I need help with sizing the solar fuses, wiring, and mppt controller.

[Mojo]

I would get one more panel and go series parallel you’ll be much better off.

[srponies]

Originally Posted by Mojo

I would get one more panel and go series parallel you’ll be much better off.

We actually do have a 4th panel. BUT - we don't quite have the space on our roof for the panel. We have (2) panels rearward of our skylight, fan & chimney. And (1) panel forward of them. A 4th panel would extend too far toward the front of the bus (shuttle), over the cab area. We might be able to have a 4th panel if we created some sort of a spoiler/wind deflector, to route airflow over the top of the panel.

Steve

[srponies]

Originally Posted by Mojo

I would get one more panel and go series parallel you’ll be much better off.

Well I did go ahead and mount the 4th panel on the roof. So we can wire series parallel. Now I am looking to figure out the solar charge controller that can handle the 1240 watts.

Steve

[dzl_]

Originally Posted by srponies

Well I did go ahead and mount the 4th panel on the roof. So we can wire series parallel. Now I am looking to figure out the solar charge controller that can handle the 1240 watts.

Steve

Input Voltage and Amperage is the most important to consider, output power is a consideration too but a secondary one.


Calculate the Open Circuit Voltage (Voc) and the Short Circuit Current (Isc) of your array (if it is a 2S2P configuration take the Voc and Isc of a single panel and multiply each by two, than multiply Voc by an additional 1.2x to account for cold weather.


These numbers dictate what the max input current and voltage of your controller needs to be.


Then take PV array watts and divide by battery bank volts this will give you the controller output amp rating you need in order to not bottleneck the array. This number is softer, it can usually safely be a bit too small or obviously be larger than needed (check the documentation for the specific controller).

[srponies]

Originally Posted by dzl_

Calculate the Open Circuit Voltage (Voc) and the Short Circuit Current (Isc) of your array (if it is a 2S2P configuration take the Voc and Isc of a single panel and multiply each by two, than multiply Voc by an additional 1.2x to account for cold weather.

(Voc)44.9 x 2= 89.8 V
(Isc) 9.08 x 2 = 18.16 A

89.8 V x 1.2 =108V

Originally Posted by dzl_

Then take PV array watts and divide by battery bank volts this will give you the controller output amp rating you need in order to not bottleneck the array.

I wasn't sure about this part regarding what numbers to use.
PMax 310W x 4 = 1240w
1240W/12V = 103.3A

OR
(Voc)44.9 x (Isc) 9.08 = 408W
408W x 4 = 1632W
1632W/12V = 136A

So worst case scenario I need a controller to handle 108V input and 136A output, or possibly 108V input, 103A output.

Will the Victron 150/100 handle this, or do I need a different setup?
https://amsolar.com/victron/cctlr-vt-mpps-100a

Thanks,
Steve

[dzl_]

Originally Posted by srponies

I wasn't sure about this part regarding what numbers to use.
Pmax x 4 = 1240w = 103.3A
OR
Voc x Isc x 4 = 1632W = 136A

The first option is correct. (Voc and Isc are the maximums for current and voltage, but they can never happen at the same time, in a sense they are opposites, so they are not relevant for calculating power (Watts))

Pmax (or Imp x Vmp which will give you the same number roughly) is the correct figure to use for the latter part of this calculation.

Originally Posted by srponies

Will the Victron 150/100 handle this, or do I need a different setup?
https://amsolar.com/victron/cctlr-vt-mpps-100a

Yes this would be a reasonable choice.

On the input side:
108V is less than the controllers max input of 150V
18.2A is much less than the max input of 70A

On the output side:
103.3A is slightly more than the 100A current limit, but unlike the input limits, this just means on the occasions that your array is actually putting out 100% power it will be current limited to 100A (96.7% of the arrays max output). Since you seldom ever achieve 100% anyways, this is not really an issue. Victron controllers can safely be overpaneled to much greater degrees than this so long as you stay within the input limits (which you are).