hi all

i have 12 panels  250 watts and 2 panels 300 

can i make 2 string 6 panels 250 watts and 1 panel 300

 

There are roughly two ways this can pan out, but in both cases the answer is yes: You can do what you suggested (Assuming the MPPT will allow a voltage that high).

SO here's the two ways it might pan out. The first way, the 300W panels will be reduced to the current of the 250W panels, and therefore work like a 250W panel. At the loss of 100W or so out of the whole, that's not bad.

The second way: If the 250W modules have 60 cells, and the 300W module has 72-cells, and since 72/60 = 300/250, it would mean the Imp/Isc values of the 300-watt module is very similar to that of the 250W models, and since current remains the same and voltage adds up in series... you might just get the full 300W out of it too!

Adding to Plonksters explanation: https://solarpanelsvenue.com/mixing-solar-panels/

Another titbit to keep in mind / way to solve it, as  had a similar scenario, 2 x 200w and 3 x 310w. 

Got two controllers of the same make, 1 x 150/35 and 1 x 75/15, connected onto the same bank after setting both controllers to the exact same settings.

Just an idea, for now or other future consideration.

To add another example, I have a perfect example on my own roof. I have a bunch of 150W panels (36 cells), and then I have some 320W panels (72-cells). If you have an eye for numbers, you can already see that "wow, those have about the same watt-cell ratio". SO the smaller panel makes about 8.3A at 18V, and the larger one makes around 8.5A at 38V. So what will happen if I series them? Well, I'm going to get 8.3A (you always get the lower one of the two), but my larger panel is not going to work at optimum voltage because it is running at the lower current, so I will not get 470W... but I will probably get at least 400, in fact in perfect conditions I'd be surprised if I don't get close to 450W... 🙂

Edited February 5, 20197 yr by plonkster

One thought in the back of my mind, one would also not like to strain the diodes on the lower specced panels.

I always try and keep in mind "plug and forget" so don't push the envelope, and panels are "plug and forget".

 

1 hour ago, plonkster said:

150W panels (36 cells), and then I have some 320W panels (72-cells)

Question, why not put 2 x 150w in series and then those 2 in parallel with 1 x 320w?

 

32 minutes ago, The Terrible Triplett said:

Question, why not put 2 x 150w in series and then those 2 in parallel with 1 x 320w?

Sure... you could do that too if you wanted.

If you really think about it, if I put two of those 150W panels in series (you know them, Tenesol jobbies), then I have a 72-cell 300W combo. And almost nobody would think too much about combining a 300W module with a 320W module (that's less than 10%). As long as:

1. Current capability of each module is similar

2. The length of the parallel strings have the same number of total CELLS, and

3. Overall voltage is below the maximum system spec of the lowest panel (usually 1000V)...

Then you are good to go.

Given that very often the 300W module uses the exact same cells as the 250W module (just 72 of them instead of 60)... putting them in series is really no problem at all.

But do your homework first.

Edited February 5, 20197 yr by plonkster

26 minutes ago, plonkster said:

And almost nobody would think too much about combining a 300W module with a 320W module (that's less than 10%). As long as:
But do your homework first.

And that was what I was waiting for ... I would not combine 250w panels with 1 x 300w panel.

More than 10% difference.

Arrays on different controllers are much safer, better production and stays within manufacturers design specs. 🙂