3.3.3. Availability

The data availability over the complete recording duration was 99.96 %. The missing data amounts to 1405 min and is mainly due to a reliability reset which we perform each day at 12:00 a.m. accounting for approximately 20 s of missing data per meter and day. Figure 14 shows the availability of each metering device over the complete recording period. The reset each day at midnight can be clearly seen in the plot. Occasionally, due to WiFi connection outages and an erroneous implementation of the TCP/IP stack on the ESP micro-controller, some data packets can be lost. However, a packet only accounts for less than 20 ms of data. Once detected, we replace missing samples with zeros to

maintain the correct timestamps for all remaining samples. It is still possible to identify these time periods as voltage, and current zero plateaus cannot occur in other situations. *PowerMeter14* and *PowerMeter22* show this behavior more frequently compared to all other meters. The reason might be an unstable WiFi condition as the RSSI values reported by both meters were the lowest of all.

**Figure 14.** Time periods when measurement data are available. Each individual meter is shown on the *y*-axis (ID 08-28) while the time period of the complete recording is shown on the *x*-axis. Red areas indicate gaps in the dataset. Please note that gaps are plotted with at least one pixel width for better visibility and therewith appear significantly larger.
