3 different solar panels on rv roof

moonlitsouls

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Updating original post : looking to add a 5th panel

Currently I have
below x 2

Output power190 W
Rated current9.45 A
Rated DC voltage20.4 V
Open-circuit voltage24.09 V
Module efficiency21%
ConnectivityMC4 connectors





X1
Maximum power (Pmax)180W
Voltage at Pmax (Vmp)16.77V
Current at Pmax (Imp)11.20A
Open-circuit voltage (Voc)19.84V
Short-circuit current (Isc)11.75A

X 1
Maximum power (Pmax)200W
Voltage at Pmax (Vmp)17.0V
Current at Pmax (Imp)11.76A
Open-circuit voltage (Voc)20.23V
Short-circuit current (Isc)12.45A



trying to add a 5th panel here are the specs F13E2CF5-0F27-4A7D-9592-3AA1E230AB81.png
 
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OffGridInTheCity

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Base case #1 - If you wire them in series using Vmp you'd have: 20.4v + 20.4v + 16.77v + 16.77v + 17v = 91.34v * (lowest amps = 9.45a) = 863w. This would be 863w/940w (max) = 91.8% of the max.

Base case #2 - If you wire them in parallel you'd have: 9.45a + 9.45a + 11.2a + 11.2a + 11.76a = 53.06a * (lowest voltage = 16.77v) = 890w. This would be 890w/940w (max) = 94.7% of the max.

Then there would be combinations - 1st 2 in parallel ----series---> 2nd 2 in parallel ----- series ----> 5th panel - as an example but the rules should apply - e.g. in series the voltages add up but its the lowest amps that rules and in parallel the amps add up but its the lowest voltage that rules.

In base case #1 you'd be at 91.34v against 100v max of the Victron - likely be OK. In base case #2 you'd be just a bit more efficient (in theory) but you exceed 50a max of the Victron at 53.06a. With 5 in series you'd be subject to loss of power on *any* shading - even 2 x 2 inches kind of thing.

Here's a youtube discussing mixing panels of different types I used as the basis for the above - start at 4:42 for different types:

Personally - 92% vs 95% is no big deal because in real life there are a lot of variables with panels including tilt, shade, clouds, heat etc. However, I would think about shading - for example on my trailer I have each side in it's own string so I can have shade down 1/2 the trailer roof from front to back and still have 1 side producing.
 
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moonlitsouls

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@OffGridInTheCity , really appreciate your help ..


In parallel , would i need to put a fuse between the panels and the scc ? or the scc and the battery? i read up on that and im still confused as hell
 

moonlitsouls

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OffGridInTheCity

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@OffGridInTheCity , really appreciate your help ..


In parallel , would i need to put a fuse between the panels and the scc ? or the scc and the battery? i read up on that and im still confused as hell
I use circuit breakers (rather than fuses) because in addition to fusing it's nice to be able to disconnect the incoming PV voltage/current right at the SCC to work on things. You definitely want to fuse / circuit breaker the battery.
 

OffGridInTheCity

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So with a total of 53amp , if i wanted to put a breaker between the panels and the SCC , would this 63amp be sufficient?

Yes - but remember that if you do 63a you need wire that won't melt until after you reach 63a :) That would be 4awg wire leading into the 63a breaker. Rule of thumb for short distances (20ft or less)
14awg = 15a max
12awg = 20a max
10awg = 30a max **This will be the pigtails from your panels** - so if you parallel all 5 panels, you'll need wire that can handle the 53a from the point where you combine them to the SCC - e.g. at the very least 6awg but 4awg if you do 63a breaker.
8awg = 40a? - never used this one.
6awg = 50a max
4awg = 80a max
 
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moonlitsouls

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I use circuit breakers (rather than fuses) because in addition to fusing it's nice to be able to disconnect the incoming PV voltage/current right at the SCC to work on things. You definitely want to fuse / circuit breaker the battery.

so what if i had two sets of breakers? one between the panels and the scc , and one between the scc and the battery?
 

moonlitsouls

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@OffGridInTheCity ok i just realized something , the wiring between the panels and the scc is currently only 10guage , i may have to wire in series to avoid changing all that , so now heres something very confusing

IF i wire in series , the voltage is higher and the amps are lower , so do you still need the breakers? and if so , now i only need a 20 amp breaker bc the voltage is higher yes?
 

OffGridInTheCity

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@OffGridInTheCity ok i just realized something , the wiring between the panels and the scc is currently only 10guage , i may have to wire in series to avoid changing all that , so now heres something very confusing

IF i wire in series , the voltage is higher and the amps are lower , so do you still need the breakers? and if so , now i only need a 20 amp breaker bc the voltage is higher yes?
Yes - you're on the right track. That's one of the reasons folks do series (besides shading) is to reduce the amps for smaller wire / smaller breakers :)
 

OffGridInTheCity

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Just FYI - I use Midnite Solar breakers as they are UL (high quality). Not pushing them, just sharing.

Here's a pretty good priced box with DIN rail - https://www.amazon.com/MidNite-Sola.../B007IAIW7S/ref=pd_bxgy_1/140-0687880-1929332

And here's the style of breakers I use - https://www.amazon.com/Din-Rail-Mount-Combiner-Breaker/dp/B01GW3T7GG/ref=sr_1_3 that mount on the DIN rail. They come in 5a, 10a, 15a, 20a, 30a, up to 100a for single pole.

In my box I have 2 strings of PV coming in with a 15a for each and combine them in the box, plus a battery breaker 80a, plus use the other slots as breakers (fusing) for some other 'direct' battery takes-offs such as for my BMS and 48v ->12v step-down for the 12v sub-system. Kind of a DC on/off control box :)
 

moonlitsouls

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Yes - you're on the right track. That's one of the reasons folks do series (besides shading) is to reduce the amps for smaller wire / smaller breakers :)
Just FYI - I use Midnite Solar breakers as they are UL (high quality). Not pushing them, just sharing.

Here's a pretty good priced box with DIN rail - https://www.amazon.com/MidNite-Sola.../B007IAIW7S/ref=pd_bxgy_1/140-0687880-1929332

And here's the style of breakers I use - https://www.amazon.com/Din-Rail-Mount-Combiner-Breaker/dp/B01GW3T7GG/ref=sr_1_3 that mount on the DIN rail. They come in 5a, 10a, 15a, 20a, 30a, up to 100a for single pole.

In my box I have 2 strings of PV coming in with a 15a for each and combine them in the box, plus a battery breaker 80a, plus use the other slots as breakers (fusing) for some other 'direct' battery takes-offs such as for my BMS and 48v ->12v step-down for the 12v sub-system. Kind of a DC on/off control box :)

ok cool , thanks again for the help. what are the advantages of the double pole compared to the single? it seems like with the double you can turn one side of and still keep some functionality? or p1 vs p2 affects different things?

adam
 

OffGridInTheCity

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ok cool , thanks again for the help. what are the advantages of the double pole compared to the single? it seems like with the double you can turn one side of and still keep some functionality? or p1 vs p2 affects different things?
As an example for DC voltage - double pole let's you disconnect BOTH the + and - at the same time. Some like this for the battery in particular. Not so much for panels. In home 240v AC breakers this is required to disconnect both hot wires wires at the same time.

In my trailer, I just breaker the + for everything (battery, solar, other) - 1 pole is enough.

Maybe someone will comment more on this aspect.
 

moonlitsouls

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@OffGridInTheCity

ok very cool , i got a plan , 2 x 32 amp double poles and im going to wire in series .


Next up , i gotta figure out how to wire my DC-DC renogy 60amp charger (this is all for my truck camper btw)

Then i need to figure out how to fuse my battery itself , ive been living in my truck camper full time for 5 months and the battery doesnt even have a fuse protecting it , ive put it off for a while and ive been fine , but with this upgrade of the system im going to make sure everything is fused properly ,

the dc-dc requires ANL fuses on both sides , starter-charger and charger-house battery

but im still confused on what breaker i need from the battery itself to all the other positive and negative wires

youve been a huge help
 

OffGridInTheCity

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Battery wise, the idea is to stop a 'dead short' (fire, wire melt-down, ...) with a fuse or breaker. Secondarily to be able to disconnect the battery for safety to work on things. However, you want to let thru the max amps that you need for your loads.

So what is your 'max' load on the battery and what voltage/size (ahs, max amps) is your battery or battery bank.

To figure out the max load - maybe you have an inverter? so what is the maximum the inverter can deliver in watts. Let's say you have a 2000w inverter and 12v battery, then 2000w/12v = 167a circuit breaker needed. A 2000w inverter/24v battery would be 1/2 that 83a and so on.

To figure out the max amps your battery can safely deliver, it will be part of the specifications of the battery - you should be able to google to find it. You want the battery to be able to deliver the max amps you need for the load :)
 

moonlitsouls

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Battery wise, the idea is to stop a 'dead short' (fire, wire melt-down, ...) with a fuse or breaker. However, you want to let thru the max amps that you need for your loads. Hopefully your battery is big enough for the loads :)

So what is your 'max' load on the battery and what voltage/size (ahs, max amps) is your battery or battery bank.

To figure out the max load - maybe you have an inverter? so what is the maximum the inverter can deliver in watts. Let's say you have a 2000w inverter and 12v battery, then 2000w/12v = 167a circuit breaker needed. A 2000w inverter/24v battery would be 1/2 that 83a and so on.
haha gotchu , i have a 280ah lithium battery bank with a 120a overkill solar bms
i have a 1000w inverter that is just wired to the battery and i run an extension cord off it to run my ac needs (not much at all)

oh i forgot , my inverter has its own fuse , so all i need is just a terminal fuse as a last line of protection

so maybe a 100amp fuse?
 
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OffGridInTheCity

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haha gotchu , i have a 280ah lithium battery bank with a 120a overkill solar bmw
i have a 1000w inverter that is just wired to the battery and i run an extension cord off it to run my ac needs (not much at all)

so maybe a 100amp fuse?
Assuming 12v, then 1000w/12v = 83a. So 80a or 100a or 120a. Remember that the fuse should not be bigger than the wire can handle - else the wire will melt (start a fire?) before the fuse will blow.

80a fuse = 4awg wire. **Its OK to have a fuse lower than the absolute max if you don't use the absolute max from the inverter.
120a fuse = at least 2awg wire.

You can run multiple smaller wires for higher amps - https://www.wirebarn.com/Combined-Wire-Gauge-Calculator_ep_42.html - if you don't have the larger wire. For example 2 wires at 4awg = 1awg.
 

moonlitsouls

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Assuming 12v, then 1000w/12v = 83a. So 80a or 100a or 120a. Remember that the fuse should not be bigger than the wire can handle - else the wire will melt (start a fire?) before the fuse will blow.

80a fuse = 4awg wire. **Its OK to have a fuse lower than the absolute max if you don't use the absolute max from the inverter.
120a fuse = at least 2awg wire.

You can double up on wire for higher amps - https://www.wirebarn.com/Combined-Wire-Gauge-Calculator_ep_42.html
For example 2 wires at 4awg = 1awg.

For 120a fuse you can do 1 x 2awg wire or 2 x 4awg wires.

ok i forgot to tell you , my inverter has its own fuse , so all i need is just a terminal fuse as a last line of protection
 
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