So my installation is for a sail boat. There's a lot things like rigging sails etc, that can create shadows on part of the array and this is constantly moving around. Some panels in the array will always be in either total or partial shade.

I've seen a lot of debate online regarding mitigating the effect of shadows on the array. It seems pretty clear that wiring in parallel is key, but a lot of people also seem to be adamant that using more MPPT controllers also improves overall average output significantly. Some will even go as far as to use a controller for every single panel.

However some professionals that I have asked about it think this doesn't make sense.

I'd like to dissolve the mystery and looking for a clear guide on the principles and why, in numbers, do people promote the use of multiple MPPT controllers?

From the comments:

  • There are two 120 W panels on the back, where shadows are less of a problem, all on one controller, and I'm adding 8 130 W 110x57 cm flexible panels, where there is always some part in shadow.
  • Panels are re-badged Sunpower semi flexible panels, like this.

1 Answer 1



Using multiple charge controllers is useful if your solar panel array exceeds the specifications for the controller. You can't exceed panel input voltage, and you can't exceed the maximum power (watts) that the charge controller supports. Otherwise, you risk damaging the charge controller and rendering it useless.

Example Scenario

For example, my charge controller is the EP Solar Tracer 3210an. According to the product documentation, this charge controller has a maximum voltage rating of 100 volts, or 92 volts at 25 celsius (77 fahrenheit). The maximum power of the charge controller is 790 watts. Hence, I need to design the solar panel configuration to match those parameters.

If I want to harvest more than 790 watts, then I need to use additional charge controllers. I can connect additional panels to a second (or third) charge controller, and increase my power. I can connect these additional controllers to the same battery bank.

Addressing Your Question

With all of this in mind, to answer your question, I'm not convinced that using multiple MPPT charge controllers will mitigate the problems with shadows on the panel. Your best bet is to place the panel in a South-facing location that has maximum sunlight. You can use a mobile application such as The Sun Ephemeris to track the Sun based on your geographic location and date / time. Proper panel placement will help to reduce shadows and maximize your power harvesting capabilities.

  • Having the panels face south would only be applicable to Northern Hemisphere locations. In the Southern Hemisphere they would need to face north.
    – Fred
    Oct 23, 2020 at 9:00
  • The asker's profile indicates that he lives in London, which would be the northern hemisphere. Oct 23, 2020 at 16:04
  • Yachts move. Just because the question is asked by someone from London doesn't mean they're in London now.
    – Móż
    Nov 23, 2020 at 6:29
  • 1
    Yes the key fact here is that as a sail boat things are in a constant state of flux. There is rigging and sails overhead casting shadows which move with the motion of waves, and there will always be some panels in an array in partial or total shade, which would bring down the entire array if treated as a unit.
    – barrymac
    Feb 11, 2021 at 14:40

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