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Enphase system instability on sunny days

Thu Mar 09, 2017 5:19 pm

I am seeing an oscillation in the power production at the top of the power curve on sunny days. This is not an isolated incident. It seems to happen every time there is a sunny day. The power goes up and down by about 300W:


The oscillation is tied to the reporting interval of every five minutes. When I look at the individual inverters, what I see is that the fourth-generation inverters (M250s and M215IGs) each move up or down about 10 W every five minutes. (The third-generation M190s are NOT doing this because they are operating at maximum output power during these times.) I suppose this could just be normal hunting for the MPP, but what does not make sense is that all of the inverters are doing this in unison. Wouldn't it make more sense for the inverters to search on independent schedules?

I'm wondering if anyone else with Enphase microinverters is experiencing this behavior. If so, do you know what causes it? TIA.
2011 Leaf SL Demo vehicle
10K mi. on 041413; 20K mi. (55.7Ah) on 080714; 30K mi. (52.0Ah) on 123015; 40K mi. (49.8Ah) on 020817; 50K mi. (47.2Ah) on 120717; 60K mi. (43.66Ah) on 091918.
Enphase Inverter Measured MTBF: M190, M215, M250, S280

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Re: Enphase system instability on sunny days

Mon Apr 17, 2017 2:52 pm

Hi RegGuheert,

Didn't notice this post previously.

My output when at peak but not clipping (back in Feb) shows some variation but nothing so consistently cyclical. I'd put mine up to variations in solar irradiance due to faint air pollution or temperature variations.

Now that we're in April and my system clips on a clear day, the peak output does hunt up and down 5-10 watts *for the entire system*, making a pattern that looks more repeating, but the variation seems quite small and thus the output more 'even'. It sounds like in your case, you're seeing 5-10 watts per inverter.

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