Solar panel combination..

[GP28]

I have 2 -12V glass 57x28 galss panels now, 1 @200w and 1 @210w and was wondering about hooking them in series for 24v and getting 1 more 24v 200w panel and hooking them into a 4 port manifold that has all inputs wired in parellel on the output end.
In the end I would have 2 @12v series for 24v and one other @ 24v into a mainifold that would have the output of 24v @ 25a into a renogy bluetooth controller rated @ 40 amps.. This is going into 2 parellel wired RV 12v batteries.??
The reason is not sure if gauge of wiring will have too much loss for 2 @ 12v and 35w,,, and just 2 @ 12v in series if one gets shaded am back to square one...
Thank you for any help..

 

[MisterSandals]

not sure if gauge of wiring

So what gauge is the wire and how long is the run?

Is this your “Renogy bluetooth controller”?

Renogy Rover Li 24-Volt 30 Amp MPPT Solar Charge Controller with Bluetooth Module RNG-CTRL-RVR30-BT - The Home Depot

Meet the newest addition to the Renogy Rover Series, the 30 Amp Rover-Li MPPT Charge Controller. The Rover-Li is not only capable of self-diagnosing errors, but it can also automatically detect 12-Volt/24-Volt

www.homedepot.com

 

[GP28]

yes but its 40 amp and not sure on wiring or exact length. What I am trying to find out is if I can mix panels up as I stated.. I could not find anything saying it was aa no-go or bad or whatever. I am trying to get more input if possible. I have a much cheaper controller Rengoy that worked great for portable set up. Hopefully this one will be as good..

 

[MisterSandals]

Your solar panel mixing and matching plan looks sound in concept. You should let us know what the Voc of the panels are so we can do the math. The term "12v solar panel" is pretty vague, to me at least. They are probably closer to 20v (Voc), which makes the math about 80% different.

 

[GP28]

The 210 watt Voc is listed as 24.9 and the 200 watt is listed as 24.3... But both say 12 volt when listed for sale.

 

[MisterSandals]

and getting 1 more 24v 200w panel

If you could get the Voc on this we will have most of the puzzle. I'll guess 40Voc.

Renogy Rover 40A: Max input 100v 50A <----key solar panel considerations

200w @ 24.3 = 8.2A
210w @ 24.9 = 8.4A
*These panels are VERY similar so that is good!
In series they should produce 400w @ 49v @ 8.2A (lower amp module sets the amp limit)

Another 210w panel at ~40v will work just fine.
Figure around 5-6A.

2 panel string connected to 210w panel should produce about:
410w @ ~85-90V @ ~14A

410w / 12v will charge at around 34A (reality will be about 20% less)

So I'd say this is a nicely designed and sized setup.
Be mindful that the 14A wire to from the junction of panels to the charge controller will require:
14AWG up to 10' (20' round trip)
12AWG up to 15' (30' round trip)
10AWG up to 25' (50' round trip)

Hope this helps.

 

[GP28]

Thats what I was thinking that they were 24V but the seller ads them as 12v..?? I was debating series or parallel but heard that if one panel gets shaded (especially the one closest to input manifold) I will lose all or most charging capacity? Also, if I go in parallel it will be 24v and not the 12V?? Parllel woud be 24V @ 16amps?

 

[MisterSandals]

Don’t get me going on people calling things “12v panels”.

In a series of panels, any shading greatly reduces the entire strings output.
When in series, the volts are totaled, amps limited to the lowest amp panel.
In parallel, the amps are added. I cannot recall what exactly happens to the volts but they are fairly similar so should be fine.

The 12v number is the SSC’s charge voltage to the battery - sorry i context shifted without explaining. Charge current should be in the 30 amp range.

 

[GP28]

I think I would be better offgoing 12v parallel in case I get one panel shaded.. Then am not having to purchase another right away and can test system out.. As they are rated at 24Voc but called 12v,, how would you rate amperage, 12v @ 16amps or 24v @ 8amps????

 

[upnorthandpersonal]

12v @ 16amps or 24v @ 8amps????

Vmp @ Imp

 

[upnorthandpersonal]

In a series of panels, any shading greatly reduces the entire strings output.

That's what bypass diodes are for.

In parallel, the amps are added. I cannot recall what exactly happens to the volts but they are fairly similar so should be fine.

This is why you need blocking diodes to prevent sending current to the shaded panel when they're in parallel.

 

[MisterSandals]

This is why you need blocking diodes

Ok, I am game. This is the thing i will learn today, thanks for any help.
How do I select a blocking diode? Is there a sizing formula or guideline (based on voltage/amperage?) ?
Can you point me to one you would recommend for the OP as an example?

 

[GP28]

""Vmp @ Imp"" you lost me on that one. The open voltage is 24V, so is amperage rated at 24v or 12v? From my understanding the Voc is to provide enough volts t open the chargr for a 12v battery, if it was supplying 24v battery system the Voc would be about 38Voc (just guessing on that voltage)... So, what gives amperage figure, the Voc or battery voltage? 12v or 24v???

 

[upnorthandpersonal]

You usually pick a (preferably Shottky because of the lower voltage drop) diode that can handle a bit more than the maximum current in your string, so let's assume 10A (this If, forward current, of the diode). The reverse voltage should ideally be as high as possible, just in case somehow your panels in your string get shorted (don't know how that would be, but anyway). In Op's case, Max Voc of a string: 60V or so. That's the reverse voltage (Vr) of the diode. Then just pick one that you can find on Mouser or whatever with those parameters.

 

[upnorthandpersonal]

""Vmp @ Imp"" you lost me on that one. The open voltage is 24V, so is amperage rated at 24v or 12v? From my understanding the Voc is to provide enough volts t open the chargr for a 12v battery, if it was supplying 24v battery system the Voc would be about 38Voc (just guessing on that voltage)... So, what gives amperage figure, the Voc or battery voltage? 12v or 24v???

Your MPPT (maximum power point tracking) controller is used to get the maximum power out of the panel, which is at Vmp and Imp. See curve:

You have to see both ends of the MPPT controller separately. Your solar side needs to have x volts higher than your battery, but that's about it. You can have in principle 600V at your panel side and 12V on the battery and it would be fine if your MPPT controller can handle it on the input.

 

[GP28]

So my panels at 200 watts and being 24Voc each will be 8.3 amps each? Even though were sold as 12v, each panel is to be formulated at being 24volt prior to being installed?

 

[upnorthandpersonal]

To pick your MPPT controller, you use the Voc value and make sure it can handle the max Voc of the entire series string on the input. It may very well be that the Vmp voltage is closer to 12V (see graph) but that doesn't matter - your MPPT controller has to be able to handle the Voc voltage. The MPPT is responsible for converting the input to the correct voltage of whatever your battery is, and putting in as much power to your battery as possible. If the input is 200W, it will try to dump 16A in the battery if it's a 12V battery, or 8A for a 24V battery, etc. Watts on the input == Watts on the output (with some losses, but let's ignore those).

 

[GP28]

Ok, so thats what the answer is then. Even if the Voc was 36v I would rate amperage by watts/battery voltage,, and not whaat the panels are rated to.. 200 watt panel @ 24Voc going into a 12v battery would be 200/12=16amps... If it was a 200watt panel @ 36Voc going into a 12 volt battery it woud be 200/12=16 amps....
To change the amperage from a fixed wattage paneI I would need to convert to aa 24V battery system then to drop the amperage..

 

[MisterSandals]

Even if the Voc was 36v I would rate amperage by watts/battery voltage,, and not whaat the panels are rated to

You have volts and amps from the panel (as listen on your panel) to the SCC.
Your SCC modifies what it gets from the panels to match your batteries with a different voltage and therefore a different amperage (watts stay roughly the same).

Your 200w, 24Voc, 8.3A panels put out those amounts for as maximums for doing your calculations (200/24 = 8.3).

You SCC converts the input volts (lets say 60Vc from the string) to the charge voltage that matches your batteries (12v). So 200w coming into the SCC can be converted into charge current to your batteries (200w/12v = 16.6A).

 

[GP28]

So what woud you rate your wire at, 8 amps for the panel 24Voc,, or 16 amps for the battery ratings? Or would you have two different wire selections, one for panels to controller then another for controller to batteries??