Panel layout / configuration

[JoshVannette]

Good afternoon newbie here!

Looking for design input for my 48v solar system

1. 2x Growatt 5000es from signiture solar
2. Auto transformer to provide neutral for 120 loads
3. 2x EG4 batteries ( I'll add more as time allows
4. 48 x 250watt solar panels Model SS250P-60 specifications attached via image.

Wondering what the recommended panel layout is for 2 arrays feeding the growatt controllers. Max 450 VDC and up to 6000watt PV input I have plenty of roof space on south facing roof in South Carolina for both arrays.

Appreciate the input in advance

 

[shot428]

This math is fun, been doin it for a few days trying to find best bang for buck LOL

30.3 is volt number and 8.27 is your amp number, with max 450v so to start we divide 245 by 30.3 to find max # of panels we can put in series

The answer is 8 but that gives us a voltage very close to max, at 242.4 and because things fluctuate a bit with temp changes a series string of 7 is your best starting point 0f 212.1

Each parallel connection adds the amps together so 2 strings is 16.54 amps and 3 strings is 24.81 amps NOTE adding any more than this requires bigger wire than standard, with the standard being 10 gauge wire which is rated to carry 30 amps

With 3 strings of 7 the wattage will be (volts x amps) 5262.2, you can NOT do 4 strings as that would be 7016 watts which puts you over your max (6000)

So 2 array's of 7s3p to be safe, but you do have enough to do 8, if it doesn't get cold (below 0) where you live you could do 8s3p which would be 6013.9 watts

I wouldn't but others might chime in differently

 

[DThames]

Good afternoon newbie here!

Looking for design input for my 48v solar system

1. 2x Growatt 5000es from signiture solar
2. Auto transformer to provide neutral for 120 loads
3. 2x EG4 batteries ( I'll add more as time allows
4. 48 x 250watt solar panels Model SS250P-60 specifications attached via image.

Wondering what the recommended panel layout is for 2 arrays feeding the growatt controllers. Max 450 VDC and up to 6000watt PV input I have plenty of roof space on south facing roof in South Carolina for both arrays.

Appreciate the input in advance

Are the panels new?

 

[JoshVannette]

This math is fun, been doin it for a few days trying to find best bang for buck LOL

30.3 is volt number and 8.27 is your amp number, with max 450v so to start we divide 245 by 30.3 to find max # of panels we can put in series

The answer is 8 but that gives us a voltage very close to max, at 242.4 and because things fluctuate a bit with temp changes a series string of 7 is your best starting point 0f 212.1

Each parallel connection adds the amps together so 2 strings is 16.54 amps and 3 strings is 24.81 amps NOTE adding any more than this requires bigger wire than standard, with the standard being 10 gauge wire which is rated to carry 30 amps

With 3 strings of 7 the wattage will be (volts x amps) 5262.2, you can NOT do 4 strings as that would be 7016 watts which puts you over your max (6000)

So 2 array's of 7s3p to be safe, but you do have enough to do 8, if it doesn't get cold (below 0) where you live you could do 8s3p which would be 6013.9 watts

I wouldn't but others might chime in different

This math is fun, been doin it for a few days trying to find best bang for buck LOL

30.3 is volt number and 8.27 is your amp number, with max 450v so to start we divide 245 by 30.3 to find max # of panels we can put in series

The answer is 8 but that gives us a voltage very close to max, at 242.4 and because things fluctuate a bit with temp changes a series string of 7 is your best starting point 0f 212.1

Each parallel connection adds the amps together so 2 strings is 16.54 amps and 3 strings is 24.81 amps NOTE adding any more than this requires bigger wire than standard, with the standard being 10 gauge wire which is rated to carry 30 amps

With 3 strings of 7 the wattage will be (volts x amps) 5262.2, you can NOT do 4 strings as that would be 7016 watts which puts you over your max (6000)

So 2 array's of 7s3p to be safe, but you do have enough to do 8, if it doesn't get cold (below 0) where you live you could do 8s3p which would be 6013.9 watts

I wouldn't but others might chime in differently

Thank you so much for your help; We are in South Carolina with avg winter lows in the 30s. So with a 7s3p we would meet our amp range and be under the 450V max Voltage. Could we add more panels in series since the max is 450v and we would only be at 212.1

Thanks,
Josh

 

[JoshVannette]

Are the panels new?

Used panels from SanTan solar

 

[DThames]

Used panels from SanTan solar

Many used panels are degraded enough that their real current output needs to be put into your calculations. The Voc will not change but the current output will change. You might want to test some of the panels on a good sunny day, test then from more than 5 minutes and see what watts you get. You might want to do fewer series in a string and some parallel if the watts are lower than you planned. If you can parallel some up and handle the real watts on one MPPT, you might leave the second MPPT (these units have 2 MPPTs per inverter, right?) for some more panels someday. Just a thought. If you get 200w out of the 250w panel after they get hot, you will be about typical.

 

[iamrich]

4 strings of 11 would be easiest. I know that is only 44 panels, but talk about simple. 1 string of 11 per mppt. With these used Trina 250w panels I might almost be tempted to run 4 strings of 12 (451.2v open) but I would hate to see the magic smoke get released..

My 3S3P usually runs 90-103v.

 

[JoshVannette]

Many used panels are degraded enough that their real current output needs to be put into your calculations. The Voc will not change but the current output will change. You might want to test some of the panels on a good sunny day, test then from more than 5 minutes and see what watts you get. You might want to do fewer series in a string and some parallel if the watts are lower than you planned. If you can parallel some up and handle the real watts on one MPPT, you might leave the second MPPT (these units have 2 MPPTs per inverter, right?) for some more panels someday. Just a thought. If you get 200w out of the 250w panel after they get hot, you will be about typical.

Thanks I'll run a test tomorrow on a few panels and report back!

 

[JoshVannette]

4 strings of 11 would be easiest. I know that is only 44 panels, but talk about simple. 1 string of 11 per mppt. With these used Trina 250w panels I might almost be tempted to run 4 strings of 12 (451.2v open) but I would hate to see the magic smoke get released..

My 3S3P usually runs 90-103v.

Would there be a way to step down the voltage slightly just ahead of the charge controller to be in a safe range and run 12 panels in a string? This does sound like the easiest solution, would my amperage be in the necessary range still for the controller? Thanks for your help

 

[JoshVannette]

4 strings of 11 would be easiest. I know that is only 44 panels, but talk about simple. 1 string of 11 per mppt. With these used Trina 250w panels I might almost be tempted to run 4 strings of 12 (451.2v open) but I would hate to see the magic smoke get released..

My 3S3P usually runs 90-103v.

Looks like this has a single Mppt can anyone confirm?

 

[JoshVannette]

Many used panels are degraded enough that their real current output needs to be put into your calculations. The Voc will not change but the current output will change. You might want to test some of the panels on a good sunny day, test then from more than 5 minutes and see what watts you get. You might want to do fewer series in a string and some parallel if the watts are lower than you planned. If you can parallel some up and handle the real watts on one MPPT, you might leave the second MPPT (these units have 2 MPPTs per inverter, right?) for some more panels someday. Just a thought. If you get 200w out of the 250w panel after they get hot, you will be about typical.

If my panels are degraded and running below the new specs of 250watts would a 8s3p be workable? 242 VOC, 24.81 amps, and at or under 6000watts if my math is correct.

 

[iamrich]

Looks like this has a single Mppt can anyone confirm?

Ah... Yeah, the spec sheet says 1 mppt...

 

[iamrich]

If my panels are degraded and running below the new specs of 250watts would a 8s3p be workable? 242 VOC, 24.81 amps, and at or under 6000watts if my math is correct.

8S3P would work fine, but you would have to use a combiner box or some other kind of fuse/breaker protection for each string.

I looked up the specs on the growatt https://signaturesolar.com/content/documents/GROWATT/1519013-specs.pdf and it says 120-430v preferred, and 80a max. Looks like you have a winner with that combo.

 

[JoshVannette]

8S3P would work fine, but you would have to use a combiner box or some other kind of fuse/breaker protection for each string.

I looked up the specs on the growatt https://signaturesolar.com/content/documents/GROWATT/1519013-specs.pdf and it says 120-430v preferred, and 80a max. Looks like you have a winner with that combo.

Thanks, I have a midnight solar box with breakers for each unit in case I needed them lol! Glad I picked those up. One array for each Mppt but both can feed my batteries and then into my panel through the AC outputs into 50amp breakers and a neutral line coming from the signiture solar combiner box. Thanks for your help in working though this. I'll try and post pics of my system as it comes together.

 

[JoshVannette]

8S3P would work fine, but you would have to use a combiner box or some other kind of fuse/breaker protection for each string.

I looked up the specs on the growatt https://signaturesolar.com/content/documents/GROWATT/1519013-specs.pdf and it says 120-430v preferred, and 80a max. Looks like you have a winner with that combo.

Also any issues with combining using this technique? David poz here at 16min in.

 

[DThames]

If my panels are degraded and running below the new specs of 250watts would a 8s3p be workable? 242 VOC, 24.81 amps, and at or under 6000watts if my math is correct.

Some setup like that is what I was thinking when I commented. I would test some of the panels to see what I got and then decide. You might not have a way to do a real test. If you can put out some panels (propped up on the ground) and have an MPPT charger connected to them with a battery that needs to be charged, you could be able to see their real output. Don't get too close to your max Voc because when it gets cold the panel Voc goes up above what is stamped on the back. You need a temp adjusted Voc for the temperature that you expect for your location.

I recently purchased some used 300w and I think they got about 235w each, charging on an EPever AN charger. I have an old laptop and can monitor output of the panels on a graph. Clouds come over, the panels cool, sun back out and they do better for about 2 minutes (until they heat up) then they settle back to something less. That something less is what to expect for hours of output. I wouldn't worry about staying under the 6000w number. It is common to "over panel" some because of sun angle and less than a perfect sky, you almost never see rated output. Normal MPPT chargers are rated for some number of output amps and they self limit output to that value regardless of how many panels are attached.

 

[JoshVannette]

Working on setting up my 10s2p array. I have the strings of 10 together positive to negitive and then with a Y putting both positive lines to one and running that line back to my disconnect and same on the negitive side. Voltage looks good but my amps reading on the array is high at 52 amps unless I am doing my reading incorrectly.

Pic attached

 

[iamrich]

Working on setting up my 10s2p array. I have the strings of 10 together positive to negitive and then with a Y putting both positive lines to one and running that line back to my disconnect and same on the negitive side. Voltage looks good but my amps reading on the array is high at 52 amps unless I am doing my reading incorrectly.

Pic attached

I don't see anything attached, but you should be seeing ~375v and 18a or so testing directly off the leads. If you hook it up to the controller, I would guess about 300v and 13-14a in full sun.