Adding a Third Solar Panel

We have a 2018 2552 with 2 factory solar panels. I am considering adding a third solar panel to the roof. My question is where do the wires for the two panels connect?

Thanks John

Make sure when you mount it it doesn't get any shadows from antenna, A/C or vents. Small shadow, no power. Just run + to + and - to -, The arrays are three batteries in parallel. You can connect on roof to the other panels.

If you connect the panels in parallel the work just as parallel batteries do.  Voltage stays the same and amps are additive. The advantage over a series connection is that if one panel gets shaded it won’t affect the other panels.

John, I added two Renogy (from Amazon) 100 watt panels to our 2350 a few years ago and love them.  The year after I put them up there on the roof, I ordered another 100 watts and constructed an adjustable stand for it.  I bought 50 feet of 12 gauge landscape lighting wire (most of it is 14 or even 16 gauge).   I put a solar plug at the panel and used the wire (basically made it into a solar extension cord) to run to a receptacle I mounted on the back of the PC to the right of the hitch.   All three panels wired parallel as others above stated. 

This allows me to have 200 watts on the roof and a 100 watts which I can move around to point directly into the sun.  This is especially helpful boondocking when parked in shade or partial shade.   I made the stand from aluminum angle that I bought from Tractor Supply.   This really works great for us.   My experience is that even on a cloudy day we will get a good charge to the  batteries.   We sometimes boondock a week at a time and always seem to have adequate power.  Of course, we use all the normal boondocking power conservation procedures as well.

This might not be a solution for you but perhaps it is worth pondering.   If it doesn't work out, you can always put it on the roof later.  The Renogy panel came from Amazon very well protected in a heavy cardboard box with a sheet of some kind of plastic foam about 3/8 inch thick to protect the panel.   I kept the packing material and use that for my portable panel when stored or for transport in my Jeep toad. 

Paul

I agree with donewprking,, a good way to go to ensure at least one panel will see the sun.
Use #10 wire wire.

I agree with donewprking,, a good way to go to ensure at least one panel will see the sun.
Use #10 wire wire.

I understand electricity, watts, amps and voltage but know about zero on solar arrays.

Which brings up a question... #10 wire is good for 30 amps, in a 100 watt array, that means the output voltage is only a little over 3 volts?

That's based on the old PIE formula, Power (in watts) = Amps (I) x Volts (E)   thus volts = watts/amps or 100/30 = 3.3 volts

Hey all you solar gurus.  I have some ignorant solar questions for you.  If you could please answer like you are talking to a 5th grader. 

1) What is the voltage output of the solar panels you are using?  Does the voltage swing wildly pending the intensity of the sun, and you have a voltage regulator?  Or is it always the exact same voltage, but the amperage swings wildly?

2) I heard solar panels can get extremely hot when absorbing full sun.  Is that your experience, and if so, are there safety concerns?  Are there concerns of compromised integrity of the motor home's roof?

3) When operating at max efficiency in full sun and perpendicular to it, what amps and volts could I expect from a 100w solar panel?  I assume I would get 100W.  What would be otherwise "typical" on a sunny day with no clouds?  What could be expected on a 50% cloudy day?

4) How sensitive is a "less than ideal" angle to the sun?  I see keelhauler has two panels mounted very nicely on his roof, but they lay flat, almost never perpendicular to the sun.

5) If I mounted one decent solar panel (100w-150w or whatever it is that you have) on my roof, what could I expect with regards to supplementing motor home operations and charging a pair of 6V AGM batteries?  Assume minimal operations during the day, just our fridge operating on propane while we are out for the day.  If my pair of 6V AGM batteries are reading 12.1V when we leave at 8:00am, what might I expect at the end of the day when we return after dark?

6) Are two identical solar panels twice that of a single one?  Or is there vudu in there somewhere?

7) Can I just install one solar panel on the roof and wire it to my two 6V AGM batteries (assumed 12v-14v output) and be done?  Or do I have to invest in other electronic controls?  Is there any risk of over-charging the batteries or otherwise damage the motor home with an over-voltage condition?

8) I read an article with pictures that a very tiny shadow on a solar panel can reduce it's output by 90% or worse.  Have you experienced that?  I wonder if the "shadow effect" is applicable only to old solar technology.

   Ron Dittmer

Ron, here are my amateur thoughts inter alia:

1) What is the voltage output of the solar panels you are using?  Does the voltage swing wildly pending the intensity of the sun, and you have a voltage regulator?  Or is it always the exact same voltage, but the amperage swings wildly?
About 18 volts on mine with about 5+ amps.   5x18 equals 90 watts.   That is under full sun direct exposure.
2) I heard solar panels can get extremely hot when absorbing full sun.  Is that your experience, and if so, are there safety concerns?  Are there concerns of compromised integrity of the motor home's roof?
I used an infrared temp gauge and didn't get enough heat to worry about.   I measured the surrounding roof and compared that to the panels mounted on the roof.  I forgot what the dif was buy it was minor.
3) When operating at max efficiency in full sun and perpendicular to it, what amps and volts could I expect from a 100w solar panel?  I assume I would get 100W.  What would be otherwise "typical" on a sunny day with no clouds?  What could be expected on a 50% cloudy day?
See my answer to (1).   On cloudy days I seem to get about half efficiency. 
4) How sensitive is a "less than ideal" angle to the sun?  I see keelhauler has two panels mounted very nicely on his roof, but they lay flat, almost never perpendicular to the sun.
I was surprised how well mine work early in the morning and later in the afternoon when the sun is at a lower angle to the panel. 
5) If I mounted one decent solar panel (100w-150w or whatever it is that you have) on my roof, what could I expect with regards to supplementing motor home operations and charging a pair of 6V AGM batteries?  Assume minimal operations during the day, just our fridge operating on propane while we are out for the day.  If my pair of 6V AGM batteries are reading 12.1V when we leave at 8:00am, what might I expect at the end of the day when we return after dark?
You should see about the same result that you would get from a 5 amp trickle charge.
6) Are two identical solar panels twice that of a single one?  Or is there vudu in there somewhere?
I assume that is correct.   Just like two batteries is twice one battery (hooked in parallel).
7) Can I just install one solar panel on the roof and wire it to my two 6V AGM batteries (assumed 12v-14v output) and be done?  Or do I have to invest in other electronic controls?  Is there any risk of over-charging the batteries or otherwise damage the motor home with an over-voltage condition?
You will need a small controller.   Mine is super simple:  two wires in from the panels, two wires out to the batteries.   Amazon has lots of these and mine costs as I recall about $25.   
8) I read an article with pictures that a very tiny shadow on a solar panel can reduce it's output by 90% or worse.  Have you experienced that?  I wonder if the "shadow effect" is applicable only to old solar technology.
Ron, I have NOT experienced that although I have also seen the reports.  Maybe I am too dumb to know the difference but I think the partial shade deal is way overblown based on my simple experience. 

I just wanted a simple way to recharge my batteries.   I spent less than $550 onthree panels and the controller as I recall.  Amazon sells a great variety of this stuff.   One of my roof panels is a flex panel mounted directly to the roof with 3M tape (same as is used to attach exterior mirrors) and additionally secured with Dicor around the edges of the panel.   No problems.  The first one I put up was conventionally mounted with brackets and I drilled into the roof and found the cross members.  I called Kermit and he told me how to find them. 

As mentioned by other posters, 10 gauge wire is preferred but I just used 12 gauge landscape wire for fifty feet for the third panel that I moved around.   It works.   That is really all I care about.   I can boondock for a week or more and my batteries are charged.   I am, you see, a simpleton.   Rube Goldburg was my daddy. 

Paul

1) What is the voltage output of the solar panels you are using?  Does the voltage swing wildly pending the intensity of the sun, and you have a voltage regulator?  Or is it always the exact same voltage, but the amperage swings wildly? Voltage varies somewhat but not wildly.  its a little complicated as your particular panel, the temperature and the solar intensity are all factors.  But its not something you worry about, your controller takes whatever the panel sends it and changes it to what your battery needs.

2) I heard solar panels can get extremely hot when absorbing full sun.  Is that your experience, and if so, are there safety concerns?  Are there concerns of compromised integrity of the motor home's roof?Not in my experience.  I've never tested with a meter but I have touched them in full sun and they were not hot enough to bother me.  It is important (most people say) to have an air gap underneath to allow ventilation.  This helps cool the panel and that's important because the hotter the panel the less electricity they produce.

3) When operating at max efficiency in full sun and perpendicular to it, what amps and volts could I expect from a 100w solar panel?  I assume I would get 100W.  What would be otherwise "typical" on a sunny day with no clouds?  What could be expected on a 50% cloudy day?There is always some loss in the system.  So a 100 watt panel will NEVER produce 100 watts.  That 100 watts is rated in ideal conditions.  Figure 80% of that in normal conditions.  And 40 to 50% on a bright cloudy day is what I am seeing on mine.  The voltage will depend on how the panel is designed.  16 to 18 volts is typical but it varies.

4) How sensitive is a "less than ideal" angle to the sun?  I see keelhauler has two panels mounted very nicely on his roof, but they lay flat, almost never perpendicular to the sun. I'm working on a house install and the experts there say anything within 25 degrees of ideal will not make any appreciable difference.  So I don't think angle is as big a factor as finding a place to park that is in the sun. Mine on the RV are flat mounted like Keelhaulers.  If you are moving much, don't worry about it.  If you are snowbirding and will be in the same spot for months then there might be some benefit it having the panels adjustable.

5) If I mounted one decent solar panel (100w-150w or whatever it is that you have) on my roof, what could I expect with regards to supplementing motor home operations and charging a pair of 6V AGM batteries?  Assume minimal operations during the day, just our fridge operating on propane while we are out for the day.  If my pair of 6V AGM batteries are reading 12.1V when we leave at 8:00am, what might I expect at the end of the day when we return after dark?I have two panels (I think 150 watt each) and they easily keep my set of 6v batteries at 14 volts if there is any significant amount of sun during the day.  We went three days boondocking with moderate electric use at night (no furnace or A/C of course) and the batteries were back to 14.1 by the next afternoon.

6) Are two identical solar panels twice that of a single one?  Or is there vudu in there somewhere?Essentially, yes.  But there are other factors, such as are they wired in series or parallel, is there any line loss involved, is either shaded to any degree.  But for general purposes, yes two panels equal 2x.

7) Can I just install one solar panel on the roof and wire it to my two 6V AGM batteries (assumed 12v-14v output) and be done?  Or do I have to invest in other electronic controls?  Is there any risk of over-charging the batteries or otherwise damage the motor home with an over-voltage condition?I believe you could do that if you are careful on selecting panels with a voltage that will not be too high for your batteries.  But I would strongly recommend getting a solar controller and let that provide the voltage to the batteries.  No worries about overcharging and a controller doesn't cost much.

8) I read an article with pictures that a very tiny shadow on a solar panel can reduce it's output by 90% or worse.  Have you experienced that?  I wonder if the "shadow effect" is applicable only to old solar technology.That is conventional wisdom, and I'm sure it is (mostly) true.  But I agree with Doneworking, in my experience I have not seen the dramatic declines as shown in those articles.  I have read that newer panels sometimes have mechanisms built in to help with partial shading but I don't know much about that.

There is a lot of good to bad info out there, and answers on this forum are opinions often and not fact.

So to start with why not get a little more information. Start with this 2 part article: http://www.marxrv.com/12volt/12volt.htm
There is a lot of info here, some is still not absolutely correct. In fact many solar panel sales companies may have bad info.

Handy Bob's Charging puzzle is another good article: https://handybobsolar.wordpress.com/the-rv-battery-charging-puzzle-2/

Here is an article about shading and angle: https://pdf.wholesalesolar.com/Download%20folder/solar-panels.pdf

There are many discussion about this subject but not as much as monitoring how your batteries are doing. I love this product by Bogart(TM-2030-RV) that lets you know exactly what is going on with your batteries. http://www.bogartengineering.com/products/trimetrics.html

So for those who want answers and don't want to read much. Solar panels provide about 17.5 volts to push the watts to your 12.7 volt batteries. The smaller and longer the cables the cables  the voltage could drop low enough to provide no push. But if you keep putting too much current you will boil or ruin the batteries. So that is what a charge controller is for, it provides the batteries the voltage the batteries want depending on their state of charge.

Though I typically don’t have to do this using the generator and solar combined has an advantage if your solar panels themselves for whatever reason are not capable of bringing your batteries up to 100% state of charge (SOC).  Depending on the charge level in your batteries and the capacity and charge voltage provided by your charger/controller the early stage of charging might allow 20 to 30 amps of battery charging for a 220 amp hr battery. A 100 watt solar can only put out a fraction of that meaning it will take much longer to bring the battery up to 90-95% SOC.  Once the battery SOC is up to 90-95% the battery amperage acceptance drops off very sharply (5-10amps).  If your coach converter is putting out proper voltage and current the battery will be brought up to 90% charge relatively quickly. 


It is this last 5-10% of battery charging that takes time because the battery itself starts to cut back how many amps it will accept.  What happens when using the generator is it is running and loafing at a very low output thus consuming gas and noise for considerable time to get the battery back to 100% SOC.  To extend the life of the battery(s) it is very important that they be brought up to 100% charge.  This last stage of charging is ideal for a solar system as it typically provides the lower amperage required by the battery while doing it for free with no noise.

With enough solar capacity and the right conditions a generator is not needed (assuming no AC use) but even an undersized solar system coupled with a generator can make sense by significantly reducing generator usage.

I agree with John Keelhauler’s post above.  His comments are based on a strong understanding of the engineering principles involved. I have been a solar user and proponent for about 7 years and have found RV builders notorious for cutting corners either because of ignorance or an attempt to save a few bucks in hopes the customer doesn’t know the difference.  I am no expert so I rely on people like John, Jatrax, and others to keep me from venturing too far off track.

Though I typically don’t have to do this using the generator and solar combined has an advantage if your solar panels themselves for whatever reason are not capable of bringing your batteries up to 100% state of charge (SOC).  Depending on the charge level in your batteries and the capacity and charge voltage provided by your charger/controller the early stage of charging might allow 20 to 30 amps of battery charging for a 220 amp hr battery. A 100 watt solar can only put out a fraction of that meaning it will take much longer to bring the battery up to 90-95% SOC.  Once the battery SOC is up to 90-95% the battery amperage acceptance drops off very sharply (5-10amps).  If your coach converter is putting out proper voltage and current the battery will be brought up to 90% charge relatively quickly. 


It is this last 5-10% of battery charging that takes time because the battery itself starts to cut back how many amps it will accept.  What happens when using the generator is it is running and loafing at a very low output thus consuming gas and noise for considerable time to get the battery back to 100% SOC.  To extend the life of the battery(s) it is very important that they be brought up to 100% charge.  This last stage of charging is ideal for a solar system as it typically provides the lower amperage required by the battery while doing it for free with no noise.

With enough solar capacity and the right conditions a generator is not needed (assuming no AC use) but even an undersized solar system coupled with a generator can make sense by significantly reducing generator usage.

This post should be a 'sticky' up top for solar panels. Well said.       

Thank you all for the clarity.  Every now and then I get to thinking "solar".  Maybe one day I will dive in and get one or two panels pending what my roof can accommodate.  If I didn't have the crank-up antenna, I know for sure I could get two up top.  What worries me is a shadow cast from the a/c unit and roof vent cover.  I don't have ideal roof space like keelhauler.  I recall him stating a while back that he had Phoenix do something different with his crank-up antenna to get clear roof space.  Did I remember correctly keelhauler?

Thanks again everyone.  It surely would be nice to have a solar sticky.
Ron Dittmer

Ron, we bought a Renogy 100 watt Solar suitcase that has controller attached. I'm not good at amps and volts and watts but I feel fairly confident in saying a solar panel should work for you in the scenario described. Here's our set up:
- 100w portable panel with
- Onboard multistage controller and
- Jumper cable type connections to clamp to batteries

- Extension cables (Two sets of 10 foot cables) bought separately
- Small steel loop end cables (4) and outdoor locks to secure panel to rig frame (keep honest people honest - true thieves can get it anyway) we loop through each other to make as long as need then lock on.

All Renogy cables quickly clip together.

We have camped for weeks with this as our only power source (and our batteries are dicey, 6 years old). Our dry camping power usage sounds similar with the possible exception of devices. We have and charge two e-readers, two tablets, two cell phones, one hot spot, two cameras and one old power suck computer.

Cloudy days - our test run started with several cloudy days and the batteries held steady - no up, no down
Sunny days - within hours of the sun hitting the panels we were charged over 13 and it climbed steadily from there
Moving - if we're in camp, we adjust the panel to track the sun for maximum gain. If we're out for the day, we aim South and she does fine
Usage - careful on cloudy days and charge everything and run the computer on sunny days. We seldom do music or TV but if you make it through the night on battery, your solar panel should charge you back up during the day.

On good sunny days the controller often reads 60 amp hours brought in for the day and that was with whatever loss you get from those extension cords and less than ideal placement.

We recently discovered the light in the macerator cabinet was on. Since we couldn't remember the last time we dumped in the dark we figure it was a continuous drain on the batteries during our dry camping/solar charging time.

Our "solar suitcase experiment" has convinced us that panels on the roof are the way to go but until we figure all that out and get it done, our little portable guy works fine. Well keep it even after the roof system goes on for when we camp in shade (my preference) - House in shade, portable panel in Sun. House in Sun, portable panel stays packed in car.

Ron,
Holly has a great suggestion if you want to learn solar.  Those 100 watt portable systems are simple and very flexible to set up and use.  A great way to get things figured out.  And I know you are very usage conservative so that might be all you need.

One thing everyone should keep in mind is that the solar industry is changing rapidly.  Information that was correct last year can be out of date as new technology becomes available.  When I first started looking into this residential panels (not RV panels) were producing around 200 watts.  The cutting edge ones today are closing in on 400 watts for the same size panel.  And the controllers and other electronics are changing even faster.

So take what I say, and what you read as a guide because any particular set of equipment that you purchase might be quite different.  But it's a great time to start learning about solar.

In 10 years panels will be so common no one will even think twice at seeing them on cars, trucks, RV's, houses, car ports....................