Too many panels in parallel?

[thetubernoober]

So, the contractor is starting the install soon. I have a EG4 18kPv which has 4 Pv Inputs, but only 3 MPPT's. PV input 1 & 2 (as MPPT 1) comes parallel on the inverter with a 25amp max on MPPT 1. See image.

The contractor says he wants to put the panels in a 8 by 8 Parallel config for MPPT 1. With 7 Panels in series on MPPT 2 and 7 panels in series on MPPT 3. For a total of 30 panels. 370 watts each, bifacial gain of 444w.

I want to follow along with the install to ensure a smooth process but instead of giving my an explanation on why this way is better his answer is always "just trust me, just trust me". My question is, putting the panels in a 8 by 8 parrel config, will this be too much amperage on MPPT1?

I've attached MPPT diagram as well as panel info.

 

[BentleyJ]

The NOCT Imp of the 370W panel is 8.8A so 2 parallel strings will provide double that amount which is 17.6Amps. This is well under the 25A limit.

 

[thetubernoober]

The NOCT Imp of the 370W panel is 8.8A so 2 parallel strings will provide double that amount which is 17.6Amps. This is well under the 25A limit.

Thanks for the info. It's nice actually learn and follow along with a build.

 

[FilterGuy]

Lets work through it.

The inverter PV specs:

First, let's look at Voc.
For MPPT 1: 8 x 40.56 = 324.48. That is well under the 600V limit and well within the MPPT operating range.
For MPPT 2 & 3: 7 x 40.56 = 283.92. That is well under the 600V limit and well within the MPPT operating range.

Now let's look at ISC
For MPPT 1: Isc will be 2 x 11.54 = 23.08 Well under the 31A MPPT1 Limit
For MPPT 2 & 3: Isc will be 11.54. Well under the 15A MPPT 2/3 limit.

Now let's look at Imp
For MPPT 1: Isc will be 2 x 10.96 = 21.92 Well under the 25A nominal current for MPPT1
For MPPT 2 & 3: Isc will be 10.96. Well under the 19A MPPT 2/3 limit.

So, the arrangement will work electrically just fine.

There are many other possible combinations. If there is no shading, any of the combinations should work just fine.
If some of the panels might get shading, try to isolate those panels to their own MPPT.

 

[thetubernoober]

Lets work through it.

The inverter PV specs:
View attachment 165245
First, let's look at Voc.
For MPPT 1: 8 x 40.56 = 324.48. That is well under the 600V limit and well within the MPPT operating range.
For MPPT 2 & 3: 7 x 40.56 = 283.92. That is well under the 600V limit and well within the MPPT operating range.

Now let's look at ISC
For MPPT 1: Isc will be 2 x 11.54 = 23.08 Well under the 31A MPPT1 Limit
For MPPT 2 & 3: Isc will be 11.54. Well under the 15A MPPT 2/3 limit.

Now let's look at Imp
For MPPT 1: Isc will be 2 x 10.96 = 21.92 Well under the 25A nominal current for MPPT1
For MPPT 2 & 3: Isc will be 10.96. Well under the 19A MPPT 2/3 limit.

So, the arrangement will work electrically just fine.

There are many other possible combinations. If there is no shading, any of the combinations should work just fine.
If some of the panels might get shading, try to isolate those panels to their own MPPT.

Thanks for the break down. When it comes to MPPT 1. There's going to be 16 panels total. 8s & 8s in parallel. Would this then equate to 324.48x2 for 648.96V? Or does it remain at the 324.48?

 

[FilterGuy]

Thanks for the break down. When it comes to MPPT 1. There's going to be 16 panels total. 8s & 8s in parallel. Would this then equate to 324.48x2 for 648.96V? Or does it remain at the 324.48?

In parallel, the voltages do not add. Consequently, the array Voc is 324.48.

BTW: This is well under 600 so there is no worry about cold temp voltage rise.

 

[thetubernoober]

In parallel, the voltages do not add. Consequently, the array Voc is 324.48.

BTW: This is well under 600 so there is no worry about cold temp voltage rise.

Appreciate the information FilterGuy. Glad I can learn a thing or two. Thank you.

 

[HRTKD]

An installer that doesn't have time to explain why he's doing something a certain way may be an installed that knows a cookie-cutter way to do things and may not have a firm understanding of the system.

 

[thetubernoober]

An installer that doesn't have time to explain why he's doing something a certain way may be an installed that knows a cookie-cutter way to do things and may not have a firm understanding of the system.

Definitely why I'm getting a second company to look it over prior to powering up.

 

[timselectric]

An installer that doesn't have time to explain why he's doing something a certain way may be an installed that knows a cookie-cutter way to do things and may not have a firm understanding of the system.

Yup, I see this a lot.
"We do it this way because we know it works. We don't know why it works. Just that it always does. "

 

[thetubernoober]

On my 3rd installer now, the first one hooked every single panel in parallel. Apparently "this is how they do it where he's from". Quickly got rid of him. 2nd installer did not have an electrician so there was not much they could do. 3rd Installer now has a full team and are nearing completion.

They have said the panel layout will be as follows.

10 Panels on MPPT 1-Channel 1 (Paralleled via inverter)
10 Panels on MPPT 1-Channel 2 (Paralleled via inverter)
5 Panels on MPPT 2
5 Panels on MPPT 3

If so, would it be correct that Voc for MPPT 1 will be 10 x 40.56 for 405.6v, and that 405.6v on MPPT 1:Channel 1 and 405.6v on MPPT 1:Channel 2 would still be under the 600 VDC for that MPPT? Or, since both Channels have an input of 405.6v, that they would add and surpass the 600 VDC for a total of 811v for the total of MPPT 1? I do know that only the Amperage would add for parallel connections, but, since MPPT 1 has 4 inputs, i'm unsure if its 600v max for each channel of the MPPT 1, or MPPT 1 on the whole can only have 600v.


@FilterGuy Please educate me, still in my infancy of the learning curve.

 

[740GLE]

IMO there is no reason why they couldn’t commission it like Filter Guy mentioned back in August.

 

[thetubernoober]

IMO there is no reason why they couldn’t commission it like Filter Guy mentioned back in August.

It's apparently due to the layout. The panel installer has 10 panels East, 10 panels West, 10 Panels South. They are planning to put the east and west panels on MPPT1. And 5 panels of each of the south panels on MPPT 2 and MPPT 3. Unsure why the first installer wanted to do 8x2 when there was 10 panels each direction. Some of the installers are mind boggling on what they're trying to achieve.

 

[kburndred]

Another thing to bare in mind is that it's ok for the PV calculations to exceed the amperage of the MPPT input (25A), because the inverter will limit the current anyway. The big advantage is that you'll have more power during lower solar (cloudy, etc) energy days. This is great so long as you have the budget and physical space to 'overclock' your PV arrays. Just remember that the PV array(s) connected to MPPT1 must match exactly as they are paralleled inside the inverter.

 

[thetubernoober]

Another thing to bare in mind is that it's ok for the PV calculations to exceed the amperage of the MPPT input (25A), because the inverter will limit the current anyway. The big advantage is that you'll have more power during lower solar (cloudy, etc) energy days. This is great so long as you have the budget and physical space to 'overclock' your PV arrays. Just remember that the PV array(s) connected to MPPT1 must match exactly as they are paralleled inside the inverter.

Thanks for that info. I did not know the inverters would limit the current. Pretty handy to know they won't overload within a certain range.

 

[kburndred]

I would suggest that your solar panels will most of the time underperform due to alignment, weather etc, etc.
So adding a few extra panels to offset these factors will help out.
FYI: The information is in the 18KPV manual and also discussed in one of the 18KPV youtube videos.

 

[pvgirl]

It's apparently due to the layout. The panel installer has 10 panels East, 10 panels West, 10 Panels South. They are planning to put the east and west panels on MPPT1. And 5 panels of each of the south panels on MPPT 2 and MPPT 3. Unsure why the first installer wanted to do 8x2 when there was 10 panels each direction. Some of the installers are mind boggling on what they're trying to achieve.

With that layout of panels the simplest config would be 10 panels in series on each MPPT. With just 5 panels in series the voltage will be too low to get in the 18kpv's maximum power operating range.

 

[400bird]

With that layout of panels the simplest config would be 10 panels in series on each MPPT.

You beat me to it, that's exactly what I was typing!

 

[thetubernoober]

I would suggest that your solar panels will most of the time underperform due to alignment, weather etc, etc.
So adding a few extra panels to offset these factors will help out.
FYI: The information is in the 18KPV manual and also discussed in one of the 18KPV youtube videos.

The layout is definitely not optimal. It's due to the shape of my roof. Many angles, curves, etc. When I post images on my other thread you'll be able to see. Definitely not the best roof for solar. Also I checked the 18kpv manual and took the screenshots to post for this thread. It mentions 100-600v per MPPT. My interpretation is that the totality of MPPT 1 can be 600v. So 405v on each channel of the MPPT 1 would then be 810v total on MPPT 1.

 

[thetubernoober]

With that layout of panels the simplest config would be 10 panels in series on each MPPT. With just 5 panels in series the voltage will be too low to get in the 18kpv's maximum power operating range.

You have a good point. I really don't understand how 3 separate installers can't figure this out.