C40 v XW60 or PWM v MPPT my observations

Earlier this year I imported a new XW60 MPPT Charge Controller and decided to split my fixed array and get some real life comparisons.

System Nominal Voltage is 24 volts
Opps just check my signature.

The important bits are as follows....12 x 200w Isophoton Mono Panels all identical.The array is fixed at my lattitude 41 degrees facing due south.

1 x Xantrex C40 wired 6 panels parallel 1200w at 24 v ((1200w STC)
1 x XW60 MPPT 6 panels wired 2 in series x 3 strings then paralled to 48v nominal (1200 w STC)

So we now have a test bed to compare the two different technologies a PWM controller and a MPPT Dynamic Controller from Xantrex

Most of my test conclusions have been obtained by monitoring the amperage output from each units display and a quality hand held DC Clamp meter. The XW amp readings are within 1-2% of my clamp meter the older C Series display was between 5/7 % accurate so I tended to rely on the clamp meter for the C40 readings

A summary of my findings

In clear skies in April/May warm panel temps I saw a constant 10-12 % extra harvest yield from the MPPT unit. As the weather inproved in June and July and Panels temps were HOT I still saw a + 8-10 % harvest yield for the MPPT unit

In blue skies but intermittent cloudy conditions in April and May I could see a gain of 30-35 % power harvest dropping to 15% as the PVs warmed up and cooled down as the sun emerged from cloud then dissappeared again. As the weather warmed in June and July the figures were still similar on cloudy blue sky days.

I have no data for cold days as the XW was only installed in Aprill

I have seen a recorded max power input of 1370 watts from the XW on a cool windy Aprill day from the 1200 stc array.

Unfortunately I am unable to give you many daily yield differences between the two units as I hit float nearly every day. However on the day that I hit a maximum input of 6.7kwhs from the XW60 (batteries were low from previous day around 82% soc) it calculated to 28% more harvest that the C40. This was in April with my panels in optimal alignement.
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