Is this worth doing?

[ColoradoRider]

I have a 12-panel array that is ground mounted and fixed to a single direction (can't do a seasonal adjustment). My array has done a good job of keeping up with my power demands (we are completely off-grid), but there are times when we squeak by, or I have to run my generator. This happens maybe once every 2-3 months when we have three or more cloudy days.

I have 3 more panels that I can employ, and room in my combiner box for another line, so my system can handle the extra juice. Here where I live, we mostly start the day fairly clear, and then during the day the clouds will build up. A good example is what I'm expecting to happen this coming week. Clear to partly cloudy skies in the morning, full clouds and snow in the afternoon / evening.

My thinking is to employ these three panels and situate them so that they take full advantage of the morning sun. Rather than orient them to due south, I'll set them up on a separate rack that is angled to the southeast rather than due south. Does this sound like a good idea? My simple and inexperienced mind thinks so.

 

[timselectric]

Sounds plausible to me.

 

[Quattrohead]

As long as the voltage from 3 panels is enough to make your MPPT run then yes, great idea.

 

[ColoradoRider]

As long as the voltage from 3 panels is enough to make your MPPT run then yes, great idea.

See, this is why I had doubts. This entire field of endeavor has way too many variables for me to juggle in my simple mind. Now I have to figure out (I think) what the minimum amount of voltage (amps, ergs, knueter sparks, et all) is for my MPPT to kick in.

 

[Brucey]

Let us know the model and we can tell you.

 

[sunshine_eggo]

See, this is why I had doubts. This entire field of endeavor has way too many variables for me to juggle in my simple mind. Now I have to figure out (I think) what the minimum amount of voltage (amps, ergs, knueter sparks, et all) is for my MPPT to kick in.

What is your existing 12 panel array configuration?

 

[ColoradoRider]

What is your existing 12 panel array configuration?

It consists of 360 w REC panels wired up in 3 strings of 4 panels each. Does that answer your question? Remember, you are dealing with a person who is a half step above a newbie.

 

[sunshine_eggo]

It consists of 360 w REC panels wired up in 3 strings of 4 panels each. Does that answer your question? Remember, you are dealing with a person who is a half step above a newbie.

4S3P. It will not work. The second array would need also be 4S to attach to the same MPPT.

You could add a dedicated MPPT for the 3 panels.

 

[Brett V]

Having to run the generator only every 2-3 months is pretty darn good!

 

[Quattrohead]

Buy another panel as close as possible spec's to the others or another MPPT that is ok to run on lower voltage from the panels.

 

[ColoradoRider]

4S3P. It will not work. The second array would need also be 4S to attach to the same MPPT.

You could add a dedicated MPPT for the 3 panels.

The new string of three would be connected into the same combiner box (the box that all the other strings feed into). Does that make a difference?

 

[ColoradoRider]

Having to run the generator only every 2-3 months is pretty darn good!

I'm actually pretty damn happy with my setup and it's performance. During the night I drop less than 10% on my state of charge, more when it's really cold. Maybe 15%. My house is just under 1000 sqft, and is insulated to the beejesus.

I live up here on the western flank of Pikes Peak, just outside of Cripple Creek. I'm up at 9600 feet of elevation, and we get an ungodly amount of sunshine. Yes, I'm blessed!

I just thought of something. I should throw out the caveat that I also have 16 - 6 volt batteries. 8 are about a year old, the others are 4 years old. The system has been up and running for about a year now.

 

[timselectric]

The new string of three would be connected into the same combiner box (the box that all the other strings feed into). Does that make a difference?

This is the reason that you need another panel.
Don't parallel a string of 3 with existing strings of 4.

 

[ColoradoRider]

Buy another panel as close as possible spec's to the others or another MPPT that is ok to run on lower voltage from the panels.

Buy another solar panel? The three that I have are the same REC 360's that I'm currently using.

 

[Brucey]

Buy another solar panel? The three that I have are the same REC 360's that I'm currently using.

He's saying to buy one more.

 

[Q-Dog]

All of the strings going into the combiner box need to be equal if they all go into the same MPPT. Or add a small MPPT to the system and connect the 3 panels to that.

 

[MisterSandals]

Don't parallel a string of 3 with existing strings of 4.

Perhaps an explanation of what happens when you do this will help.

When combining strings in parallel, all the strings get their voltage dragged down to the lowest voltage string. The amps of course are added as usual.

So if you have 3x 4S strings producing 40V at 9A (360W), that is 160V.
If you combine that with a 3S string producing 120V, all strings become 120V.

So you currently have 3x 160V x 9A = 4320A

With your proposed addition of a 3S string, you'd end up with:
4x 120V x 9A = 4320A (the same output, i had to run that again!)

 

[ColoradoRider]

This is the reason that you need another panel.
Don't parallel a string of 3 with existing 4.

Don't get old, you'll make a ton of mistakes...

I have FOUR strings of THREE panels! I just walked down to the array just to make sure. Jeeeez, I feel so... old.

 

[ColoradoRider]

Perhaps an explanation of what happens when you do this will help.

When combining strings in parallel, all the strings get their voltage dragged down to the lowest voltage string. The amps of course are added as usual.

So if you have 3x 4S strings producing 40V at 9A (360W), that is 160V.
If you combine that with a 3S string producing 120V, all strings become 120V.

So you currently have 3x 160V x 9A = 4320A

With your proposed addition of a 3S string, you'd end up with:
4x 120V x 9A = 4320A (the same output, i had to run that again!)

This really is appreciated! I had not known that, but it makes complete sense. Fortunately, for me, I went down to the array to verify that I actually have 4 strings of 3 panels.

 

[MisterSandals]

Don't get old, you'll make a ton of mistakes...

Your mistake did not cost you anything. Too many times folks buy stuff or do stuff and then ask.

You are doing just fine!