backchannel: panel voltage

This is from a thoughtful reply on reddit. The poster is replying to a low-information solar user and so has simplified his answer.

Solar [panel] voltage doesn’t really tell you much

It doesn’t tell OP much, but it can reveal much after we learn what the controller is doing.

A glance at a typical panel power curve might help them see that “high panel voltage” does not mean “high power output”. Quite the opposite – once voltage climbs past Vmp the panel’s power output drops dramatically. MPPT takes advantage of this to tweak power output as needed to hold a given setpoint. Therefore, Vpanel > Vmp suggests the controller is intentionally reducing panel output.

For any whose eyes have not already glazed over, I’ve written a guide to interpreting what solar charge controllers are doing. It leans heavily on Vpanel observations.

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