Why not one large Panel on RV?

[Geokilroy]

Just curious. Why not use one large (350w or larger) on an RV. Would it not be easier and less holes in your roof?
Alt-e-store offers a 49volt - 415watt panel for $217. This is cheaper than 4x100w panels. Then you only need one set of holes in your roof and only one set of wires instead of sets of splices to go to your SCC. Make it a 100v 30a and you have room to expand. If I am wrong please tell me.

I have one 165w panel on my rig now and want to change to a larger panel. I can use three of the existing mounting brackets on one side and only need to drill for three others to mount the other side of the panel. Less extra holes in my roof. Am I off base?

 

[chrisski]

Not at all as long as it fits.

Although it may defy logic, sometimes more smaller 100 watt panels can be fit when avoiding obstacles on the roof like Air Conditioners and vents. So much more expensive for panels, but leaves more options for series and parallel hookups.

You don't need a lot of panels on your RVs roof until you want to do a lot of high wattage things like electric cooking or Air Conditioners.

 

[12VoltInstalls]

3-1/2 feet by 5-1/2 feet. Trina mono crystalline.
Says 24 volt unless they have something that didn’t display for me? Two could be awesome.

But I’m quite intrigued.
I was looking up my AN40 SCC specs cuz I couldn’t remember and I’m assuming this is a typo: “Max. PV input power:520W(12V Battery) & 1040W(24V battery)”
I assume that 1040W was meant to be “24V panel inputs” not battery.

 

[time2roll]

One large 2000-3000 watt panel to use as the actual roof would be fantastic. Skip all the vents etc too or place them all in the rear or something.

 

[Lt.Dan]

3-1/2 feet by 5-1/2 feet. Trina mono crystalline.
Says 24 volt unless they have something that didn’t display for me? Two could be awesome.

But I’m quite intrigued.
I was looking up my AN40 SCC specs cuz I couldn’t remember and I’m assuming this is a typo: “Max. PV input power:520W(12V Battery) & 1040W(24V battery)”
I assume that 1040W was meant to be “24V panel inputs” not battery.

Its not a typo. It will charge the battery with more wattage at 24v. Im assuming you have an MPPT SCC, which means it will most likely accept up to 100-150v DC from the solar panels.

As far as the larger panels, yes it is better, but you can't fit very many of them. I can only fit 2x or maybe 3x 400-500watt solar panels on the roof of my rig, but I was able to put 12x 240watt panels, so there is give and take there.

 

[chrisski]

But I’m quite intrigued.
I was looking up my AN40 SCC specs cuz I couldn’t remember and I’m assuming this is a typo: “Max. PV input power:520W(12V Battery) & 1040W(24V battery)”
I assume that 1040W was meant to be “24V panel inputs” not battery.

SCCs are designed to push a constant amperage. So if your AN40 pushes 40 amps max, that’d be 480 watts at 12 volts, or at 24 volts 40 amps would be 960 watts. The extra 40 watts for 12 volt and 80 watts for 24 volts is for over paneling since these panels will rearely see their full voltage.

 

[12VoltInstalls]

Its not a typo. It will charge the battery with more wattage at 24v. Im assuming you have an MPPT SCC, which means it will most likely accept up to 100-150v DC from the solar panels.

Ya, I get that (I’m 2S2P with 100W panels)
but I’m charging into 12V batteries.
The wording in the listing is weird to me, warping my head.

 

[Geokilroy]

3-1/2 feet by 5-1/2 feet. Trina mono crystalline.
Says 24 volt unless they have something that didn’t display for me? Two could be awesome.

But I’m quite intrigued.
I was looking up my AN40 SCC specs cuz I couldn’t remember and I’m assuming this is a typo: “Max. PV input power:520W(12V Battery) & 1040W(24V battery)”
I assume that 1040W was meant to be “24V panel inputs” not battery.

When I continued to the full specs page I found that those Trina mono crystalline panels were 48 volts or did I miss something.

 

[12VoltInstalls]

panels were 48 volts or did I miss something.

There’s a typo somewhere
A little math will prove what they are, or a pic of the manufacturer’s label

 

[Lt.Dan]

Ya, I get that (I’m 2S2P with 100W panels)
but I’m charging into 12V batteries.
The wording in the listing is weird to me, warping my head.

@chrisski answered your questions better than i did, but bottom line, your charge controller can charge at 40a, or roughly 512 watts via 12.8v. But at 25.6v (24v nominal) you can still charge at 40 amps, which is 1024 watts.

Based on the specs you gave, your SCC can accept 100v max VOC. So if your panels are 2s2p outputting roughly 60-70v, then you can push roughly 8a at 65v into the SCC, which steps it down to 12v nominal and 40a out to the battery

 

[sunshine]

I doubt if a large panel would have the structural integrity of the smaller panels combined. You may end up drilling more holes and doing more work to overcome this.
Panels to go on RVs should be designed for that purpose!

 

[Just John]

3-1/2 feet by 5-1/2 feet. Trina mono crystalline.
Says 24 volt unless they have something that didn’t display for me? Two could be awesome.

But I’m quite intrigued.
I was looking up my AN40 SCC specs cuz I couldn’t remember and I’m assuming this is a typo: “Max. PV input power:520W(12V Battery) & 1040W(24V battery)”
I assume that 1040W was meant to be “24V panel inputs” not battery.

No, it's rated in amps. I'd guess you have a 40 amp solar charge controller. It can out put either 40 amps at 12v, or 40 amps at 24v.

 

[12VoltInstalls]

doubt if a large panel would have the structural integrity of the smaller panels combined.

(I was wondering about that for the OP)

No, it's rated in amps. I'd guess you have a 40 amp solar charge controller. It can out put either 40 amps at 12v, or 40 amps at 24v.

Yes 40A. That was my understanding.
Not meaning to hijack, sorry.
I apparently didn’t put the epever manual in the cabinet with the others so I looked on Amazon and the wording is…confusing.
I looked in my order history for the one I bought: this tile from that listing makes sense that one might use 1000W/24V but it’s of course max 40A output.

However, the listing text says, “Max Input Power: 520W @ 12V battery | 1040W @ 24V battery （Solar panel voltage must be greater than the voltage of the battery 2V to charge）” which seems to be saying one cannot use 830W / 24V input if you have 12V batteries?! The words “input power” referring to the panels with the word ‘battery’ - since the output is to the battery- I think that’s a typo or mindcramp that assumes one would not run 24V panels and charge 12V batteries…
If that wording is correct, then most of the reason I chose that SCC is negated- eventual goal was ~800W 24V 2S4P nominal input or 3S3P 900W / 36V nominal into the SCC with 12V output to maximize November to February, and up cloudy day charging potential. The specs in the listing seem to limit me but my understanding says I’m fine…the “unusable” watts just get “wasted”

So for OP @Geokilroy : if panels are 24V or 48V output then what charge controller are you planning?

The Alt-E website page is unsure if it’s 72 or 144 cell, 24 or 48V.
~40 VOC is roughly double the 19.x VOC of nominal 12V panels

The other comment about flex for that size panel has some validity, too.

 

[Short_Shot]

I doubt if a large panel would have the structural integrity of the smaller panels combined. You may end up drilling more holes and doing more work to overcome this.
Panels to go on RVs should be designed for that purpose!

The large panels are usually designed for high wind and hail loads. Doubt anyone will have an issue with a quality unit.

 

[pvdude]

I put the largest panel I could find (in 2018) on the largest open space on the RV roof.
Photo is testing placement, before I built the mounts (Aluminum, 3M VHB tape)
330 watts, Victron charge controller, two Trojan T-105AGM.
Drove it from Florida to Alaska and back for the Summer of 2019, worked great camping in Alaska, except when it rained for a few days.



Mounts under construction:

 

[12VoltInstalls]

So for OP @Geokilroy : if panels are 24V or 48V output then what charge controller are you planning?

The Alt-E website page is unsure if it’s 72 or 144 cell, 24 or 48V.
Since. The data sheet:

https://www.altestore.com/static/datafiles/Others/Trina%20DE15M%28II%29%20415W%20Datasheet.pdf

 

[Isla]

At least a 120 watts solar panel will be required to meet their daily power needs. Therefore, it's important to understand that a single solar panel is normally not enough and most people will want at least two solar panels.

 

[Just John]

However, the listing text says, “Max Input Power: 520W @ 12V battery | 1040W @ 24V battery （Solar panel voltage must be greater than the voltage of the battery 2V to charge）” which seems to be saying one cannot use 830W / 24V input if you have 12V batteries?! The words “input power” referring to the panels with the word ‘battery’ - since the output is to the battery- I think that’s a typo or mindcramp that assumes one would not run 24V panels and charge 12V batteries…
If that wording is correct, then most of the reason I chose that SCC is negated- eventual goal was ~800W 24V 2S4P nominal input or 3S3P 900W / 36V nominal into the SCC with 12V output to maximize November to February, and up cloudy day charging potential. The specs in the listing seem to limit me but my understanding says I’m fine…the “unusable” watts just get “wasted”

Basically what it is saying is that input power above 520w or 1040w will not be used. Provided you don't exceed the voltage limits of the charge controller, you can overpanel. If you don't have enough panels for 1040w at 24v, it will just use what you have. You can hook up 800w of panels for a 12v battery, but it won't use more than 520w. That is useful to start charging earlier, and charge longer and is commonly done.

 

[Geokilroy]

I doubt if a large panel would have the structural integrity of the smaller panels combined. You may end up drilling more holes and doing more work to overcome this.
Panels to go on RVs should be designed for that purpose!

The 165w panel that is on my rig now is over 5ft long and about 38inches wide. Not much size diff.

The existing panel is almost enough for my needs. Doubling the watts of my panel will make it perfect.

I only run led lights, phone chargers, laptop computer, my propane furnace at night, the rig water pump, and the basic electronics for my propane fridge. I have 2 100ah LFP batteries in parallel. Batteries without the solar to charge them will last 2 days unless temps really plunge. But that leaves them quite low.

I live in Las Vegas, NV and camp out in the desert here to gold prospect. Lots of sun all winter long. 30 to 40 others doing the same. We belong to prospecting clubs with organized outings once a month September to May (but not during the hottest months). I may be out there anywhere from 2 to 6 days at a time. No shore power and I don't have a TV in my rig.

 

[12VoltInstalls]

Provided you don't exceed the voltage limits of the charge controller, you can overpanel.

That is my understanding
I guess I never read the listing. I still think the wording is odd