Mppt solar array system

[Noitoen]

Hi,

Need some help. For a RV (12v) I have 2 100w solar panels with a open circuit/nominal voltage 21,6/18,7 volts, 5,39A and a 75/15 MPPT controller. To connect to the 12v system what is the best way? Connect the panels in series or parallel?

Htf Portugal

[Mary B]

Not sure on your MPPT controller specs... 75 volt 15 amp?

[SparWeb]

Connect the panels in Parallel.
As Mary asked, it would be helpful to know that your controller can handle the load, and a manufacturer name and model is important.

[Noitoen]

75v open voltage 15amps Smart Solar, 2 12v 120Ahr batteries in parallel. The panels were the maximum size for the available roof top.

[Mary B]

Then I would series the panels for nominal 42 volts into the charge controller. Higher efficiency that way and lighter copper needed for the run to the charge controller.

[Noitoen]

Ok, thanks

[Noitoen]

Just finished the install and was surprised by the result. The 2 100w panels with 36 cells each were connected in series to the controller and to 2 120 Ahr 12v batteries in parallel.  The day was a little clowdy but the Bluetooth interface showed an output to the battery of 196w instantaneous power. I did not leave the RV in the sun but I wonder if the 30% increase of power advertised by the controller manufacturer is true. Only time will tell.

[OperaHouse]

The question is 30% of what. As the panels heat up, the power drops.  Specs are at room temperature. Sometimes there isn't that much to gain especially with two panels in series. I give a stink eye to quoted conversion efficiencies.  These vary with voltage and current. They di their best to fool you.

[Noitoen]

The question is 30% of what. As the panels heat up, the power drops.  Specs are at room temperature. Sometimes there isn't that much to gain especially with two panels in series. I give a stink eye to quoted conversion efficiencies.  These vary with voltage and current. They di their best to fool you.

I agree that there is a "try to fool you factor" but using a 18V panel to charge 12V battery, using pure PWM varying just the duty factor, when the panel voltage drops, there is not much room to take advantage of the little but available energy. In the case of what I saw, the 5.41 A of the panels there was 14 A being "pushed" into the battery. Even inside the warehouse without any sun, there was a 200mA charging current.

With the proper circuit, you can drain all the juice from alkaline batteries far beyond their "usable" capacity.

It was my first contact with a MPPT controller and I will study it further to see to what extent the results are true.

[OperaHouse]

I use multiple modified $5 buck converters operating MPPC which allows me to use cheap grid tie panels in series for about 60V.  These supplement the regular PWM charger on 12V to give a "boost" in low light levels.  Their output is set at 13.8V and any extra power goes to heating water.  I'm surprised that this method isn't more common as a cheap way to expand a system.

[Mary B]

Just finished the install and was surprised by the result. The 2 100w panels with 36 cells each were connected in series to the controller and to 2 120 Ahr 12v batteries in parallel.  The day was a little clowdy but the Bluetooth interface showed an output to the battery of 196w instantaneous power. I did not leave the RV in the sun but I wonder if the 30% increase of power advertised by the controller manufacturer is true. Only time will tell.

The 30% gain is at either end of the day, not at full sun when panels are operating at peak...