We have a new Solar Roof (12.7 kW on 5 strands) and one of the things that's been very surprising (and disappointing) is that the "slope" of the production curve is very steep in comparison to older installations. There's virtually no output during early morning/late evening and on heavily cloudy days, in comparison to older panels.
I've been monitoring the output from our Delta inverters: using BLE and the M Professional app, I can watch the output of the strands throughout the day. One strand will be a small amount (a few hundred watts) and the other 4 will be completely at 0. It seems that a particular strand needs to get to the critical level of brightness before any production on that strand happens. This is in contrast to an older systems or even a modern standalone solar generator where there's current flowing in even near-dark conditions (though quite weak).
For example, two days ago, it was a stormy day and we produced only 7 kWh whereas an older system would have eked out around ~15 kWh on a day like that.
I asked Tesla about this and they said that the NEC 2017-required MCI (mid-current interrupter?) rapid-shutdown devices (RSD) are the culprit: they do not allow low production to flow. I found these Delta RSS (PDF) referenced in a public Tesla submittal. If those are the ones that they use today, then they have a minimal operation current of 4W (to power itself). Based on Tesla training materials I've found in Google searches, it looks like they do about 10 tiles per 1 MCI. Doesn't seem like that would account for the behavior that I'm seeing unless I made a mistake with the math.
Can anyone confirm what I'm seeing? Why are they designed like that, if so?
I've been monitoring the output from our Delta inverters: using BLE and the M Professional app, I can watch the output of the strands throughout the day. One strand will be a small amount (a few hundred watts) and the other 4 will be completely at 0. It seems that a particular strand needs to get to the critical level of brightness before any production on that strand happens. This is in contrast to an older systems or even a modern standalone solar generator where there's current flowing in even near-dark conditions (though quite weak).
For example, two days ago, it was a stormy day and we produced only 7 kWh whereas an older system would have eked out around ~15 kWh on a day like that.
I asked Tesla about this and they said that the NEC 2017-required MCI (mid-current interrupter?) rapid-shutdown devices (RSD) are the culprit: they do not allow low production to flow. I found these Delta RSS (PDF) referenced in a public Tesla submittal. If those are the ones that they use today, then they have a minimal operation current of 4W (to power itself). Based on Tesla training materials I've found in Google searches, it looks like they do about 10 tiles per 1 MCI. Doesn't seem like that would account for the behavior that I'm seeing unless I made a mistake with the math.
Can anyone confirm what I'm seeing? Why are they designed like that, if so?