Parallel versus Series panel connections

nickdearing88

Hi everyone.

I was just given two Renogy poly 100w panels from a friend. I want to incorporate them into my current system which is using two Renogy mono 100w panels. My current two panels are wired in series and I'm using a Morningstar MPPT charge controller that can accept up to 125v max open circuit voltage.

My question is should I add the new panels in series or parallel with the current panels? Max OC voltage wouldn't be a problem (<90v) in series. and all panels are rated at 100w each. 

I already have some unused branch connectors so I could wire the two new panels in series themselves and join in parallel with the current panels but I was concerned about slight voltage difference in the panel specs. The Voc is only 0.1v different in the panel types but the MPP voltage for the mono panels is 18.9v and the poly panels 17.8v.

What do you think is my best option?

Estragon

To me the voltage is close enough. You might want to confirm max voltage at your lowest expected ambient temps in your location vs temp/voltage curve for those panels if you get cold. I would probably prefer series to save wire if going any distance.

Horsefly

I agree the voltages are probably close enough that paralleling them would be OK, but as @Estragon said limiting the loss on the PV wire going to your charge controller would argue to put them all in series.

You didn't mention the current (Imp) for the two types of panels. Keep in mind that if you put them all in series, the total current will be limited to the lowest Imp of all the panels. That is, if the poly panels have an Imp of 6A and the mono are 5A, you'll only get 5A out of the 4 put in series, effectively reducing the wattage out of the higher current panels. It may be the difference isn't enough to matter much.

Steve

nickdearing88

Thanks for the replies.

Sorry, I forgot to stick the current ratings in the first post. The mono panels Imp = 5.29A and the poly panels Imp = 5.62A, just under 10% difference. I've only worked with panels that were exact matches and specs so this is new to me.

This is for my "experiment project" on my small backup system. I've been messing around with different configs and equipment for a few years, preparing for a future off-grid homestead in the next 5 years or so. I just got a Morningstart MPPT 40A controller from NAWS and what an amazing difference from PWM! This test will be to log some data on the mono versus poly panels with the same rated output. I will start by testing with only the two new poly panels (in place of the mono panels), but wish to combine them later this spring.

However, before trying either series or parallel, I wanted to ensure I wouldn't cause any damage to the panels. I've heard <10% difference between voltage and/or current is the rule but wanted some opinions. It sounds like I'll be OK either way, and will likely test both connection types over time.

I agree that voltage drops make series more appealing but currently, the panels are only about 25 feet from charge controller and battery bank so the current voltage drop is small, about 0.3 volts. The wire from the panels to the controller is 10ga and the two current panels in series run about 40V and about 5-6A.

Thanks again for the helpful comments. I've already read through the forums a great deal and found a lot of interesting material.

mcgivor

Since this is an experiment, try putting one mono and one poly in series then parallel the two and see what the results are, my thinking is because the current of each is so close, it may be benificial, only a theroy, but that's what experiments are all about.

littleharbor2

mcgivor said:

Since this is an experiment, try putting one mono and one poly in series then parallel the two and see what the results are, my thinking is because the current of each is so close, it may be benificial, only a theroy, but that's what experiments are all about.

Good suggestion McGivor. Now that you have a quality MPPT controller you might also try all four panels in series to see if there is a difference in output.

mcgivor

littleharbor2 said:

mcgivor said:

Since this is an experiment, try putting one mono and one poly in series then parallel the two and see what the results are, my thinking is because the current of each is so close, it may be benificial, only a theroy, but that's what experiments are all about.

Good suggestion McGivor. Now that you have a quality MPPT controller you might also try all four panels in series to see if there is a difference in output.

And be sure to  post you results of the experiment, the whole comuinity benifits from the information gained.