Best panel for 12 volt system?

[S Davis]

I am starting to look for panels for a 12 volt backup system, they will be charging four 12 volt 280ah LifeP04 batteries and I will be adding four more so eventually eight.

This is being installed on a detached garage about 50’ from the house. I am limited for panel space, I have room for one row 18’ long.

What panels would give me the best output? I am leaning towards Outback inverters so I would probably go with one of their solar charge controllers.

 

[sunshine_eggo]

Best panel is the one that fits the area you have, your budget and delivers the power you need.

 

[S Davis]

Ok, thanks.

 

[Don B. Cilly]

Probably newer 24V monocrystalline ones, you get 4-500W (nominal) for about €160.
Yes, you can charge your 12V batteries with them :·)
.

 

[sunshine_eggo]

Probably newer 24V monocrystalline ones, you get 4-500W (nominal) for about €160.
Yes, you can charge your 12V batteries with them :·)
.

If he's in the EU, maybe. Since they're not using meters, they're probably not in the EU. Further, since you don't know his dimensional constraints, you can't recommend 24V.

Mono is also horribly overrated. They do not significantly outperform poly in any measurable way and are often not worth the premium attached.

 

[12VoltInstalls]

They do not significantly outperform poly in any measurable way

Wellll… I can measure them smaller with a tape measure but a Watt is a Watt
(just picking on you for fun)

 

[S Davis]

I am in the Seattle WA area, so highest wattage that will fit.

 

[sunshine_eggo]

I am in the Seattle WA area, so highest wattage that will fit.

Seattle weather is not conducive to solar. Keep your expectations on performance at the bottom of the barrel.

A "row" 18' long doesn't provide enough information. I assume there's some vertical constraints. If there is any shading or partial shading risk, you should take that into consideration. Some locations are horrifically poor choices for solar. Partial shading can devastate production.

Typical 300W+ panels are about 1 meter wide and up to 2 meters tall, so the most you could fit in the vertical orientation is 5 panels.

Sticking with 12V is also going to be limiting. Let's say you do put 5 300W panels on it... 1500W. That means you're going to need 1500W/12V = 125A of charging current - that's 2X expensive MPPT controllers vs. a single cheaper MPPT controller at 60A with 24V battery.

It's also limiting on the output side. 12V systems at > 2000W start to get cumbersome on wiring requirements because you're moving so much current on the DC side.

 

[rmaddy]

A "row" 18' long doesn't provide enough information.

And what direction does this "row" face?

 

[S Davis]

Ok this is my limitation, I have a lean to single car garage with the roof facing north. I Will need to make a rack at the peak. I also have a porch roof on the house that I will put panels on in the future, I need to run conduit.

 

[rmaddy]

North facing? That's about as bad as it can get. Unless you can mount the panels at the peak so the panels are at least level with the ground, you need a non-solar solution. And you will have terrible shading issues with the taller part of the house and the tall trees. Even the trees to the south of the house will be an issue this time of year. Even if the panels are mounted level to the ground at the peak of the roof, you'll be lucky to get more than two hours of sun on most of the panels even in the summer. And that doesn't cover the 9 months of clouds you have in Seattle. Everything you have here is working against you. Sorry.

 

[sunshine_eggo]

If you're in the US, you will be subject to NEC2017 or 2020, which required module level shutdown. That will add $60-75 each per panel. Check with your local AHJ (Authority Having Jurisdiction).

Like this?

 

[S Davis]

Seattle weather is not conducive to solar. Keep your expectations on performance at the bottom of the barrel.

A "row" 18' long doesn't provide enough information. I assume there's some vertical constraints. If there is any shading or partial shading risk, you should take that into consideration. Some locations are horrifically poor choices for solar. Partial shading can devastate production.

Typical 300W+ panels are about 1 meter wide and up to 2 meters tall, so the most you could fit in the vertical orientation is 5 panels.

Sticking with 12V is also going to be limiting. Let's say you do put 5 300W panels on it... 1500W. That means you're going to need 1500W/12V = 125A of charging current - that's 2X expensive MPPT controllers vs. a single cheaper MPPT controller at 60A with 24V battery.

It's also limiting on the output side. 12V systems at > 2000W start to get cumbersome on wiring requirements because you're moving so much current on the DC side.

I understand about 12/24 volt this is going to be a part of my system, I am making multiple 12 volt 280ah all with 200amp BMS all the batteries will mount the same, three will be in a mobile application and interchangeable with the house backup system. I am shooting for a Outback VFXR 2812 in the truck and two for the house. If one part of the system dies I have options.

 

[S Davis]

If you're in the US, you will be subject to NEC2017 or 2020, which required module level shutdown. That will add $60-75 each per panel. Check with your local AHJ (Authority Having Jurisdiction).

Like this?


View attachment 77039

Yes that was my plan, the panels will face 190*

 

[S Davis]

It looks like I could fit five 420watt panels.

 

[sunshine_eggo]

I understand about 12/24 volt this is going to be a part of my system, I am making multiple 12 volt 280ah all with 200amp BMS all the batteries will mount the same, three will be in a mobile application and interchangeable with the house backup system. I am shooting for a Outback VFXR 2812 in the truck and two for the house. If one part of the system dies I have options.

5600W @ 12V is going to be brutal.

Yes that was my plan, the panels will face 190*

Orientation-wise, that should be fine; however, you are going to have multiple regulatory hurdles. You will almost certainly be obligated to meet city or county building codes, and a roof mounted array has deeper implications.

I would thoroughly research those before spending any money.

It looks like I could fit five 420watt panels.

If you're going to have a pretty steep angle, you might also benefit from the bifacial panels.

 

[S Davis]

I should be able to mount them at whatever angle makes sense or even have two angles one for summer and adjust for winter if that has any value.

 

[S Davis]

I am not planning on grid tie, I am planning a critical load panel with a transfer switch so the backup system runs as normal power supply and if when it drops out it will switch to grid power.

 

[S Davis]

5600W @ 12V is going to be brutal.

In what way, wire size?

Orientation-wise, that should be fine; however, you are going to have multiple regulatory hurdles. You will almost certainly be obligated to meet city or county building codes, and a roof mounted array has deeper implications.

I would thoroughly research those before spending any money.



If you're going to have a pretty steep angle, you might also benefit from the bifacial panels.

 

[sunshine_eggo]

I am not planning on grid tie, I am planning a critical load panel with a transfer switch so the backup system runs as normal power supply and if when it drops out it will switch to grid power.

It doesn't matter. You will still have to comply with building codes, and they likely invoke NEC2017 or newer.

Concerning 5600W @ 12V, 5600W/12V/.85 = 549A