MPPT vs. Shunting Solar Controller - SailNet Community
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post #1 of 6 Old 11-25-2012 Thread Starter
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MPPT vs. Shunting Solar Controller

I get asked quite a bit to describe the difference between an MPPT (multi-point power tracking) solar controller and non MPPT controllers.

Basically all 12V nominal solar panels run voltages of 16 - 18V+. With a PWM or shunting controller the excess voltage goes to waste when the panel voltage is stepped down to a safe charging voltage. An MPPT controller can convert this excess voltage to current so there is less waste and more efficient charging..

To show how this works I decided to use my bench top power supply to simulate a solar panel yet provide consistency in output for an A/B scenario. I set the power supply at 17.4V and 4A or the rough equivalent to a 70W solar panel. I then fed the power supply through a switch to choose which solar controller got the power. I used a battery bank that had been depleted to "bulk" for the 4-5A of current it would see.

The video below shows the results. Basically the MPPT controller had an output of roughly 22% - 24% more than the simple shunting controller. There is no magic just an A/B switch and two different solar controllers...

Hope this helps give some clarity...


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post #2 of 6 Old 11-26-2012
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Re: MPPT vs. Shunting Solar Controller

Great video!!!
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post #3 of 6 Old 11-26-2012
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Re: MPPT vs. Shunting Solar Controller

Great video, I'll just throw in another analogy in case it helps.

The MPPT controller is like a transmission in a car. The transmission seeks out the most efficient ratio to convert the torque/RPM's (voltage/current) from the engine (panel) to the torque/RPM's it needs to drive the car (charge the battery). It can convert torque to RPM's and vice versa.

The transmission does the conversion efficiently AND lets the engine operate at the ideal point. Both are good.

The shunting controller on the other hand is like a clutch. It can only reduce the torque/RPM's it's given by allowing slippage and creating a heat in the process.

So the clutch is both inefficient at doing the conversion (because it creates heat) AND limits the freedom of the engine operating point. Both are bad.

Last edited by asdf38; 11-26-2012 at 11:22 AM.
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post #4 of 6 Old 11-26-2012
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Re: MPPT vs. Shunting Solar Controller

Another wonderful effort by MaineSail! Thanks, RC.

I certainly agree that MPPT controllers can be very useful, and I believe they're well worth the cost.

Not mentioned in your video is the effect that MPPT controllers can have when multiple solar panels are connected in series, boosting the OC voltage to 36, 60 or even higher. In this scenario, the MPPT controllers are even more effective in using the available energy from the panels to charge the house batteries.

Another advantage of using panels in series: in low light levels (e.g., early morning or late afternoon or cloudy conditions), the panels still put out enough usable voltage for battery charging.

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post #5 of 6 Old 11-27-2012
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Re: MPPT vs. Shunting Solar Controller

So, for a 500-600w panel array of these puppies (http://www.motechsolar.com/en/doc/mo...lear3BB_A4.pdf ) - which MPPT would you have on YOUR boat?

I'm looking at the midnite classic, haven't bought anything yet.

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post #6 of 6 Old 11-27-2012 Thread Starter
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Re: MPPT vs. Shunting Solar Controller

Quote:
Originally Posted by chucklesR View Post
So, for a 500-600w panel array of these puppies (http://www.motechsolar.com/en/doc/mo...lear3BB_A4.pdf ) - which MPPT would you have on YOUR boat?

I'm looking at the midnite classic, haven't bought anything yet.
I like the Outback & the Morningstar controllers and also use a lot of the Blue Sky controllers but you really need the extra IPN Pro remote to set them up properly...

On my own boat I have a Genasun but the array is only 140W........

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