PWM or MPPT for a Uni-Solar thin film with Vmp=16.2V ?

Oct 3, 2011 07:43 pm
PWM or MPPT for a Uni-Solar thin film with Vmp=16.2V ?

I want to build a 12V system with thin film flexible panels, which have Vmp=16.2V. It will be installed in an area having 90F during summer, and days as low as 30F-40F just a month, it is a more hot than cold area.

I'm not sure if a MPPT will make a difference and is a better choice, or if a PWM will be almost as good.

The thin film has Vmp=16.2V, and a regular glass module usually is Vmp=17.5, so a MPPT would make more sense on a glass module... but as the thin film has less power drop due to hot temperature, an MPPT would be useful also...

8 Posts
Oct 13, 2011 02:16 pm
Re: PWM or MPPT for a Uni-Solar thin film with Vmp=16.2V ?

Hello Gabriel,
You raise a great question regarding which type of charge controller to use for your system.  It's a tough call, but like most situations we encounter in PV, the answer is “it depends.”

An MPPT charge controller should do a better job of sending more power to your battery bank than a PWM controller would, but the lower Vmp of the thin film modules does decrease the gain when compared to typical crystalline modules.  That said, you should still see an improvement over a PWM controller. 

If the solar array is relatively large compared to the storage capacity of the battery bank, then my opinion would be that a PWM controller would be fine since the array would be capable of charging up the battery bank without the "extra" power that an MPPT controller would supply.  If the array is sized so that you need every last watt hour of production to keep the batteries charged, then an MPPT controller starts to make a bit more sense. 

Something else you could consider would be to use an MPPT controller and wire the PV array at 24V.  This would give the controller a bit more voltage to work with, and would also help with voltage drop in the wire runs.  Most MPPT controllers will allow you to come in at a higher nominal array voltage to charge a lower battery bank voltage.

One last option, depending on the PV module you are using, would be to just add another PV module to the array.  This may not always be an option, and it may be much more expensive than the cost of an MPPT controller, but with the cost of PV coming down so much recently, some modules actually cost less than the more expensive MPPT controllers and will definitely increase your production.  This may not work for your situation, but it may be worth considering if the scenario would allow it.

Regardless of how you configure the system, the question remains, is the small gain you would receive worth the higher cost of an MPPT controller?  When you consider the life span of the array and the charge controller, then that small daily gain can really add up.  If your array is having a tough time keeping up with the loads upon the battery bank, then anything you can do to increase production is going to be useful.  Ultimately, the decision is yours, but hopefully some of this was helpful!

Eric Pedersen
altE Staff
eric @

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