Shade effect on series panels.

The OPs mismatched panels will perform well but will not be optimum. The panel amps will get reduced to the lowest common denominator as will Vmp from the individual panels. The IR curve (knee) is different for different amps for a single panel plus there is a mixture of panels with different curves, different technology or manufacturing parameters, etc. The MPPT controller chooses the best output based on what it sees and is unaware of multiple panels with their individual nuances.

But the OPs panels are close enough to give good results.

BTW It's common for DIY solar systems to evolve over time when more power is desired or the the falling price point.

Very interesting! So they do add their Vmps as the voltages to be added (less a little for heated panel as she said)

yes


https://www.youtube.com/watch?v=JfzT8u205co

If I put a 135w with Imp of 7.5 amps and Vmp of 18v in series with a 250w (total 385w) with Imp of 8.3 amps and Vmp of 30v, would I get about:

48 volts and 7.5 amps (360w) to the MPPT controller's input? Then output at 97% efficiency 349w, and if battery is 13.5v, amps output would be 25.8?

the controller is NOT trying to keep to keep 'each' panel at max vmp

drop that idea, there is no way for that to happen
the controller doesn't know one 90v panel from a string 18v panels
or a string of mixed voltage panels

the controller looks at total voltage compared to amps flow aka 'watts in'

and attempts to keep max amps into the 48v battery bank

"its done with math comparing power in to power out, and adjusting the output voltage"

I find with my MPPT controller that output voltage is the battery voltage (which the controller cannot adjust AFAIK)

In Bulk, "panel" or "array" voltage is the Vmp of the panel and is adjusted by the controller ("Tracking")

I do not understand what is going on with 2oldman's array for displayed input voltage while in Bulk, where there are mixed panels in series.

How can the controller keep each panel at its individual Vmp? If the total input voltages is the sum of the different Vmps, what is keeping each panel at its Vmp?

I think the "balancing" that happens in Float is where "demand" at the output has an effect on what the MPPT buck converter does for input. But the topic is about when in Bulk.

no.. the mppt does not force the panel to do anything

mppt is a conversion circuit

it attempts to use a voltage that will give the max amps into the battery from the 'power available from the panel'

its done with math comparing power in to power out, and adjusting the output voltage

as the battery charges, the Resistance goes up, amps acceptance (aka watts) goes down, mppt raises voltage

it does not do anything to the panels

if enough sun is available, yes panel volts will rise some as amps needed is reduced, but this is a byproduct side effect
not a control function

"mppt voltage is based on the output to battery not any individual voltage of a series string "

I am not sure it is related to output. It could be correct I don't know.

I have the notion that the "panel voltage" (chosen Vmp) with MPPT in Bulk is the best voltage (to go with the input amps? I am unclear on that too) that will get the most input watts.

The controller forces a single panel to be at the voltage the controller wants, so what the panel's "real voltage" is doesn't count. If the string has panels of all different "real voltages", you could add up the "real voltages" to get the string "real voltage" but the controller would have to pick its own idea of the best voltage to use to get the most watts. Some Vmp amount.

Output watts are then divided by battery voltage to get whatever amps that is.

In Absorption and Float, the controller uses PWM on off timing between the "real voltage" and zero to get a sort of average voltage for the input voltage that will maintain the set point output voltage---aha is that where output comes in? Except that is not as in Bulk when the controller is in Tracking mode using Vmp. ( I think :( )

BFL13 wrote:

2oldman wrote:
The numbers seem fine to me. What's the problem?

CA Traveller was giving me a hard time about a panel having a Vmp of 14V for one thing. I don't know what your BPs are supposed to be compared with what they are. I don't know anymore if it is correct to add the Vmps of mixed panels to come up with the Vmp the controller will choose. We have heard that the controller gets confused about what to choose.

My plan is to wait and see what you get next, and note what others have to say.

remember his panels are in ' series'
it is the amps that must match up not the volts
EXAMPLE if one panel is 4 amps and the rest are 6 amps
the 4 amp panel will restrict the string to 4amps or eventually burn out from trying to carry 6 amps

MATCHING VOLTAGE is for parallel panels

his series panels will have series total addup voltage
if all his panels are within a few 'tenths' in AMPS he should be OK
any significant different say 1/2 amp or more and the circuit will be restricted to the amps ability of the lowest panel

if his lowest panel his 6.5amps and his max panel is 8.2 amps
he will never see over 6.5 amps max input because that panel cannot pass 8 amps

i don't think he has that much difference in his panels
it just an example to show you the way the series circuit works

mppt voltage is based on the output to battery not any individual voltage of a series string

2oldman wrote:
I fail to see what is 'wrong' with my last post of numbers. And I really don't understand "choosing" a voltage.

Isn't having 5 panels in series the same as one big panel with the same voltage and amps?

AFAIK yes.

I don't know if there is anything "wrong" with your numbers. I am confused.

I am using "choosing" to mean the same as "tracking" by the MPPT controller.