Adding another Solar Panel

[Bwht4x4]

I'm currently running a 160 watt panel mounted to the Yakima tracks of my camper with the panel plugged into the roof top plug. I'm wanting to buy another 100 watt panel to use as a portable panel that would be deployed whenever we needed it and it would be plugged into the plug located on the rear wall of the camper.

The wires for each of the panels would terminate directly into the Sunsaver MPPT controller and they would not be wired in parallel or series. My interpretation is that by going this route there's no need to be concerned with whether the panels are close to the same voltage as you would do if you were running them in parallel or series.

Is there anything else I am missing? There's no worries with the controller as it can handle an input of more than 15 amps, but will only output 15 amps max. Right now my 160 watt panel produces between 6-9 amps and with the additional 100 watt panel that should increase to 10-15 amps.

What am I missing?

 

[billharr]

I'm currently running a 160 watt panel mounted to the Yakima tracks of my camper with the panel plugged into the roof top plug. I'm wanting to buy another 100 watt panel to use as a portable panel that would be deployed whenever we needed it and it would be plugged into the plug located on the rear wall of the camper.

The wires for each of the panels would terminate directly into the Sunsaver MPPT controller and they would not be wired in parallel or series. My interpretation is that by going this route there's no need to be concerned with whether the panels are close to the same voltage as you would do if you were running them in parallel or series.

Is there anything else I am missing? There's no worries with the controller as it can handle an input of more than 15 amps, but will only output 15 amps max. Right now my 160 watt panel produces between 6-9 amps and with the additional 100 watt panel that should increase to 10-15 amps.

What am I missing?

If they both terminate directly to your controller they are in parallel. This is how I have mine wired. 250 watts on the roof now that I have added a 120w to the roof. I have a 120w portable that terminates to my 30 amp controller.

 

[craig333]

Should be no problem. I'm hoping I won't need to carry my portable as much now that I have 250 on the roof. I'm sure it'll still come in handy when camped under the trees.

 

[Trailbob]

I'm not so sure... Will the controller take the input from two panels separately, or are the panels connected to the same input lugs on the controller? If they are on the same lugs (two panels on one + and two on one - lug), then isn't that the same as parallel?

I wanted to add another panel to the roof of our travel trailer, and was told by AM Solar that I would have to use a PWM controller instead of an MPPT if the panels were not matched in voltage. They said the MPPT will not work properly unless the panel voltages match.

I did what you want to do on our Hawk. I have a 160W Zamp panel on the roof and a 90W portable panel that I run through an Anderson connector in the rear. The wires from both panels tie together (parallel) just before they enter the controller, which is a Bogart 2030SC PWM. I put the system together over the winter, so I can't say how well it works yet. I can say that I was disappointed at how little power I got out of the 160W roof panel in the winter with the low sun angle.

As a suggestion, contact Morningstar and run your question by them. Another option, if you have not already bought the 100W portable panel, is to buy one that is the same brand and voltage as your roof panel. Then you should be able to parallel them into your MPPT controller.

 

[longhorn1]

Just my 2 cents. My 2014 Grandby came with the Zamp 100W on the roof, Zamp controller, and rear plug. After conferring with both Zamp and FWC and being told the rear plug runs to the controller, Zamp said I could install the 80W portable without the controller on the back side of the panel. So both panels are Zamp and the controller is Zamp. I use the portable during the winter to charge once a month while the camper is Covered and take the portable when we will be boondocking. I'm no electrical wiz. There have been several posts on solar which I find fascinating. We have so many people on WTW with such deverse backgrounds and capabilities to do these special projects. For me, I let FWC Camper handle everything and called it a day. Jd

Sent from my SM-G900V using Wander The West mobile app

 

[billharr]

Just my 2 cents. My 2014 Grandby came with the Zamp 100W on the roof, Zamp controller, and rear plug. After conferring with both Zamp and FWC and being told the rear plug runs to the controller, Zamp said I could install the 80W portable without the controller on the back side of the panel. So both panels are Zamp and the controller is Zamp. I use the portable during the winter to charge once a month while the camper is Covered and take the portable when we will be boondocking. I'm no electrical wiz. There have been several posts on solar which I find fascinating. We have so many people on WTW with such deverse backgrounds and capabilities to do these special projects. For me, I let FWC Camper handle everything and called it a day. Jd

Sent from my SM-G900V using Wander The West mobile app

This is what I did for my Solar in a bag portable panel. I has a small controller on the back, I took it out of the loop and run the panel to the controller in the camper. I have a Renogy PWM controller so all runs are parallel. If I go to a MPPT controller I would run my roof panels in series. Then add a switch so if I plugged in the portable it would be in series. I am hoping that the 250w will run all I need and I will not need to carry the portable panel.

Note: If I did it all again I would do what another member did (would have to search) and put up a higher voltage panel and run a MPPT controller.

 

[craig333]

Okay, I didn't quite understand your question. My panels on the roof are 17.85 and the portable is 17.5. I don't think thats significant but I'll go out and check tomorrow. How big a voltage difference are you thinking? A while back someone here talked about the advantages and disadvantages of series vs. parallel and the argument for parallel won me over.




http://solarpanelsvenue.com/mixing-solar-panels/

• If you are using an MPPT charge controller, mixing panels of different voltages and/or currents within an array will have an adverse effect on the entire system. Different module outputs make it impossible for the controller to determine the optimal operating voltage and current because they will be different between the different types of panels.

http://www.mpptsolar.com/en/solar-panels-in-parallel.html

http://forum.solar-electric.com/discussion/15487/solar-panels-with-different-voltages-connected-in-series-using-an-mppt-controller

Hmmm, some food for thought. I'm going to have to do some real world testing. Might be the excuse I need to go get a decent meter. I still have my old pwm controller to conduct some tests with. Just looking at my initial results on adding the second panel it did what I expected, but I have to wonder if the mppt controller isn't working at maximum efficiency with panels of differing wattage.

 

[Bwht4x4]

I'm totally ignorant to what I'm about to say....

I can understand there being an issue with running two panels in series or parallel if they have different voltages, but I'm not seeing how using panels with slightly different voltages that are wired to the same lug on the controller causing an issue. I could be wrong, but doing it this way doesn't seem like it's a parallel run either.

I need to call AM Solar and ask.

As for my Morningstar Sunsaver MPPT controller...the product data sheet clearly says you can use panel(s) that are greater than 200 watts (@12 volts). The controller will simply lower it's output to the batteries. In fact, some one told me it's actually a good idea to run my controller above the 200 watt nominal maximum operating power (i.e. 250 watts) as it will allow the controller to provide maximum output to the batteries for a longer period during the day than if I was using a single 160 watt panel.

http://www.morningstarcorp.com/wp-content/uploads/2014/02/SSMPPT_ENG10_1111.pdf

*Input power can exceed Nominal Maximum Operating Power, but controller will limit and provide its rated continuous maximum output current into batteries. This will not harm the controller (reminder: do not exceed Voc).

 

[thatsatechnique]

I'm currently running a 160 watt panel mounted to the Yakima tracks of my camper with the panel plugged into the roof top plug. I'm wanting to buy another 100 watt panel to use as a portable panel that would be deployed whenever we needed it and it would be plugged into the plug located on the rear wall of the camper.

The wires for each of the panels would terminate directly into the Sunsaver MPPT controller and they would not be wired in parallel or series. My interpretation is that by going this route there's no need to be concerned with whether the panels are close to the same voltage as you would do if you were running them in parallel or series.

Is there anything else I am missing? There's no worries with the controller as it can handle an input of more than 15 amps, but will only output 15 amps max. Right now my 160 watt panel produces between 6-9 amps and with the additional 100 watt panel that should increase to 10-15 amps.

What am I missing?

This is exactly the setup I have - no issues.

 

[carld]

I can't see that it will hurt if the voltage difference is small. The solar cells are electrical current generators, so electric current will add when they are wired in parallel. The solar cells are just diodes and the output voltage (about 0.5 to .6V) depends on the number (32 or 36) of cells (diodes) in the panel connect in series . The panels operate at voltages anywhere between 0V and the open circuit voltage Voc (32cellsx.6V=19.6V or 36cellsx.6V=21.6V for typical 12 system panels). Panels have different current ratings, short circuit current Isc, depending on the area and efficiency of the of the cells. When different panels are connected in parallel the resulting voltage will balance out to the sum of the panel currents divided by the load resistance. At high power conditions (good sun and low resistance) the voltage will be less than the normal (or optimum) voltage and both panels will dump all their current into the load resistance. For low power conditions (low light and or high resistance) the higher voltage panel may partially reverse bias the low voltage panel and reduce its current. If there is a large Voc difference between the panels, I'm guessing 5 V or more, the lower voltage panel will be revered bias more often and will not contribute as much of its power to the system. Also don't connect panels where the open circuit voltage Voc on one panel exceeds the maximum voltage of the other panel or of the system controller.

For MPPT controllers connecting panels in series avoids the voltage problem, but if the current ratings Isc are different the smaller current panel will limit the maximum current.

 

[carld]

On second thought, at low load resistance I think the higher voltage panel will forward bias the lower voltage panel. For PV cells the IV curve is inverted. So the lower voltage panel will steal current from the higher voltage panel. If the voltage difference is more than about 0.1 volts per cell (the difference in Voc > 3 V for the panels), this will reduce the performance significantly. In fact for a large voltage difference and say for example with no load (open circuit conditions), the low voltage panel is the load. If low voltage panel is in the dark and high voltage panel is in the sun it might turn the low voltage panel into a light emitting panel, where all the cells become LEDs. Maybe you can try it out.