Author Topic: Design check - Small offgrid PV system, my first attempt at DIY.  (Read 294 times)

ricardo

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Hi everyone.

I'm putting togerher a very small offgrid system, and would appreciate any comments re: safety and/or correctness of the design.  The system loads is landscape lighting and a temperature probe, the entire system lives in a backyard shed (roof mounted panels, system inside shed).  --  My goal is to learn,  do something new, and have a system that works year round offgrid (in seattle, with 1.5 sun hours in the winter)

winter Loads: lighting 15w x 12hours (180wh), temp probe 12w x 24h (288wh)   => 468 (round up to 600wh).

System: 600W of PV (2x300 panels in series, 9.7Isc), Midnite Solar Kid CC, Samlex 600W inverter, 24V 135Ah battery  (2x Trojan Solar AGM in series).

I think i have the balance of the panels to battery correct for winter .. with about 2.5 days of energy in the batteries at 50% DOD.

The following is a description of how i'm going to wire it all up.

- Roof mounted panels in series to a JBOX on the roof, JBOX has junction to 10AWG THHN wires to conduit.  (#6 bare copped stranded wire used to ground panels)
- 1/2" liquid tight Conduit has 2x #10 THHN wires and #6 stranded bare copped grounding wire. -- Ground wire travels unbroken to earthed grounding rod.
- #10 THHN enter MNDC-C enclosure. -> 63A GFCI breaker -> 15A breaker for PV.  (9.83 x 1.25 x 1.25 = 15.3  rounded down to 15A) -> Kid CC PV IN
- KId CC Bat OUT -> 40A breaker (30A x 1.25 = 37.5 round up to 40A) -> battery  (wired using 6 AWG wire)
- Battery Negative to Isolated Shunt (not bonded to ground)  (Using #6 AWG wire)
- Battery Pos -> 50A Breaker -> 600W Inverter  (Using #6 AWG wire)
- Inverter to separate AC enclosure (15A backfeed breaker, 3 - 15A circuits for shed lights, shed outlets, and outdoor outlets). wired using 12-2 NM.  -- I'm lifting the NG bond on the inverter, and making the NG bond in the AC panel. (also replacing the GFCI outlet on the inverter with a regular 15A outlet)

Grounding: PV direct to rod, Kid ground in NMDC which goes to rod, inverter ground in AC panel which goes to rod, NG bond in AC panel.

Upgrades planned for near future: add a midnite solar lightning arrestor to the PV side,  maybe add one to the battery side connect in the MNDC.

I know that this is overkill for a landscape lighting system, but i'm not doing it for efficiency (of $ or power) but because i wanted to see if i could design, and do the install myself. (I've never been very handy around the house)

In the summer i also think that this system can provide power to my house battery (a 1.5kwh goal zero that runs my fridge + lights for about 16 hrs in case of emergency) -- i think in the summer i could recharge that battery indefinately and the spring and fall could go a long ways to provide emergency power)

If you've read this far, thank you! -- and i appreciate any comments, suggestions to improve safety, or just something i may have missed.
« Last Edit: May 28, 2018, 01:07:51 PM by ricardo »

ClassicCrazy

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Re: Design check - Small offgrid PV system, my first attempt at DIY.
« Reply #1 on: May 28, 2018, 01:55:46 PM »
Ricardo
Are your loads AC or DC ? Are you running the inverter all the time to run the lights ?
If so you could gain  power by converting the lights to DC and turn the inverter off if lights are the only loads needing to be run.

I believe you can go to 60 amp breaker for the 6 gauge wire - though no problem going lower amp breaker if you already have them. You can fuse for maximum that the wire will handle . Same with your 10 gauge wire -- you could have gone to 30 amps on it .

Sounds like good installation to me but others may have comments I don't see . f

Larry

system one
Classic 150 , 5s4p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system two
Classic 150 ,5s 135 watt Kyocero , 16s Calb 100AH LiFePO4 , Outback VFX 3648 inverter
system three
Midnite KID MPPT 24 DC in to  12 volt AGM batterie

ricardo

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Re: Design check - Small offgrid PV system, my first attempt at DIY.
« Reply #2 on: May 28, 2018, 04:00:38 PM »
The load could all be DC .. (lighting is 12V and the temperature probe is a 5V device) with the proper DC-DC conversion ..  when first installed i'm going to just wire them up through AC since thats already setup in the shed..  but not having to run the inverter all the time would reduce the load.

You are right, i've oversized the wires on purpose (first DIY, so i'm being overly cautious) -- knowing that if i upgrade parts of the system i'll have to possibly upgrade the breakers.

thanks for commenting larry!

ClassicCrazy

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Re: Design check - Small offgrid PV system, my first attempt at DIY.
« Reply #3 on: May 28, 2018, 05:54:04 PM »
Are you running 12v batteries ? Would be easy to just take the output of whatever is making the 12v for the lights , cut that cord and bring it over to a line directly from 12v that comes from batteries . Just put a fuse or breaker in that would be right for whatever size wire the lights are running on. 
Yes good to oversize for expansion.
Larry
system one
Classic 150 , 5s4p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system two
Classic 150 ,5s 135 watt Kyocero , 16s Calb 100AH LiFePO4 , Outback VFX 3648 inverter
system three
Midnite KID MPPT 24 DC in to  12 volt AGM batterie

ricardo

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Re: Design check - Small offgrid PV system, my first attempt at DIY.
« Reply #4 on: May 29, 2018, 02:58:45 AM »
I am using 12v batteries , 2 of them in series to make a 24v system. 

The outdoor landscape lights are connected to two (2) 300W 12v transformers (AC to DC) .. big heavy mofos.

I see plently of affordable DC step down transformers -- taking a load out from the KID and stepping it down to 12v should work. (and then use the kid to control the timing of the lights).

So far, i'm making reasonable progress -- the racking on the roof is in, and i've ran the wiring down to the shed from the roof, and drove the new ground rod into the earth.. (that was a burly task!) .. waiting for FEDEX to deliver many packages in the coming week.

Photo shows the new ground rod with the single unbroken #6 braided bare copper line coming from the roof.  (since the photo was taken i have clipped back the screws for the ground rod bond)

ClassicCrazy

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Re: Design check - Small offgrid PV system, my first attempt at DIY.
« Reply #5 on: May 29, 2018, 11:48:54 AM »
Oh - I thought maybe you had it all in already .
If you can change it go with the larger breakers for your wire size and save having to replace them in the future.
I recommend Samlex DC to DC converter SDC-23  or the larger or smaller models depending on your needs. They are very good quality. And will match your inverter - ha ha !

Larry
system one
Classic 150 , 5s4p  Kyocera 135watt , 12s Soneil 2v 540amp lead crystal for 24v pack , Outback 3524 inverter
system two
Classic 150 ,5s 135 watt Kyocero , 16s Calb 100AH LiFePO4 , Outback VFX 3648 inverter
system three
Midnite KID MPPT 24 DC in to  12 volt AGM batterie