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Old 02-15-2023, 08:00 AM   #1
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Solar ideas

Considering solar. I already have Victron MP 2, Cerbo, display and BMV712 installed, so I'll use a Victron MPPT controller.

I have #10 wire from roof to basement (prewired from factory) but not opposed to pulling new larger wire, if needed.

I've received 2 quotes from 2 different companies. I easily have roof space for (8) 200 watt panels, so I want to design for that even if I go with less panels for now. Both companies say I can use the existing #10 as long as I wire series/parallel. I believe I would use a 150/60 MPPT.

But 1 of the quotes is suggesting I go to a #2 wire from roof to MPPT location. This quote suggested I wire all panels in parallel and use a 150/100 MPPT.

This is a DIY so labor cost is not an issue. But the 150/100 controller is more $$ along with the #2 added wiring.

Is it worth going to the parallel installation to minimize effects of shading?

Looking for other thoughts, ideas and comments?
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Old 02-15-2023, 09:10 AM   #2
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It really depends on the controller you use and its respective limits. I put on 1200W of rooftop solar and used a Renogy 100A MPPT controller. Since my house batteries are 12V, 1200W and 100A is about right.

But to your question, I ran them in three parallel sets of 4x each. So the 4 in series with these panels produced 100V. The reason I did this was because the panels are rated for around/slightly above 25V each. If I did in two sets of 6, that would be ~150V at peak, and the controller was rated at 140-150V max, would shut off past that. Realistically it probably would've been fine most of the time.

To me, it makes the most sense to run the maximum voltage you can without going over the limits of the controller. Running them all in parallel doesn't make much sense to me. That's less efficient, and you will need more wiring because you will have higher amperage. As far as which gauge wire to use, there are plenty of charts out there based on amperage and run length. I ran 10AWG for all my runs just to minimize losses even though I could've gotten away with less. So I have 3 sets of 10AWG wires running from the roof down to the controller. I don't think I would go with this second option you were given that suggested 2 AWG wire.

I have a video on my YouTube channel (linked in my signature) that shows what I did if you want to get a data point. I am very happy with the system, I installed it last summer.
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Old 02-15-2023, 09:15 AM   #3
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What voltage panels can you fit? The Voc and Isc values for the panels are needed to calculate the SCC and wire size you need.

What is your battery bank voltage?

1600W would probably need two separate SCCs
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Old 02-15-2023, 09:50 AM   #4
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Quote:
Originally Posted by TravelSolo View Post
What voltage panels can you fit? The Voc and Isc values for the panels are needed to calculate the SCC and wire size you need.

What is your battery bank voltage?

1600W would probably need two separate SCCs
I should have posted that info. 12 volt system. The place that suggested I add the #2 and go parallel was quoting 45+ Voc, 5.3 imp, 5.8a Isc
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Old 02-15-2023, 10:49 AM   #5
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There was a typo on my first quote suggesting a single 150/60 SCC with panels in series/Parallel. In fact I do need 2 scc and I would have to run another #10 pair. So basically 2 separate systems.
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Old 02-15-2023, 11:12 AM   #6
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It’s interesting how 2 reputable rv solar companies will approach this from 2 totally different angles. Maybe individual designers personal ideas, training and experience, idk.
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Old 02-15-2023, 12:16 PM   #7
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I would look at 24v panels and do two arrays of 2S2P, each with its own SCC. Yes you need to run another pair of wire, but it should be smaller wire, likely 10ga will suffice.

But run it through the calculators at Explorist.life site to be sure, once you pick your panels. that will also allow you to do it in phases
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Old 02-15-2023, 04:31 PM   #8
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2 gauge wire? That makes zero sense. You want as many volts as your MPPT can handle then can use thinner cable. 10 gauge can handle 30 amps at 120V. That's 3600w.

Never have more volts than the MPPT can handle. It won't shut off it'll fry.

I have 3000w running off 2 pairs of 10 gauge wire. I could have went 1 pair but planning on 2 MPPTs. Only have 1 150/100 Victron right now and it's fine. With solar you should expect to get about half the max rating since its flat roof mounted.
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Old 02-15-2023, 04:46 PM   #9
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Quote:
Originally Posted by TravelSolo View Post
I would look at 24v panels and do two arrays of 2S2P, each with its own SCC. Yes you need to run another pair of wire, but it should be smaller wire, likely 10ga will suffice.

But run it through the calculators at Explorist.life site to be sure, once you pick your panels. that will also allow you to do it in phases
I did run 800 watts 2S2P through Nate's calculator and it does come out just fine. I'm leaning towards that first quote I got that was for 2 150/60 SCC's and doubling up the #10. Running another #10 pair isn't a big deal.
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Old 02-15-2023, 04:53 PM   #10
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Quote:
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2 gauge wire? That makes zero sense. You want as many volts as your MPPT can handle then can use thinner cable. 10 gauge can handle 30 amps at 120V. That's 3600w.

Never have more volts than the MPPT can handle. It won't shut off it'll fry.

I have 3000w running off 2 pairs of 10 gauge wire. I could have went 1 pair but planning on 2 MPPTs. Only have 1 150/100 Victron right now and it's fine. With solar you should expect to get about half the max rating since its flat roof mounted.
I don't recommend this approach but I can understand the quote. If the panels are all combined on the roof and the Parallel wire is coming in that way then I understand the quote.

The 150/100 on the other hand can only handle #4 wire coming in so I'd probably go that way IF I was going to wire that way.

OTOH I would recommend that you bring down 2 lines and have 4 sets of 2 panels. This is how I had my 1600W (8X200W panels) wired into our 150/100 MPPT and it can theoretically produce more than 100A (Perfect conditions). Based on this you should run away from the shop recommending
a 150/60 unless they are quoting a 24V system (not to be confused with 24V panels )
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Old 02-15-2023, 06:57 PM   #11
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Quote:
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I don't recommend this approach but I can understand the quote. If the panels are all combined on the roof and the Parallel wire is coming in that way then I understand the quote.

The 150/100 on the other hand can only handle #4 wire coming in so I'd probably go that way IF I was going to wire that way.

OTOH I would recommend that you bring down 2 lines and have 4 sets of 2 panels. This is how I had my 1600W (8X200W panels) wired into our 150/100 MPPT and it can theoretically produce more than 100A (Perfect conditions). Based on this you should run away from the shop recommending
a 150/60 unless they are quoting a 24V system (not to be confused with 24V panels )
I'm not totally following you about 'run away from the shop'. They are quoting based on a 12 volt system. I've put the panel specs into Exploristlife calculator (and 1 from the company that gave me the quote), and I'm getting the exact same results for (4) 200 watt panels 2s2p--both recommend the 150/60. It works out the SCC input voltage is 49 and sending 56 amps to the batteries, in a perfect world.

What am I missing?

Btw, I've pretty much dismissed the #2 wire single SCC proposal.
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Old 02-15-2023, 07:10 PM   #12
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Why not just put them in 4S so you'll be at 100v and 27amps. Then in the future you can just add another group and 4s2p it'll be 100v and 54amps.
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Old 02-15-2023, 07:23 PM   #13
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For large systems I prefer more than one SCC. As you separate the panel arrays, you minimize the drop in output due to shading, etc.
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Old 02-15-2023, 08:23 PM   #14
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Why not just put them in 4S so you'll be at 100v and 27amps. Then in the future you can just add another group and 4s2p it'll be 100v and 54amps.
yes you could and that's even better.
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