Question about Voltage from Solar Panels

[Rick39]

Hey everyone!

I just installed my first solar setup and I wanted to run some things by you guys to make sure I didn't mess anything up. I have 2 100 Watt Renogy Solar Panels, a 200aH Renogy Sealed Battery, and a Rover Elite Charge Controller. I live in Phoenix Arizona, and currently the peak Voltage I've pulled in from those panels has been around 19 Volts. Is that normal? All I really need to run with it is my laptop, a Maxxair fan, a 12V fridge, and some small lights. Thanks!

 

[tx2sturgis]

Sounds about right, If you have the panels wired in parallel. If you have the panels wired in series, I would expect to see higher voltage from the panels, and showing on the display at the controller.  

Either way, voltage at the controller will vary according to load and how much sun is hitting the panels during those loads. 

The MPPT controller you have will vary the load applied to the panels, based on the load it sees (full battery or depleted battery, external loads etc) which will vary the apparent voltage that you see on the display.

 

[maki2]

You should have sufficient depending on how many hours a day you run your laptop and the fan. If you lights are LED they won't be a big impact unless you have some really high lumen output lights going for long periods of time.

 

[Rick39]

Sounds about right, If you have the panels wired in parallel. If you have the panels wired in series, I would expect to see higher voltage from the panels, and showing on the display at the controller.  

Either way, voltage at the controller will vary according to load and how much sun is hitting the panels during those loads. 

The MPPT controller you have will vary the load applied to the panels, based on the load it sees (full battery or depleted battery, external loads etc) which will vary the apparent voltage that you see on the display.

Thanks for the advice! Should I be wiring them in series? Would that be more efficient?

 

[tx2sturgis]

The Renogy Elite is an MPPT controller which will accept the voltage from two panels in series. 

With that controller, to get maximum power to the batteries, you should wire the panels in series.

Understand tho, that there are pros and cons to either configuration.

Parallel wiring means the entire array is more shade and fault tolerant: If one panel output drops due to shade from a tree or a large piece of debris on the panel, or if one of the panels simply fails open, it should not affect the other panel or the output from it.

Series wiring will generally provide more peak power IF both panels are working at 100%...but shading one panel (or a panel that fails open) will reduce the output from BOTH panels to nothing, or nearly nothing.

So it all depends on your situation and preferences.

 

[DannyB1954]

The advantage of series is you can use smaller wire and it will charge for a bit longer in lower light. The disadvantage is if one panel gets in the shade, the panel in full sun will only produce what the shaded panel produces. Think of it like a chain, it is as strong as it's weakest link. If you camp where there are trees. this may not be ideal. I put 960 watts of solar on my van to run a window air conditioner. The controller did not handle the conversion from the higher voltage of series to 12 volt well, so I rewired them in parallel.

What I would suggest to you is run all the wires from the solar panels to where the controller is using heavy gauge wire, (like maybe 10 gauge). Then you can try both systems pretty easy by how you attach all the wires.

 

[highdesertranger]

that's is what's nice about the higher voltage panels. the MTTP controller can take advantage of the higher volts and you can leave the panels in parallel. highdesertranger

 

[B and C]

I have 4-100 watt panels. The two on the roof are wired in series and the other two are my portable panels wired in series (all flex panels). This allows me to place my portables in the sun if I have some shading or some rainy days to make up for. I don't get much voltage drop on my 50 Ft., 10 Ga. extension cord. When I put the portables out, they are wired in parallel with my roof panels. So I have two sets (each series wired) and then they are connected in parallel to the controller.

 

[jimindenver]

The last time I set up a pair of 200 watt 12 volt panels I started in parallel and switched them to series and saw a instant 1 amp improvement in the controller output to the batteries.

 

[KarlH]

... The disadvantage is if one panel gets in the shade, the panel in full sun will only produce what the shaded panel produces.

Wouldn't a diode in parallel with each panel fix that?

 

[barleyguy]

Some panels have multiple bus bars to make shading a lot less of issue. But when you wire panels in series to add the voltage together, you are essentially turning 2 or more panels into a single panel by adding their cell count together. Two 60 cell panels become a 120 cell panel for example. I don't think a single diode per panel would help.

 

[user 423]

This allows me to place my portables in the sun if I have some shading or some rainy days to make up for.  I don't get much voltage drop on my 50 Ft., 10 Ga. extension cord. 

How often have you needed 50ft?  I'm adding a portable panel and trying to figure how long a cord I'll need.

I already have a 12ga. cord but it's only 10'.

 

[highdesertranger]

when I ran portables I used 25ft cables. you would be surprised how often I wish they were longer. however you must remember that with low voltage DC voltage drop is a huge problem. highdesertranger

 

[user 423]

...however you must remember that with low voltage DC voltage drop is a huge problem.  highdesertranger

The leads from the 80W panel are 14ga.  Would a 25' long 12ga. cord be OK?

 

[highdesertranger]

I would go with 10 gauge. that's what mine are. 10 gauge extension cables are relatively cheap and widely available. highdesertranger

 

[user 423]

^
Yeah, it's always better to go up.

Do portable panels need to use 3-conductor wire so they can be grounded?

 

[highdesertranger]

I never have grounded them although they say to. highdesertranger

 

[barleyguy]

^
Yeah, it's always better to go up.

Do portable panels need to use 3-conductor wire so they can be grounded?

A chassis ground is fine, which is connecting the frame of the panel to the ground. So no, you don't need to run three wires to the charge controller, nor should you. If the panel is placed on the ground, it's grounded. That's what a ground is, a connection to the earth.

 

[Tom_M]

I do not ground my panels. If using a standard 3 conductor extension cord you can jumper two of the conductors together cutting the resistance in half for the paired conductors.

 

[highdesertranger]

"If using a standard 3 conductor extension cord you can jumper two of the conductors together cutting the resistance in half for the paired conductors"

that would be nice but it doesn't work that way.

highdesertranger