OK, OK!

I'll get 300W panels, and then place them at a crappy angle so they don't make too much power....

41 minutes ago, The Terrible Triplett said:

1)) Get another controller for 200w array - but I bet the MPPT in the Voltronics cannot be adjusted to sync the two controllers.
2)) Get all 300w panels and be done.
3)) Or my favorite one: Reduce the load to fit the existing array - then you do not need more panels. 

1) If you parallel the same ones of course, different brands nope(Don't think the blue can even do this)
2) Agreed
3) No - @DeepBass9 I'm sure you will be enjoying the extra comfort the extra panels will bring you

7 minutes ago, viper_za said:

(Don't think the blue can even do this)

Off course they can. HADMD? (Hoe Anders Doen Mens Dit)

Made the Blue (connected to 2 x 200w) and the Morningstar (3 x 310w) settings identical, from voltages right through to equalization settings, to charge same bank ... Morningstar even has temp compensation that one can adjust.

... wait you know they can all be adjusted, you are pulling my leg ... ?

Just now, The Terrible Triplett said:

Made the Blue (connected to 2 x 200w) and the Morningstar (3 x 310w) settings identical, from voltages right through to equalization settings, to charge same bank ... Mornginstar even has temp compensation that one can adjust.

This is fighting it out not synching

5 hours ago, DeepBass9 said:

But you can get 36V 200W panels, the same as the 36V 300W panels that I have.

Yes, do get those, but as I've said, if it comes from the same manufacturer and the same cells are used to manufacture the 2 panel sizes, the panels voltage is the only thing that would be different since the properties of the individual cells are exactly the same.

5 hours ago, DeepBass9 said:

Are you sure this will work SuperDIY?  3 strings of 300W+300W+200W+200W

It will work perfectly if the same cells are used in the 300W and in the 200W panels and if the charge controller can handle the higher voltage.

Think of it this way - a 300W panel and a 200W panel made up of exactly the same cells are nothing else than if you are using 3 x AA Energizer Max batteries connected in series and the set connected in series with another set of 2 x AA Energizer Max batteries connected in series. The batteries are exactly the same, the current through them will be exactly the same and the set of 2 x AA Energizer Max batteries connected in series will have ²/₃ available power compared to the set of 3 x AA Energizer Max batteries connected in series. I don't know how else to explain it. 

1 hour ago, The Terrible Triplett said:

Don't mix and match panels unless they are as close as damn to each other. 

300w and 200w are not a close match.

In most PV panels the individual cells are all connected in one serial string. When manufacturers assemble different sized (e.g. 150W & 300W) panels they usually make use of cells with similar characteristics, but use more of these cells in larger panels (e.g. 300W) and less cells in smaller panels (e.g. 150W). Since the cells are all connected in series the open circuit voltage and max power point voltage of the larger panels will be higher than that of the smaller panels, but the short-circuit current and max power point current will be exactly the same in both panels. Therefor if you buy a 150W panel and a 300W panel from the same supplier and the datasheets of both panels indicate the same short-circuit current and max power point current, you can be fairly certain that they've used cells with similar characteristics in both panels. That 150W panel and 300W panel connected in series will perform exactly the same as one 450W panel using similar cells.

If you however connect a 150W panel and a 300W panel in series and they consist of dissimilar cells e.g. where the panel voltages are the same, you will have a very mismatched combination.

To summarise:

• When connecting panels in series ensure that the max power point current (I_MPP) of all the panels are as close as possible to each other
• When connecting panels in parallel ensure that the max power point voltage (V_MPP) of all the panels are as close as possible to each other
• When you have to connect panels in series and parallel e.g. 4 parallel strings of 3 panels each, the I_MPP of all the panels in a string must be as close as possible to each other and the combined V_MPP of each string must be as close as possible to the combined V_MPP of every other string.

1 hour ago, viper_za said:

This is fighting it out not synching

Ditto

2 controllers charging the same bank - not recommended. Even if you can adjust both controllers to change charge modes at specific voltages etc. etc. no 2 charge controllers will be calibrated to the millivolt and or milliamp and at some point in time they will fight. It is a different story when charge controllers or inverters can be linked as in the case of the Axperts where they have a shared battery bank and communication between the inverters.

I have followed this debate without commenting since I do not know.

http://constructionreviewonline.com/2016/02/is-it-right-to-mix-and-match-different-solar-panels-in-one-solar-system/

This article I think is balanced (excuse the pun). Just imagine trying to find panels that match the 12 x 40w panels my father bought in 1982 to power a pump. My instinct is that so long as the panels in an individual string are the same and the strings do not differ too much in terms of voltage one can mix and match a bit.

Ditto Chris. As I posted above a 200w panel and a 300ww panel do not have the same amps nor volts and that is with both panels from same supplier, cells look identical, bought few months apart. What SuperDIY says does make sense, but then why do the manufacturers not say we can do it? I have asked with my 200w and 300w panels. 

@superdiy Yes I know the controllers are arguing, the larger one taking charge most of the time. Joke is, one is MPPT, other is PWM, real mess.
Late morning I see the Blue MPPT in float whilst the larger one is in Bulk. When the batts need juice however, and the load is powered same time, the two controllers "laat loop". So I still charge faster and can power a bigger load, at no extra cost or risk. But I do agree, if it is a permanent setup, don't do it.

However, I got the idea from Morningstar newsletter. As per their engineers it is 100% acceptable to use as many controllers as you want to charge the same bank provided the model, firmware's are identical, settings are identical for they will work in sync by default. No connection needed between the controllers. They tested it.

So I then extrapolate and would hazard the same will go for all controllers if they are the same make and model, age, settings are identical, firmware are identical, on the same bank, with no interconnection, that they will stay in sync. Will I do it, yes, with Morningstar controllers.

Aaai man... a little bit of common sense really. If they are the same voltage and you put them in parallel, then they can be different wattage. P=VI, but V is the same (because they in parallel), so they will simply contribute current according to their capacities. This is more or less true, except for one little caveat, the power curve might not be matched.

So back to basics, a PV panel is a constant current device over the linear voltage range (if you look at the power curve, you'll see the middle of the chart is more or less a straight line, hence "linear"). See the stolen attached with different curves for light levels and temperatures. This breaks down at the edges, at low light and as you approach Voc. Now imagine you have two panels with slightly different Vmax levels. You will then have two panels in parallel that behave similar to what you see in the attached chart at different light levels: One of the panels (or strings) will be pushed out of that linear region (off the cliff on the right) if you push the voltage towards the Vmax of the other panel (or string).

Now consider what the MPPT does. Most of them do perturb and observe: You perturb the voltage a little and see if the power increases. If it does, you continue perturbing it in the same direction until you see the power come down, then you perturb it in the other direction, until the same happens, until you oscillate around Vmp. What happens when this is done with two strings where one has a lower Vmax? I cannot conclusively say or prove this... BUT... what I would expect is that the drastic power drop that happens in the string with the lower Vmax will be noticed by the MPPT and it will therefore approach the lower of the two Vmax values. This means your panel with the higher Vmax will run at a less than optimal voltage and you will lose some power there. How much? Well, subtract the two voltages from each other and multiply it by the current rating of the suboptimal panel, that's how much you will lose.

So say you have a 300W panel (37V at 8 ampere) and you parallel with a 200W panel (36V at 5.5ampere, for illustrative purposes), then you will lose 8 amps at one volt, or 8 watts per module.

That's not optimal, but it is FAR from losing a third of the power, which is what happens if you series them.

What I read Plonkster, and I am laughing out loudly copying this:
A little bit of common sense really with a more or less true, except for one little caveat thrown in, not forgetting the slightly different Vmax levels and I cannot conclusively say or prove this... BUT... what I would expect ... 

That instills a lot of confidence I say old chap. 

Seriously you guys are debating theory here, and I cannot fault it, it does make sense. but let me ask you guys this: 
If I was your customer, paying you for your advice, holding you "responsible" if it does not do as you say, will you still tell me it is fine to mix and match 200w/300w panels?

I stand by this: If the manufacturer / supplier of said panels says it is fine and will take responsibility for advises given, then I see no problem, as it can "cost" them money if they get it wrong, and that, boys and girls, that is the good advice.

When I asked the question to Tenesol, exactly the 200w/300w panels, they said nope, don't, panels are too far apart. Yes, I have 310w's making the difference slightly bigger.

8 minutes ago, The Terrible Triplett said:

If I was your customer, paying you for your advice, holding you "responsible" if it does not do as you say, will you still tell me it is fine to mix and match 200w/300w panels?

I'd tell you to get the 300W panels :-)

Seriously, if you don't have a lack of space on the roof or a lack of money in the bank, get the bigger panels. That makes the array oversized, but it is not a bad thing. You see, as I explained, if you attempt to hit 3kwp exactly by using smaller panels to make up the difference, the mismatch is going to steal a hundred watts somewhere and you'll end up at 2.9kwp anyway. Keep it Simple.

However... if you are ME, you do your own work, you just got a special somewhere on 200W panels, you have a money problem (in the sense that the residual bit doesn't buy any of the fun toys you want!)... then get the 200W panels :-)

1 minute ago, plonkster said:

However... if you are ME, you do your own work, you just got a special somewhere on 200W panels, you have a money problem (in the sense that the residual bit doesn't buy any of the fun toys you want!)... then get the 200W panels :-)

And if you where ME you split the systems, 2 x 200w panels power X and 3 x 310W panels power Y - KIS. :-) 

I ALSO said, if you have a small system, on a tight budget ... 

Just now, The Terrible Triplett said:

I ALSO said, if you have a small system, on a tight budget ... 

I'm going somewhere else wity my system. Mid-range inverter (between 1.2kva and 3kva) with feedback and a grid-limiter. It means the expansion side of things involve "buying more PV" and the magic happens in the data processing, which happens to be my area of expertise. Wiring is not my area of expertise :-)

Lekker MAN Plonkster!!! Cannot wait to read about your journey. 

On 2016/07/13 at 12:11 PM, OomD said:

Don't mix panels, get 300W ones.

It is easy to forget that current is drawn from a source, while voltage is "pushed" from the source. This means that the panels cannot "give" the MPPT more watts than what the MPPT wants... the MPPT will use as many wtts as it can get, up to it's own maximum. Why do I say this? Well, if your MPPT maxes out at 3KW of PV then it simply means it cannot use more than 3KW. You can put a 5KW collection of panels on, it will not damage the MPPT... the MPPT will simply only use up to 3KW and the other 2KW will be wasted.

In other words, use 300W panels, go up to 3.6KW or whatever, and let your MPPT use as much of it as it can.

This is the same as using very large capacity batteries instead of smaller ones... as long as the voltage is correct it does not increase the power you suddenly get. The batteres just last longer but your instantaneuous power remains the same.

Hi @OomD

I have a dilemma related to this post on not needing to match panels on an mppt.

i have 12 by 650W panels connected in series to an 8Kw Deye inverter. I have read that sometimes the voltage of the panels can fluctuate in winter, so i am concerned that I may exceed the max v input of 500V (my max currently is 480v). If I split them into 6 each will my solar generation be reduced?

 

Both my strings face north and from 11am to 4pm i get full sun on all the panels. Should i split them into 8 on one mppt array and 4 on another, would that be more efficient than a 6, 6 split or does the inverter just total whats being generated regardless of the split? I live in Gauteng, South Africa.

 

i hope my questions makes sense. I am a newb.

 

I would split it 6 / 6. You could actually get more solar as you say you only have full sun from 11am. If it is split and you have shading on only one string, it would not influence the other one.