The ECU can connect to a max of 100 microinverters. What if I have 101 microinverters? DO I need a second ECU?

While we highly recommend using no more than the 100 microinverters per ECU one additional unit should be fine. Just keep in mind that using more than the recommended number of Microinverters could lead to inconsistent communication and for optimal performance we actually recommend limiting the number of microinverters to 80 microinverters per ECU.