Newb design for RV 800W solar, 48V 200Ah batteries, Victron system. Reasonable? Suggestions?

[MegaMosquito]

I read Will Prowse's very helpful book, read product specs, watched videos, and dove right in to designing a solar+battery system for my 24ft motorhome. It would be great if you experts could comment on how this looks so far. I haven't bought anything yet. Here's my first draft of the design. What do you think? Thanks in advance for any help.

 

[Brucey]

How long are those runs? The use of 4/0 for 48V may be excessive. Victron recommends 1 AWG for short runs on the 3k multiplus, and 2/0 for long runs. Unless you are leaving capacity for a 2nd inverter?

 

[Brucey]

The UL listed versions wire box is a fair bit larger/taller you may have trouble getting 4/0 into the standard one.

 

[Brucey]

8AWG isn't needed for your solar panels, 10 or 12 would be ok. If you anticipating a full 100A of charging at some point you'll need to upsize the 8AWG from SCC to distributor, I think manual specs 4AWG? But for your 800W and less than 20A would be fine.

 

[Zwy]

I read Will Prowse's very helpful book, read product specs, watched videos, and dove right in to designing a solar+battery system for my 24ft motorhome. It would be great if you experts could comment on how this looks so far. I haven't bought anything yet. Here's my first draft of the design. What do you think? Thanks in advance for any help.

View attachment 208123

Instead of the 48V Multiplus II, I'd opt for the 24V Multiplus II 2x120V and a 24V battery bank. More flexible for use with a RV, especially a 50A RV hookup.

 

[littleharbor2]

For about the same price you could buy 500+ watt panels. 12 volt panels come with a terrible per watt price.

 

[MegaMosquito]

This is the best forum ever! Damn. You folks respond fast with great insights!

@Brucey, thanks for the wire size feedback. My intention on that is over-engineering. The batteries and the other components that I showed using 4/0 AWG wire will will be inches apart from each other with cable segment lengths of about 1ft - 3ft in length. At those short lengths I figured the cost difference between 4/0 and 1/0 would be small enough that I might as well over-engineer. However, thanks for nudging me to re-evaluate those 8AWG runs. When I have a clearer idea of the real run lengths I'll reconsider (I happen to have quite a bit of 10AWG stranded copper on hand, so I may go with that and save a bit of cash (and use it to pay for the over-engineered 4/0 stuff, haha).

@Zwy, thanks for the comment. My tiny motorhome only has a 30Amp system, and only a single 120 phase. Am I right that the reason one would want a 2x120 system is to get a 2-phase system and 240V? That's not something I can make use of.

@littleharbor2, I would truly love to use 500+ watt panels but my RV roof is tiny. I have been searching for panels and "playing Tetris" with them on my roof for weeks, and 4 x 200W was the best scheme I have come up with. It was a squeeze to get these four panels on there too (one panel even has to overlap my shower's skylight by 4 inches to fit it in). Here's a diagram mapping out what I plan for my roof:

 

[Zwy]

@Zwy, thanks for the comment. My tiny motorhome only has a 30Amp system, and only a single 120 phase. Am I right that the reason one would want a 2x120 system is to get a 2-phase system and 240V? That's not something I can make use of.

I thought maybe you had a 50A RV connection. I have a 30A on my truck camper and use a 24V Growatts 3Kw inverter.

As you are intending to use 4/0 cable, that will work well with a 3Kw inverter on 12V, just a tad bit on the high side for amps but doable. I consider the 48V system excessive for an RV unless it is a large coach or 5th wheel which of course would be 50A.

You should consider sticking with 12V or possibly running 24V. Makes it much easier to convert 24V to 12V than 48V to 12V plus it is cheaper. 48V requires switches and other components rated for 48V DC. Higher priced and harder to source.

View attachment 208232

I actually used 100W panels on my truck camper, they fit better. I'd actually look at the 100W and see how those fit your roof.

 

[MegaMosquito]

8AWG isn't needed for your solar panels, 10 or 12 would be ok. If you anticipating a full 100A of charging at some point you'll need to upsize the 8AWG from SCC to distributor, I think manual specs 4AWG? But for your 800W and less than 20A would be fine.

Ahah! Good catch on the 8AWG. 8AWG maxes out at 55A apparently! As you note, that's fine for now, but for 100A (if I ever get there) I will need 6AWG, which enables 41ft for 56V@100A to keep it below 3% loss. So I wil use 6AWG, I will also use 10AWG on the panels (which will keep it under 3% loss for a staggering 118ft! at the nominal 48V and 11.6A). Again, thanks so much for looking at the details of this stuff!

 

[Zwy]

The panel VOC is 22V x 4 = 88V with all 4 panels in series, but low temps need to be added to the equation, it just depends on what low temps the array will see. The string amps will be about 12A. You could even use 12AWG.

The 150V charge controller will suffice as will 10AWG. Keep VOC high but below max VOC for the charge controller and amps as low as possible.

 

[MegaMosquito]

I thought maybe you had a 50A RV connection. I have a 30A on my truck camper and use a 24V Growatts 3Kw inverter.

As you are intending to use 4/0 cable, that will work well with a 3Kw inverter on 12V, just a tad bit on the high side for amps but doable. I consider the 48V system excessive for an RV unless it is a large coach or 5th wheel which of course would be 50A.

You should consider sticking with 12V or possibly running 24V. Makes it much easier to convert 24V to 12V than 48V to 12V plus it is cheaper. 48V requires switches and other components rated for 48V DC. Higher priced and harder to source.



I actually used 100W panels on my truck camper, they fit better. I'd actually look at the 100W and see how those fit your roof.

Hey @Zwy, I just wanted to say thanks again for your reply on this thread. I was skeptical, but at your advice I did go shopping again, and found the unusual Renogy 100W "Slim" panels. These are only 13.8" wide! So I went back to playing "Rooftop Tetris" again and you are so right! I was able to fit another 200W on the roof by using them. 25% more solar power (a bit more expensive, but well worth it). So I'm very grateful for your nudge in this direction. Also, FYI, I watched a great video from a guy at Victron Energy (

). Toward the end he explained why more smaller panels in series generates power starting sooner in the morning and charges later into the afternoon too. So that's another reason for going with 10 x 100W versus 4 x 200W. Here's the layout I have planned with these "slim" panels) in case you are interested:

 

[littleharbor2]

I'd b very concerned with shadowing, especially with a single series string.

 

[Zwy]

Hey @Zwy, I just wanted to say thanks again for your reply on this thread. I was skeptical, but at your advice I did go shopping again, and found the unusual Renogy 100W "Slim" panels. These are only 13.8" wide! So I went back to playing "Rooftop Tetris" again and you are so right! I was able to fit another 200W on the roof by using them. 25% more solar power (a bit more expensive, but well worth it). So I'm very grateful for your nudge in this direction. Also, FYI, I watched a great video from a guy at Victron Energy (

). Toward the end he explained why more smaller panels in series generates power starting sooner in the morning and charges later into the afternoon too. So that's another reason for going with 10 x 100W versus 4 x 200W. Here's the layout I have planned with these "slim" panels) in case you are interested:

View attachment 209363

If you intend to use the Victron 150/100, you will need to split in 5S2P panel strings. 195V is over the VOC rating of the 150/100. The roof air unit will shade the panels next to it in low sun from the sides. I just finished installing a mini split on my truck camper and the roof air is coming off. This will also allow 2 more panels to be installed, I am using a roof fan in the hole and it will just fit under my tilting panel array.

Golden rule is keep VOC high but under the charge controller rating and amps low. Run the panel specs thru the Midnite calculator to determine VOC at colder temps.

I'd b very concerned with shadowing, especially with a single series string.

Shading will be a problem even with parallel strings in heavily wooded areas from my experience, there just isn't any sun. If the RV is moved on a regular basis such as there isn't a towed vehicle and either travel or sightseeing during the day, parking lots work well with little chance of shading. In the areas of AZ to Montana that I commonly head to, one might have a day of wooded areas, the next day no trees for miles.

The best yield is always at mid day and if positioned to catch the full sun at mid day, there usually is enough yield to carry thru the nights. Larger battery banks combined with energy efficiency help for those days of shade.

 

[mactech]

The BougeRV panels have worked out well for me in my ground mounted array. VOC went up 20% one cold afternoon here in Ohio and blew out their SCC which they replaced promptly. It was consistently running less than 130v in 10F weather. They are paired with a Victron 250/100 now.

 

[littleharbor2]

Shading will be a problem even with parallel strings in heavily wooded areas from my experience, there just isn't any sun. If the RV is moved on a regular basis such as there isn't a towed vehicle and either travel or sightseeing during the day, parking lots work well with little chance of shading. In the areas of AZ to Montana that I commonly head to, one might have a day of wooded areas, the next day no trees for miles.

Even in an open, tree free area, I would still be concerned about the panels being butted up against taller items on the roof. The sun has to be exactly overhead to keep those shadows from falling on your panels.

 

[Zwy]

Even in an open, tree free area, I would still be concerned about the panels being butted up against taller items on the roof. The sun has to be exactly overhead to keep those shadows from falling on your panels.

I've been running my truck camper system for 3 years now. I have yet to have a sunny day where I could not get full charge unless I'm parked in heavy trees/shade.

 

[littleharbor2]

I've been running my truck camper system for 3 years now. I have yet to have a sunny day where I could not get full charge unless I'm parked in heavy trees/shade.

With the panels tucked right up to the A/C and other things and all in series?

 

[corn18]

My roof ac's can throw quite a large shadow.

 

[Zwy]

My roof ac's can throw quite a large shadow.
View attachment 209531

If you park facing south it won't........

Not always possible in some sites but with your panels tilted left and right, you would do better running 2 parallel strings.

 

[corn18]

If you park facing south it won't........

Not always possible in some sites but with your panels tilted left and right, you would do better running 2 parallel strings.

I am going to add 2 more panels and run this as 2 sets of 2S/2P. I have two sets of wires from the roof going into 2x100/50 MPPT controllers. Just haven't decided which ones to S and which ones to P.