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MPPT vs PWM charge controllers

We have recently conducted tests into whether or not MPPT charge controllers can really produce up to 30% more power under partially shaded or overcast conditions than PWM units as claimed by many maufacturers.

                               

We conducted our tests at 14.00 on the 17th of July 2013, facing one of Sunstores 80w monocrystalline solar panels directly south at a 60 degree angle.

Before connecting the charge controllers we measured the open circuit power of the solar panel and recorded the following results:

-          Voltage = 20.1v

-          Current = 2.53a

-          Power = 50.85w

The two charge controllers selected for this test were the Ep Solar Viewstar VS1024 PWM and the EP Solar Tracer 1215 RN MPPT, both charge controllers are rated at 10a. We recorded a self consumption rating of 10 milliamps for both charge controllers.

Charging rates were measured with our multimeter connected in line on the positive conductor from the charge controller to the battery

The first charge controller we tested was the EP Solar VS1024 PWM unit, we connected the 80w Monocrystalline solar panel to this with a 2 meter length of 2.5mm twin core solar cable and used the same cable to connect the system to a 12v leisure battery. We recorded the following charging values with no shading, 25% shading and 50% shading longitudinally across the panel:

-          No shading = 2.36a being delivered to the battery

-          25% shading = 1.00a being delivered to the battery

-          50% shading = 0.09a being delivered to the battery

We then changed over to the Ep Solar Tracer 1215RN MPPT charge controller and conducted the test in exactly the same way. We recorded the following results:

-          No shading = 2.44a being delivered to the battery

-          25% shading = 1.3a being delivered to the battery

-          50% shading = 0.02a being delivered to the battery

As you can see we recorded a 30% increase in efficiency with 25% shading from the MPPT charge controller over the PWM unit. Although we did see a reduction of 70 milliamps at 50% shading this could be due to a slight drop in irradiance and would be considered too small of a variation to be evidence of inefficiency from the MPPT charge controller.

                     

After we had conducted these tests we looked into claims that MPPT charge controllers can be used to charge a 24v battery bank form a 12v solar supply.  For a fully rounded test we attempted the same with a PWM charge controller as well. We found that, as we had expected, neither the MPPT nor the PWM charge controller could successfully charge a battery bank at a higher voltage than that of the solar supply.  

In summary, the claims that MPPT charge controllers can give improved efficiency over PWM units under partially shaded or overcast conditions seem to be valid.

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