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Old 08-06-2020, 04:23 PM   #1
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DIY Solar Suitcase Question: Series or Parallel?

I'm working on the design for a DIY solar suitcase using 2 100W panels and an MPPT charge controller. With such low voltage, the MPPT controller will support either series or parallel wiring of the panels.

I'd like to wire in parallel so the amperage is additive since my peak hours of sun are about 3.6 in spring and fall, and 4.3 in summer. I know that sets me up for a larger loss through the 30' of cabling to the controller, but I don't mind spending the bucks for some 6 or 8 AWG for the connection.

Thoughts?
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Old 08-06-2020, 04:58 PM   #2
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I wired ours in series, with LiFePO4 batteries running in the 13V+ range and the controller needing to see +5V over the batteries to operate I didn't have a lot of choice.

Plus I can move the panels to avoid shading (the point of a suitcase in my opinion) and minimize losses between the panels and controller with the higher voltage output.
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Old 08-06-2020, 05:06 PM   #3
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As 01tundra said go series. The main advantage of parallel is shading of panels in the system. With a suitcase you can just move the panels and take advantage of the higher voltage.
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Old 08-06-2020, 05:39 PM   #4
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Definitely wire in series if you have an MPPT controller. The unit will start charging sooner in the day with low sun angle and stay charging later again with lowering sun angle.

My suitcase (two 80 watt panels in series) does a great job of charging my Battleborn batteries even if I just set it for mid-day sun.

If you wire in parallel any perceived gains will be offset by the loss of early and late charging times.

If you go that route you might as well just use a PWM controller and save money.
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Old 08-06-2020, 08:46 PM   #5
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I'm new to solar, but saw this elsewhere "If your panels do not have bypass diodes, you almost have to go parallel. With no bypass diodes, shade on just one panel will drop the output of your entire PV string to zero."

If I was going to spend the money on an mppt controller, I'd go series with the panels. Otherwise save your money and go with a PWM controller.
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Old 08-07-2020, 07:35 AM   #6
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Did some further research last night regarding MPPT controllers and it DOES appear that series is the way to go.

Thanks for the help, everyone. As you can tell, I'm a solar newbie with enough electrical experience to make me stupid!

My motto: Always Be Learning.
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Old 08-07-2020, 12:22 PM   #7
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Quote:
Originally Posted by Theo View Post
Did some further research last night regarding MPPT controllers and it DOES appear that series is the way to go.

Thanks for the help, everyone. As you can tell, I'm a solar newbie with enough electrical experience to make me stupid!

My motto: Always Be Learning.
So was every "solar expert" at one time in their lives
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Old 08-07-2020, 02:06 PM   #8
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Quote:
Originally Posted by flyflotrtim View Post
I'm new to solar, but saw this elsewhere "If your panels do not have bypass diodes, you almost have to go parallel. With no bypass diodes, shade on just one panel will drop the output of your entire PV string to zero."

If I was going to spend the money on an mppt controller, I'd go series with the panels. Otherwise save your money and go with a PWM controller.
Our Renogy panels came with bypass diodes.
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Old 08-07-2020, 06:30 PM   #9
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Shading is usually never an issue with a portable panel since you are moving them around all the time anyway.
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