The last stage of my project is getting near, I have doubled my battery capacity and wired in my inverter the next step is solar.The problem I'm facing is the small roof of my 25' fifth wheel. Between the roof vents (covered), air conditioner and TV antenna there isn't too much room left for panels that won't be hit by some % of shade during daylight hours. From what i have read mono panels are the most effected unfortunately I can't seem to find quality poly panels with a width less than 23" necessary to fit multiple panels on the roof.Renogy has a nice 100 watt panel @ 21", looks like good quality and their "kit" prices on Amazon look like great deals but they are mono.Will how I wire them, parallel or series effect the loss in shade? PWM vs MTTP have an effect?Can someone point me in the right direction for "narrow" Poly's at a price point of less than a dollar a watt?ThanksRon W.

No, I don't believe you will find polys less than 26" wide. I looked high and low. But I would not be afraid of mono's. I've seen companies who sell both say that the monos are better in low light than their polys. It's not a settled point one way or the other. Going with what fits is more important than mono vs poly in any event.Make a map of your roof. Include the heights of the objects. It's up to you whether or not you allow for vent lids and TV antenna to be in the up positions. Obviously you have some control over those depending on how badly you need the sun to hit the panels on a given day. Remember that the TV antenna rotates, so if you allow for it to be up and in use, it can throw a shadow a LONG way.Then, draw boundary lines as far from each object as the object is tall. The open space is where you can put panels with very little shading. For a small system 300W or less, most people go with 12V panels in parallel, and PWM.Here is a thread I started on how to measure your roof for panels:http://www.rv.net/forum/index.cfm/fuseaction/thread/tid/27520007.cfm

$1 per watt is a pretty good price, and I would have been really happy to find a solar system at $3 per rated watt when I was shopping back in 1999! I paid $750 for a 90 watt kit back in 94, and $375 for a 75 watt panel in 97. By 2000, the price dropped to $429 for my pair of 120 watt panels. I was somewhat shocked to see in 2011 that prices where near $1 per rated watt at this place.SunElec.comYes you will have to wire several 100 - 150 watt panels together to get the desired wattage, and still not have to relocate any roof vents. Shading with a larger solar system is less critical, because you will reach 'full' anyway by 3 pm, so if shading caused it to take another 15 minutes, it really is no big deal!I had a PWM controller back in 94 and it worked great. By 1999, MPPT was "The thing to have" however even though my SB 50 amp controller has worked flawlessly, I am not so sure that MPPT will actually provide 10% more amperage to the battery. Solar panels tend to flow more amperage as the voltage output needed to the battery drops. MPPT increases the input voltage and then changes that increased input voltage to increased amperage into the battery. So say there are 10 amps at 15 volts going into the controller (150 watts) MPPT can convert the output to 12 amps at 12 volts (144 watts). (just a quick example that my brain can figure the numbers at 6 am). However my 15 amp PWM controller put out 7.5 amps with my 90 watt system when it was only 25F outside, we where camped at 4,500' elevation, and the battery was at 12.0 volts in the morning. Sun was reflecting onto the tilted solar panels, and it was mid-November.For my money, the cost of 12 volt panels are so low that installing a $700 system, I would spend more on the panels and less on the controller. So PWM controllers will work fine. You can get a 10 amp PWM controller for about $14. You can wire one to each pair of panels, and not worry about shading effects, as one or two of the controllers will be in full sun.For panel mounts, I cut 6" long 2" angle aluminum from home depot. I drilled 3 holes 3/16" for #10 screws into the roof, and 5/16" hole for a 1/4-20 bolt into the panel frame. Rubber roof sealant completed the job. I would no longer recommend tilt arms. Just to much hassle to go up on the roof and move the panels around each day and before leaving to go back home. It would be easier to work 4 more hours, and buy a 100 watt panel, than to tilt the panels twice on each camping trip, and the more walking on the roof, the less 'good' that can happen to the roof. I used to tilt my panels on camping trips longer than about 3 days, but now do not tilt them. I would rather run the generator for a few minutes per week, it needs to be run once in a while anyway. Reflecting back on my system cost (about $3000 including extra batteries, Trace inverter/charger, all the wiring and above panel costs, I can safely say it has paid for itself at least 3 times. Just by saving $10 a night in campground fees, I saved $3000 in the first 10 years that I had the system. Between 2004 and 2006, when I started full timing, I also spent about 300 nights in the RV, saving power then as well. While full timing, I would seek out free camping places, and again spent 365 nights in the RV, rarely using a campground from 2006 - 2008. And I can sell all this equipment for some amount of money, even though it is 20 years old and still working around 90% of it's original rating. Good luck! and have fun camping!Fred.

charging batteries in the same for solar and converter in the amount of time it takes. If your added solar panel could keep up with the discharge rate of your batteries for the day/night battery run it would be great but we both know that ain't going to happen with three or four panels installed on the roof.To charge a battery up to its 90% charge state in a three hour time period it still takes 14.4VDC at 17-20AMPS of DC CURRENT per battery. You would need a pretty large solar system to accomplish this as a typical 120WATT SOLAR PANEL will only produce 5-6AMPS when in full high sun... The fact that the solar panels will produce high current for around 5-6 hours in the high sun solar day you will be able to get to high percent of charge before the high sun goes away.I am also in the thinking state of what to go with on my even smaller size roof on my OFF-ROAD POPUP trailer.I have been looking at what MELLO MIKEs has done with his truck camper solar setup and will use this as a good guide. I plan on putting two 120WATT Panels on either side of the Fantastic vent fan on the tongue end and then hopefully a 240 WATT panel across the roof between the Air Conditioner and rear end of the trailer... This should give me a good 20 AMPS of DC current to charge my four batteries with. I am planning on replacing my current battery 255AH capacity bank with two groups of 300AH capacity batteries with one group on the trailer tongue area and the other group in the back of my truck bed. I have two reason for battery banks being my Emergency radio operations from my truck alone at time as well as camping. I will be able to combine both battery banks when camping to give me a good 550-600AMPS of battery capacity. I will not have enough solar power to get to the 90% charge state in three hours but should do alot of charging in the average 6 hours of full sun each day.My back-up plan will be my 2KW Generator which I may have to run for an hour or so each day to get past the high current part of the charge cycle then allow the remaining time of the high sun day to get the batteries back up close to full charge.You will need to have the generator anyway and you can't rely on having full high sun everyday. Might be raining or cloudy so the generator is must have item for me. I have been camping off the power grid now for over five years using around 255AHs of battery capacity so I am already in the know of what I can run appliance wise using an Inverter for the 120VAC items and 12VDC items direct connected to the battery system. I run until 8AM each morning and still have at least 12.9VDC showing on my batteries. This allows me to use the generator to power up my trailer so that the on-board smart mode converter/charger will re-charge me back to the 90% charge state in a three hour generator run time when allowed to the run the generator so I can do this all over again for the next day/night run off the batteries. Its all second nature for us now...The bottom line is to never allow your battery bank to get below the 12.0VDC level (Approximately 50% charge state) without re-charging back up to at least 90% charge state each day. My POPUP roof requires to be raised for setup and the added weight of the panels may force me to mount them after the roof is raised. I am planning on going with the lightweight aluminum uni strut mounting frame work. This also allows me to use the edge of the trailer roof to bolt to. This also will allow me to keep two of the panels on the ground and position for best results if the need arises... These are some of the things I will be thinking about doing for my solar install.Just passing all of this along to show my idea of planning and some of it may be useful for your thinking. Its all in the planning...This will be a first for me SOLAR PANEL wise as well...Roy Ken

If shading is a big problem, use taller mounting brackets,....4", maybe even 6".If you do any winter desert camping, for sure make the panels tiltable, for the longer stays.

Solar questions for small RV roof | Good Sam Community

39 Replies

pianotuna
Nomad III
Dec 02, 2014
Hi Ron,

Ummmmm 3 panels can only be series or parallel. I would bump up to four panels.

I have the same need so I have arranged switching in a manner that allows me to use one bank while charging the other.

I can charge either bank from shore, alternator, or solar, while the other bank is powering the RV.

I would recommend a minimum of about 280 watts for the system, if there is not a lot of inverter use.

If you full time, squeeze on as much wattage as you can.

For a 280 watt MPPT I'd suggest looking at the Rogue 3048 (good to 500 watts).

Rogue 3048

If you want to max out the roof and stay MPPT it is hard to beat the Tristar 60 amp MPPT.

Tristar MPPT
rjsurfer
Explorer
Dec 02, 2014
I'm running two banks of 2 T-105's feeding an a/b/both selector switch. The reason for the switch is so i can charge the two banks independently because one set of batteries is a few years old.

What would the series/parallel wiring diagram look like if I'm using three panels?

Ron W.
pianotuna
Nomad III
Dec 02, 2014
Hi rjsurfer,

How much battery capacity do you have?

I chose to do parallel/series to get the best of both worlds.

I'd do no less than 60 watts per 100 amp-hours of storage. If space is a problem then MPPT may give you about 8% more battery charging in the day. Some folks say the charging day starts earlier, too, but I have no way to document that.

Use a quality controller that has temperature compensation.

Tall mounts may help the panels to get "out of the shade". Being tall may allow for more cooling on the underside of the panels.

I'd love to replace my awning with solar panels.

Solve the "less output" by adding an extra panel.

Flat on the roof is much better than stored away when trundling down the road. That is more of an issue with trailers than motor homes, as alternator charging may often be made quite effective.

There is no way I'm climbing a roof in the middle of a wind storm to detilt panels. Besides, I get about 3 amps in the rain and 7 amps in leafy shade at solar noon.

RV daytrader wrote:
you like to get less output cause you cant tilt and point the panel at the sun...THEN flat on the roof makes sense!!
Salvo
Explorer
Dec 02, 2014
However, the answer is correct. Parallel is better in the shade.

Initially, the 22 page thread did not test for shade correctly. Throwing a blanket over a panel is not the same as shade from a tree.
2oldman
Explorer II
Dec 02, 2014
rjsurfer wrote:
parallel spelling?...
Yah, you wouldn't expect parallel to be spelled wrong from a solar tech. Oh wait, that's a "sales representative."

'Always' is a dangerous word, especially when there are bypass diodes. Yes, you'll be running thicker wire.
rjsurfer
Explorer
Dec 02, 2014
Op back,

Here is the reply from Renogy about connection method for panels in partial shade.

"Hi,

When there is partial shading it is always better to use a parrellel connection.

Thanks

Kevin Schroyer

Renogy Sales Representative"

Too bad, now there is more and thicker wire to run...:-)
Parallel spelling?...

Ron W.
2oldman
Explorer II
Dec 02, 2014
rjsurfer wrote:
.. read the 22 page thread, all the more reason to call Renogy ;-)
Synopsis: It doesn't matter whether they're series or parallel. As long as you're in the sun, you're fine.

Renogy might tell you series...no way, just like Xantrex told me not to whole-house my inverter, or a directv man said I can't set up a Slimline dish without a meter.

We'll see.
rjsurfer
Explorer
Dec 02, 2014
2oldman wrote:
rjsurfer wrote:
As far as series vs parallel I will be calling Renogy Monday and see what they have to say.
Here's a thread from 2012. 22 pages of solar- series v parallel.

Just read the 22 page thread, all the more reason to call Renogy ;-)

Ron W ....OP
jrnymn7
Explorer
Dec 01, 2014
"You can also perhaps rig up a gen running while driving but that is a lot of work"

That's what I've been doing until I get an alternator set-up installed. It requires no more work, in my case. Just start the genset like usual, and drive away.
2oldman
Explorer II
Dec 01, 2014
pnichols wrote:
(Also, apparently all the roof install fans don't worry about leaks from the panel bracket screws combined with not being able to get to the bracket areas conveniently for periodic re-chaulking.)
In 12 years of roof solar I've yet to have a leak. I am physically able to climb the 5er ladder to tilt, and I inspect the mounts every time.

I think I've had to re-caulk them maybe twice, and that was not because of any leaking.

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