What would happen if say for instance you using 3 x 12 v panels that are 120 w and you add 2 x 180 w. How would this affect the charging. Would all panels operate at 120 w or would they operate at their own wattages.

Many thanks Dean

 

34 minutes ago, Dean K said:

own wattages

Panels operate on voltage, so you'd have to try and match the voltages, if your 120W panels, let's say, produce maximum smoke at 16V (Vmp) and you are running them in parallel and lets also assume the 180W panels run at the same Voltage, but more current at Vmp, then you can just parallel them up and voila, you should at best be able to extract ( 3 X 120W + 2 X 180W) out of that lot... but I suspect you may not have the same Vmp's between the 120W and 180W panels and thus my explanation would be not applicable... the point being that Voltage is what matters, if you run your 120W panels in series and lets assume for a moment say their Vmp is 16V, that would give you 3 X 16 = 48Vmp, now if the 180W panels had a Vmp of 24V, then the two in series would also be 48Vmp and could run in parallel with the 3 X 120W panels. But it also depends on your load/charge controller/inverter/whatever you are feeding the panels into, what is this device expecting Voltage wise and what can it cope with...

You are not providing enough information for a sensible answer, unfortunately. You would have to provide, the specs of the 120W panels as well as for the 180W panels, state how the existing ones are wired up and what they are connected to and what, the unit to which they are connected, can cope with Voltage wise...

Edited May 4, 20215 yr by Kalahari Meerkat

Thanks that makes sense, they are all 18 volts through a 30 amp 12/24 volt control unit charging a 350 amp hour 12volt battery.

 

 

4 hours ago, Dean K said:

18 volts through a 30 amp 12/24

ok, there's the limit, the 30A charging unit 3 X 120W = 360W / 12V (more like 14V for charging) = close to 30A, so the extra panels wouldn't do much most of the time, except when things are cloudy, then they would add some extra power.

what if the difference is by mppt? 120w on one and 280 on the other. Will that work?

On 2021/06/03 at 5:07 PM, nightcrawlernic said:

what if the difference is by mppt? 120w on one and 280 on the other. Will that work?

Again you are not really providing enough information for me to figure out what you are asking, I assume you want to mix 2 panels, again Voltage is the most likely limitation...

but just for interests sake, let's say you have a 120W panel that can produce 10A at 12V for its MP values and you have a 280W panels than can strangely also do 10A, but now at 28V for its MP value... if the MPPT connecting these can handle 40V or more at 10A, then putting the two panels in series, would/should give you 40V at 10A going into the MPPT and thus both your panels should produce as much as they are rated at, but I'd imagine that the 120W panels would probably be more like 18V and thus 6-odd amps and the again if the amps at MP (Max Power in case its not clear) are the same for the 280W panel and the total MP voltage for both in series is in line with what the MPPT can manage, then puttng them in series would be best option, I'd say... if the panel Voltages match in terms of MP and the voltage is enough for the MPPT and it can consume/use all the amps provided by the two parallel panels, then all is fine in this scenario as well.

I guess one can put down the following as the thumbsuck rule for mixing panels...

panels in series will add up the Voltage at MP for their respective MP Voltage and the current limit will be the panel with the lowest IMP value, thus the panel providing the lowest A at MP will be the limiting factor*

panels in parallel will add up the current at their respective MP Current and I suspect then, that the Voltage will be limited to the Voltage for the lowest VMP panel Voltage and this will be the power limiting factor*

* NOTE I am theorising here, I have not tested this in real life, but these would make most sense to me...