Please advise me on expanding my system

Hello solar dudes,

I ended up with two EG4 6000XPs now and want to add 3 strings to utilize the extra capacity. Sig Solar set me up one year ago with an EG4 6000EX (which I upgraded to the XP and am loving it), 3 EG4 48V 100AH batteries, and 12 Canadian Solar 320 panels which I have set up 6s2p. The panels are producing 3836.16w/199.79V/19.2A on perfect day.

I have kicked around the idea of adding 3 Aptos 370 to each string and making it a mixed bag producing 6220W/324V/19,2A in a 9s2p configuration. Also thought of a 8s2p configuration producing 5425W/282,6V/19.2A. Lastly, a 7s2p would make 4631W/242.2/19.2A.

I think all that cipher'n hurt my brain and I will just leave well enough alone on my first string even though the 6000XP isn't running optimally on the 199V/19.2A input.

I think I want to add 3 strings and set the inverters up in parallel, hopefully quadrupling my solar production.

What do you all recommend? I'm thinking 3 strings of 8 Aptos 370, each in series to the individual MPPTs. 8 Aptos 370 in series would produce 3702W/328.8V(optimal V for the 6000XP/and 11.26A). Either that, or maybe 9 Aptos 370 in series (4195.48W/372.6V/11.26)

The Aptos will, unfortunately, be mounted on a steel roof due to spousal considerations.These 4 strings should produce 14,942.16KwH on a perfect day I hope.

My math may be wrong so no offense will be taken if anyone more smarter than me wishes to correct my thinking. I just want to get it right. I average a little over 2000KwH per month usage now using the array I have. I only started measuring output this week since I just got the one 6000XP up and running and I am averaging about 20KwH/day production. It has been a hot sunny/cloudy week here in central Indiana.

Thanks for your input

> 3 EG4 48V 100AH batteries, and 12 Canadian Solar 320 panels which I have set up 6s2p. The panels are producing 3836.16w/199.79V/19.2A on perfect day.

Let's start by making sure I understand your array. 6S2P implies you are putting strings in parallel to make them a single circuit going into the inverter. Is that what you are doing or do you have two strings wired to your inverters separately?

Each of your inverters have 2 MPPTs so you could have up to 4 strings before needing to do any parallel strings.

I currently have one string of Canadian Solar panels (2-6 panel wired in series paralleled together and running to one mppt on the 6000XP).
As I was waiting for a reply I ran across a video touting REC panels as better than Aptos. The REC 370 panel at Sig Solar runs 47.8V, so I could do 3 strings of 7 and save quite a bit of money. Especially considering that the REC panels are so well reguarded.

FilterGuy said:

6S2P implies you are putting strings in parallel to make them a single circuit going into the inverter.

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Yes. That is how I have it configured

edfowler said:

Yes. That is how I have it configured

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Any particular reason for doing it that way? The 6000XPs have two MPPTs so you could run each string to the inverter. The only downside is that you have to wire more conductors between the array and the inverter(s).

Even if you decide not to change the existing array, you could wire your new REC panels to another MPPT at the inverters.

BTW: In general, the more MPPTs used, the less impact you will have from any shading.

Sig Solar advised that configuration with the 6000EX. I like the idea of leaving that one alone cause I built a ground mount for those panels specifically. I think they produce more power on one mppt, leaving the other three mppts available.

One tech at Sig Solar did tell me to run 10 of the Canadian Solar 370s in series. That would give me 333V/9.6A but only 3196.8W. I've seen over 3500W running the 6s2p configuration I have now.

edfowler said:

One tech at Sig Solar did tell me to run 10 of the Canadian Solar 370s in series.

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I have not run the numbers but that sounds about right. More would probably raise the voltage too high

edfowler said:

That would give me 333V/9.6A but only 3196.8W. I've seen over 3500W running the 6s2p configuration I have now.

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Is the 9.6A Imp or Isc. If it is Imp, two strings in parallel may not be fully used. The spec sheet shows this:


If the two parallel strings produce 9.6A each, the MPPT is clipping (Only using 17A). However, if you put 6 panels on two different MPPTs, you would not have the possibility of clipping. Furthermore, running an MPPT that can take 17A and 9.6 A is much easier on the MPPT.

Note: Depending on your specific situation with temperature and angle to the sun, there may not be clipping.

If the 9.6A is Isc, there is less likelihood of clipping because your actual current during operation will always be lower than Isc.

Either way, I would put your new panels on a different MPPT.