The short answer is: Both are correct!
Each device is measuring a different value at a different stage in the power generation journey.
Tigo's System Monitoring shows the DC energy created at the PV Module (panel) level, before it gets to the inverter. This is important to know, as the inverter has a later startup and earlier shutdown period, than the PV Modules (due to lower current at twilight).
It is also important to know that during prime hours of production, the inverter incurs conversion losses from the process of converting DC to AC. For this reason, the energy reported after the inverter conversion will always be (usually -2% to -5%) less.
Tigo reports = 38.25 kWh (DC energy produced)
Inverter production view = 36.29 kWh (AC energy outputted from inverter)
With these two values, you can calculate the overall efficiency of the inverter, before the energy is passed on to the grid (36.29 kWh/38.25 kWh = .95 or 95% efficiency).
Note: This amount also includes losses from other system components, like: DC wires, connectors, combiner boxes, fuses, and breakers.
Why have a DC Module Level view?
The DC power is good to know for historical comparisons of module-level performance. It allows you to see trends in shading, weather events, and even potential issues such as:
- Blown string fuse
- Broken or degrading panel
- Closed or shorted diodes in the PV Module
- Production issues in parallel strings