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RVing message boards => Tech Talk => Solar => Topic started by: keith c on July 17, 2017, 03:32:54 PM

Title: Adding Solar Panels
Post by: keith c on July 17, 2017, 03:32:54 PM
At present, I have 2 160Watt solar panels and am thinking of adding 1 more panel.  The 2 panels I have now are wired in parallel.  I have a 40 amp MPPT charge controller, so another solar panel shouldn't be an issue.  Can I add a different wattage solar panel and wire it in series (eg 200 watt panel)? 
Title: Re: Adding Solar Panels
Post by: Paul & Ann on July 17, 2017, 03:57:26 PM
I believe adding another solar panel in series will be ok if the voltage of the 200 watt panel is close to the voltage of the 160 watt panels, but the output of the 200 watt panel will be limited to 160 watts.
Title: Re: Adding Solar Panels
Post by: keith c on July 18, 2017, 06:35:20 AM
Thanks Paul & Ann.  Why would I be limited by the 160 watt panel?  I would keep the 2 160Watt panels wired in parallel and then add the 200 watt panel by wiring that one in series.  Wouldn't the voltage be additive to what the 2 160 watt panels are producing?  Thanks for your help.
Title: Re: Adding Solar Panels
Post by: Paul & Ann on July 18, 2017, 08:47:48 AM
I will have to think about that for a minute.  I thought you were going to put all three panels in series.

Here is some information on series and parallel connections of solar panels.

http://solarpanelsvenue.com/mixing-solar-panels/
Title: Re: Adding Solar Panels
Post by: Kevin Means on July 18, 2017, 11:35:12 AM
I believe Paul is giving you good information. I did a lot of reading, and talked with some very solar- knowledgeable people before installing our system, and learned that the output of individual solar panels should be as close to the same as possible, whether they're wired together in series or parallel. That isn't to say they won't work if they're not the same, but the lower output panel(s) will, essentially, reduce the output of the higher output panel to that of the lower output panels (Did I say that clearly?)

Basically, using panels with different outputs means you'd be wasting, roof space, power and, perhaps, money.

Kev
Title: Re: Adding Solar Panels
Post by: kdbgoat on July 18, 2017, 11:51:15 AM
I know Handy Bob runs (3) 75 watt, and (1) 120 watt on his rig with no issues.

https://handybobsolar.wordpress.com/about/
Title: Re: Adding Solar Panels
Post by: Kevin Means on July 18, 2017, 12:12:08 PM
...and Bob Shearer (HandyBob) was the one who told me to use panels with the same output. I paid Bob a stipend to advise me on the installation of our system. Like I said, an array consisting of panels with different outputs will work, you just won't realize all the power that the panels are capable of putting out.

Kev
Title: Re: Adding Solar Panels
Post by: keith c on July 18, 2017, 12:38:24 PM
Kevin, Paul, thanks for the information.  By adding the 3rd one in series, I was trying to reduce line losses by increasing the voltage ilo current.  Right now, I have 8 gage wire for the 2 solar panels hooked up in parallel.  I'll do more reading before adding anything. 
Title: Re: Adding Solar Panels
Post by: kdbgoat on July 18, 2017, 01:39:43 PM
...and Bob Shearer (HandyBob) was the one who told me to use panels with the same output. I paid Bob a stipend to advise me on the installation of our system. Like I said, an array consisting of panels with different outputs will work, you just won't realize all the power that the panels are capable of putting out.

Kev

I believe Bob has his wired in parallel, not series. If I remember correctly, he did advise against wiring different size panels in series. It's been a long time I've visited his site except to copy the URL, so I could be wrong there too.
Title: Re: Adding Solar Panels
Post by: AStravelers on July 18, 2017, 06:30:53 PM
Just like wiring batteries in series or parallel, they must match.

If wiring solar panels in parallel, they must match in voltage.  If wiring in series they must match in amperage.

You can think of your pair of 160 watt panels, wired in parallel, as one 320 watt panel.  Now when you wire in your 200 watt panel is series with the 320watt panel you have a large mismatch of amperage.  I don't know if any damage would occur, but I am pretty sure you will wind up with a pair of 200watt panels instead of a 320 watt and a 200 watt.

Think of wiring a 100AH battery in series with a 200AH battery.

Title: Re: Adding Solar Panels
Post by: AStravelers on July 18, 2017, 08:24:33 PM
Finally found a reference to quote about matching panels when wiring parallel or series.  http://www.alternative-energy-tutorials.com/energy-articles/connecting-solar-panels-together.html (http://www.alternative-energy-tutorials.com/energy-articles/connecting-solar-panels-together.html)

Don't ask me to describe the physics behind the limiting factors.  I just remember reading references to the problems with mis-matching the voltages or currents over the last 10 years or so.
Title: Re: Adding Solar Panels
Post by: butchiiii on July 19, 2017, 12:19:46 AM
Finally found a reference to quote about matching panels when wiring parallel or series.  http://www.alternative-energy-tutorials.com/energy-articles/connecting-solar-panels-together.html (http://www.alternative-energy-tutorials.com/energy-articles/connecting-solar-panels-together.html)

Don't ask me to describe the physics behind the limiting factors.  I just remember reading references to the problems with mis-matching the voltages or currents over the last 10 years or so.

Excellent article.
Thanks
Title: Re: Adding Solar Panels
Post by: keith c on July 19, 2017, 02:58:51 PM
Al, thanks for the article.  I also read a lot of what HandyBob had written.  Very helpful.  If I do decide to add more panels, I'll try to match the new panel with my existing panels' voltage and amperage.
Title: Re: Adding Solar Panels
Post by: kdbgoat on July 19, 2017, 07:11:40 PM
Some good reading here also:

http://www.jackdanmayer.com

Title: Re: Adding Solar Panels
Post by: supermanotorious on July 20, 2017, 08:58:00 AM
Where is the chart that shows voltage drop for charge controller wire size in 12V, 24V, 36V, and 48V? I found it yesterday, can't find it today
Title: Re: Adding Solar Panels
Post by: Kevin Means on July 20, 2017, 11:47:57 AM
Here's one of several that are online in which you can enter the parameters. http://www.rapidtables.com/calc/wire/voltage-drop-calculator.htm

Kev