# Democratization of PV Micro-Generation System Monitoring Based on Narrowband-IoT
## 5 Results  
The proposed solution--both including hardware components and sensors--was tested in a laboratory environment, aiming to assess its performance under different  
Figure 8: General scheme of the system electronics.  
Figure 7: Prototype voltage and current sensors.  
Figure 9: Power supply scheme of the system and prototype example.  
conditions. The solution was connected and assembled under outdoor conditions in a PV self-consumption installation to evaluate the solution feasibility to be implemented in a variety of real situations and conditions. The proposed system was initially tested at the solar laboratory of CETENMA, located in the Industrial Park of Cartagena (Spain). Such a facility includes measurement equipment to check the performance of PV power plants and modules. For testing purposes, a single 250 Wp monocrystalline PV module connected to an SF 250 W Soltec SolarFighter microinverter was used--V\({}_{MPP}\) = 28.5 V, I\({}_{MPP}\) = 8.8 A, V\({}_{oc}\) = 34.6 V, I\({}_{sc}\) = 9.4 A. Figure 10 shows some examples of field test campaigns and Figure 11 shows results corresponding to this calibration process.  
From the power supply scheme shown in Figure 9, Figure 12 depicts voltage evolution and current demanded (positive) or supplied (negative) by the battery. The Pycom module consumption is around 200 mA over WiFi and 250 mA when the LTE communication protocol is selected. During the information sending process, up to 350 mA can be achieved. Figure 13 shows a detail of Pycom and battery power demand comparison. Regarding the received data through NB-Iot communications versus inverter data, voltage and current have enough precision, 2.45% and 3.9%, respectively, to evaluate the operation of the plant with security. A total of six packages were sent with one-minute sample time: 8 bytes/package for five packages and 10 bytes/package for the additional package. In  
Figure 11: Calibration of the reference cell: comparison of data for two days.  
Figure 10: Case study. Example of field test campaign. Charging solar panel and reference cell assembled to the monitored PV module panel.  
Figure 16: Example of collected data received in-plane irradiance.  
Figure 14: Example of collected voltage data: PV module monitored.  
Figure 15: Example of collected current data: PV module monitored.  
Regarding communication quality of the proposed solution, additional metrics used in previous works of the authors [22] are also discussed because no data of works with similar systems have been found to compare the results. These metrics are Packet delivery ratio, defined as the ratio between the packets successfully received and the total data packets sent by the end nodes and time intervals between different data packets (inter-arrival time) that is determined by the time interval value corresponding to each packet received. In the previous work that used Lorawan communications [22], the payload had a length of 38 bytes, almost equal size of this work, where the size of the sent string was 37 bytes, 4 \(\times\) 5 floating bytes (measurements of each sensor) and 17 bytes of temporary fingerprint. With these similar conditions, our study reveals that the proposed system provides a reliable connectivity with a packet delivery error around 4.6% and stable time interval between packets of 60 s. These results validate the feasibility and reliability of our proposal improving the results obtained in previous works and overcoming limitations related to missing data packets and frequency of received data. Figure 18 shows these results.