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This page is a collection of notes from my experience with the SMA Sunny Island and the Enphase microinverter in an AC coupled configuration. This is a WIP.
Part Numbers:
- 800-00555-r03 (IQ Envoy)
- 800-00632-r02 (IQ7X), SKU IQ7X-96-ACM-US
System configuration: Grid Profile: "CA Rule21 201902 VV VW FW"
The SMA Sunny Island (SI) US inverters operate each on one side of the split phase power. Meaning that each inverter operates on 120V and communicate with each other in a master/slave operation to provide the L1/L2 240V split phase power. Qty 2 inverters are required to provide split phase power. Note: To increase capacity, the system can be increased to qty 4 inverters.
The iq7x micro inverters are connected to the output of the SI inverters, with one leg connected to the master L and one leg connected to the slave L. The iq7x do not have a neutral or gnd connection. Once the SI is operational and inverting, the iq7x begin the wake-up sequence (provided there is sunlight on the panels). There is a 5 min delay before the iq7x begin producing power.
The IQ Envoy (envoy) is not required for iq7x operation, however, the envoy is the only way to configure the correct grid profile so the iq7x operate in the manner needed for AC coupled connection. Note: This is not entirely true, the crude cut-off method is always available, which turns micro inverters off by raising frequency to 62.5 hz temporarily, which starts the 5 min delay before the iq7x begin producing again.
When the iq7x inverters are operating, they generally provide as much power as possible. They use MPPT on each connected solar panel and thus optimize the power generation. Each iq7x is connected in AC parallel to the next creating an AC string of 12 or less inverters. These strings are combined and fed into the main output of the off-grid inverter. As long as the off-grid inverter is bidirectional, the batteries will be charged with any excess power not being consumed by the AC loads. This is all well and good as long as the batteries are at a state of charge to consume all available excess power, but what happens when the batteries are charged and can no longer receive any power? This is where the grid profile CA Rule21 (Specifically: FW = Frequency Watts) comes into play. The SI will use Frequency-Shift Power Control (Operating Manual pg 154, section 17.5) to control the output of the iq7x micro inverters. As the BMS changes the requested charge current to an amount lower than what the iq7x's are providing, the SI will begin to raise the frequency from 60 Hz. The iq7x (when in the correct grid profile) will lower their output as the frequency is raised. The SI will continue to raise the AC frequency until the actual current is equal or less than the requested current.
Note: When the SI is set to Li-Ion battery mode, the SI disables its BMS and requires an external BMS to provide the state of charge and requested charge current, which is part of the capability of this project.