Solar Panel Choice for RV Application

babyrocket

I have a Lance travel trailer with 2 190 watt Go Power solar panels (specs here) wired in series on top.  I have recently upgraded my solar/electric system with Victron components and expanded my lithium battery bank to 400Ah.  I would now like to expand my solar capacity as well.  I have a Victron MPPT 150/70 solar controller, and using their calculator I have determined that the my controller can handle the addition of two Rec Alpha 365 watt panels (specs here).

I'm planning to run each of the two 365 watt panels, as well as the pair of 190 watt panels (in series), all three in parallel to the controller.    I plan to upgrade the wiring from panels to controller to handle the additional current.  I have the specs for all panels.  Can someone tell me what I need to find out with both the Go Power and Rec panels to determine if this proposed setup will work? 

Thanks for any help you can provide!

mike95490

More than 2 strings of panels in parallel, you need to use fuses/breakers in your combiner box.

Panels in parallel should be within 10% of Vmp voltage.  The array will be pulled to the lowest voltage panels', voltage

BB.

For Mike's comments:

Your 190 Watt panels have Vmp=20 volts (voltage maximum power)

The 360 Watt panels have Vmp=37 volts

2x 20 volt panels in series = 40 Volts Vmp

40 Vs 37 volts is "close enough" (within 10%)

The 190 Watt panels have a max series fuse of 15 amps

The 365 Watt panels have a max series fuse of 25 amps

So--Each string will need its own/different fusing. 15 amps for the 2x190 Watt panels. And 25 (or 20-25 amps) for the 365 Watt panels.

-Bill

babyrocket

Thanks much guys, very helpful.  Any suggestions on a good combiner box with fuses/breakers built in?

mike95490

I like the MidnightSolar 3 or 6 position, with breakers.

 https://www.solar-electric.com/mnpv6.html
breakers: https://www.solar-electric.com/mnepv.html

Breakers provide a very easy way to test a PV array against all the strings in the array.
Fuses & fuse holders are often not rated to break a live circuit.

babyrocket

Looks like that is for a home solar installation, whereas mine is going on the roof of my RV.  Any good sources for a mobile installation?

mike95490

electricity at 40V is the same, on a home or a RV or a boat.  Don't cheap out and get automotive stereo parts, they are not rated beyond 30V and seldom are able to handle a solid 20A for hours, that solar generates while charging.

babyrocket

It's not a cost issue, but rather finding a box that can handle the abuse and waterproofing required for installation on an RV roof.  One that has been recommended is here on Amazon.  I'd need to upgrade the breakers.

mike95490

I'd use a good weather head and put all that stuff inside.  Gotta get the power inside somehow .

BB.

I posted this to the wrong thread... Repost here:

You might also think about bringing the separate cables from the panels down into the van and installing (for example) DIN Rail breakers:

https://www.solar-electric.com/search/?q=din+rail+breaker
https://www.solar-electric.com/dinrail-6-inches.html

And you can get some bus bars (as needed) to combine wires (nice for mixed AWG wires instead of using wire nuts):

https://www.solar-electric.com/search/?q=bus+bars

Breakers are nice because they are also on/off switches. Fuses and fuse holders--Cannot usually be switched under loads. There have been issues with "touch safe" fuse holder--Push to open and they start arcing/catching fires.

As you have found, the NEC (national electric code for North America homes/businesses/buildings) require easy access to any connections (covered box--No installations behind drywall--for example).

Also, check that all sharp edges are rounded and/or protected with grommets/etc. so that there is no chance for shorts/cuts in insulation.

Another reason to bring wiring from panels down (beside rain proof interior, no wasted space on roof for electrical boxes/access), is you can use an AC/DC current clamp type meter to measure the current for each panel (if you have breakers, easy to turn breaker off/on to check current flow--If fuses and for other current measurements a clamp meter is really nice).

For example one mid-priced AC+DC Current Clamp DMM:

https://www.amazon.com/gp/product/B019CY4FB4

Current Clamp meters are very easy and safe to use--Just clip and insulated current clamp over the wire you want to measure current in. Very nice for Van/Boat/Car debugging (and the AC setting for AC inverter output/home checking/monitoring).

One suggestion if you have "sealed" boxes on the exterior of the van (boat/etc.)... Even sealed boxes need to have a small weep hole drilled in the low point of the box. Any condensation is expelled out the hole as it warms up (sun/ambient air).

-Bill

PS: I should add... Cables should come up from "bottom" of box, have drip loops from horizontal runs and such... Keep water from being directed into the seals, glands, and boxes.