Mixing different panel sizes

[Solarexploits]

I have a couple of different panel sizes & trying to work out the optimum way of using them they are 310W, max O/C V 44.9, optimum output V 36.4, opt output A 8.52 & 240W max O/C V 37.4, opt output V29.6, opt output A 8.11 

 

Now I realise if I "daisy chain" in series, I'm simply going to be adding the output voltages together, but say I have 2 of the 310W & 1 x 240W in series, can that cause any damage to the 240W panel due to higher current generated by the 310W panels, or does it simply reduce the output of the 310W panels slightly if at max output.

 

Equally if I put dissimilar panels in series is the unequal voltage a problem, i'm seeing that I'm putting 36.4V in parallel with 29.6V, which my gut tells me isn't good, will I finish up with a median voltage somewhere in the middle, again, can it damage either of the panels & again, does it in effect reduce the output of the more powerful panel?

 

 

 

[ProDave]

How many of each type do you have and what are you hoping to connect them to?  e.g grid tie inverter, battery charging etc.

[Dillsue]

For the max voltage have a look at the label on the panel or the data sheet.  Ive just looked at one Ive installed recently and its 1500 volts. Youre unlikely to have problems with the voltage applied by a series of upstream panels and the max panel voltage could well be higher than the input to your inverter??

 

By series wiring differing panels youll limit the string current to that of the lowest current panel,  so if you put a 250w in series with a 310w that strings current will be limited to 8.11A even though the 310w could push 8.52

 

By wiring in parallel each panel drives whatever current it can but higher voltage panels have their voltage pulled down to that of the lowest voltage panel.

 

Not sure what system youre installing but micro inverters or optimsers do away with this problem and allow mixed size panels. On the optimised solaredge system weve just put in weve got 405w and 335w on one string and 310w and 320w on the second string. The optimisers deal with all the current/voltage regulation and the panels just feed the optimisers with whatever they are rated at. Makes later extensions a piece of cake👍

[Carrerahill]

3 hours ago, Solarexploits said:

I have a couple of different panel sizes & trying to work out the optimum way of using them they are 310W, max O/C V 44.9, optimum output V 36.4, opt output A 8.52 & 240W max O/C V 37.4, opt output V29.6, opt output A 8.11 

 

Now I realise if I "daisy chain" in series, I'm simply going to be adding the output voltages together, but say I have 2 of the 310W & 1 x 240W in series, can that cause any damage to the 240W panel due to higher current generated by the 310W panels, or does it simply reduce the output of the 310W panels slightly if at max output.

 

Equally if I put dissimilar panels in series is the unequal voltage a problem, i'm seeing that I'm putting 36.4V in parallel with 29.6V, which my gut tells me isn't good, will I finish up with a median voltage somewhere in the middle, again, can it damage either of the panels & again, does it in effect reduce the output of the more powerful panel?

 

 

 

It can be done but you need to know specific technical details of the cells to check compatibility. Generally, you should not really mix different panel sizes, even if you were to do a parallel/series mix it would not be great. Best bet is 2 smaller inverters or one with dual string.

 

It would be a bit like mixing different battery sizes, one might pull the other down etc.

 

PV panels are made up of smaller cells, the cells in most panels are usually open circuit, 0.5V - so a 1 V panel would have 2 cells, a 60V panel would have 120cells, however, cell efficiency's and things improve, so a cell from 10 years ago will be far less efficient, i.e. less peak W than a cell from today, so your then mixing apples and pears.

 

 

 

 

[Solarexploits]

39 minutes ago, ProDave said:

How many of each type do you have and what are you hoping to connect them to?  e.g grid tie inverter, battery charging etc.

I have 10 of each the higher wattage ones will be feeding a new 4kW 48v inverter, it takes a max of 3kW solar input, so 10 x 310W is just too large, hence I'm intending to use 3 x 3 series strings in parallel, which leaves me an odd 310W panel. The other 240W panels are feeding 2 x 24v solar controllers for additional battery charging, I only have 6 connected so far all in parallel

 

It sounds as though it might be best to find another purpose for the odd 310W panel, maybe a small 24v battery with another baby charge controller I have & use it for my garage lighting, I'll do some maths, but sounds like mixing them is going to be counter constructive.

 

 

 

 

[Carrerahill]

13 minutes ago, Solarexploits said:

It takes a max of 3kW solar input, so 10 x 310W is just too large.

You will rarely get anything like even 2.8kW from a 3.1kW string, it is common to add about 20% over max - all it means is that on the rare day you get perfect conditions (and if your install is perfect) then you will only make use of the 3kW, but the other 364 days you will get the benefit of being a bit closer to max input. It is only 100W, chances of you ever getting the 3.1kW are slim. 

 

So, not knowing the full story here, I could be wrong. Can you not just put all 10 of them on a string? Or 5 + 5 in a series/parallel string if voltage too high. 

 

 

Edited August 22, 2022 by Carrerahill