Installing mini splits, inverter and panels, a couple questions before I burn stuff down

[harvardbeans]

Hi, and thanks for reading. I'm beginning an off-grid mini split ac/heat install on a cabin in middle Tennessee. I have a construction/remodeling company and have an intermediate level of knowledge about AC power but am a beginner when it comes to solar and DC power. I want to install 9 blue sun 460w bifacial panels on a shed roof and run them to an EG4 6000ex-48HV. The first questions are about how to most effectively position and string the panels together. The roof has a gable in the middle and the pitch is roughly 4/12 or perhaps 3/12 so as the sun passes overhead, it will shine on one side of the roof until about noon and then the other side until sundown, but neither side is shaded, just not direct sunlight. Should I wire all 9 in series with 4 on one side of the gable and 5 on the other or will different amounts on sunlight on each half the array bog it down? If so should I put them all on the same side and collect more sunshine for half the day and less during the other half? I read somewhere that there is good reason to parallel two strings in series but I don't remember why.

The next question is about installing a DC breaker between the inverter and the array. The manual says the inverter's typical amperage is 27A and cautions to use a DC breaker between the inverter and array, but doesn't give any specs on the breaker. Should I use a 30A breaker? The panels are 50.8v each and the inverter's max VOC is 450. Every diagram I look at shows a DC isolator between the panels and inverter. It seems like a breaker serves the same purpose. Would installing both be redundant?

The inverter will be connected to and charge/draw power from two 30KWH battery banks, each with six 5KWH eg4 server rack batteries. Power going out from the inverter will be 240v to the mini split outdoor unit. The mini split will also be powered directly by a second pv array mounted above it on the house. I think all I need between the mini split and the inverter is an AC breaker and between the mini split and the array is either an isolator or a dc breaker.

As for battery to inverter cables, I have 1 gauge wires and I ordered an adjustable torque wrench to make sure all my connections are to spec.

Hopefully once these questions are cleared up (unless I'm not asking the right questions) I'lll be ready to begin the install. Thanks in advance for anyone willing to help out a newb.

 

[harvardbeans]

Ok, Looks like I asked too many questions. Let me try again with the biggest question first.

The inverter manual says to install a "breaker" between the array and the inverter. Is overload protection needed between the two or are they using the term breaker to mean a disconnect? If I need overload protection, how to I figure out how many amps the breaker should be? The max voc the inverter can handle is 450 and the panel isc is 11.22 amps.

 

[Supervstech]

If only in series, or only in two strings parallel, overload protection isn't needed on the PV, a voltage capable breaker or dc rated isolation switch would be wise for service etc.
Keep in mind, pv in the 400V range will create one heck of an arc, so avoid opening the disconnect under load.

 

[harvardbeans]

Great, thanks. That simplifies things.

They'll be wired in series. Any thoughts on having half of the panels (4 or 5) on one side of the roof and the other half on the opposite side vs having them positioned so that every panel is getting the same amount of sun at the same time? I was up there today and I'd doubt it's even a 3/12 pitch. Both sides will get indirect sunlight when the sun is shining more on the other side and neither will be shaded until 4pm or so this time of year.

 

[Supervstech]

If strings tied together aren't pointing same way, production will be limited to the lowest production side...

 

[400bird]

Should I wire all 9 in series with 4 on one side of the gable and 5 on the other or will different amounts on sunlight on each half the array bog it down?

The entire string needs to be in the same condition, facing the same direction at the same angle.

I read somewhere that there is good reason to parallel two strings in series but I don't remember why.

Parallel strings can point in different directions but need to have the same number of identical panels.

The next question is about installing a DC breaker between the inverter and the array. The manual says the inverter's typical amperage is 27A and cautions to use a DC breaker between the inverter and array, but doesn't give any specs on the breaker. Should I use a 30A breaker?

The panels are 50.8v each and the inverter's max VOC is 450.

50.8 x 9 is over 450 volts. Plus the voltage will increase when cold. How cold does it get there?
You're probably risking killing that inverter if it gets cold in the winter where you're doing this install.
There are plenty of calculators for this online, here's one, punch in your panel specs and min temp for the area and see what you get for max voltage, some random numbers and 0° F came out to 526 volts. That will let the smoke out of your inverter.

MPPT Calculator - Victron Energy

MPPT Calculator - Victron Energy

www.victronenergy.com

 

[harvardbeans]

The entire string needs to be in the same condition, facing the same direction at the same angle.

Parallel strings can point in different directions but need to have the same number of identical panels.



50.8 x 9 is over 450 volts. Plus the voltage will increase when cold. How cold does it get there?
You're probably risking killing that inverter if it gets cold in the winter where you're doing this install.
There are plenty of calculators for this online, here's one, punch in your panel specs and min temp for the area and see what you get for max voltage, some random numbers and 0° F came out to 526 volts. That will let the smoke out of your inverter.

MPPT Calculator - Victron Energy

MPPT Calculator - Victron Energy

www.victronenergy.com

Thanks for the info. The original thought was using a 9th panel because half won't be in direct sun and due to the angle of the shed roof really none of them will be positioned ideally. Now that I know to face the entire series the same way, I'm thinking of doing a series of 4 or 5 on one side of the roof paralleled to the same on the other side. If I understand correctly, that will keep the voltage around 250 and double the max amperage to 22.5. Any potential issues with this setup?

 

[harvardbeans]

If strings tied together aren't pointing same way, production will be limited to the lowest production side...

Thank you