Partly cloudy

Note: Data was not recorded for 5/05 due to maintenance on data logging computer.

Note: Data was not recorded for 5/05 due to maintenance on data logging computer.

Both Xantrex representatives were very open and honest about the product's performance, and they seemed very genuinely concerned that the product was still not performing as it should. We got into detailed discussions of why the MPPT still had issues, and I at this point agreed that these details would remain in confidence. The average user doesn't usually care about the details of why a product is performing below expectation, just that it is. Xantrex verified that my logging was within 2 to 3 percent, and they verified that the west and east arrays were close to identical in performance.

The Data Speaks

I performed efficiency tests to confirm the manufacturers' efficiency specifications. I connected Valhalla Scientific 2100 power meters to the DC input and AC output of the inverter under test. Using the Webcam, I captured the values displayed by the meters during the day. In my system and climate, the STXR peaks at 90.1 percent efficiency, and the Sunny Boy peaks at 94.8 percent. The Xantrex inverter is almost 4 percentage points below their published specification, while the Sunny Boy actually exceeds their spec.

The MPPT has been the Achilles heel of the Xantrex ST/STXR2500 inverters since their inception. I do not doubt that engineers are hard at work at Xantrex attempting to resolve the issues. I believe that the root cause isn't simply a code issue, but lies in how the ST/STXR2500 attempts to implement MPPT tracking from a hardware perspective.

The cooling of the ST/STXR2500 is an engineer's nightmare. The design attempts to push air though the

Sunny Boy on West Array vs. Trace ST on East Array


Inverter East ST2500 AC KWH

on Array West SB2500 AC KWH




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