New 40' container power house build.

[DCDave]

We are starting this off grid project with the following equipment just received:

Parts, starting place;
* 40' container located at 6800' Summer 97 degrees, Winter 10 degrees.
* Growatt 3000w 120v output, 48vdc input from Watts247
* 20 solar panels, 327w used Sunpower
* 800KW Lithium, 48v BMW batteries, from Battery hookup
* 2awg cables with disconnect below the panel, 60w breakers on each of the two battery packs to de-rate them a bit.
* Plan to string second Growatt 3000 to add input charging and run the AC on camper next summer.

Loads:
* Small RV Camper, one AC unit, microwave
* Charging battery powered tools
* Laptop

Unkowns:
How to group and connect the 327w solar panels to not exceed voltage limitations.
* 80A MPPT / 6.5Amps per solar panel + 12.3 panels.

Growatt's limitations.
* 48v
* Input 80A MPPT
* Input 40 from Generator

Solar panels limitations;
* Rated power max 327 Watts
* Voltage 54.7 Volts
* Current Input 5.98 Amps
* Open circuit VOC 64.9 Volts
* Max series fuse 15 Amps

** By my calculations, I can only attach 12 panels to the Growatt 3000w. Even if I chose the 6000w unit I gain 220v AC but can only attach some 15 of my 327w panels. I am not sure which is the better option.

 

[Craig]

Why not just add another stand alone SCC?

 

[Hedges]

The MPPT's rated current is normally at battery voltage, 48V or maybe 60V. 80 A would be 4800W at the higher voltage.
Imp of panels would normally add up to less than that, because Vmp is higher than battery voltage.
But, it is OK to "over panel" the MPPT charger. Most of the time, current will be lower because panels get hot, and because sun is hitting at an angle.
Set up multiple strings of panels at different angles so sun is always off angle for some. That will spread power production over the day and year, fitting 6600W (STC) of panels nicely within 4500W capability of charger into a 50V battery.

What is the Voc spec of your MPPT (or GroWatt PV input)? Need to calculate max series string of panels so they don't exceed that on record cold day.

Nice panels. I bought four pallets.

 

[DCDave]

The MPPT's rated current is normally at battery voltage, 48V or maybe 60V. 80 A would be 4800W at the higher voltage.
Imp of panels would normally add up to less than that, because Vmp is higher than battery voltage.
But, it is OK to "over panel" the MPPT charger. Most of the time, current will be lower because panels get hot, and because sun is hitting at an angle.
Set up multiple strings of panels at different angles so sun is always off angle for some. That will spread power production over the day and year, fitting 6600W (STC) of panels nicely within 4500W capability of charger into a 50V battery.

What is the Voc spec of your MPPT (or GroWatt PV input)? Need to calculate max series string of panels so they don't exceed that on record cold day.

Nice panels. I bought four pallets.

Hedges,
This description helps greatly;
Growatt 3000TL LVM
* "Inbuilt MPPT 80Amps per the manual" Not sure if that is a misprint. Manual later states, "PV connection, SPF 3000TL LVM Typical output 80 Amps".

 

[mopat]

I think Voc max on that growatt is 145VDC, with MPPT range of 60-115 vdc.
Seems like 2 panels in series .

 

[Hedges]

Using the data sheet I have for what I think is the same panel, temperature coefficient of Voc = -176.6 mV/degree C
At 10 degrees F, Two panels in series would be 143 Voc, staying just within the 145V limit.
So long as 10 F is record cold.

 

[DCDave]

So I have the of the manual, I was going by P2. Features and P5. Battery Connection (LVM 48P = 82amps)

https://watts247.com/manuals/gw/Growatt%20SPF%203000TL%20LVM%20Series%20User%20Manual.pdf

To Mopat: From the PDF Manual P9. Yes, 145 Voc, PV array MPPT Range 60-115vdc, (Minim 34Vdc) So I am limited to under three panels??

Watts247.com Ian just replied stating I have 4500watts of solar input available.
S

Regarding SPF 3000 TL LVM Inverter Charger;
Re: Solar 9000w capacity for two SPF3000's or 4500w per SPF 3000TL LVM, so if I divide 4500 / 327 I am golden. However the manual and the Solar Panel Configuration state 145 VOC for this inverter, with my panel putting out 64.9VOC, I am limited to two panels in series. On bullet point "VOC in series" it confirms this.

Q- So I can arrange my 327 Watt panels (65.9VOC), Two in Series with six panels in Parallel each series? to a maximum of 4500watts per SPF3000 TL LVM?

 

[Hedges]

Definitely under 3 panels in series, that would hit 198 Voc at ambient temperature and kill the inverter.
Don't use just 64.9 Voc from panel to compute Voc. You also need "temperature coefficient of Voc" which will indicate Voc is higher in cold weather.
This might be on the panel label, otherwise see data sheet. The sheet I found, if the correct one, showed you were OK with 2 panels in series down to 10 degrees F but not colder.

"divide 4500 / 327"
Panel will put out a bit less than 327 W under most conditions, maybe 15% to 20% less when warm. I've also seen them put out 5% to 10% more. You can generally attach more panels in parallel, more current than what MPPT wants and it will just not draw more current than it can handle. "over paneling". (no guarantee, but most protect themselves.)
If you calculated 2S6P arrangement, I think you can do 2S9P or 2S10P with some strings at different orientations.

"Two in Series with six panels in Parallel each series?"
Connect the strings of two first, and add a fuse for each string (could be MC4 use holders). But total current with several in parallel is too much for the wire gauge in an MC4 "Y" connector, so better to put MC4 pigtails into a box with fuse holders or breakers. Midnight is one of the manufacturers.

 

[DCDave]

This summary may clarify my questions around calculating solar panel maximum count for the Growatt SPF 3000TL LVM



I think I see why I have been confused:

* My new SPF 3000watt TL LVM at 80 amps is actually 4500watts.
* I need the VOC of my Solar panels AND from VOC from Growatt 3000Watt TL charge controller, to accurately size and purchase a charger/controller, however nowhere in the manual or the Data Sheet (Still do not have a copy of this). Growatt has not provided a VOC for the Charge controller/Inverter. I can find VDC on Page 9. which is assumed to be interchangeable?

* If I am limited to how many panels I can parallel by Growatt total watts of 4500Watts, (Still an Unknown, however presumed to be 6 parallel panels x two strings in series, unless I can be slightly over at 14 panels rounding up from 13.76 panels to 14 panels).

The calculation seems fairly simple;
1. Divide the VOC/VDC from the proposed Charge controller, by the VOC from the Solar panels or. "2.6 or 2 Panels in series".
2. Divide the total Watts available on the 3000TL LVM, (4500watts), by the 327watts total from one SunPower panel, resulting in my case 13.76 Panels so even number rounding down is 12 in total.
3. Divide total panels from Step 2 above, by results from Step 1 above, or 2 from VOC,VDC / VOC equals 6 panels in parallel x two strings in series.

Note: If this is the whole of the solar configuration this could be simplified by a simple spreadsheet in PDF. (Providing I am not missing something?)

Is this an accurate calculation?

 

[Steve_S]

I'd like to mention a point not solar related.
The Shipping container is a very practical and solid thing to use provided it is perfectly level (doors will twist). Their tiny vents at the top, pretty useless for much. As temps swing condensation inside the beasts get's problematic and with electrical, potential issues can arise. Grounding the "can" itself is most likely a very good idea, it can be a faraday cage but....

You haven't mentioned what if any prep planed/done for the shipping container, so I thought I should mention these issues. I have a one and it's been a learning experience I could have avoided by listening to others. One regret is not putting a roof on it (in my case 12:12, 45Deg pitch) and my solar panels on that. Humidity/Damp has t be managed and airflow as well because they Bake in the sun and freeze in the dark.

 

[DCDave]

I'd like to mention a point not solar related.
The Shipping container is a very practical and solid thing to use provided it is perfectly level (doors will twist). Their tiny vents at the top, pretty useless for much. As temps swing condensation inside the beasts get's problematic and with electrical, potential issues can arise. Grounding the "can" itself is most likely a very good idea, it can be a faraday cage but....

You haven't mentioned what if any prep planed/done for the shipping container, so I thought I should mention these issues. I have a one and it's been a learning experience I could have avoided by listening to others. One regret is not putting a roof on it (in my case 12:12, 45Deg pitch) and my solar panels on that. Humidity/Damp has t be managed and airflow as well because they Bake in the sun and freeze in the dark.

To Steve_S,

Good tip, this 40' can is water tight "I was told", and this is a good point to keep in mind possibly placing desiccant inside and venting to the outside to remove the "Sweating" of the big can. My location is in the Southwest but temps do fluctuate greatly, summer to winter due to the elevation.

 

[DCDave]

FYI, So Ian confirmed VOC and V- dc is an interchangeable term, and I verified it on the fine print on the side of my Growatt. I need an 2S 7P configuration, per Ian delivering 125volts and 42Amps at the charge controller, keeping voltage under the required 145VOC /Vdc.

FYI This allows us to add a second Growatt 3000TL later to achieve 30A split phase when required.
This outcome seems so simple following my struggle with terms; I will create a simple spreadsheet to make this simple for the next newbie to understand.

 

[DCDave]

Thanks for the insight, to Hedges, Mopat, Craig and Steve_S. I ordered some 7 to 1 connectors for a 2S 7P panel input. Now I need some racking for the panel mounts on the 40' container.. Suggestions ?

 

[Hedges]

Thanks for the insight, to Hedges, Mopat, Craig and Steve_S. I ordered some 7 to 1 connectors for a 2S 7P panel input. Now I need some racking for the panel mounts on the 40' container.. Suggestions ?

Yea, don't use those 7 to 1 connectors.
What is the wire gauge?
How many amps Isc do the panels produce?
The connector will have to carry 7x what one panel produces.

You need fuses for each string, probably get a combiner box (Midnight Solar or similar) with a busbar for 7 negatives and 7 fuseholders or breakers.
Just buy short MC cables and cut in half for pigtails coming out of the box.

 

[DCDave]

Yea, don't use those 7 to 1 connectors.
What is the wire gauge?
How many amps Isc do the panels produce?
The connector will have to carry 7x what one panel produces.

You need fuses for each string, probably get a combiner box (Midnight Solar or similar) with a buss-bar for 7 negatives and 7 fuse holders or breakers.
Just buy short MC cables and cut in half for pigtails coming out of the box.

* I did receive the 7 to 1 connectors and have my doubts, so I am interested in a combiner box option, as outlined in my set up photo.
* Solar panel delivery wire size: 10 AWG
* Amps Current IMP 5.98, Short circuit amps ISC 6.46 Maximum series fuse 15 amps
* Midnight Solar combiner box, instead of connectors: I haven't seen a combiner box with fuses, just breakers.
Note:
* I am limited to 2S 7P to meet the limits of the hardware.
* 2S 7P configuration, delivering 125 volts and 42 amps at the charge controller, keeping voltage under the required 145 VOC /Vdc.

In the photos below, I am just short one lug and two butt crimp connectors on the DC side so I can proceed with the Solar side. The yellow 12-2 cord is very temporary, just for proof of functionality. I have a 15a / 30a RV weather proof box for long term.

 

[Hedges]

I figured the 7:1 connector was 10 awg, which does have ampacity 40A but normally gets fused at 30A. The connector itself might not do well at 40A.
Once you get a combiner box with fuses or breakers, something like 8 awg or 6 awg would be good to connect it.
Breakers are more convenient. More than 6 might be hard to find, but some of the boxes are dual 6. We're not "supposed" to put two wires in one screw terminal, so I strip some insulation in middle of wire an feed it through one lug to the second lug.

 

[DCDave]

Yea, don't use those 7 to 1 connectors.
What is the wire gauge?
How many amps Isc do the panels produce?
The connector will have to carry 7x what one panel produces.

You need fuses for each string, probably get a combiner box (Midnight Solar or similar) with a buss-bar for 7 negatives and 7 fuse holders or breakers.
Just buy short MC cables and cut in half for pigtails coming out of the box.

* I did receive the 7 to 1 connectors and have my doubts, so I am interested in a combiner box option, as outlined in my set up photo.
* Solar panel delivery wire size: 10 AWG
* Amps Current IMP 5.98, Short circuit amps ISC 6.46 Maximum series fuse 15 amps
* Midnight Solar combiner box, instead of connectors: I haven't seen a combiner box with fuses, just breakers.
Note:
* I am limited to 2S 7P to meet the limits of the hardware.
* 2S 7P configuration, delivering 125 volts and 42 amps at the charge controller, keeping voltage under the required 145VOC /Vdc.

In the photos below, I am just short one lug and two butt crimp connectors on the DC side so I can proceed with the Solar side. The yellow 12-2 cord is very temporary, just for proof of functionality. I have a 15a / 30a RV weather proof box for long term.

 

[DCDave]

Am I configuring this correctly?

7 PV's on two strings, ISC of 6.48A each, 7 x 6.46 = 45.22 amps per string. So do you use a 50A DC breaker or 40A DC breaker?

 

[Hedges]

More than that. A breaker should be at least 25% greater than expected current so it doesn't trip when it shouldn't.
Under direct sunlight, plus additional light coming from nearby clouds, current can exceed Isc. I've measured one panel and saw several percent over.

In the case of PV, that means it will never trip, unless you add more panels, or there is a shorted wire and current backfeeds from the battery (which would require a fault in the charge controller as well)
I would use 60A breaker and probably 6 awg, possibly 8 awg if single wire in free air.
But if wire is heavy enough, maybe no breaker is actually required there (although convenient as a disconnect).
Not sure, but I think the code was ampacity 150% or 156% of Isc, which those wire gauges would meet.

So maybe 15A fuse for each string and 70A breaker as disconnect, or else just 15A breaker for each string.

 

[DCDave]

Following your advice I ordered 6 AWG red and black fine wire cables for the long run from the combiner box to the Solar Charger, and we ordered the Midnight solar 3 breaker combiner box. WIth a 63a Midnight Solar breaker.

I do need help to figure out how to combine the 14, 327v PV panels. Possibly with simple bus bars in the two groupings close to the PV array? (Thanks to Explorist.life Youtube)

My plan for the 2s 7P design was 7 in parallel in each string then put the two strings of 7 in parallel. It has been suggested I actually put the 14 panels, 2 in series then in parallel. Which is preferable?