Hi,
I am building an off grid system for a cabin.
It has two 220 Amp hour Time USB 12 Volt batteries Wired in parallel via bus bars, which power a 12 volt fridge, lights, cigar and USB outlets, as well as a 2000 Watt inverter. The inverter runs a small microwave for a max of 10 minutes a day, and a coffee pot for 10-15 minutes. The inverter is a back up for gas and wood cooking/heating, and when I am lazy, which isn’t often. The maximum draw on the system is 110 Amp hours. Average use on days the inverter isn’t used is 75 Amp hours.
I plan to power the system with 4 Rich Solar 200 Watt, 24 volt panels, wired 2S2P. It should produce a peak of 56 amps per hour at 12 Volts. I have two separate panel array locations I am considering; one is 75’ from the battery bank location, and the other is 140’. The shorter gets a max of 3 useable hours of sun, the longer gets 5. The 3 hour sun location has some early and late partial shading, though not in the 3 hour window. The 5 hour location has no shading. Both locations are very close to true south.
Data on panels is;
Pmax 200W
VMP 37.6 V
IMP 5.32 A
VOC 45.4 V
ISC 5.83 A
VMAX 1000V
NOCT 113+_ 35F
Temp range-40+185
Max series fuse rating 15A
Power tolerance+_ 5%
Coldest temp in my area is -25
I plan to use a Victron MPPT 150/70 in a 2S2P configuration, and a 250/60 if I choose a 4S1P configuration.
The calculators say either run (long or short) can be done with 10 AWG cable, though the long run suffers more Voltage drop. (3.37 versus 1.80)
It appears I should be able to keep the bank charged using either the 3 hour, or 5 hour panel location.
The bank size of 440 Amp hours, discharged no more than 80% (352 Amp hours) should provide backup power for 3 days using the inverter, and 4.4 days without, in no sun conditions.
I question two things in my plan, and request ideas about them, and the overall setup in general.
Question one is; the MPPT the calculators specify for a 2S2P configuration of 114 Volts-56 Amps, is a 150/60. Is that “too close” to the max of 60? (4 Amps away from max)
When I calculate 2 separate panel arrays (2S2P, 48 Volts nominal) using two MPPT controllers, the Amps show as 28, and the calculator calls for a 150/35, and not a 150/30. So based on these numbers, 4 Amps lower than max is safe, but 2 Amps below max is not?
The second question is configuring the array as 96 Volts nominal.
In the 2S2P configuration the 140’ run shows a Voltage drop of 3.37 and the 75’ run a 1.80 Volt drop.
I could wire it as 4S1P (4-24 Volt panels @ 96 volts nominal, and 45.4 VOC) which produce 227 Volts and 56 Amps. This calls for a 250/60.
The 4S1P configuration on the shorter 75’ run seems my best option, as I have only a 0.91 Voltage drop versus 1.69 at 140’ and it will be far easier to install the panels, and run the wire.
Either configuration provides 56 Amps output, but the shorter run provides 2 hours less sun per day, equating to around 132 Amp hours lost. Ouch!
These numbers are based on low angle winter sun. Summer sun and pruning a few trees may offer a half hour+ of extra exposure.
Thanks for any info you can share!
Rob
I am building an off grid system for a cabin.
It has two 220 Amp hour Time USB 12 Volt batteries Wired in parallel via bus bars, which power a 12 volt fridge, lights, cigar and USB outlets, as well as a 2000 Watt inverter. The inverter runs a small microwave for a max of 10 minutes a day, and a coffee pot for 10-15 minutes. The inverter is a back up for gas and wood cooking/heating, and when I am lazy, which isn’t often. The maximum draw on the system is 110 Amp hours. Average use on days the inverter isn’t used is 75 Amp hours.
I plan to power the system with 4 Rich Solar 200 Watt, 24 volt panels, wired 2S2P. It should produce a peak of 56 amps per hour at 12 Volts. I have two separate panel array locations I am considering; one is 75’ from the battery bank location, and the other is 140’. The shorter gets a max of 3 useable hours of sun, the longer gets 5. The 3 hour sun location has some early and late partial shading, though not in the 3 hour window. The 5 hour location has no shading. Both locations are very close to true south.
Data on panels is;
Pmax 200W
VMP 37.6 V
IMP 5.32 A
VOC 45.4 V
ISC 5.83 A
VMAX 1000V
NOCT 113+_ 35F
Temp range-40+185
Max series fuse rating 15A
Power tolerance+_ 5%
Coldest temp in my area is -25
I plan to use a Victron MPPT 150/70 in a 2S2P configuration, and a 250/60 if I choose a 4S1P configuration.
The calculators say either run (long or short) can be done with 10 AWG cable, though the long run suffers more Voltage drop. (3.37 versus 1.80)
It appears I should be able to keep the bank charged using either the 3 hour, or 5 hour panel location.
The bank size of 440 Amp hours, discharged no more than 80% (352 Amp hours) should provide backup power for 3 days using the inverter, and 4.4 days without, in no sun conditions.
I question two things in my plan, and request ideas about them, and the overall setup in general.
Question one is; the MPPT the calculators specify for a 2S2P configuration of 114 Volts-56 Amps, is a 150/60. Is that “too close” to the max of 60? (4 Amps away from max)
When I calculate 2 separate panel arrays (2S2P, 48 Volts nominal) using two MPPT controllers, the Amps show as 28, and the calculator calls for a 150/35, and not a 150/30. So based on these numbers, 4 Amps lower than max is safe, but 2 Amps below max is not?
The second question is configuring the array as 96 Volts nominal.
In the 2S2P configuration the 140’ run shows a Voltage drop of 3.37 and the 75’ run a 1.80 Volt drop.
I could wire it as 4S1P (4-24 Volt panels @ 96 volts nominal, and 45.4 VOC) which produce 227 Volts and 56 Amps. This calls for a 250/60.
The 4S1P configuration on the shorter 75’ run seems my best option, as I have only a 0.91 Voltage drop versus 1.69 at 140’ and it will be far easier to install the panels, and run the wire.
Either configuration provides 56 Amps output, but the shorter run provides 2 hours less sun per day, equating to around 132 Amp hours lost. Ouch!
These numbers are based on low angle winter sun. Summer sun and pruning a few trees may offer a half hour+ of extra exposure.
Thanks for any info you can share!
Rob
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