One charge controller, or two? For opposite facing panels.

Hello,
Ok, I'm a little bit stuck and could really do with some advice.

I have four 300W panels. Two of them face east, and two of them face west. That is the way the roof faces and they can't be arranged any other way.
I'll be running a24V battery system.

Now, my original logic was to use two charge controllers (one for the east facing panels, and one for the west facing panels) and have essentially two strings of series panels. This was to try and deal with the issue of shading between the east and west facing panels.

However, I want to use an MPPT charge controller which works with lithium cells. This feature doesn't seem to be included with any of the controllers at thecheaper end of the range. But, this feature is included with many of the 300+ controllers.

Now, not wanting to buy two 300+ charge controllers (due to budget), also spending nearly 700 on charge controllers for a 1kW array seems a little excessive...Is there a way of wiring all four panels into one charge controller, even with them facing opposite directions?

I'm thinking maybe the PCM60X like everyone seems to be using, or one of the morningstar TristarMPPT controllers would have the capacity to handle 4 panels.

I've been reading about bypass diodes being used for shading issues but not specifically for whole strings facing opposing directions, but I'm thinking the same rules apply.

Does anyone else have panels facing different directions?


I don't know if I'm over thinking this, or if I've missed something obvious. For me this solar project is just a bit of fun, doing something I find interesting. So spending vast sums on kit which I am not 100% sure will do what I need it too, is mildly troubling for me.

I've included a quick sketch of what I think may work for my setup.

Any help or advice would be greatly appreciated.



Thanks. Alex

Sorry mate, if you want to use the most out of your panels, the way your setup is laid, only 2 MPPT SCs can achieve this.

You need 2 chargers to get full power out of it. Otherwise you only get power from 1 side or the other.

Either you get 1 charger with 2 MPPT or you get 2 MPPT chargers or you go the simple route and go 2 PWM chargers or lastly but least effective 1 MPPT and hook them up in paralell.

Thats my 5 cents.

Note that on cloudy days the 2 sides will generate same amount so its only when its sunny you need 2 controllers

silverse2m6 and daromer are right, since your panels are faced opposite and we only have one sun, only one side will give you max. power. so, in order to get the maximum out your panels, you'll need two strings and seperate charge controllers.
But as far as I can see from your drawing, you have the two panels on one side connected in series and the panels on both sides connected in paralell. This setup should also work ok and I would try it. I also have panels facing in different directions connected to the same string (althoughI have 3 charge controllers for 3 strings, my panels are faced from south-east all the way to north-west). And I also connected panels facing in different directions in parallel and it works fine. The panels in the shadow don't bring down the whole string (as it would be with series connections). So I would give it a try.

Btw, I'm using 3 EPsolar Tracer 3215RN MPPT charge controlers, each costs around 130$.

Have sun!
Oliver

Yeah it works to have each side in series and then paralell. As I said in shade this will produce equal amount but in sun only kind of 1 side will produce... So it depends on the money you want to spend. But on the other hand look at for instance the cheap 7210 charger that is on ebay.. If it fits your voltage range. Its rather crappy but could be a start....

Preferable is better controllers though.

I run 5 actually.

2x pcm60 for 1 roof. Wasnt enough with one...
1x pip4048 fr south for one angle
2xMPPT on the MPI charger. East and south on that one. All to cover it all.

Thank you all for the advice. I've been slowly convincing myself to get going with something cheap, that way I can get some real world numbers (I like having numbers for things).
I think I need to accept that I will inevitably be purchasing several different charge controllers in the search for my ideal balance between price and efficiency.

It's good to know that all of the above setups will work, albeit with varying degrees of efficiency.

I'm very tempted to go with some cheap controllers, then play around with the wiring and the setup and see how much difference different configurations actually make.

It is quite daunting, with so many different bits of kit on the market, all with their own advantages and disadvantages for every individual application. There really is no 'one size fits all' for solar.

I think my longer term plan will be 2 MPPT controllers. I was initially looking at the 30A Tracer actually, as a cheaper option to the PCM60X. I like the way the software interface looks on the PCM though.

I'll have a look at that 7210 while i debate which way to go with the more expensive controllers.

On things like these, I "buy once, cry once". Even with cheaper equipment you will likely only get a portion of what a good charger would deliver (look at efficiencies and idle consumptions)

Watch this... look at just 6 panels how much you can draw from the sun only on one facing direction...

Slightly off question but can you have 2 or more chargers for one battery pack or do you need a pack for each?
Thanks

More chargers on a pack is no problem, i have 4 in use.
Must be the same voltage of course.

Same here. I got 4 chargers on same battery system

4 PiPs on one battery pack. Since they work in pairs of two in parallel, I sometime have one pair charging the battery while the other one is discharging.

daromer said:

Same here. I got 4 chargers on same battery system

Click to expand...

Do you use the parallel kit to connect your PCM60X or do you just connect them as-is?

No paralell on pcm. You only do that on the inverters and Only on the inverter outputs.

Ie my pcm are all on its own.

daromer said:

You need 2 chargers to get full power out of it. Otherwise you only get power from 1 side or the other.

Either you get 1 charger with 2 MPPT or you get 2 MPPT chargers or you go the simple route and go 2 PWM chargers or lastly but least effective 1 MPPT and hook them up in paralell.

Thats my 5 cents.

Note that on cloudy days the 2 sides will generate same amount so its only when its sunny you need 2 controllers

Click to expand...

Can you pls explain why one controller will use the least powered panels?
Isn't that the point of mppt?finding the most powered panels?
Also , mppt is done over time so shouldn't it learn that in different times during the day each area has different power?

Ymor22 said:

mppt is done over time so shouldn't it learn that in different times during the day each area has different power?

Click to expand...

Nope. Mppt is a function of the most power output based on voltage/amperage output combination of the panels. It has nothing to do with where the panels are situated or time of day or anything. A cloud passing over the panel will cause the mppt to readjust the parameters to get the most power output. Or a planes shadow, or a flock of birds, etc. It's total random what would cause the panels to be limited

Ymor22 said:

Can you pls explain why one controller will use the least powered panels?

Click to expand...

If all the panels are connected together, the weakest panel is the one that will govern the amount of power available. It would be like having a hose with a kink in it. Doesn't matter what the capacity capability is of the all the panels if one of them is holding the whole system back.
This is why using 2 strings of panels is better for the different times of day when the sun hits the east most or the west most sides of the roof.

Korishan said:

Nope. Mppt is a function of the most power output based on voltage/amperage output combination of the panels. It has nothing to do with where the panels are situated or time of day or anything. A cloud passing over the panel will cause the mppt to readjust the parameters to get the most power output. Or a planes shadow, or a flock of birds, etc. It's total random what would cause the panels to be limited


If all the panels are connected together, the weakest panel is the one that will govern the amount of power available. It would be like having a hose with a kink in it. Doesn't matter what the capacity capability is of the all the panels if one of them is holding the whole system back.
This is why using 2 strings of panels is better for the different times of day when the sun hits the east most or the west most sides of the roof.

Click to expand...

Why would the weakest panel dominate? Is that an electricity law or panels behaviour?
I can't find an explanation for why. It is simply assumed

Korishan said:

If all the panels are connected together, the weakest panel is the one that will govern the amount of power available. It would be like having a hose with a kink in it. Doesn't matter what the capacity capability is of the all the panels if one of them is holding the whole system back.

Click to expand...

If connected as one long string of 4, then yes, that would be correct. But connected like the OP is planning I suspect that they will get nearly as much power with only one MPPT vs two MPPTs.
Why? Because each string is two panels (ie same number) so voltages are going to be close.
Any voltage differences would be from panel temps only, eg full sun = hotter vs shaded= cooler, but this is not huge difference.
Total current would be the sum of the east & west side.
One MPPT should track this arrangement at nearly the same as two MPPTs with max a few % loss.

I have 3x Victron MPPTs feeding the one battery pack system (3 due to max power handling of each MPPT). Each MPPT has 8 panels in strings of 2.
The 3 arrays face the same direction but see different shade.
I've attached graphs from today's output. You can see around 8am that the voltages are nearly the same but the power output varies (lower purple line). So the voltages on each array stays similar, ie effectively it's just the current drawn varies to track MPPT even though my arrays are not joined.

Ymor22 said:

Why would the weakest panel dominate? Is that an electricity law or panels behaviour?
I can't find an explanation for why. It is simply assumed

Click to expand...

This apply for series strings, not for parallel, but bypass diodes help there too.

Ymor22 said:

Why would the weakest panel dominate? Is that an electricity law or panels behaviour?
I can't find an explanation for why. It is simply assumed

Click to expand...

The way solar panels work is by photons landing on the panels knocking electrons around to make them move out of the panel. These electrons won't move if the sun doesn't hit them. If they aren't pushed out of the panel, there are no electron holes for replacement electrons to take up space in. Which slows the whole system down.
As mentioned before, it would be like having a hose and somewhere in the middle you squeeze it off or kink it. Water can't flow because of the obstruction and not enough water can get out of the way for more water to follow.

Here's another explanation of how the panels arrangement works:

I just did a google search: https://www.google.com/search?q=why...+series+drop+power+when+one+panel+is+in+shade

Redpacket said:

But connected like the OP is planning I suspect that they will get nearly as much power with only one MPPT vs two MPPTs.

Click to expand...

I missed this as I was answering just Ymor22's question directly. However, this is correct, according to OPs original design I agree.

Redpacket said:

This apply for series strings, not for parallel, but bypass diodes help there too.

Click to expand...

Agreed 100%. Plus while panels are in parallel they will have equal voltages on the output wires regardless of shading on the panels. Would definitely use blocking diodes for added protection and back feeding though in case the shaded panels are completely shaded.
Altho, they should have blocking diodes built into the panels anyways.