Why do I receive a NaN instead of a value for some registers at night?
SMA inverters are controlled by two processors:
a central processing unit (CPU; usually a DSP) for controlling the power electronics and measuring PV and grid variables, and a communications processor (CP; ARM or similar) for the outward-facing interfaces.
The following apply in this respect:
- The CPU is supplied via the PV voltage and therefore runs only when solar irradiation is available.
- The CP is supplied via both the PV system and the grid and is therefore active at all times.
If the CPU is not active, “NaN” is shown for registers with CPU data. In most cases, this can be interpreted as “0” for the power fed in, as feeding in does not take place without the CPU.
Below a particular PV voltage (much less than 80 V), it is expected that the CPU supply voltage is no longer stable and that the measured values are therefore no longer sufficiently precise. In this case, “0” is output for some devices instead of the actual measured value. This applies in particular to the measured value for PV voltage. However, this is not relevant to the grid variables, as feeding in no longer takes place below this PV voltage.
In summary, NaN can be interpreted as “0” in practically all relevant cases for the power fed in.