Adding solar with existing inverter/charger

[kbehrent]

I have a factory installed Xantrex RV2012 2000w inverter/charging installed in my motorhome. I am looking to add solar panels to help reduce generator runtime when we are dry camping, which is most of the time. I'm looking to add upwards to 400W of solar capacity.

I have 4 Interstate batteries (GC2-XHD-UTL 6V, CAP-20: 232AH, ReserveCapacity25: 474AH) connected in series/parallel to provide 12VDC and @ 474AH (If I calculated it right)

It seems all the articles I've read assume you have nothing but an existing battery and no inverter capability. Since I have both an existing inverter/charger capability in my Xantrex, How do I integrate solar charging with my Xantrex to help charge/maintain the batteries? Note, I also have auto generator start capability to charge my batts when batteries reach a specific % of SOC, which is currently set to 50% SOC.

If the generator should start and cause my Xantrex to start charging the batts, do I need to disengage the solar panels? Is this done manually or will a solar control panel of some type auto sense this and disconnect the solar panels?

Thanks

[2oldman]

Canadian Rainbirds wrote:
The one drawback to series panels is the basic rule (from Ohm's Law) that in a series circuit the current remains the same throughout the circuit. This means that if one or more panels is shaded, the total current will be what that panel produces, even if it is only an amp or two..

Bypass diodes should alleviate that problem.

[Canadian_Rainbi]

If you want to use the pre-installed wire, I am assuming #12 or hopefully #10 you should series all the panels and use an MPPT controller, though my 420 watts of panels are paralleled with #10 on the input side of the controller.

You can afford some voltage drop on the input side but not on the output side. Controller must be very near the batteries and connected with as large a cable as feasible. If within a couple of feet you could get away with #10. I have about 25feet of mostly #6 which gives me an unacceptable loss of 1 volt drop @ 20 Amps.

The one drawback to series panels is the basic rule (from Ohm's Law) that in a series circuit the current remains the same throughout the circuit. This means that if one or more panels is shaded, the total current will be what that panel produces, even if it is only an amp or two.

If/when I redo mine I will use series/parallel with the rear two in series, the front two in series, and then both sets paralleled. Where we park in Mexico for three months the rear panels are shaded by a building a couple of hours before the front ones.

When connecting panels, panels in series should have equal current output. In parallel, both panels should have the voltages as near to equal as possible.

[kbehrent]

christopherglenn wrote:
They are 30+ volt panels, 310 watts each. The charge controller will down convert the voltage and increase the amps. Combined into discharged batteries it should bulk between 40 and 50 amps, absorb is whatever the batteries can take (plus other loads).
I plan on (5 year plan) having 2 mid ship, 2 over the garage (Toy Hauler). I am planning on sliding racks so I can stack one on top of another, normally having 4 exposed, once set up deploy the second set and have 8 on the roof. Sliding out from under the static panels with linear actuators it is a push of a button to deploy or retract. Tied into the slide control so when the slides retract the panels retract (manual deploy) should keep me out of trouble.
2400 watts of solar on the roof should run 1 ac easily as well as charge the batteries at the same time, and reduce need for the genset to when multiple ac's are required.

We will see in 5 years what actually happens....

Thanks for sharing you plan. I should have googled the reduction of panel voltage to 12v before asking the question. I did find some excellent youtube videos showing in detail how to use these higher rated panels in lower voltage batt storage. Picking the right controller is key! With my current set of batts, I have @ 474AH capacity so I want to build a solution that can handle at least 500AH in case I upgrade my batts to slightly higher capacity batts like Trojan.

My MH also has the solar prep to the roof. Once of the biggest complaints with these solar prep options is that the wire gauge is too small. However, it seems that with the higher voltage panels, your pushing less amps (depending on how you wire) so you could use the lower gauge wire. Of course it takes a higher cost controller to do this.

I like your plan. I haven't studied the details of the controller you mentioned, but you may want to verify the limits of the controller in reducing the panel voltage to 12v.

[christopherglen]

They are 30+ volt panels, 310 watts each. The charge controller will down convert the voltage and increase the amps. Combined into discharged batteries it should bulk between 40 and 50 amps, absorb is whatever the batteries can take (plus other loads).
I plan on (5 year plan) having 2 mid ship, 2 over the garage (Toy Hauler). I am planning on sliding racks so I can stack one on top of another, normally having 4 exposed, once set up deploy the second set and have 8 on the roof. Sliding out from under the static panels with linear actuators it is a push of a button to deploy or retract. Tied into the slide control so when the slides retract the panels retract (manual deploy) should keep me out of trouble.
2400 watts of solar on the roof should run 1 ac easily as well as charge the batteries at the same time, and reduce need for the genset to when multiple ac's are required.

We will see in 5 years what actually happens....

[kbehrent]

christopherglenn wrote:
I am looking at putting a pair of THESE on my roof, sandwiching the AC between them. I should be right at 102 inches wide (trailer is 102) and with a MMPT controller, close 40 amps to the batteries.
$630 for the panels, and another $607 for the MMPT CONTROLLER.

Are these panels for 12V system? For that watt rating, I would think that they would be 24v or 48v.

[christopherglen]

I am looking at putting a pair of THESE on my roof, sandwiching the AC between them. I should be right at 102 inches wide (trailer is 102) and with a MMPT controller, close 40 amps to the batteries.
$630 for the panels, and another $607 for the MMPT CONTROLLER.

[Muddydogs]

Portable is great for optimizing input from the sun but do become a hassle setting up and taking down all the time especially if only stopped for a day or so.

I started with 2 100 watt panels as portable and quickly figured out that the roof was the way to go. Roof mounted panels are always charging even while driving down the road so the batteries are charging between camp spots. Once I came to the realization that there's already probably 100 screws poked through my roof holding on the vents, AC, antenna and other things I figured what's a few more holes in the roof going to hurt. Figure out the correct sealer for your roof type and all will be fine.

[AndyfromTucson]

kbehrent wrote:
Any recommendations for 100W panels and controller? Are they usually paired or do you buy the best panel for the money and than buy the controller separately?

As of last fall the best deal I found on 100 watt panels was Renogy panels on Amazon. Amazon also had a great selection of solar controllers at good prices.

You can use any controller with any panels as long as the voltage and amp specs are appropriate for each other. Look at the panels output voltage and amps and the controllers max voltage and amps. If you spend a few hours doing web research on solar systems you should be able to do it yourself if you are moderately handy.

[Canadian_Rainbi]

We run 420 watts of solar to 480 AH of 6V GS, and also have a Xantrex Prosine 2.0 pure sinewave inverter/charger. They work well together.

Important note: The solar controller needs to be VERY CLOSE to the batteries to avoid or at least minimise voltage drop.

[westend]

I'd visit Solar Blvd and see if they have something that fits your use. Shipping has to be a consideration, too. If you can find a vendor close to you, there will be substantial savings by eliminating shipping. FWIW, most solar modules are fairly alike and for a portable situation, choice would be focused on amount of output watts and portability.

For controllers, I'd suggest to buy a name brand controller with functionality in mind. With the better controllers you can adjust setpoints for voltage, duration, and cycle choice. They also tend to have temperature compensation, a good feature to have. If budget is more important, any of the cheaper Asian controllers will do the job, just more futzing with setpoints and such.

[2oldman]

kbehrent wrote:
Any recommendations for 100W panels and controller? Are they usually paired or do you buy the best panel for the money and than buy the controller separately?

You'll find 120-135 panels more popular. No, yes, then, yes.

[kbehrent]

Any recommendations for 100W panels and controller? Are they usually paired or do you buy the best panel for the money and than buy the controller separately?

[rjsurfer]

Remote panels are a great option, don't bother with adjustable mounts on the roof for optimization. Climbing up and down the roof gets old real quick.

Ron W

[zach477]

kbehrent wrote:

pianotuna wrote:
232 x 2 = 464 amp-hours.

Minimum solar panel size no less than 279 watts

If you plan to use the inverter much then the sky is the limit on solar wattage.

I'm looking at @ 400W of solar. I really don't want more than 4 panels so I'm limited to that. I don't want to attach them to the roof, so I'll build/buy a portable stand. I realize I might not get the best optimization this way, put I like the portability of it in case I want to use the panels for something else if not being used for the motorhome.

You might actually get better optimization this way. You can angle them towards the sun, adjust the throughout the day, park in the shade and put the panels in the sun, etc.