RV Solar System

[scott.rathburn1]

Hi, I'm new to the forum and working on designing a solar system for my RV. I'd like to do a 48V system with Epoch Rack Batteries, a Victron solar charge controller, and a Victron Inverter/Charger. I'm trying to get the maximum solar wattage on the roof but with the layout of the AC units, vents, and Skylights, only the smaller-size solar panels work. If I use the Rich Solar 12-volt 250W panels (about 61" x 30") I can fit nine panels for a total of 2250 Watts. I'm wondering if it's a good idea to connect all nine in series for 170-volts @ 18.9-volts each to have enough voltage to charge the 48-volt batteries? Any help would be greatly appreciated.

Thanks, Scott

 

[sunshine_eggo]

Hi, I'm new to the forum and working on designing a solar system for my RV. I'd like to do a 48V system with Epoch Rack Batteries, a Victron solar charge controller, and a Victron Inverter/Charger. I'm trying to get the maximum solar wattage on the roof but with the layout of the AC units, vents, and Skylights, only the smaller-size solar panels work. If I use the Rich Solar 12-volt 250W panels (about 61" x 30") I can fit nine panels for a total of 2250 Watts. I'm wondering if it's a good idea to connect all nine in series for 170-volts @ 18.9-volts each to have enough voltage to charge the 48-volt batteries? Any help would be greatly appreciated.

Thanks, Scott

Shading is devastating. Partial shading is way more devastating than you'd think possible.

Roof protrusions can shade small portions of panels causing massive losses.

Panels in parallel help mitigate shading issues vs. series panels.

When considering solar panel voltage, you need to look at Voc. Those 9S panels will likely subject the MPPT to about 205Voc - more in cold conditions. You must never exceed the MPPT maximum voltage under any conditions.

You don't need more than about 70Vmp to efficiently charge 48V batteries.

Given the panels you've selected, a 4S2P arrangement using only 8 panels is the only workable option. Going to 60 or 72 cell panels may be more practical. allowing more panels in parallel and fewer in series. if those were 60 cell panels instead of 36, a 3S3P arrangement would be best.

 

[scott.rathburn1]

Thanks for the reply. I thought that I had read about that problem with series connected panels on an RV, but wanted to be sure.
Would I be better off with 3s3p and a 24-volt battery bank or 9p with a 12-volt system? I was trying to limit the wire size that would be required with the lower-volt system, but I can't seem to find any other panel size that will fit and come close to the 2250 Watts of these panels. Thanks again for the reply.

 

[sunshine_eggo]

Thanks for the reply. I thought that I had read about that problem with series connected panels on an RV, but wanted to be sure.
Would I be better off with 3s3p and a 24-volt battery bank or 9p with a 12-volt system? I was trying to limit the wire size that would be required with the lower-volt system, but I can't seem to find any other panel size that will fit and come close to the 2250 Watts of these panels. Thanks again for the reply.

The DC voltage of your system also depends on your output needs, so you need to consider that. On the MPPT side, the 2250W would need nearly 100A of MPPT output at 24V and 200A @ 12V, so that's added expense.

It might cost you more in PV, but are you sure you can't tetris a bunch of smaller 100W panels up there?

While you might hate losing that 250W by only using 8 panels, that's probably a much more flexible solution than 9S @ 48V or 3S3P @ 24 or 48V.

 

[chrisski]

I like the idea of many smaller panels.

Pictures and diagrams show obstructions.

I have 5 sets of parallel panels pictured to 2 different SCCs. There’s an additional parallel string I put in the side and 900 watts on the groynd.

In my signature block, I show how I got 1650 watts of power on the roof. I also can add 300 watts to the side, and 900 watts on the ground.

 

[scott.rathburn1]

Thanks, Did you mean 2s4p with the 250W and just using the 8 panels? I'll also take a look at the possibilities with 100W panels.