Loss by mixing different sizes panels with same voltage (vmp)

[sunrise]

Hi,
I am a bit lost with mixing panels in parallel. I have read through this article and it makes sense to me:
https://solarpanelsvenue.com/mixing-solar-panels/

However when I watched this video

The 2 panels are of same voltage(vmp), connected in parallel, I'd expect the MPPT output( amps ) would be very close to the 2 individual amps added together when they are connected separately. but there was a 1 amp output loss (10%) which is significant given the voltage spec is the same, Any ideas why?
Was it because the 2 panels actually produced different voltage even with the same spec'd vmp?

Thanks!

-SR

 

[gnubie]

First thing is, is what ever is on the output of your solar charger in a state that allows it to sink all the current the controller is producing when you have both panels connected? If you have 4kW of panels on the input but the load can only draw 100W, you will only ever see 100W from the array.

 

[sunrise]

First thing is, is what ever is on the output of your solar charger in a state that allows it to sink all the current the controller is producing when you have both panels connected? If you have 4kW of panels on the input but the load can only draw 100W, you will only ever see 100W from the array.

That's a good point, seems like in that video a battery(sealed lead acid?) was used, it's possible the max charging current the battery can take was below expected value. Too bad the author didn't mention this factor.

 

[gnubie]

If the battery is approaching fully charged that could certainly be the case. Put a load on your system that draws more current than your panels can possibly produce, then compare them individually and in parallel. I'm also assuming your charger itself is capable of providing all the panel's power to the load. If it's a low amp controller that might be an issue too.

 

[SolarQueen]

Hi! It's me, the person who did the video. The battery was not full, and I had the fan running to burn off most of energy generated during the video. I think the unsatisfying answer is just that there are losses involved in anything that is less than ideal standard test conditions, and so what you would expect to see theoretically is not always true in the real world.

During the lock down I've been squirreling away some equipment to do more detailed tests, so let me know exactly what you want me to do, and I'll see if I can make it happen.

 

[SolarQueen]

If the battery is approaching fully charged that could certainly be the case. Put a load on your system that draws more current than your panels can possibly produce, then compare them individually and in parallel. I'm also assuming your charger itself is capable of providing all the panel's power to the load. If it's a low amp controller that might be an issue too.

It was a Midnite Kid 30A, so plenty big for 300W to a 12V battery (300W / 12V = 25A). If you see the battery voltage before the charge controller was on, it was 12.5V, so plenty of room. I do think it was a small battery, so I will do it again with a nice big battery I've got my hands on now.

 

[SolarQueen]

All that being said, the results of the fact that the lower amperage panel created a bottleneck when in series, and if you have the same volts, but different amps, wire them in parallel was irrefutable.

 

[sunrise]

@SolarQueen first thank you for making these videos! I found them to be super helpful. Currently I am working on a small trailer setup that in order to maximize the very limited roof space, I have to mix different size panels. the panels I am mixing are of similar if not identical voltages, so I want to know if there is any penalty when I connect them in parallel.

I suspect that the input voltages of 2 panels were different, and it dragged down the one with higher voltage thus overall lower output amps. I think it would be helpful to measure the actual operating voltages and amps of 2 panels individually, then in parallel. so we can calculate input watts and output watts.

To my setup, in series isn't even the option, even I have identical panels. They will *never* be able to operate at same conditions due to curved roof surface(thus different angle), shading caused by roof AC unit, tree shades, etc.

Thanks again!

 

[gnubie]

My answers were provided in the abstract and make no reference to any video clip. It's clear to me that sunrise is asking why can it be, my answers were some possibilities of why the situation can arise.