Mix 12v and 24v solar panels

[Chasein70]

I currently have 2 12v solar panels. I want to buy 2 24v panels. I'm assuming I can rewire the 2 12v panels in series then connect to the 24v panels in parallel then off to the charge controller?

[John61CT]

You can, assuming you're still within the SC spec'd input limits for power and voltage.

But to maximize efficiency of power conversion between the input and what gets into the bank

all the panels on a given SC should be the same model.

For a PWM setup that is already suboptimal, the difference will not be as much as with MPPT where the owner cares about that issue more.

Also, realize that fewer panels per MPPT SC handles a partial shading scenario better, 1:1 ratio in theory being the ideal.

With Victron for example, four smaller SCs can be just as inexpensive as one bigger one.

But do take more space and wiring.

[Chasein70]

Ok, thanks. I'm at work and had a hardware engineer working with me at the time of reading so he put your reply into English for me. I'm a software person.

[twinight]

From what I read, it's not good to mix panels. It will reduce the efficiency of the system to the weakest component. It's best to run the 24V panels through a second charge controller.

[Chasein70]

From what I read, it's not good to mix panels. It will reduce the efficiency of the system to the weakest component. It's best to run the 24V panels through a second charge controller.

Curious, where did you read that? Can you post a link

[John61CT]

Like asking for a reference for "the sky is blue".

All panels feeding a given SC should match if you want max efficiency.

[MtnDon]

When there is a mix of panels the general rule of thumb is to match the Vmp and Imp values within 10%.

For panel sets in series, the Imp value (amps) should be within 10% of each other. The total current will be limited by the panels with the lowest amp output.

For panels in parallel, it is the Vmp (voltage) that should be within 10%, as the output will be limited by the panel with the lowest voltage output.

The mismatches drag the output of the highest output panels down to match the lowest values. So you need to decide if the loss is worth spending more money for more controllers so you can keep the panels in matched sets.

All that assumes the controller you have can handle to total volts, amps and watts that would be connected to the inputs.

[Cosmo]

Sorry no first hand experience mixing panel voltage. My 12V panels put out about 17V open circuit. Sounds like 24V panels put out over 30V and the battery can handle the voltage. I will repeat what others said - maximum amps or watts should not exceed capacity of the controller or you might fry it.

I did find this link which sounds like the panels can be mixed as noted above - maybe not the best solution but if its what you have - why not try, if everything is fused...

https://www.quora.com/Can-I-use-a-24-V- ... -V-battery

=Cosmo

[John61CT]

When there is a mix of panels the general rule of thumb is to match the Vmp and Imp values within 10%.

For panel sets in series, the Imp value (amps) should be within 10% of each other. The total current will be limited by the panels with the lowest amp output.

For panels in parallel, it is the Vmp (voltage) that should be within 10%, as the output will be limited by the panel with the lowest voltage output.

The mismatches drag the output of the highest output panels down to match the lowest values. So you need to decide if the loss is worth spending more money for more controllers so you can keep the panels in matched sets.

All that assumes the controller you have can handle to total volts, amps and watts that would be connected to the inputs.

Well stated.

Getting things as efficient as possible costs a bit more, many don't care that much, happy with "good enough".

Personally if the SC cost ratio to panel cost goes from 5% to 50%, and I get a 20% increase in total output, that's worth every penny.

[Chasein70]

The mismatches drag the output of the highest output panels down to match the lowest values.

HA HA HA HA HA HA

[tony.latham]

The mismatches drag the output of the highest output panels down to match the lowest values.

HA HA HA HA HA HA

I must have missed the joke. MtDon is about as knowledgeable as one can get with off-grid electrical systems.



T

[Chasein70]

It's hooked up right now the way I stated in my original post and I assure you, he's wrong!!! It works great.

2 180 watt 12v panels in series and 2 265 watt 24v panels in parallel then hooked together

[John61CT]

It works great.

Not compared to the optimum, but if good enough for you, that's all that counts here?

What is the peak amps current going into your battery when it's depleted below 60% SoC?

[MtnDon]

HA HA HA HA HA HA

???
I never stated it would not work. I stated it would not work at top efficiency. ( I did not use those exact words but I assure you the gist was the same. )

I thought my reply with an explanation would have been better received than with laughter. At times, system efficiency is important to some people, so I took the time to expand my reply to include the reasons. I hope others may read it and learn something that may be useful to them at some point

Thank you, Tony and John.

[Chasein70]

The mismatches drag the output of the highest output panels down to match the lowest values.

I was laughing at this statement which is just not true. If that statement was true I would not have seen any boost by adding
530 watts of solar to my existing 360. There was a huge jump!