Solar Panel question?

The advantage of multiple panels is higher voltage output by wiring them in series and this results in less current loss going from the panels to the battery bank. With the panels wired in series any shading of a panel will reduce the output from the entire array in the series so parallel is better when one of the panels will be in the shade.

With an RV the space is limited and full size panels, like the ones used on homes and commercial buildings will often not fit and the dealers will not sell them to you in the first place.

You do want to match the Voc output for all the panels and keep it within 0.5 volts as it will maximize the output and efficiency of the MPPT charge controller.

There are many variables to answer the OPs question of one large vs more smaller panels. I suspect that many current systems start small and then upgrade which effects their choices.

I did 2 calculations for my rig with roof space being a constraint. Note that limited roof space is not a given as panels can be mounted above vents and ACs, but few do this.

2x 270W 65*39” Solar Blvd panels and MS MPPT 60 controller: 540W, 35 sq ft, $2.56/W cost.
4x 140W 59*27” Solar Blvd panels and MS PMW 60 controller: 560W, 44 sq ft, $2.28/W cost.
Roof space is limited to the 4 parallel panels but I might be able to use a smaller controller.

This included all hardware and wiring, DIY project, no panel shipping costs which are pricey .

However given the above two I’d choose the 270W panels especially because I can add a third panel.
3x 270W 65*39” Solar Blvd panels and MS MPPT 60 controller: 810W, 53 sq ft, $1.96/W cost.

Many panels have 3 bypass diodes where each one typically bypasses 2 of the 6 rows. These diodes don't come into use for parallel panels.

For serial panels and an MPPT controller the diodes may help but typically only with a full shadow. For soft shadows like a tree the array amps may be reduced on one panel reducing both panels. In this case parallel would be better.

There is a lot of discussion on serial vs parallel in the archives, especially those more that 1 year old.

JiminDenver wrote:
roc

Have you seen the poster that has his panel mounted on the side of his RV. He can leave the as is, tilt them on hinges or take them off and use them as portables.

My only worry about combining before the controller would be if the mounted panel was in the shade and if it could affect the portables output.

I was seriously considering mounting a portable on the side of my MH (and still may) but it seemed like it would be easier to see and steal there. Also for now the DW doesn't like the idea.

Just a question from a newbie but don't the solar panels have diodes in the output that would prevent the degradation of one panel affecting the other?

roc

Have you seen the poster that has his panel mounted on the side of his RV. He can leave the as is, tilt them on hinges or take them off and use them as portables.

My only worry about combining before the controller would be if the mounted panel was in the shade and if it could affect the portables output.

What I was thinking was a junction box just before the controller so you could plug in a portable panel to the roof mount setup. Of course the controller would be sized correctly.

rocmoc n AZ/Mexico

We use a single 230 watt panel left portable on a set of 25 ft cords. We can park in the shade if we want and if needed can track the sun all day averaging 15a from sun up to sun down. Tracking was more important this last weekend when it turned cloudy, cold and rainy and I needed to squeeze every last amp out to keep a grp 27 charged up.

Moving and storing a big panel can be a hassle. Ours travels on the bed, in the walkway or on the truck. I did consider getting one of the Solarblvd 160w folding kits but they sold out so fast.

One thing I have noticed is my 24v panel and MPPT control love sunshine but hate the clouds. Sunday it started out cloudy and that lowered the voltage put out by the panel. The MPPT function struggled to get the batteries voltage up so that it could drop out of MPPT. Luckily the sun peaked out just long enough and the controller dropped to absorb where it was putting out more amps than it did in bulk. I would have better off being able to shut off the MPPT function but that's not a option on my controller.

There are controllers that can be paralleled so that you could have one system mounted and another portable. I would think the output of the two panels would be different and might be a issue using a single controller. I am toying with the idea of setting up our second panel but it will be a separate system that will keep the inverters 8-D going on longer trips.

Put 200w on the roof and see if you even need the 200w portable.

How about both fixed and portable panels? One can use two charge controllers or use solar connectors and use one CC that is at a high amp rating. I'm looking at this down the road for my next rig, where it will have a few panels on the roof, but will also have the ability to use electricity from a portable panel bank if I'm boondocking and bring a trailer. When travelling, the trailer remains at home, and only the onboard panels are used.

rocmoc wrote:
An idea I had last night was a hybrid, one mounted 200ish watt panel and one 200ish watt portable panel. Anyone do this, heard of it or have thoughts? Wiring would be simple but would it be an issue with the control? It would also solve half of the storage problem and at times the one mounted panel would be enough.

rocmoc n AZ/Mexico

As long as the controller can handle the power requirements of both panels there should be no problem.