OffGrid Newbie

TPrice · August 2018

I've done plenty of grid-tie roof and ground arrays and it's my first time doing off-grid. I have done a lot of homework on this.
I need a sanity check and some pointers, if anyone could help it would be greatly appreciated!

There are 2 roofs which are separated by 20'.
Roof 1 is on a shed with (6) Solarworld 255W (600V modules)
Roof 2 is on the house with (8) Yingli 230W (600V modules)
7 Strings with 2 panels each
Total array size is 3.37kW
I wanted to use the same manufacturer for all the equipment (BOS):
Roof 1, I was going to use Outback FWPV6-FH600-SDA with 3 strings fused and with Rapid Shutdown
Roof 2, I was going to use Outback FWPV6-FH600-SDA with 4 strings fused and with Rapid Shutdown
If I'm going to use Outback Flexmax 80 as Charge/Controller, how do I get the outputs from both Combiner/Rapid Shutdown Boxes to connect to the Rapid Shutdown Initiator and the FlexMax?
After the Charge Controller, continue on to the 48V Battery Bank, then to the Inverter GS4048A with disconnects on either side of the battery bank
The inverter will then be connected to a load panel. There is a generator in place which would be connected to the inverter. Correct?

If you need more info, I will be glad to post.
Thanks!

BB. · August 2018

TPrice,

I have not looked at wiring the newer Outback hardware--But Outback does have an extensive catalog of very detailed wiring diagrams for their products. I would start here first:

http://outbackpower.com/wiring-diagrams

-Bill

Dave Angelini · August 2018

If this is the first offgrid install, why use the roof? The rapid shut-down is not needed for a ground mount. All of those strings go away with a hv mppt.Yuk too much work..... Good Luck

TPrice · August 2018

Dave Angelini,
I agree a ground mount would be so much better. The issue is there is not enough solid gro

Photowhit · August 2018

TPrice said:
Roof 1 is on a shed with (6) Solarworld 255W (600V modules)
Roof 2 is on the house with (8) Yingli 230W (600V modules)
7 Strings with 2 panels each

You have problems!

The good;
These appear to both be 60 cell panels, so strings of both will work together!

The bad;

These are 60 cell panels so strings of 2 won't give you enough voltage to use MPPT charge controllers to properly charge a 48 volt battery bank.

There is no way to configure these to use a single charge controller. So you need to use strings of 3, pretty much the only configuration that will work, so easiest fix is to add another Yingli panel.

TPrice · August 2018

Photowhit, Thanks for your input!
The concern I had was there was a lot of buzz with keeping the voltage below 150V.
I redid the calculations with 3 panels in series, so, using 3 solarworld panels in series I have VOC at 38.0
Multiply 38.0v x 1.22 (NEC Table 690.7 for Temperature correction values) which is 46.36v per module
46.36V x 3 modules in series is 139.08V
The Yingli modules with 3 in series is 135.42V (I am able to throw another Yingli panel in for a total of 9)
The difference is 2.6%
Am I good so far?

Estragon · August 2018

The temp correction should really be done using record low temps at your specific location. The factor will be different in south Florida vs Fargo.

That said, 3 at Voc of 38v should be okay. Mine are about the same, and it gets pretty cold (-40°).

You could probably get a 2% difference just with different wind conditions on parts of an identical array, so close enough IMHO.

TPrice · August 2018

Estragon, Thank you!
Yes, the temperature gets to -17 degrees F
So, the next issue is getting 2 strings on roof A into RSD/Combiner Box and 3 strings on Roof B into a 2nd RSD/Combiner Box, then combining the 2 outputs from the RSD/Combiner Box into another before the DC disconnect before the Charge Controller.
Or if I can install pass-thru Boxes on each roof to go to a combiner box before the DC Disconnect prior to the Charge Controller.

Thanks for your help!

Estragon · August 2018

I'm unsure of potential code or other issues with rapid shutdown location, but in terms of combiner location, I think it comes down to distances involved and logistics. Voltage drop vs wire size on the paralleled connections, trenching, conduit, etc.

I like to keep things as simple as possible, so if practical, my preference would be all strings going to a single location/box.

TPrice · August 2018

I found out the MidNite Solar has solutions I can probably use.
I can use the MNPV4HV 3R DELUXE at both roofs with 15A fuses for the strings input (which then will be combined), it also has the Power Supply Board embedded (for the Rapid Shutdown) and Disconnect.
The combining of these boxes would happen in the MNPV6HV DISCO (which I need to confirm) with 1 combined output going to the Charge Controller.

TPrice · August 2018

Estragon,
I'm unsure of potential code or other issues with rapid shutdown location, but in terms of combiner location, I think it comes down to distances involved and logistics. Voltage drop vs wire size on the paralleled connections, trenching, conduit, etc.

I like to keep things as simple as possible, so if practical, my preference would be all strings going to a single location/box.

I would wholeheartedly agree except the NEC Code is tripping this whole thing up.

Estragon · August 2018

Midnite is a good choice for the gear, and I'm sure they can help with any NEC issues.

TPrice · August 2018

Estragon said:

I'm unsure of potential code or other issues with rapid shutdown location, but in terms of combiner location, I think it comes down to distances involved and logistics. Voltage drop vs wire size on the paralleled connections, trenching, conduit, etc.

I like to keep things as simple as possible, so if practical, my preference would be all strings going to a single location/box.

I was finally able to resolve the system with using OutBack's ISC-Plus1 package which has 2 combiner boxes, 1 Rapid Shutdown Initiator and a Relay Trip Breaker installed in the GS Load Center. I got the help I needed with some phone calls. So, yes, Rapid Shutdown can be installed on an Off-Grid system if needed.
Thanks for everyone's input!

Dave Angelini · August 2018

Good that you found a solution. If I were the owner I would pay you to make sure this is not going to cause me to lose a freezer full of food to a false alarm triggered by something that really should not be used offgrid. Other than to keep a non-informer building inspector happy
I would be looking for ways to make this reliable.

To me there are only two reasons to lose power offgrid, they are a dead battery or over current protection.

TPrice · August 2018

Good point! Fortunately, this is a "Summer Home" for the weekends and the Fridge is powered by Propane, all other loads are "non-critical".

Dave Angelini · August 2018

That sounds great, and reasonable.

OffGrid Newbie

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