great if someone could produce a realistic simulation.

The blocking diodes in parallel connection are unnecessary.

It is also necessary to assume realistic wire sizes. Parallel connection does require larger cable sizes between the panels and the controller. This is a disadvantage. However, to use wire sizes appropriate for series connection and assuming people would use these for parallel connection is not realistic.
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Old 01-12-2014, 13:15   #127
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Re: Solar Panels - Series or Parallel ?

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Re series vs. parallel, here is something to read...
Interesting article. I seem to have missed something, though. Nigel recommends parallel based on experiments with a low voltage panel. He also says that we should use the lowest voltage panel we can. That seems to fly in the face of conventional thinking and I can't see his justification for the comment?
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Old 01-12-2014, 14:33   #128
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Re: Solar Panels - Series or Parallel ?

Slightly off topic. Three days ago I was in a class 2 cyclone in Australia. Hail went through one panel and killed that whole section. Because I had systems as stand alone and only the outputs fed and isolated with diodes on the battery output, it was no big deal. Whilst we are all talking about amps and voltage, I had not given any thought to the type of glass used. In my case, the el cheapo folding camping solar panels lasted so much better than my expensive marine solar panels. Just a thought.
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Old 01-12-2014, 14:50   #129
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Re: Solar Panels - Series or Parallel ?

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Yes there have been a million threads on the subject on various forums with many different opinions. It seems to me there should be a simple correct answer.
Well this is a 3 year thread, have you found the simple correct answer because I would like to know?

I currently have a 290W panel with a Vmp of 35.6V feeding a FlexMax60 controller for my 12V system. I'm considering adding another panel same size because the current panel gets some shading once in a while, but the second would probably rarely get shade.

I sized the wiring from the start for 2-290W panels in parallel, but it would be easier to wire them in series.

Where's that simple correct answer (one word answer, either parallel or series)?
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Old 01-12-2014, 14:56   #130
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Re: Solar Panels - Series or Parallel ?

That one is easy for you - parallel. You already have high voltage panels, so will not see a significant gain from your MPPT controller when in series. Your wiring is also probably sized correctly, so you won't see any significant gain by going higher voltage on it.

The parallel/series thing really becomes more important for nominal 12V panels used with MPPT controllers. Here, the panel operating voltage is often very close to the charging voltage and the voltage drop in the wiring is more damaging.

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Old 01-12-2014, 15:07   #131
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Re: Solar Panels - Series or Parallel ?

Just how does a MPPT controller know what to do if 2 panels in parallel are feeding it??????????????? How does it solve the conflict between the panels if 1 is getting shaded and the other isn't?

BTW - I can accept the concept of PFM (pure f***ing magic)
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Old 01-12-2014, 18:01   #132

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Re: Solar Panels - Series or Parallel ?

sparrow-
When that article says to use the "lowest" voltage panels you can get, that's just a poor choice of words. He apparently means the lowest voltage that will charge your battery, i.e. a nominal "12" volt panel for a "12" volt system.
His logic is that any shade on any single cell will effectively kill an entire panel. So by using as many separate panels as you can, in parallel, you are allowing for shade to knock out individual panels and do the least damage by "only" knocking out one panel, which is one small string of cells in parallel.
All well and good, but there are panels that have two or three or four strings of parallel cells in them, with varying diode setups, and if you have the right panel with two or three parallel strings in it...one cell in shade still only knocks out one string.


I think the bottom line is still going to be that you have to consider mounting locations, and panel configurations, and how to minimize the problem of shading in consideration of how many strings or panels it might knock out. One of those situations where a "professional" installation can make a big difference.
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Old 02-12-2014, 14:27   #133
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Re: Solar Panels - Series or Parallel ?

One of the first solar panels I purchased was a 30 cell, marketed as self regulating. But I later found out that 30 cells weren't quite enough especially once the panel got hot or if there's any shading, it's my understanding thats why 36 cells are standard. But now we have maximum power point tracking and I can't find the answer to what is the best number of cells. Which is is what it comes down to when you're doing series or parallel or your choice of panels. I agree most of the large panels are several small panels in the same frame. And a very important consideration is how they're orientated. most shadow is fore-and-aft ... the mast.. And by aligning the panels up so only one panel at a time gets shaded instead of several makes a huge difference
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Old 07-07-2016, 11:27   #134
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Re: Solar Panels - Series or Parallel ?

This Thread is over 2 years old. Is there any advantage of starting a new one because I think this is very important but want to keep all the information together. The YouTube channel - gone with the Wynn's did a video : sailboat solar power- series vs parallel and shading where they show that if two panels are hooked up in parallel and one is shaded you lose half your power but if they're in series you lose all of your power.
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Old 07-07-2016, 11:58   #135
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Re: Solar Panels - Series or Parallel ?

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Just how does a MPPT controller know what to do if 2 panels in parallel are feeding it??????????????? How does it solve the conflict between the panels if 1 is getting shaded and the other isn't?

BTW - I can accept the concept of PFM (pure f***ing magic)

You know that is real close to asking how the thermos knows to keep hot stuff hot and cold stuff cold don't you?
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